Yellowstone Science - National Park Serviceducting formal research in the Yellowstone area. To submit proposals for articles, to subscribe to Yellowstone Science, or to send a letter

Yellowstone ScienceA quarterly publication devoted to the natural and cultural resources

Volume 11 Number 2

110˚35'W 110˚30'W 110˚25'W 110˚20'W 110˚15'W

110˚35'W110˚30'W 110˚25'W 110˚20'W 110˚15'W

44˚20'N

44˚25'N

44˚30'N

44˚20'N

44˚25'N

44˚30'N

PelicanRoost

SedgeBay

Mary Bay

TurbidLake

Indian Pond

PelicanValley

Yellowstone River

Bridge Bay

GullPoint

SandPoint

RockPoint

Pumice Point

StevensonIsland

Dot Island

FrankIsland

BreezePoint

WolfPoint

EagleBay

Delusion Lake

Flat Mountain Arm

ElkPoint

ThePromontory

PloverPoint

South Arm

SoutheastArm

West Thumbbasin

Elliott'scrater

inflated plain

the fissures

outletgraben

Mary Baycrater

ParkPoint

BiscuitBasin

AlderLake

YellowstoneRiver

StormPoint

Steamboat Point

northern basin

east central basin

west central basin

Lake Butte

DuckLake

EvilTwincrater

spirefield

TheYS Interview: Lisa MorganMapping Yellowstone Lake

Predator and Prey at Fishing Bridge

As Director of the National Park Service from 1940–1951, Newton B. Drury spent a great deal of his tenure fending off a constant flow of demands that the national parks be plundered for the resources they could contribute to wartime and post-war necessity. In that last year of his directorship, in the midst of the Korean War and a growing with the Cold War, he penned thesewords as an introduction to Freeman Tilden’s The National Parks: What They Mean to You and Me.

Now, as these words are written, with prospects of a third world warlooming up, with the need all the greater for a haven from the tensions ofmodern life, for an environment of quiet and peace and serenity, a book likeTilden's leads people's thoughts into channels upon which proper mentalbalance and perhaps even national sanity may depend. So much the moreimportant, therefore, to cherish these crown jewels among the lands of thenation, to keep them unsullied and intact, to conserve them, not for com-mercial use of their resources but because of their value in ministering tothe human mind and spirit. In war or in peace the national parks have theirproper and proportionate place in the life of America. These lands are lessthan one percent of our area. Surely we are not so poor that we need todestroy them, or so rich that we can afford to lose them.

“In War or in Peace”

EditorRoger J. Anderson

[email protected]

Assistant Editor and DesignAlice K. Wondrak

Assistant EditorsTami BlackfordVirginia Warner

Technical Assistanceand PrintingArtcraft, Inc.

Bozeman, Montana

Special Color Issue!

Yellowstone ScienceA quarterly publication devoted to the natural and cultural resources

ContentsScience with Eyes Wide Open 2YS talks with USGS geologist Lisa Morgan about science, discovery, and the joys of life in the caldera

The Floor of Yellowstone Lake is Anything but Quiet! 14New discoveries from high-resolution sonar imaging, seismic reflection profiling, and submersible studies show there’s a lot more going on down there than we may have thought.by Lisa A. Morgan, Pat Shanks, Dave Lovalvo, Kenneth Pierce, Gregory Lee, Michael Webring, William Stephenson, Samuel Johnson, Carol Finn, Boris Schulze, and Stephen Harlan

7th Biennial Scientific Conference Announcement 31

Yellowstone Nature Notes: Predator and Prey at Fishing Bridge 32In prose and on film, Paul Schullery captures a little-seen phenomenon: the aesthetics of survival in the world of a trout.

by Paul Schullery

News and Notes 40Gray wolf downlisted • Bison operations commence outside North Entrance • Spring bear emergence reminder • Winter use FSEIS released • YCR 10th anniversary

Around the Park 43Springtime in Yellowstone.

Volume 11 Number 2 Spring 2003

Cover: New high-resolution bathymetricrelief map of Yellowstone Lake, acquired bymultibeam sonar imaging and seismic map-ping, surrounded by colored geologic map ofthe area around Yellowstone Lake. Courtesy USGS.

Left: 1883 woodblock engraving of Yellow-stone Lake, probably produced for publica-tion purposes and handcolored at a latertime.

Above: A trout rises to the surface of the Yel-lowstone River.

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Yellowstone Science is published quarterly. Submissions are welcome from all investigators con-ducting formal research in the Yellowstone area. To submit proposals for articles, to subscribe to

Yellowstone Science, or to send a letter to the editor, please write to the following address:Editor, Yellowstone Science, P.O. Box 168, Yellowstone National Park, WY 82190.

You may also email: [email protected].

Support for Yellowstone Science is provided by the Yellowstone Association, anon-profit educational organization dedicated to serving the park and its visitors.

For more information about the association, including membership, or to donate tothe production of Yellowstone Science, write to: Yellowstone Association, P.O. Box

117, Yellowstone National Park, WY 82190.

The opinions expressed in Yellowstone Science are the authors’ and may not reflecteither National Park Service policy or the views of the

Yellowstone Center for Resources.

Copyright © 2003, Yellowstone Association for Natural Science, History & Education.Yellowstone Science is printed on recycled paper with a linseed oil-based ink.

2 Yellowstone Science

YS (Yellowstone Science): Lisa, whenwe first met, you described your back-ground as a little bit different than that ofmost geologists, in that you started out asa fine arts major. Could you tell us a littlebit more about that, and how it affects howyou go about looking at your work today?

LM (Lisa Morgan): I did start out as afine arts major. Along the way, I took amineralogy and optical crystallographycourse in my pursuit of fine arts because Iknew we’d be studying color and light the-

ory, which I always thought was prettyinteresting. My hope was that the coursewould enable me to have a better under-standing of the color spectrum and howlight works. So I took that class and had totake prerequisites in physical and histori-cal geology and before I knew it, I waskind of hooked into geology. And I lovegeology. One of the things I think fine artsbrings to geology is the ability or interestto look in detail at things, and to see thingsthat you might not normally look for. Likewhen you’re drawing, how you’re going

to draw something is going to be very dif-ferent than if you just took a photograph ofit, and you’re going to consider the rela-tionships somewhat differently whenyou’re drawing something than if you’rejust going to document it with a photo-graph. So I think fine arts brings this abil-ity to see or look.

I guess I would describe myself as afield geologist who studies the geologyand geophysical characteristics of volcanicterrains, and I think having a fine arts per-spective gives me another set of tools with

Science with ‘Eyes Wide Open’An interview with geologist Lisa Morgan

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A research geologist with the U.S. Geological Survey, Dr. Lisa Morgan has devoted 23 years to studying the geologyand geophysics of volcanic terrains. Since 1999, she has been working in Yellowstone, mapping and interpreting thefloor of Yellowstone Lake and its associated potential geologic hazards—an undertaking that was completed last sum-mer. We felt that an achievement of this magnitude warranted extensive coverage in Yellowstone Science, and areexcited to publish its results. In 2002, YS editor Roger Anderson had the opportunity to discuss this project and otherissues with Lisa at her Boulder, Colorado, home. We are pleased to include this interview, which provides interestinginsights into the mapping process as well as into her personal approach to the science of geology.

Dave Lovalvo, Lisa Morgan, and Pat Shanks launch a remotely-operated vehicle (ROV) into Yellowstone Lake. TheROV aids in ground-truthing recent bathymetric and aeromagnetic mapping of the lake floor conducted by the USGS.

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which to understand the Earth. Myapproach is to do science “with eyes wideopen.” And that’s where I see the connec-tion with art, because when you take on acanvas, you start with a specific drawing orpainting in mind but as you work on it, thepainting begins to shape itself. You don’tstart a painting saying, “I know exactlywhat colors I’m going to use. I knowexactly what I’m going to draw or painthere.” You don’t know exactly what thefinal results will be. And I think youshouldn’t, either, with science. When youstart out on a proposal, certainly you haveideas of what you want to look at, how toproceed, certain goals, objectives; but youneed to make sure thatyou keep your optionsopen enough so that youdon’t miss anything thatmight be necessary inyour final interpretationof what you’ve seen, orwhat you’ve recorded. SoI think a lot of our work inYellowstone Lake hasbeen a perfect example ofgoing into an area usingtechniques we really had-n’t used before, using abroad group of differentindividuals from differentdisciplines all bringingdifferent skills to the sametable, allowing us to iden-tify things we didn’tknow were there. Andallowing us to come toconclusions that we didnot know we were going to come to whenwe started the original study.

YS: Right. So if you had a pre-set par-adigm, and you found something else andit didn’t fit into that, you don’t go with thepreconceived notion of what you’re goingto find. That’s what you mean, “eyes wideopen.”

LM: Exactly. And a lot of times, you’llfind, in science, and maybe in other things,too, people want preferred outcomes. Theyalready know where they’re going to getto, and they have their product that they’resupposed to produce, and that’s whatthey’re going to do. And I think it’s impor-

tant that we get out our products that wepromised we’ll get out, but I think it’s alsoimportant, as natural scientists, to makesure we’re not missing something. Sowhile I have models in mind, I get reallyfrustrated when I’m in the field and some-body tells me, “well, this model tells me itcan’t be this.” I don’t care what your modeltells you. Just look at the relationship. For-get any model, and just look at that, studywhat you’re seeing in that relationship, andthen see how that compares with yourmodel. But sometimes, people go in theresaying “well, it’s got to be something otherthan this.”

YS: Is your approach unusual, do youthink, among scientists?

LM: I don’t know; probably not. Ithink there are a lot who don’t come to thetable already working within a prescribedmodel. But I’m sure there’d be people whowould disagree with me on that, too. Inmy experience, when I meet with people inthe field and we’re looking at differentthings, some people already have kind ofan idea what it has to be. But I think it’sokay to say “well, I don’t know what it is.”I think nature is a continual puzzle formost of us. And there are a lot of things westill don’t know or understand, whichkeeps us going.

A great example from our 2001 field-work is, we discovered charcoal and treemolds in the Lava Creek Tuff. We haveactual pieces of charcoal present in someof the tree molds, which was surprisingbecause these pyroclastic flows are typi-cally erupted from very large calderas atpretty incredible speeds, and emplaced atvery high temperatures, probably on theorder of 800-850ºC.

YS: And it’s unusual, because in thatheat you would expect everything wouldbe consumed.

LM: That’s correct. At this location,we were close to an areainterpreted as an eruptivevent for the Yellowstonecaldera, and there’s a lotof evidence to suggestthat there may have beensome water involved inthis particular part of theemplacement of thedeposit, which probablydecreased the tempera-ture.

Tree molds are com-mon in basaltic lavaflows, such as those inHawaii and at Craters ofthe Moon, Idaho, butvery little study has beendone on the preservationof tree molds in rhyolitepyroclastic flow deposits,like the Lava Creek Tuff.Tree molds and charcoal

are somewhat rare occurrences in thesetypes of environments. To find charcoal inthis deposit, preserved charcoal, is aninteresting discovery, and contributes towhat we know about the climate 640,000years ago when the Yellowstone calderaerupted.

YS: Where in the park did you findthis?

LM: It’s in the vicinity of Fern Lake,close to the topographic edge of thecaldera.

YS: Now, if I was out with you lastsummer on the trail, walking through that

Lisa points out a "twig mold" in the 0.64-Ma Lava Creek Tuff. A modern twighas been placed above "twig mold" for comparison purposes.

COURTESY LISA MORGAN


part of Yellowstone, what would you seethat I wouldn’t necessarily see that wouldmake you want to stop and take a closerlook? What are you seeing in the land-scape that makes you want to investigatethis particular spot, and then how do you,in all of Yellowstone, get to that place andmake that kind of find?

LM: Here’s exactly what happened. Ithad been raining on and off that day. PatShanks and I were in one work group andSteve Harlan, Lydia Sanz, and Beth Erlandwere in another work group, and Pat and Iwere discussing where to go next. It wasstarting to rain again, and we had to crossthe creek. I had taken my backpack off andwas putting my raingear on. I’m constant-ly, just always looking at everything. Andas I was tying my shoelaces, I put my eyeson this little piece, that was just a surfacepiece, probably no more than a couple cen-timeters long. It had a very fine rim, orcoating of silica on it, and then inside ofthat was this twig impression—this treemold. And it was very, very tiny. So it wasa fluke. Just like a lot of things in science.

And so I saw that little thing, but thenit started pouring. And so we skedaddled.We only had the next day left, and I justhad this feeling that I had to go back to thissite and have a closer look at the impres-sion and site in general. Anyway, we wentback up there, and I said, “look at this. It is

a tree mold.” And I just happened to pickthis piece up, and there was all this char-coal, and also pine needles and impres-sions.

And Pat said, “well maybe that got inthere through some kind of later fluvialaction, or maybe there was just naturalplating forsome reason,and you hadsome flood-ing, and yougot the pineneedles inthere,” and so then I went to another, and Isaid, “what appears as the characteristicfeature of this particular site and deposit isthe unusual nature of the platyness of theunit and that’s a reflection of its content oforganic matter.” I said to Pat, “I think theplatyness and the organic matter in the ign-imibrite are part of the original deposit. I’llbet you a beer that when I go over to thatplaty zone and that platy zone and that oneand all of these zones will be full of char-coal and have impressions of pine nee-dles.” He said ok to the bet. So I went andlooked at all these different places in therock exposure, and each one was full ofcharcoal and pine needle impressions. SoPat ended up buying me a beer after our13-mile trek out of the backcountry. Butyou see, the beauty of having people workwith you with different backgrounds, is

that everyone brings a somewhat differentperspective and set of experiences. It’smuch better than just having your ownideas and self to bounce concepts off. It’salways good to have somebody who willchallenge one’s thinking. It keeps youhonest and keeps you thinking.

Later, whenI told KenPierce [of theUSGS] aboutthe tree moldsand pine needleimpressions

found in the Lava Creek Tuff, his reactionwas, “Oh my gosh! That is so cool,”because in the field of paleoclimatology, adebate exists about whether the Yellow-stone caldera erupted during a glacial orinterglacial period. And he said, “I thinkyou’ve got key evidence now for showingthe Yellowstone caldera erupted during aninterglacial period. It has to be, to have allthose pine needles and trees.” So that waskind of cool.

YS: It’s amazing. Without that collab-oration, without people looking at theresource from different perspectives, youmight not have made that really criticalconnection.

LM: That’s right. So anyway, back tothe eyes wide open, that allowed us to seethat. A lot of the discoveries on Yellow-stone Lake have happened the same way.Before we started our West Thumb sur-vey, the current thinking was that mostfeatures in the lake are from the last glacialperiod since it’s pretty well establishedthat over a kilometer of ice was over thelake 20,000 years ago. That certainly hadto have had a pretty profound influence inshaping the lake. But what we’ve found isthat it certainly is not the only, nor was itthe most important, influence on shapingthe floor of the lake.

People had previously mapped Steven-son, Frank, and Dot Islands as being gla-cial remnants. And, certainly, if you wentout there today, the rocks exposed on theislands are glacial tills. But what we’vefound with our high-resolution, aeromag-netic map, (based on the magnetic surveydone with an airplane), in tandem with oursonar and seismic surveys of the lake, was

Lisa Morgan and fellow USGS geologist Ken Pierce kick back on the Mary Bay explosionbreccia deposit.

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I guess one of the things our projecthas exemplified is that not any oneperson has all the answers.

Spring 2003 5

that the majority of the underwater topog-raphy, or the bathymetry of the lake, isreally due to rhyolitic lava flows that wereemplaced some time after the Yellowstonecaldera formed. Now, in retrospect, I think,“Oh, well, that’s so obvious,” becausewhat do you see around there? It’s all lavaflows. And why would you think that all ofa sudden, just because you have a lake, thelava flows wouldn’t be in there? But it wasa big, major discovery in mapping WestThumb.

We’ve found that discontinuities, oranomalies, on the aeromagnetic map coin-cide with the mapped extent of the rhy-olitic lava flows on land, and you can fol-low those out into the lake. Our detailed

new bathymetricmaps of the lakefloor show thatmany of the mag-netic anomaliescoincide with hum-mocky areas of highrelief. We interpretthese as rhyoliticlava flows, and sug-gest that Frank, Dot,and StevensonIslands are on theselarge lava flows. Sothe glacial tills thatoccur on Dot,Frank, and Steven-son Islands are real-ly just mantlingmuch larger fea-tures; rhyolite lavaflows underlie theislands and shape

the lake bottom. And if we had held on tothe old model, we may have been blind toseeing that those flows were there.

YS: Explain to the uninitiated aboutthese aeromagnetic maps you’re talkingabout. What’s the process, and what doesit generate?

LM: Basically, we attach a magne-tometer onto a fixed-wing airplane, andthen this airplane flies over the topographyat a constant elevation above the terrain. In

this particular survey, the plane flew lines400 meters apart on an east-west orienta-tion, in a continuous pattern over the park.The magnetometer measures the totalmagnetic intensity of the Earth’s field, andthat can be broken down into two maincomponents, the magnetic remanence andmagnetic susceptibility. Generally, themagnetic remanence records the signaturefrom the earth’s magnetic field that therock acquired at the time of its formation.

Volcanic rocks are emplaced at tem-peratures above the Curie temperature,which refers to the temperature belowwhich a mineral of a specific compositionbecomes magnetic. Minerals in the vol-canic deposit acquire the magnetization ofthe Earth’s field at the time that that rockwas emplaced and give the rock its specif-ic magnetic remanence direction. Theearth’s magnetic field changes its polarityover time so that volcanic rocks erupted atdifferent times will have different and spe-

cific magnetic rema-nence directions. Withmagnetic intensity, we

also measure the mag-netic susceptibility,which is basically ameasurement of howsusceptible that rock isto an ambient magneticfield.

Susceptibility valuescan vary depending on arange of conditions. Inthe case of Yellowstone,what seems to be themajor variable for sus-ceptibility is howhydrothermally-alteredthose rocks are. Whenyour rock is extremely

hydrothermally altered, the magnetic min-erals in that rock are also altered, andbecome much less magnetic. A lot of timeswhat we’re seeing is titanomagnetitesgoing to hematite or ilmenite. Hematite isnonmagnetic and ilmenite is weakly mag-netic, so the magnetic susceptibility of therock goes to almost nothing. Most of therocks we’re looking at in much of the Yel-lowstone Lake area were erupted in thelast 700,000 years, after the last big rever-sal in the Earth’s magnetic field. So whenwe’re looking at the total magnetic inten-

Dave Lovalvo at the controls of the ROV hedesigned and built. What the ROV sees isvisible on the computer monitor seen at thefar right. A second monitor (not seen) dis-plays water temperature readings and a sec-ond picture of the lake floor. This photo wastaken inside the cabin of the NPS’s Cutthroat,which is dedicated for research purposes.

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sity of the rocks in Yellowstone Lake, thevariable that is changing most is the mag-netic susceptibility, which in this casereflects the amount of hydrothermal alter-ation in the rock.

In many places in Yellowstone,hydrothermal alteration is associated withthermal springs. Hot waters come up alongconduits and alter the rockand magnetic mineralsthrough which they’re flow-ing. The hydrothermal alter-ation of the rock lowers themagnetic susceptibility.When you look at the newlyacquired total magneticintensity map of Yellow-stone, you see a map thathas areas with magnetichighs and areas with mag-netic lows. In some areas,we can use this map as aguide for where we mightexpect hydrothermal alter-ation to be present; in otherareas, we can use the map toidentify faults and otherstructures.

YS: So this is how yougo about looking at the park,and looking at the rocks, andtrying to piece together allof the stories that they haveto tell?

LM: I guess one of thethings our project really hasexemplified is that not anyone person has all theanswers. I think if we wentinto Yellowstone Lake justdoing a bathymetric map,we’d have a pretty appeal-ing map, but the bathymetrycombined with the totalmagnetic intensity map andthe seismic reflection pro-files enable our producing amore powerful product witha higher level of confidence. Add to thisthe data we collect with the submersibleROV (remotely operated vehicle), and thedata set is pretty complete. The ROV iswonderful, because it allows us to ground-truth what we have imaged with the multi-

beam and seismic sonar systems. TheROV is a one-meter-by-one-and-a-halfmeter vehicle, built and piloted by DaveLovalvo of Eastern Oceanics. It’s attachedto the boat by a 200-meter tether, whichallows continuous observation of the lakefloor. At its front is a pan-and-tilt videocamera, which records images from the

floor of the lake. On the front is alsomounted a 35-mm camera. The videocamera is on at all times so we can reallysee the floor of the lake. That aids us in oursampling, and the still lifes are wonderfulto see. The ROV is great also because it’s

able to measure temperatures and collectsolid and fluid samples of hydrothermalvents, lake water, and sinter. Later thesecan be taken to the laboratory and be ana-lyzed for mineralogy, chemical and iso-topic composition, and microscopic struc-tures.

So the ROV allows us to observe andsample what we haveimaged bathymetrically andseismically. And that’s beencritical. The multi-beammapping of YellowstoneLake presented challengesseldom found elsewhere.Thermal vents so dominantin different parts of the lakecause frequent changes inthe temperature structure ofthe lake, and therefore, thesound velocity profile. Inour first year (1999), whenwe mapped the northernpart of the lake, we identi-fied several features, whichturned out to be artifacts inthe data. So we collectedmore frequent sound veloc-ity profiles than one wouldin a non-thermal environ-ment. Having the ROV asour eyes and hands on thebottom of the lake allowedus to confirm the bathymet-ric images.

While we’re very confi-dent of our imaged data, theability to sample fluids andsolids, measure tempera-tures, and photographicallydocument the lake flooradds an incredibly valuablecomponent to our lake stud-ies. In 2000, we went withthe ROV to linear featureswest of Stevenson Islandthat were imaged in 1999.As a result, we have photo-graphic evidence that thefeatures are fissures with hot

water coming up along open cracks in softmud and precipitating iron and manganeseoxides on the fissure walls. The fissuresare parallel to and part of the Eagle Bayfault zone, which is a young fault systemmapped south of the lake at Eagle Bay.

Remotely-operated vehicle (ROV). The large orange balls are flotationunits. Water samples are drawn through the large tube mounted on theleft. A thermometer/camera is visible in the mid-foreground, directlyabove the basket used for scooping up sediment samples from the lakefloor.

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This system probably continues northwardof the fissures to the young graben north ofStevenson Island.

YS: Does that continue with the faultnear the Lake Hotel?

LM: That’s right. The Lake Hotel isnear the fault. Soagain, our mappingof the Lake hasenabled us to lookat its geology inmore detail and ina broader context.And YellowstoneLake isn’t an easylake at all to figureout, or to work on.You think of mostlakes as beingquiet, calm, andgood passiverecorders of thelocal climate andgeologic process-es. But Yellow-stone Lake is any-thing but quiet.

YS: Which ofthose technolo-gies—the aero-magnetic survey,the ROV, thebathymetry—played a role in determiningthe caldera boundary under the water?

LM: I would say the two most impor-tant ones were probably the recentlyacquired aeromagnetic data and thebathymetry. Much discussion has been hadabout where to draw the caldera boundarythrough the lake. Using both of these datasets, we trace the topographic margin ofthe Yellowstone caldera right throughFrank Island.

YS: Weren’t you going back and forth?You were describing once about how youwere out on the boat, and you were takingmeasurements on what you thought wasinside the caldera, outside the caldera.

LM: Yeah. Once we got the bathyme-try, it coincided perfectly with where we

had put the boundary based on the magdata. And so that was so cool, and then wewere able to take the ROV, and we couldsee the caldera margin in the lake. It lookslike a bunch of discontinuous, bathtub-shaped troughs, kind of marching throughthe central basin. The multiple data setsgive the same conclusion, so that one can

say with much better confidence that thisis definitely where the caldera margin is.

YS: I’m going to just back up for a fewminutes, and get us back to how we beganthe discussion, from the fine arts to geolo-gy, to this philosophy of looking at yourwork with your eyes wide open, and askyou to elaborate a little more about yourbackground. Once you found geology, tellus a bit about your schooling, where youwent, your degrees…

LM: I went to the University of Mis-souri at Kansas City, and at that time itwas just a small undergraduate geologydepartment, and I had great mentoring andopportunities there. That was key. I got ajob in the department, starting probably inmy junior year. I was a lab technicianthere. After I graduated, I worked for a

short time in a jewelry store with the inten-tion of eventually becoming a gemologist,but then I got a job that paid twice as muchwith an oil company. I stayed with the oilcompany about 10 months but left toreturn to the University to teach labs forintroductory geology classes and work asa technician in their analytical lab. I then

moved to Coloradoand got my Mas-ter’s degree at theUniversity of Col-orado at Boulder,focusing onigneous petrologyand volcanology.

I then had agreat opportunityin 1980 to work atMt. St. Helens, andon August 7, I wit-nessed one of itssmaller pyroclas-tic-flow-producingeruptions from aplane about a kilo-meter or two awayfrom the vent. Thateruption was sig-nificant because itcreated quite agood eruptivecloud, and in thatcloud you couldsee part of it col-

lapsing and forming pyroclastic flows onthe flanks of the volcano. While the pyro-clastic flow was moving, one could seehow this flow concentrated in areas oflower topography, such as valleys comingoff of St. Helens. I could see fine ash beingblown out of the front of the deposit. AndI just decided then I wanted to focus onhow pyroclastic flows are emplaced. Beingat St. Helens gave me a great opportunityto see what volcanologists do. And so inthe following year I decided to go for myPh.D., and study with George P. L. Walk-er, at the University of Hawaii, whose pri-mary focus at the time was ash deposits,their facies, and emplacement processes.

YS: When did you first work in Yel-lowstone on geology?

LM: I started coming to Yellowstone

Lisa Morgan in 1980, doing field work for her master's degree. She is sitting next to the baseof the 6.65 million year old Blacktail Creek Tuff, the oldest caldera-forming ignimbrite fromthe Heise volcanic field. The Heise volcanic field (4-7 Ma), on the eastern Snake River Plain,is similar in origin to the Yellowstone Plateau volcanic field, and immediately preceded itsformation in space and time along the volcanic track of the Yellowstone hot spot.

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probably 1979–1980, because I was work-ing on the Snake River Plain and therewere many similarities between the Qua-ternary rhyolites in Yellowstone and theslightly older rhyolites on the Snake RiverPlain. I was working on my Master’s the-sis; its focus was a stratigraphic study of athick section of pyroclastic flow depositsexposed on the northern margin of the

eastern Snake River Plain. As we knownow, but didn’t know then, the Snake RiverPlain is a whole bunch of old Yellowstone-like calderas and volcanic fields. I was firstformally assigned to Yellowstone in 1995,but, over the previous 15 years, I used themore complete exposures and caldera-related features present in Yellowstone asa way to better understand what I waslooking at on the Snake River Plain, whereexposures of rhyolites are mostly limitedto the margins of the Plain. Today, mostYellowstone-like features in the SnakeRiver Plain are covered by Quaternary orvery recent, young basalts. Eventually, likethe eastern Snake River Plain, Yellowstonewill be much lower in elevation than it isnow and also will be covered by basalts.

YS: Explain to me how in the futureYellowstone will be much lower.

LM: Currently scientists can image

molten, very hot material underneath Yel-lowstone, and, in general, this mass of hotmaterial causes the general Yellowstonearea to be topographically higher than thesurrounding areas. Over time, if the Yel-lowstone caldera is similar to earlier Qua-ternary calderas in the Yellowstone Plateauvolcanic field, which we have every reasonto believe is true, basaltic lavas will erupt,

eventually fill the caldera floor, and con-ceal the Yellowstone caldera. What is nowmolten magma will eventually crystallizeand become denser, and thus less buoyant.The overall topographic elevation will sub-side from today’s current elevation. Withcontinued southwest movement of theNorth American plate over the thermal dis-turbance that causes Yellowstone today, anarea northeast of the present-day locationof the Yellowstone Plateau will becomeelevated and rise above Yellowstone. Infact, we can already witness this. Thisprocess of uplift followed by volcanismhas been occurring for the past 16 millionyears along the Snake River Plain startingin southwest Idaho. So today, Yellowstoneis anywhere from 1 to 2 kilometers abovethe Snake River Plain, depending on whereone takes measurements.

YS: When did you begin to work withthe USGS?

LM: In 1977, when I moved to Col-orado.

YS: What was your first job withthem?

LM: It was great. I made a Denverdump map. My job was basically compil-ing a map showing where all the landfillsin the greater Denver area were. And thatmap transformed a lot of how I live my lifetoday, and how I look at what our respon-sibilities are as citizens on Earth. TheUSGS had been asked to do this becausethere had been a series of accidents asso-ciated with former landfills. Some acci-dents were due to spontaneous combus-tion of methane that caused some fires,some explosions. I think a couple of peo-ple were either seriously burnt or killed.Also, housing developments constructedon top of these landfills were developingcracked foundations and walls due to dif-ferential subsidence in the landfills. It wasimperative that a comprehensive look betaken at where these landfills were locat-ed, so that city and county planners couldmake more informed choices of where toallow or deny development. I was blownaway by how many dumps there were, andwhat went into these landfills. So muchof it could be recycled, reused, and not putin there in the first place. And since then,I’d say starting in like the mid-80s, ourfamily has probably put out no more thanmaybe three to four bags of garbage in ayear.

YS: Really.

LM: (Smiling) Yeah. We don’t sub-scribe to the landfill too much; they shouldbe kept to a minimum. There’s a berm outin our yard where we put all the inertbuilding material that would have gone tothe landfill, but that we took care of here.Right now I’m on the Boulder CountyRecycling and Composting Authority, andour goal as a county is to divert, by 2005,our solid waste levels from 1994 by 50%.And I think we’re going to achieve thatgoal. In the City of Boulder, our single-family residential diversion rate is at 49%,so we have almost met our 2005 goal sev-eral years ahead of schedule. However, inthe arenas of commercial and industrial

Ground-truthing with the ROV means visiting several sites each day, requiring that the crewdrop and haul anchor numerous times. Here, Lisa displays some hydrothermally-altered claythat came up with the anchor.

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waste and for multi-family units, our diver-sion rates are only about 15-20% from1994 levels, so these are areas where westill need to focus and significantlyincrease our diversion rates. And we’repushing the stakes up higher and trying toget to 80% diversion from 1994 levels. It’san informal goal for the City of Boulder.Last year, the city council passed a newordinance, referred to as the “pay-as-you-throw” ordinance, that really forced indi-viduals to pay the true cost of their trash.This has resulted in major behaviorchanges and a significant increase in ourlevel of recycling and reuse. People cando it, but you have to have the infrastruc-ture in place, like curbside pickup andmixed paper and commingled containers.So that’s a long story, but that was my firstjob with the USGS.

YS: What’s your current job?

LM: Now I work at Yellowstone. Thisyear I’m assigned to Yellowstone 100% ofmy time. We’ve finished the map of Yel-lowstone Lake, and are working on variousaspects of the postglacial hydrothermalexplosion craters and deposits that areprobably the most immediate serious haz-ard in the park. The last very largehydrothermal explosion event that weknow of was 3,000 years ago at IndianPond. Of course, in recent years smallerhydrothermal explosion events haveoccurred in the Norris basin, Biscuit Basin(1915), West Thumb, and Potts thermalbasins and elsewhere in the park. Sothey’re very much a current feature ofactivity that Yellowstone National Parkhas to deal with. I’ve also been working onthe physical characteristics of the LavaCreek tuff and its emplacement, and how itrelates to the formation of the Yellowstonecaldera. And then there’s the mapping ofYellowstone Lake that’s basically con-sumed me for the past four years.

YS: Was your work in Yellowstone onthe caldera what ultimately brought you todo the extensive work on YellowstoneLake? What intrigued you about Yellow-stone Lake that has led you to do so muchwork there?

LM: Yes, originally I came to Yellow-

stone to work on the Lava Creek Tuff,which erupted from the Yellowstonecaldera, to better understand its formation.But I also came to do the ground-truth forthe aeromagnetic survey we flew in 1996.With Steve Harlan, I’ve collected orientedcore-samples from most of the Quaternaryand Tertiary volcanic rocks in the park forour magnetic studies.

As far as the lake, if you think of all ofthe geologic maps in Yellowstone Nation-al Park, the one place that didn’t have ageologic map was the Lake. What reallygot me into Yellowstone Lake was myinterest in the hydrothermal explosiondeposits. We were already engaged indetailed studies of the deposits from MaryBay, Indian Pond, and Turbid Lake onland, and I was very interested in trying tounderstand the eruption of Mary Bay. Inour 1999 survey, one of our big discover-ies was what we are now calling Elliott’scrater, which is an 800-meter widehydrothermal explosion crater complex onthe floor of the lake in the northern basin.

YS: The work you and others havedone in recent years has really kind of rev-olutionized the way we look at the lake. Ifwe could look at the bottom of Yellow-stone Lake, from the mapping you’vedone, what would it look like?

LM: If you took all the water out, you

would have a very hummocky terrain.You’d have a terrain very similar to whatyou see in the Central Plateau now, wherethere are a lot of very steep-sided, hum-mocky terrain dominated by rhyolitic lavaflows. And these lava flows would have acap of glacial and lacustrine sediments.Intermixed with this hummocky terrainwould be a whole series of hydrothermalvent fields throughout the lake. Thehydrothermal vents are associated with thelava flows, generally near their edges. Andso, one of the largest thermal fields in Yel-lowstone National Park is on the floor ofthe lake. It’s pretty magical exploring theseareas. On top of this very hot area, we’veseen a lot of fissures, which are linearcracks in the lake bottom. I can’t think ofan area on land in Yellowstone where youhave big open fissures like these. Maybe insome of the thermal fields, but some of thelake-bottom fissures that were discoveredin 1999 and 2001, in the northern and cen-tral lake, extend for several kilometers.Another feature one would see are the very

large lake-bottom explosion craters, simi-lar to Turbid Lake and Indian Pond onland.

YS: Duck Lake, too?

LM: Yes, Duck Lake is a large explo-sion crater immediately west of West

Spring 2003 9

The sun rises on Yellowstone Lake. The lake’s unpredictable summer weather makes it bestto get an early start.

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Thumb basin. You may have noticed asteep slope west of the West ThumbGeyser Basin. This is an apron of debristhat was ejected during the hydrothermalexplosion of Duck Lake. A morphologicaldifference between the large explosioncraters on land and those on the floor of thelake is the radial apron of debris around thecraters we see on land. In the lake, a well-defined rim around the central crater isabsent. Most of this difference may have todo with the medium in which the eruptionoccurred.

YS: And the vents, and the spires…

LM: And then you’d have spires, orconical features, that are anywhere fromone meter all the way up to about 8 metershigh, over in Bridge Bay. We think Monu-ment Geyser Basin, near the northwesternedge of the Yellowstone caldera, may beanalogous in its origin to Bridge Bay. Andthen just north of Stevenson Island, you’dalso see a large young graben, which is adown-dropped block with bounding faults.About two meters of displacement is on

the west side, and about six meters of dis-placement on the east side. And we founda lot more vents in West Thumb basin thanwe had previously thought.

YS: Where else did you find them?

LM: They’re in the south-central partof the West Thumb basin as well as in thenorthern part of the basin, along the edgesof rhyolitic lava flows.

YS: How about Mary Bay?

LM: Mary Bay is a huge crater com-

plex. It’s a whole series of smaller cratersinside a much larger main crater. One ofthe things that we need to get a better han-dle on is that not all of these craters areproduced by explosions. We think someof these craters may also be produced bydissolution collapse. As you know, thelake has areas of very high heat flow,which came out of research by previousworkers such as Paul Morgan, Bob Smith,and Dave Blackwell. The high heat flow is

responsible for the occurrence of hundredsof hot springs on the lake floor. Thehydrothermal fluids are very acidic andchange the composition of the rocksaround them. And so in the lake, most ofthe rock composition originally was rhyo-lite, which is mostly quartz, silica,feldspar, and plagioclase. Feldspars andplagioclase are altered easily by this acidicfluid and are changed into clays. And thenthese hydrothermal minerals precipitatein this system forming a kind of imperme-able seal. At some point all the vents andfissures that were conduits for these fluidsseal up. The acidic hydrothermal fluids

and gases continue to do their work, whichis to alter the substrata, and at some time,either these things explode and there’s acatastrophic failure of that sealant, orthere’s collapse of all this material under-neath. Now, I don’t think we understandhow we distinguish these two at this point,or how we can forecast what’s going tohappen. But I certainly hope some of ourseismic profiles give us more insight intoour ability to look at the structural integri-


“We got bubbles!” Although GPS units are the crew’s primary mode of navigation, patches of bubbles rising to the lake’s surface can act ashydrothermal landmarks as those aboard the Cutthroat search for the exact spot to launch the ROV.

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Spring 2003 11

ty of the rocks underneath the lake. Or thelake sediments.

YS: Of all the findings you’ve madeon the lake, what surprised you the most,would you say?

LM: I don’t know, I mean, the wholething has been like a discovery a day. Andso it’s been really exciting, and has openednew ways to examine multiple activeprocesses, and has been quite fun alongthe way. You never are quite surewhat you’re going to find. Iguess I’d say the biggest surprisewas either the fact that the rhy-olitic lava flows played such animportant role in shaping thefloor of the lake and controllingthe location of the hydrothermalvents, or that the caldera marginshowed up so clearly in thebathymetry and coincided withareas of magnetic lows. Thatwas really cool.

To see the caldera margin isreally fascinating. And thehydrothermal craters are justphenomenal. When you seethese large structures, you knowa very complex process isinvolved, because not only doyou have 800- to 2000-meterdiameter structures, but through-out the floor of these structureshydrothermal processes areactive and one can see and sam-ple active hydrothermal vents.And so you think “well, wherecan you go on land where youcould see something like that?”and so in the summer of 2001,we started mapping Indian Pondand Duck Lake, and right now we onlyhave the seismic reflection profiles. Butthat should give us a lot of indication ofwhat’s going on in those lakes. I think it’simportant for the park, from a public safe-ty perspective, to understand activityoccurring in the hydrothermal explosioncrater lakes as well, because like geology,nothing’s static. We know from our recon-naissance seismic surveys in Duck Lakeand Indian Pond that active hydrothermalvents are on their floors.

Also, large landslide deposits, includ-

ing a couple large detachment blocks, havecome off the eastern, and to a lesser extent,western shores of Yellowstone Lake.These are kind of hummocky, but not aspronounced as the lava flows. The causesof these landslides and their effects on Yel-lowstone Lake are an important topic forfurther study.

YS: How much of the lake bottom hasbeen surveyed?

LM: We finished surveying the Southand Southeast Arms in 2002, so the bathy-metric mapping of the lake is completed!About 75–80% of the lake is within theYellowstone caldera. Outside the calderaare the South and Southeast Arms, whichare fault-bounded valleys whose shape hasbeen enhanced significantly by glacialprocesses. Much of the floor of the South-east Arm is characterized with a hum-mocky bathymetry with many depressionsreflective of kettle and glacial meltwaterterrain seen elsewhere in Yellowstone and

Grand Teton National Parks. After melt-ing, voids left by the ice were later partial-ly filled with slumped sediment leavinglarge, tens of meters wide, irregularly-shaped depressions.

YS: Earlier, you talked a little bit aboutthe interplay between geology and bio-logy. Could you elaborate?

LM: As you know, lake trout havebeen discovered in Yellowstone Lake, and

the native cutthroat trout is preyto the lake trout. Pat Shanks hasbeen working on the geochem-istry of the sublacustrinehydrothermal fluids, looking attoxic elements that we knowexist in other hydrothermal sys-tems, including mercury, anti-mony, and thallium. Crus-taceans are a primary foodsource for cutthroat trout, so thequestion arose, what kind oftransmission is there from thevents to the lowest life formsthat we could identify, on upthrough the food chain to thecutthroat trout and up to the laketrout? So he started looking atmercury content of fish muscle,vital organs, and skin. And hefound a higher than normal con-centration in both the lake andcutthroat trout.

The park is interested inidentifying areas in the lakewhere lake trout spawn. Laketrout are anadromous, meaningthey stay within the lake theirentire lives. Cutthroat are poto-modromous meaning theyspawn in the streams that feed

into the lake during the early summer andlater they come back and live in the lake.When they are spawning in the streams,they become potential food sources formany species, some threatened or endan-gered such as grizzly bears, bald eagles,otters, and osprey. If the cutthroat disap-peared, the lake trout, which never leavethe lake, would not take their place in theecosystem. It’s a major resource issue forthe park and understanding where laketrout spawn is key to controlling theirnumbers and to the ultimate survival of the

Even graduate students need a break every now and then.

COURTESY LISA MORGAN

cutthroat trout. Our understanding when we started

this study is that lake trout like to spawn ingravelly areas. So we thought if we couldidentify gravelly areas in the lake withhigh-resolution bathymetry and seismicprofiles, we could lead the biologists to thespawning areas for the lake trout. As itturns out, we’re findingthat the lake trout hangout in other areas in addi-tion to the deep gravellyareas. The cutthroat troutlike to hang out in warm,thermal shallow areas,which have been called“cutthroat jacuzzis.” ThePark Service has foundlake trout coming intosome of these jacuzzi ventareas to prey on the cut-throat trout.

So biology has amajor role in the Yellow-stone Lake studies. Forone, identifying whateffects toxic metals pres-ent in hydrothermal fluidshave on lake water chem-istry and how they affectits ecosystem is impor-tant. Secondly, how thoseeffects are rippled up intothe larger animals outsidethe lake is equally impor-tant. Chuck Schwartz,Charles Robbins, and theInteragency Grizzly BearStudy Team working withBob Rye and Pat Shanksrecently have analyzedhair from four bears in thepark. Two of those bearscome from areas veryclose to the lake, two are from fartheraway. The two bears close to the lake haveelevated levels of mercury in their hairwhereas those bears not living near thelake do not. So in this example, it seems astrong relationship exists between thegeology of the lake and grizzly bear andcutthroat trout ecology.

That’s one issue. Another is the spiresand how they formed. Scanning electronmicroscopic (SEM) images show that thespires are composed of a variety of

diatoms and silicified bacteria. And thatwas a big surprise. We had supposed thatthe hot silica-enriched waters hitting thecold lake water interface would precipi-tate amorphous silica without biologicinvolvement. When we went and looked atthe spires under the SEM, sure enough,our compositions were for pure silica but

the material was primarily silicified bacte-ria with diatoms. And so there’s somethinghappening on the floor of the lake that isvery much involved in some of the verybasic life forms that operate very closelywith development of these hydrothermalvents. So it’s kind of interesting to see thefull circle come back.

YS: What work remains to be done?What questions still need to be asked whenyou look at the lake?

LM: Well, for starters, I think the lake,the park, and science would be well servedby doing a series of cores on selected sitesin the lake. That would shed a lot of infor-mation about the timing of differentevents: timing of seismic events, ofhydrothermal explosion events, of land-slides. Cores collected in specific areas

would give informationabout what triggers thelandslides. Were they trig-gered seismically, or werethey triggered from thehydrothermal explosionevents? Or from some-thing else? Potentially,data from selected corescould tell us somethingabout evolution of the dif-ferent hydrothermal sys-tems. Not just thehydrothermal vents, butalso the large hydrother-mal explosion complexes.I would also like to knowmore about the climate ofYellowstone in the last12,000 years. Certainly,coring into the lake wouldgive us a clearer idea ofwhat the climate was likeduring these differentevents, and what kind ofinfluences there mighthave been.

We need to have a bet-ter understanding of theissue between large-scalecollapse of hydrothermal-ly altered features versuslarge-scale hydrothermalexplosions and associatedhazards. We need toimprove our understand-

ing of doming activity on the lake floor.Do these doming events always end up inan explosion, or do they end up in a col-lapse, or do some of them not do anything?I think that’s important. Are the domes thathave been identified in our surveys poten-tial precursors to hydrothermal explo-sions? If so, how do we monitor these fea-tures? Also the young and active grabennorth of Stevenson Island should be mon-itored, especially given this structure’sproximity to the Lake Hotel. Putting CO2


Lisa Morgan’s field notebook.

and SO2 sensors next to vents in the domesis important. I would like to see more workdone using LIDAR (light detection andranging) outside the lake. Ken Pierce andRay Watts’s initial work with this tech-nique in association with some other peo-ple shows that Storm Point may actuallybe an inflated structure.And so we might want toexamine that pretty close-ly. Much work remainsand, to summarize, thiswould include mapping,coring and associatedstudies, assessing thepotential hazards, andidentifying the instru-mentation needed formonitoring.

YS: How about in thebroader context of thecaldera outside the lake?

LM: Well, I wouldhope that we get a betterunderstanding of thehydrothermal explosionpotential inside thecaldera. Most, if not all ofthe hydrothermal explo-sions that we’ve identi-fied occur inside thecaldera. So that needs tobe assessed. I think it’salso very important tounderstand the “heavybreathing” aspect of theYellowstone caldera.And again, Ken Piercehas shown a lot of inter-esting data that looks atthe coincidence betweenuplift and subsidence ofthe Yellowstone caldera with relationshipto timing of some of these hydrothermalexplosion events. So I think that’s veryimportant. From my perspective, probablyone of the greatest and most likely poten-tial hazards in the park is the potential fora hydrothermal explosion. In terms ofscale, it’s not going to affect North Amer-ica, but it potentially could affect thepark’s facilities, infrastructure, and visi-tors. And when you think of the transientpopulation that goes through Yellowstone

on a daily basis, it’s very much an urbanpopulation. If you took the number of vis-itors that you have coming to Yellowstoneon an annual basis and divided it by thedays, you basically have the city of Boul-der, Colorado in Yellowstone every day.The problem with your population is it’s

moving all the time. But the park prettymuch controls where it moves. And so it’simportant that the park have a better under-standing of where these hazards mayoccur.

Clearly, assessment of other potentialhazards, such as volcanic and seismicevents, are big items and will be includedin the ongoing hazard assessment con-ducted under the auspices of the recentlyestablished Yellowstone Volcano Obser-vatory, a joint effort between the USGS,

the University of Utah, and the NationalPark Service (Yellowstone National Park).

A lot of work remains that will contin-ue to build on previous investigators’research and findings. We still have a farway to go in improving our understandingof the connections between geology and

biology, and how thebiota react to differentgeologic events in thepark.

YS: Finally, pleasedescribe some of yourmemorable momentsworking in the park.

LM: It’s been a chal-lenging and rewardingresearch experience towork in Yellowstone. It’sbeen so much fun towork in Yellowstone.And it’s just been kind ofa dream, like the summerwhen we did our back-packing trip up to FernLake, it was like, “I can’thandle any more discov-eries!” (Laughing) Justthe number of discover-ies we’ve been able tomake through the courseof our research has beenphenomenal, so I feelvery lucky to have hadthis opportunity. It’s alsobeen pretty awesome towork in this environmentwhere the sight of a griz-zly makes one realizewhat a unique, special,and still wild place Yel-lowstone is. To under-

stand the geologic framework in whichbears and other species inhabit allows us amore comprehensive understanding ofwhy certain species live where they do andthe challenges they face in their environ-ments in order to survive and what wemight do to enable their survival. For sev-eral of these species, Yellowstone is theirlast outpost, so it’s up to those of us whowork in the park to make sure that they’reprotected.

Spring 2003 13

LISA MORGAN

Yellowstone Lake.


The Anna.

Evolution of mapping Yellowstone Lake, 1871-2002

Henry W. Elliott, 1871 Hayden survey Hague report, 1896

Kaplinski, 1991 U.S. Geological SurveyNational Park Service

1999-2002

“The lake was very rough. The waves coming in were equal to waves on the sea coast. Elliott says they were able to take but three soundings, it being rough all the time.

The wind once was so strong that the mast was broken off and carried away. The boat rode splendidly."

Albert Peale, mineralogist, US Geological Survey Hayden survey, August 14, 1871

Spring 2003 15

HISTORY OF MAPPING YELLOWSTONE

LAKE

Yellowstone Lake is the largest high-altitude lake in North America, with anelevation of 2357 m (7731 feet) and a sur-face area of 341 km2 (Plate 1, inset). Over141 rivers and streams flow into the lake.The Yellowstone River, which enters at thesouth end of the Southeast Arm, dominatesthe inflow of water and sediment. The onlyoutlet from the lake is at Fishing Bridge,where the Yellowstone River flows northand discharges 2000–9000 cubic feet/sec-ond. The earliest attempt to produce adetailed map of the shoreline and bathym-etry of Yellowstone Lake occurred duringthe 1871 U.S. Geological Survey expedi-tion, when Ferdinand V. Hayden led 28scientists, scouts, and cooks in a survey ofwhat is now Yellowstone National Park.The sheer effort expended by this group,under the most primitive of working con-ditions, is impressive on its own, but espe-cially when considered in tandem with themany accomplishments of the survey. Aprimary goal of the party was “mak(ing) amost thorough survey of [YellowstoneLake],” reflecting Hayden’s general inter-est in watersheds and river drainagebasins.

A 4.5 × 11-foot oak boat with a woolenblanket sail was used to map Yellowstone

Lake. Mapping took 24 days and includedapproximately 300 lead-sink soundings.Navigation was carried out using a pris-matic compass. Albert Peale, the survey’smineralogist, described the process in hisjournal (see box).

The survey mapped a shoreline of 130miles; the most recently mapped shorelinegives the perimeter of Yellowstone Lake to

be 141 miles (227 km). Over 40 sound-ings were taken along the north and westshores, the deepest being around 300 feet.The survey estimated the deepest part ofthe lake would be farther east and no deep-er than 500 feet. This depth range is com-parable to what we know today; the deep-est point in Yellowstone Lake is due east ofStevenson Island (Plate 3B) at 131 m (430feet) deep. In addition, the Hayden surveyidentified the long NE/SW-trending trough

crossing the central basin. Plate 1 showsthe map of Yellowstone Lake as drawn byHenry Elliott of the Hayden survey. Themap not only shows a detailed topograph-ical sketch of the Yellowstone Lake shore-line but many of the points where sound-ings were taken for the survey.

A second map of Yellowstone Lake,published in 1896, incorporated elements

of the original 1871 Elliott map from theHayden expedition. While no mention ismade in the official USGS report of addi-tional mapping or modifications made tothe Elliott Yellowstone Lake map, or evenof any additional work on YellowstoneLake during the years of the Hague survey(1883–89, 1890–91, 1893), the lake wasclearly resurveyed and triangulated byH.S. Chase and others, as published inmaps in the Hague report and reflected in

The Floor of Yellowstone Lake is Anything but Quiet!New Discoveries in Lake Mapping

by Lisa A. Morgan, Pat Shanks, Dave Lovalvo, Kenneth Pierce, Gregory Lee, Michael Webring, William Stephenson, Samuel Johnson,Carol Finn, Boris Schulze, and Stephen Harlan

Facing page: Plate 1. From top left: (A) Henry Elliott's 1871 map of Yellowstone Lake. The headwaters of the Snake River, Upper Valley ofthe Yellowstone River, and Pelican River are shown. The area now known as West Thumb is referred to as the South West Arm. (B) W.H.Jackson photo of the survey boat, The Anna, with James Stevenson (left) and Chester Dawes on July 28, 1871. (C) 1896 map of YellowstoneLake and surrounding geology as mapped in the Hague survey. (D) 1992 Kaplinski map. (E) New high-resolution bathymetric map acquiredby multibeam sonar imaging and seismic mapping. The area surrounding the lake is shown as a gray-shaded relief map.

“A man stands on the shore with a compass and takes a bearing to the man in theBoat as he drops the lead, giving a signal at the time. Then the man in the Boattakes a bearing to the fixed point on the shore where the first man is located andthus the soundings will be located on the chart...[Elliott will] make a systematicsketch of the shore with all its indentations [from?] the banks down, indeed, mak-ing a complete topographical as well as a pictorial sketch of the shores as seen fromthe water, for a circuit of at least 130 miles. He will also make soundings, at var-ious points.”


Plate 1. The 1896 map built upon theElliott map and refined areas on the shore-line, such as in the Delusion Lake areabetween Flat Mountain Arm and BreezePoint. Where the Elliott map of Yellow-stone Lake shows Delusion Lake as an armof the lake, the Hague map delineates itsboundaries and identifies swampy areasnearby. The maps from the Hague surveyalso include a rather sophisticated geolog-ic map of the subaerial portions of the parkaround the lake.

The next significant attempt to mapYellowstone Lake came a hundred yearslater and employed a single-channel echosounder and a mini-ranger for navigation,requiring interpolation between tracklines. Over 1475 km of sonar profiles werecollected in 1987, using track lines spacedapproximately 500 m apart and connectedby 1–2 km-spaced cross lines. An addi-tional 1150 km of sonar profiles were col-lected in 1988 to fill in data gaps from the

1987 survey. The map identified manythermal areas on the floor of the lake. Theresulting bathymetric map has served asthe most accurate lake map for Yellow-stone National Park for over a decade, andhas proven invaluable in addressing seri-ous resource management issues, specifi-cally monitoring and catching the aggres-sive and piscivorous lake trout.

Ten years after that bathymetric map,development of global positioning tech-nology and high-resolution, multi-beamsonar imaging justified a new, high-reso-lution mapping effort in the lake. Mappingand sampling conducted in 1999–2002 asa collaborative effort between the USGS,Eastern Oceanics, and the National ParkService utilized state-of-the-art bathymet-ric, seismic, and submersible remotely-operated vehicle (ROV) equipment to col-lect data along 200-m track lines with laterinfill, where necessary. The 1999–2002mapping of Yellowstone Lake took 62

Figure 1. (A) Index map showing the 0.64-Ma Yellowstone caldera, the distribution of itserupted ignimbrite (the Lava Creek Tuff, medium gray), post-caldera rhyolitic lava flows(light gray), subaerial hydrothermal areas (red), and the two resurgent domes (shown asovals with faults). The inferred margin of the 2.05-Ma Huckleberry Ridge caldera is alsoshown. (B) (facing page) Geologic shaded relief map of the area surrounding YellowstoneLake. Yellow markers in West Thumb basin and the northern basin are locations of active orinactive hydrothermal vents mapped by seismic reflection and multibeam sonar. (C) (facingpage) Color shaded-relief image of high-resolution, reduced-to-the-pole aeromagnetic map.Sources of the magnetic anomalies are shallow and include the post-caldera rhyolite lavaflows (some outlined in white) that have partly filled in the Yellowstone caldera. Rhyoliticlava flows (outlined in white) underlying Yellowstone Lake are shown clearly in this map.

ii

1A

N

0 10 20 30 40 50 KM

X

X

Yellowstone Lake

Yellowstone National Park

2.05-Ma Huckleberry Ridge caldera boundary

postcollapse rhyolite lava flows

hot spring areas

0.64-Ma Yellowstone caldera boundary

Lava Creek Tuff

Norris-MammothCorridor

resurgent domes

l l l l ll

Yellowstone Plateau

Acronyms used in figures

BFZ: Buffalo Fault ZoneEBFZ: Elephant Back Fault ZoneEF: Eagle Bay Fault ZoneHFZ: Hebgen Fault ZoneIP: Indian PondLHR: LeHardy RapidsLV: Lake VillageMB: Mary BayPV: Pelican ValleyQa: Quaternary alluvium (deltaic sedi-ments)Qg: Quaternary glacial depositsQh: Quaternary hydrothermal depositsQhe: Quaternary hydrothermal explo-sion depositsQl: Quaternary shallow lake sediments(shallow water deposits and submergedQld: Quaternary deep lake sediments(laminated deep-basin deposits)Qls: Quaternary land slide depositsQpca: Quaternary Aster Creek flowQpcd: Quaternary Dry Creek flowQpce: Quarternary Elephant Back flowQpch: Quaternary Hayden Valley flowQpcl: Quaternary tuff of Bluff PointQpcm: Quaternary Mary Lake flowQpcn: Quaternary Nez Perce flowQpcp: Quaternary Pitchstone PlateauflowQpcw: Quaternary West Thumb flowQpcz: Quaternary Pelican Creek flowQps: Quaternary tuff of Bluff Point Qs: Quaternary sedimentsQt: Quaternary talus and slope depositsQvl: Quaternary Lava Creek Tuff Qy: Quaternary Yellowstone GroupignimbritesSI: Stevenson IslandSP: Sand PointSPt: Storm PointTFZ: Teton Fault ZoneTl: Tertiary Langford Formation vol-canics TL: Turbid LakeTli: Tertiary Langford Formation intru-sivesTv: Tertiary volcanic rocksYR: Yellowstone River

Spring 2003 17

IP TLPV

Frank Is.

SoutheastArm

SouthArm

LV SPt

SP

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Tv

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northern basin

YELLOWSTONE CALDERAMARGIN

Qy

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centralbasin

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The Promontory

Flat Mtn. Arm

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Dot Is.

QpcnQpcn

AsterCreekflow

Elephant Back flow

Qmf

Qy

Qy

1B

Qpc?

WestThumb flow

Qpc?

1C

Spruce Creekflow

Tv(?)Tv

Tv

Tv

Qpcd

l l

l ll

ll

ll

ll

l

-47.1

-134.8

-257.3

-310.1

-413.6nT

105.4

-203.5

ll

ll

l

ll l l

0 10 kmll

44º20'

44º15'

44º25'

44º30'

44º35'

44º36'44º36'

44º15'

-110º10'-110º40'-110º10'-110º20'-110º40'-110º40'

Glossary of termsamphipods: crustaceans of small size and laterally-compressed bodyanastomozing: joining of the parts of branched systemsbathymetric: relating to the measurement of depth and floor contour of bodies of waterbreccia: sharp fragments of rock embedded in a fine-grained matrix (as sand or clay)brittle-ductile transition zone: area where brittle and malleable rock meet beneath the earth’s surfacedB: decibeldiatomaceous: consisting of or abounding in diatoms (unicellular or colonial algae having silicified cell walls)en echelon: referring to an overlapped or staggered arrangement of geologic features fathometer: tool used to measure fathoms (6-foot units used to measure water depth)graben: a depressed segment of the earth’s crust bounded on at least two sides by faults and generally longer than it iswideH2S: hydrogen sulfideka: thousand years agolacustrine: of, relating to, formed, or growing in lakeslaminated: composed of layers of firmly united materiallobate: having lobesMa: million years agomW/m2: milliWatt per square meterpotamodromous: migratory in fresh waterreduced-to-the-pole map: aeromagnetic map designed to account for the inclination of Earth’s magnetic field. Princi-pal effect is to shift magnetic anomalies to positions directly above their sources.seismic reflection profile: a continuous record of sound waves reflected by a density interfacesilicic: of, related to, or derived from silica or siliconstrike-slip displacement: displacement whose direction of movement is parallel to the direction of its associated faultU-series disequilibrium dating: a method of determining the age of a desposit by analyzing the isotopes produced byradioactive decay of uranium isotopes

Most definitions from Webster’s Third New International Dictionary (1981)


days over a 4-year period, compared toHayden’s survey of 24 days in 1871. Itbegan in 1999 with mapping the northernbasin and continued in 2000 in WestThumb basin, in 2001 in the central basin,and in 2002 in the southern lake includingthe Flat Mountain, South, and SoutheastArms (see Plate 1E). Unlike any of the pre-vious mapping efforts, the 1999-2002swath multi-beam survey produced con-tinuous overlapping coverage, collectingmore than 220,000,000 soundings and pro-ducing high-resolution bathymetricimages. Seismic reflection records of the

upper 25 m of the lake bottom wereobtained along with the bathymetry in theentire lake excluding the South and South-east Arms. This effort has produced a mapthat is accurate to the <1-m scale in mostareas. The following report focuses onresults of this mapping effort and the inter-pretation of the newly discovered features.

GEOLOGIC SETTING

Powerful geologic processes in Yel-

lowstone National Park have contributedto the unusual shape of Yellowstone Lake,which straddles the southeast margin ofthe Yellowstone caldera (Figure 1A), oneof the world’s largest active silicic volca-noes. Volcanic forces contributing to thelake’s form include the explosive, caldera-forming, 2.05-Ma eruption of the Huckle-berry Ridge Tuff, followed by eruption ofthe 0.64-Ma Lava Creek Tuff. Followingexplosive, pyroclastic-dominated activity,large-volume rhyolitic lava flows wereemplaced along the caldera margin, infill-ing much of the caldera (Figures 1A, B). A

smaller caldera-forming event about 140ka, comparable in size to Crater Lake, Ore-gon, created the West Thumb basin. Sev-eral significant glacial advances and reces-sions continued to shape the lake and over-lapped the volcanic events. Glacial scourdeepened the central basin of the lake andthe faulted South and Southeast Arms(Figure 1B). More recent dynamicprocesses shaping Yellowstone Lakeinclude currently active fault systems,

development of a series of postglacialshoreline terraces, and postglacial (<12-15 ka) hydrothermal-explosion events,which created the Mary Bay crater com-plex and other craters.

The objective of the present work is tounderstand the geologic processes thatshape the lake floor. Our three-prongedapproach to mapping the floor of Yellow-stone Lake located, imaged, and sampledbottom features such as sublacustrine hot-spring vents and fluids, hydrothermaldeposits, hydrothermal-explosion craters,rock outcrops, glacial features, slump

blocks, faults, fissures, and submergedshorelines.

RESULTS AND DISCOVERIES OF HIGH-RESOLUTION MAPPING

Topographic margin of the caldera.

Geologic maps show the topographicmargin of the Yellowstone caldera as run-ning below lake level in Yellowstone Lakebetween the western entrance to Flat

landslidedeposits

hydrothermalvents

ejectadeposits

explosioncraters

graben

spirefield

fissures

PelicanRoost

lavaflows

lava flows

StormPoint

Indian Pond

Qhe

Mary Bay

TurbidLake

SteamboatPoint

hydrothermal vents

submergedlakeshoreterraces

StevensonIsland

Elliot'sCrater

PelicanValley

A

A'

B

B'

GullPt.

BridgeBay

West Thumb Basin Northern Basin

Qs

44o30'

44o

31'

44o32'

44o33'

44o34'

44o35'

Qpce

Qpce

Qpce

Qs

Qs QylQci

Qhe

Qhe

Tl

Qyl

Tl

Qyl

QsTl

Qpcw

Qpcw

Qpcw

110 16o '110 18

o '110 20o

'

110 24o

'

110 26'o

YellowstoneRiver

Qpcw

Qyl

SandPt.

Qyl

LakeVillage



DuckLake

N

QsQs

Qs

Qs

Qps

Qps

Qh

Qhe

Qpce

Qpcd

Qpcd

Qpcw

QpceQpcw

110o34' 110o30'110o32'

44o24'

44o28'

44o26'

Qh

Qpcd

1 km

hydrothermalvents

hydrothermal vents

explosioncrater lava

flows

lavaflows

1 km

West Thumboutlet toYellowstoneLake

Figure 2. (A) New high-resolution bathymetric map of the West Thumb basin of Yellowstone Lake, acquired by multibeam sonar imagingand seismic mapping in 2000, showing a previously unknown ~500-m-wide hydrothermal explosion crater (east of Duck Lake), numeroushydrothermal vents, submerged lakeshore terraces, and inferred rhyolitic lava flows that underlie 7- to 10-m of post-glacial sediments. (B)High-resolution bathymetric map of the northern basin of Yellowstone Lake, acquired in 1999, showing large hydrothermal explosion cratersin Mary Bay and south-southeast of Storm Point, numerous smaller craters related to hydrothermal vents, and landslide deposits along theeastern margin of the lake near the caldera margin. Post-caldera rhyolitic lava flows underlie much of the northern basin. Fissures west ofStevenson Island and the graben north of it may be related to the young Eagle Bay fault (see Fig. 1B).

Spring 2003 19

Mountain Arm and north of Lake Butte(Figure 1B). Our mapping of the centralbasin of Yellowstone Lake in 2001 identi-fied the topographic margin of the Yel-lowstone caldera as a series of elongatedtroughs northeast from Frank Island acrossthe deep basin of the lake. Based on ournew data and high-resolution aeromagnet-ic data, we infer the topographic margin ofthe Yellowstone caldera to pass throughthe southern part of Frank Island.

Rhyolitic lava flows.

Large-volume, subaerial rhyolitic lavaflows on the Yellowstone Plateau controlmuch of the local topography and hydrol-ogy. Characteristic lava-flow morpholo-gies include near-vertical margins (someas high as 700 m), rubbly flow carapaces,

hummocky or ridged tops, and stronglyjointed interiors. Stream drainages tend tooccur along flow boundaries, rather thanwithin flow interiors.

A major discovery of the lake surveysis the presence of previously unrecognizedrhyolitic lava flows underlying much ofthe lake floor. Field examination of rhyo-lite flows shows that many areas identifiedthrough the aeromagnetic mapping as hav-ing low magnetic intensity values corre-spond to areas with hydrothermal activity,

or faulting or fracturing along whichhydrothermal alteration has occurred. Webelieve the lava flows are key to control-ling many morphologic and hydrothermalfeatures in the lake.

Areas of the lake bottom around theperimeter of West Thumb basin (Figures2A, 2B) have steep, nearly vertical mar-gins, bulbous edges, and irregular hum-mocky surfaces, similar to postcollapserhyolitic lava flows of the YellowstonePlateau. Seismic reflection profiles in thenear-shore areas of West Thumb basinshow high-amplitude reflectors (indicat-ing low magnetic intensity) beneath about7–10 m of layered lacustrine sediments(Figure 3A).

Areas such as the West Thumb andPotts geyser basins in West Thumb basin,and Mary Bay in the northern basin, cur-rently have extremely high heat flow val-ues (1650–15,600 mW/m2). Current heatflow values in Bridge Bay (580 mW/m2)are relatively low compared to Mary Bay,

Figure 2D. High-resolution bathymetricmap of the South, Southeast, and FlatMountain Arms, acquired by multibeamsonar imaging in 2002, showing the glaciat-ed landscape of the lake floor in the south-ernmost part of Yellowstone Lake and sever-al faults. The bathymetry in the SoutheastArm contains many glacial meltwater andstagnant ice block features; the area is infor-mally referred to as the "Potholes of theSoutheast Arm," and resembles much of thekettle dominated topography mapped byKen Pierce and others in Jackson Hole(inset image).

Figure 2C. High-resolution bathymetric mapof the central lake basin, acquired by multi-beam sonar imaging and seismic mapping in2001, showing the Yellowstone caldera topo-graphic margin, a large hydrothermal explo-sion crater south of Frank Island, and numer-ous faults, fissures, and hydrothermal vents asindicated.

central basin

Tv?

Tv

Qs

Tv

Tv

Tv?

ParkPoint

FrankIsland

DotIsland

lavaflows

calderamargin

explosioncrater

hydrothermalvents

hydrothermalvents

lavaflow

l l1 km

Qpca

Qpca

Eagle Bayfaultzone

Qpce

Qpca

Qy

Central Basin

Qpcw

-110o27'30" -110o20'

44o25'

44o30'

Delusion Lake

ElkPoint

Qs

Qs

Qs

Qs

Qs

South, Southeast, and Flat Mountain Arms

1 km

1 km

"Potholes of the Southeast Arm"


yet the Bridge Bay area has low magneticintensity values. Evidence for pasthydrothermal activity is present as inac-tive hydrothermal vents and structures, andmay have been responsible for demagnet-

ization of the rocks there. South of BridgeBay and west of Stevenson Island, lowmagnetic intensity values reflect activehydrothermal venting and relatively highheat flow values. Low magnetic intensityvalues in the northern West Thumb basinalso may be due to past hydrothermalactivity, as evidenced by vent structuresthere. Comparison of geologic maps (Fig-ure 1B) with the high-resolution aeromag-netic maps shows a crude relation of mag-netic anomalies to the mapped individuallava flows on land (Figure 1C).

The magnetic signatures, combinedwith the high-resolution bathymetric andseismic reflection data, allow identifica-tion and correlation of sediment-coveredrhyolitic lava flows far out into the lake(Figures 1, 2). For example, the AsterCreek flow (Qpca) southwest of the lake(Figure 1C) is associated with a consis-tent, moderately positive, magnetic anom-aly that extends over the lake in the south-

east quadrant of West Thumb basin, alongthe southern half of the West Thumb chan-nelway, and over the central basin of thelake well past Dot and Frank Islands (Fig-ures 1, 2). The Aster Creek flow has fewmapped faults, and few areas that havebeen hydrothermally-altered. Similarly,the West Thumb flow (Qpcw) can betraced into the lake in northeastern WestThumb basin, along the northern half ofWest Thumb channelway, and into thenorthern basin beneath Stevenson Islandand Bridge Bay (Figure 2C). In contrast,the Elephant Back flow contains a well-developed system of northeast-trendingfaults or fissures that has been extensivelyaltered so that the magnetic signature ofthis unit is fractured with a wide range ofvalues in magnetic intensity (Figure 2D).

Field examination of subaerial rhy-olitic lava flows indicates that negativemagnetic anomalies, for the most part, areassociated with extensive hydrothermal

1 km

3A

B.

3B

ll

l

0.00

36.25

72.50

dept

h (m

)

B'

A'

B

A

domalfeature

gaspocket

uplifted, tilted blockwith deformedsediments

vent

domed sediments

fault domed sediments

high-amplitude reflector

draped lacustrinesediments

lacustrinesediments

water bottom

lacustrinesediments gas

pockets

ventdomalstructures

vent

gas pockets

water bottom

1 km

0.00

36.25

72.50

108.75

145.00

dept

h (m

)

ll

ll

l

r (rhyolite flow)

Figure 3. (A) High-resolution seismicreflection image from northwestern WestThumb basin showing high-amplitude(red) reflector interpreted as a sub-bottomrhyolitic lava flow. Glacial and lacustrinesediments, marked in blue, overlie thisunit. (B) High-resolution seismic reflec-tion image across part of Elliott's explo-sion crater, showing small vents, gas pock-ets, and domed sediments in the lacustrinesediments that overlie the crater flank.Lacustrine sediment thickness in the maincrater indicates 5-7 thousand years of dep-osition since the main explosion. Morerecent explosions in the southern part ofthe large crater ejected post-crater lacus-trine sediments and created new, smallercraters and a possible hydrothermalsiliceous spire.

Spring 2003 21

alteration or, in places, alterationdue to emplacement of lava flowsinto water, such as ancestral Yel-lowstone Lake. For example, theWest Thumb rhyolite flow duewest of the Yellowstone River isglassy, flow-banded, and fresh;the magnetic intensity values inthis area generally are high (Fig-ures 1B, 1C, 2C). In contrast, inareas where flows were emplacedinto water, such as the WestThumb rhyolite flow exposed onthe northeast shore of WestThumb basin (Figures 1B, 2B),magnetic intensity values are low(Figure 1C). The low magneticvalues of flows emplaced intowater may be primarily carriedby the fine-grained and alteredmatrix in the massive rhyolitic breccias,highly fractured perlitic vitrophyre, clasticdikes, and entrained stream, beach, andlake sediments in an altered matrix.

Large hydrothermal explosion craters.

Subaerial hydrothermal explosionshave occurred repeatedly in YNP over thepast 12 ka, and are confined primarilywithin the boundaries of the Yellowstonecaldera (Figure 1). Large (>500 m), circu-lar, steep-walled, flat-bottomed depres-sions are mapped at several sites in Yel-lowstone Lake in the West Thumb, cen-tral, and northern basins (Figure 2). Theseare interpreted as large compositehydrothermal explosion craters similar inorigin to those on land, such as DuckLake, Pocket Basin, the Turbid Lakecrater, and the Indian Pond crater (Figures1B, 2B, 2C).

A newly-discovered, 500-m-diameter,sublacustrine explosion crater in the west-ern part of West Thumb basin, near thecurrently active West Thumb GeyserBasin, is only 300 m northeast of DuckLake (Figures 2A, 2B), a postglacial (<12ka) hydrothermal explosion crater. Here,heat-flow values are as high as1500mW/m2, reflecting the hydrothermalactivity that contributed to the formation

of the offshore explosion crater. The 500-m-wide West Thumb explosion crater issurrounded by 12– 20 m high, nearly ver-tical walls, and has several smaller nested

craters along its eastern edge. These nest-ed craters are as deep as 40 m, and areyounger than the main crater. Tempera-tures of hydrothermal fluids emanatingfrom the smaller northeast nested craterhave been measured by ROV at 72°C.

Another newly-discov-ered, large, subaqueoushydrothermal explosion crateris the >600-m-wide elongate,steep-walled, flat-flooredcrater south of Frank Island(Figure 2D). Muted topogra-phy suggests that this explo-sion crater is one of the oldeststill recognizable in Yellow-stone Lake. Further, this crateroccurs in an area where heatflow values are at present rela-tively low. Submersible inves-tigations do not indicatehydrothermal activity withinthe crater.

In the northern basin ofYellowstone Lake, Mary Baycontains a roughly 1-km by 2-

km area of coalesced explosion craters(Figures 2A, 2C), thus making it theworld’s largest known hydrothermalexplosion system. Boiling temperature in

the deep part of Mary Bay is about 160ºC.Submersible investigations show that flu-ids from a 35-m-deep hydrothermal venthave temperatures near the 120ºC limit ofthe temperature probes used, reflectingextremely high-heat flow values in this

44.5167o

44.5111o I

-110.361o

-110.356o

i i

_

_

_

_

_

_

_

_

_

_

_

36.2

43.8

51.3

58.9

66.4

73.9

81.5

89.0

96.6

104.1

111.7

I

Depth (m)

The Deepest Hydrothermal Vent on The Floor of Yellowstone Lake

Plate 3. (A) High-resolution bathymetric image of hydrothermal siliceous spires on the lake floor. (B) High-resolution bathymetric image ofhydrothermal vent craters along a northwest-trending fissure east of Stevenson Island. The deep hole at the southeastern end of the trend isone of the largest hydrothermal vent areas in the lake, and is also the deepest point in the lake at 133 m.

Spring 2003 23

0 10 km

110o21'46.01"44o31'56.01"

105.4

-47.1

-134.8

-203.5

-257.3

-310.1

-413.6nT

5.56

11.07

16.59

22.10

27.62

33.13

38.65

44.16

49.67

depth (m)

4A 4B

4C 4D

4E 4F

northeast linear trend

Elliott's crater

StormPoint

"InflatedPlain"

EBFZ

Gull Point

Sand Point

0 200 400 600 800 1000 m

21'50" 21'40" 21'30" 21'20" 21'10" 110o21'

32'20"

44o32'

32'10"

32'30"

110o21'07.52"

N

5.7 m

46.6 m

0 100 200 300 400 500 m0 100 200 300 400 500 m

44o

32'

32'05"

32'10"

32'15"

21'30" 21'20" 21'10"21'40"110o 21'30" 21'20" 21'10"21'40"110o

44o

32'

32'05"

32'10"

32'15"

44o32'18.78"

5.7 m

46.6 m

Rock Point

Qs

Qpce

Qhe

Weasel Creek

northeast linear trend


area. Radiocarbon dates from charcoal inbreccia deposits and underlying soilsexposed in the wave-cut cliffs along theMary Bay shore indicate that eruption ofthis crater occurred at 13.4 ka. Detailedstratigraphic measurements of the brecciadeposit indicate that multiple explosionsand emplacements occurred during for-mation of this large and complex feature.

A dark, clean, well sorted, cross- toplanar-bedded, generally fine-grained sandoverlying varved lake sediments occurs asa sedimentary interbed between brecciadeposits within the Mary Bay brecciadeposit. These types of deposits are likelyephemeral, and the likelihood of theirpreservation in the stratigraphic record isslight. The sand unit below the Mary Baybreccia is 1.5 to > 2 m thick and containsnumerous small en echelon faults. Thesedeposits are similar to other paleoseis-mites. We conclude that this sand unit rep-resents a deposit from a possible earth-quake-generated tsunami-like wave, whichmay be related to triggering the explosionof the Mary Bay crater complex.

One kilometer southwest of the MaryBay crater complex is another newly-dis-covered, large (~800-m-diameter), com-posite depression informally referred to asElliott’s crater (Figure 2C, Plate 3A),named after Henry Elliott who helped mapYellowstone Lake in the 1871 Hayden sur-vey. Development of Elliott’s hydrother-mal explosion crater is best illustrated in anorth–south seismic reflection profile(Figure 3B). Zones of non-reflectivity inthe seismic profile on the floor and flanksof the large crater probably representhydrothermally altered, and possibly het-erolithic explosion-breccia deposits, simi-lar in character to those exposed on landand associated with subaerial explosioncraters. Seismic profiles in the hummockyarea southeast of Elliott’s crater are alsonon-reflective, and may represent a layerof heterolithic and/or hydrothermallyaltered material erupted from this crater. Incontrast to the subaerial craters, whichhave radial aprons of explosion-brecciadeposits that rim the crater, many of thesublacustrine circular depressions lack anobvious apron. This may indicate eithermore widespread dispersal of ejectiondeposits in the lake water or that someother process, such as catastrophic col-

lapse of sealed cap rock, created thedepressions.

Following the initial major explosiveevent of Elliott’s crater, lacustrine sedi-ments accumulated in the floor of thecrater and on its south flank. Based on sed-imentation rates in the lake, post-eruptivesediment thickness of ~8 m indicates themain hydrothermal explosion occurredbetween 8 and 13 ka. Opaque zones with-in the stratified sedimentary fill of thecrater indicate the presence of hydrother-mal fluids and/or gases. The presence oftwo younger craters at the south end of themain crater floor further indicates morerecent hydrothermal activity, and possiblyyounger explosions. A north-south seis-mic profile across Elliott’s crater showsabout 10 m of vertical difference in heightbetween the rims. This difference mayresult from doming associated withhydrothermal activity prior to initial explo-sion.

Hydrothermal vents on the floor ofYellowstone Lake.

Geochemical studies of the vents indi-cate that ~10% of the total deep thermalwater flux in Yellowstone National Parkoccurs on the lake bottom. Hydrothermalfluids containing potentially toxic ele-ments (arsenic, antimony, mercury, molyb-denum, tungsten, and thallium) signifi-cantly influence lake chemistry, and pos-sibly the lake ecosystem. ROV observa-tions indicate that shallow hydrothermalvents are home to abundant bacteria andamphipods that form the base of the localfood chain that includes indigenous cut-throat trout, grizzly bears, bald eagles, andotters that feed on the potamodromous cut-throat trout during spawning in streamsaround the lake.

In seismic reflection profiles (Figure3B), hydrothermal vent features are typi-cally imaged as V-shaped structures asso-ciated with reflective layers that aredeformed or have sediments draped acrosstheir edges. Areas of high opacity or noreflection occur directly beneath them, andare interpreted as gas pockets, gas-chargedfluids, or hydrothermally-altered zones.Evidence for lateral movement ofhydrothermal fluids is seen beneath andadjacent to hydrothermal vents identifiedin the seismic reflection profiles. The areas

of opacity in the seismic data, and of lowvalues of magnetic intensity in the aero-magnetic data, represent larger zones ofhydrothermal alteration than seen in thesurficial hydrothermal vents.

Seismic reflection profiles of the sur-veyed areas in the northern, central, andWest Thumb basins of Yellowstone Lakereveal a lake floor covered with laminated,diatomaceous, lacustrine muds, many ofwhich are deformed, disturbed, andaltered. High-resolution bathymetric map-ping reveals that many areas contain small(<20 m) depressions pockmarking the lakebottom (Plate 2, cover).

Many vent areas are associated withsmaller domal structures in which the lam-inated, diatomaceous, lacustrine sedimentshave been domed upward as much as sev-eral meters by underlying pockets of gas orgas-charged fluids, presumably rich insteam and possibly CO2. Hydrothermalactivity beneath the domes silicifies thesediments causing them to become sealed,impermeable, and weakly lithified so thattheir resultant compaction is minimal. Theunaltered zones of muds surrounding thesedomes become more compacted over timeand contribute to the overall domal mor-phology. These domal structures may beprecursors to small hydrothermal explo-sions, collapse zones, and areas whereactive hydrothermal venting may developin the future.

An active domal structure informallyreferred to as the “Inflated Plain” was orig-inally recognized in the 1999 bathymetricsurvey of the northern basin as a relative-ly large “bulge-like feature”. The “InflatedPlain” covers a roughly circular area witha diameter of ~1 km, and rises several 10sof meters above the surrounding lake floor.This area hosts numerous active and vig-orous hydrothermal vents, smaller domalstructures, and vent deeps.

As seen in Figure 4A, the “InflatedPlain” lies along a northeast linear trend inline with Storm Point and Indian Pond,both areas of hydrothermal explosion ori-gin, to the northeast; an unnamed trough tothe southwest; and Weasel Creek farthersouthwest, west of the lake (Figure 2B,4A). We informally refer to the northeastlinear trend as the “Weasel Creek linea-ment.” Weasel Creek is an unusuallystraight drainage, as are two smaller sub-

Spring 2003 25

parallel drainages due north of it, and mayrepresent a linear zone of weakness. The“Weasel Creek lineament” also is reflect-ed as a linear zone of low magnetic inten-sity in the high-resolution magnetic map ofthe area (Figure 4B), and may reflect azone of upwelling hydrothermal fluids thathave contributed significantly to thedemagnetization of the rocks present. Thisstructure appears to left-laterally offset tothe “outlet graben” to the north from anincipient graben to the south associatedwith the “fissures.”

In summer 2002, while traversing the“Inflated Plain” area in the boat, RV Cut-throat, we noted a strong scent of H2S, a10–30-m diameter plume of fine sedi-ments, and large concentrations of bub-bles, many of them quite vigorous, at thelake surface. The fine sediment plume wasdetected by the fathometer as a strongreflector, concentrated ~3 m below thelake surface. For Dave Lovalvo, this wasthe first time in 18 years of working in thisarea that any of these phenomena havebeen observed. The depth of the lake floorhere is ~28 m.

A close-up, bathymetric image of the“Inflated Plain” (Figure 4C) shows abulging, domal structure, pockmarkedwith numerous hydrothermal vents andcraters. Clear evidence of hydrothermalalteration is seen in the amplitude map(Figure 4D), where bright areas are reflec-tive due to their relative hardness anddegree of silicification. Figures 4E and Fshow the “Inflated Plain” in 2-dimension-al and 3-dimensional perspectives, respec-tively, and plainly demonstrate how thisfeature rises as much as 30 m from the lakefloor.

Siliceous spires.

Siliceous spires in Bridge Bay (Figure2B), in the northern basin of YellowstoneLake, were discovered by Dave Lovalvo in1997, and are described here because theyrepresent an end-member of hydrothermaldeposit development in the lake, clearlyimaged by multibeam sonar studies.Approximately 12–15 spires are identifiedin water depths of 15 m. These roughlyconical structures (Figure 5A) are up to 8m in height and up to 10 m wide at thebase. A small, 1.4-m-tall spire collectedfrom Bridge Bay in cooperation with the

National Park Service in 1999 shows thespire base to be shallow (~0.5 m below thesediment-water interface), irregular, androunded; spire material above the lakefloor constitutes about 75% of the entirestructure. The lake floor level is recordedon the spire as a zone of banded ferro-manganese, oxide-stained, clay-rich, anddiatomaceous sediments. Below the lakefloor, the spire is not oxidized, whereasabove it, the spire has a dark, reddish-brown, oxide coating (Figure 5B). The

interior of the collected spire is white, fine-ly porous, and has thin (from 0.3 cm to <3cm diameter), anastomozing vertical chan-nels through which hydrothermal fluidsflowed. Little oxide occurs in the interiorof the spire structure, but oxidation sur-faces are present on former growth fronts(Figure 5B). Chemical and oxygen-isotopeanalyses and scanning electron micro-scope (SEM) studies of spire samplesshow them to be composed of silicifiedbacteria, diatom tests, and amorphous sil-

5C

5B5A

Depth (m)

10 µm

5D

1

10

100

1000

10000

ll llllll

ll

ll

ll

ll

ll

lll

l

As Ba Mn Mo Sb Tl W

lllll llllllllllllllllllllllllllllll

ll

ll

ll

lll

ll

ll

ll

lll

ll

ll

ll

lll samples fromoxidized exterior

samples fromsiliceous interior{

{

18.32

13.66

14.13

14.59

15.06

15.53

15.99

16.46

16.92

17.39

17.85

ll

ll

ll

ll

ll

l

10 cm

cutinterior section

growth fronts

exterior interior

4 m

*

10 cm

Figure 5. (A) Bathymetric image of spires in Bridge Bay, showing roughly conicalshapes. About a dozen such siliceous sinter spires occur near Bridge Bay, some as tall as8m. Many of the spires occupy lake-bottom depressions (possible former explosion orcollapse craters). (B) Photographs of the exterior and interior of a 1.4-m-tall spire samplerecovered from Bridge Bay by NPS divers. The sediment-water interface of this spire isapparent near the base of the exterior section, as seen in the dramatic change in color inthe outer rind of red-brown ferromanganese oxide to the light gray interior. (The redasterisk on the photograph showing the exterior is on a natural external surface of thespire below the sediment-water interface.) Former growth fronts on the spire can be seenas shown in the photograph of the interior section. (C) SEM image of diatoms, silicifiedfilamentous bacteria, and amorphous silica from a spire sample. (D) Summary bar graphof chemical analyses of spire samples showing substantial concentrations of potentiallytoxic elements arsenic, barium, manganese, molybdenum, antimony, thallium, andtungsten.


Monument Geyser Basin

4947500

4947550

4947600

4947650

4947700

4947750

4947800

4947850

519500 519550 519600 519650

498.3 and 3518.18.2 (g)88.7oC 88.5oC1.8 1.1

498.1 and83.7oC1.1

498.4 and87.7oC2.5

3518.14.186.8oC

3518.19.3 (g)88.7oC

3518.15.1a (g)86.8oC

3518.17.182oC1.6

498.521.9oC2.3

495.188.5oC1.1

495.288.4oC1.3

495.490.6oC1.1

498.223.4oC1.2

528.1, 528.5(duplicates)71.1oC1.1

UTM coordinates, Zone 12, NAD27

50 meters

ACID ALTERATION AREA

HOT SPRINGS

SPIRES

WATER SAMPLES

SPIRE #1MonumentGeyser (steam)

SPIRE #6

SPIRE #5Whale

SPIRES #2 & 3Sphinx & Walrus

SPIRES #4A &4BBison & Shrub

6A

6B

6C

6D 6E

6F

Figure 6. (A) Monument Geyser Basin caps a larger hydrothermal system along a north–northwest-trending fissure. The area in white is com-posed of hydrothermally-altered Lava Creek Tuff. (B) Index map of Monument Geyser Basin showing the extent of hydrothermal alteration anddistribution of the spire-like structures, hot springs, and water-sample localities. The values in the boxes represent individual sample numbers,temperatures, and pH. (C) Looking south into Monument Geyser Basin. Note that the basin has a central trough and contains as many as sevenspire-like siliceous structures. (D) Spire-like structure on the northern edge of the basin, informally referred to as the Walrus. (E) Another spire-like structure actively venting steam and H2S. This structure is ~2m tall. (F) Underwater photograph of a large (~8 m) spire structure in BridgeBay in the northern basin of Yellowstone Lake. The subaerial structures at Monument Geyser Basin are very similar to the spires in Bridge Bay(in terms of size, scale, distribution) and are irregular in form.

Spring 2003 27

ica produced by sublacustrine hydrother-mal vent processes (Figure 5C).

Geochemical studies of lake waters,hydrothermal vent fluids, and waters intributary streams show that YellowstoneLake waters and vent fluids are enriched inAs, Mo, Tl, Sb, and W. Similarly, theBridge Bay spires are strongly enriched inAs, Ba, Mn, Mo, Tl, Sb, and W (Figure5D). Oxygen isotopic values suggest for-mation of the spires at about 70–90°C. U-series disequilibrium dating of two sam-ples from one spire yields dates of about11 ka; thus, the spire analyzed is immedi-ately postglacial. Spires may be analogousin formation to “black-smoker chimneys;”well-documented hydrothermal featuresassociated with deep-seated hydrothermalprocesses at oceanic plate boundaries.They precipitate on the lake floor due tomixing between hydrothermal fluids andcold bottom waters.

Subaerial features analogous to thespires in Bridge Bay may be found atMonument Geyser Basin, located alongthe western edge of the Yellowstonecaldera (Figure 1A), on a ridgetop along anorthwest-trending fault in altered LavaCreek Tuff (Figure 6A). As Figure 6Bshows, the number and distribution of thesiliceous, spire-like structures at Monu-ment Basin are similar to what is seen inBridge Bay. In Bridge Bay, the spires arecold and inactive. The structures at Monu-ment, like the spires in Bridge Bay, haveirregular forms, and similar dimensions(Figures 6C, D, E, F). Currently, Monu-ment Geyser Basin sits about 250 m abovethe water table, and emits highly acidicsteam consistent with the intense alterationof the Lava Creek Tuff host rock. It isunlikely that the monuments formed froman acid-steam system, because steam has avery limited carrying capacity for SiO2.We hypothesize these deposits also formedfrom a hot water system in an aqueousenvironment, probably related to a glacial-ly-dammed lake during the waning stagesof the Pinedale glaciation about 12–15 ka.

Fissures and faults.

Features identified in the western areaof the northern and central basins (Figures2A, C, D) include a set of sub-parallel,elongate, north-northeast-trending fissures

west of Stevenson Island extending south-ward toward Dot Island (Figure 2A); aseries of en echelon, linear, northwest-trending, fissure-controlled, small depres-sions east and southeast of StevensonIsland; and a graben north of StevensonIsland, nearly on strike with Lake Village(Figure 1B).

The subparallel fissures west ofStevenson Island (Figures 2A, C) cut asmuch as 10–20 m into the soft-sedimentlake floor 0.5-km southeast of Sand Point.These fissures represent extension frac-tures whose orientation is controlled byregional north–south structural trends, rec-ognized both north and south of Yellow-stone Lake. Active hydrothermal activityis localized along the fissures as shown bydark oxide precipitates and warm shim-mering fluids upwelling from them. Thefissures, inspected with the submersibleROV for about 160 m along their NNEtrend are narrow (<2 m wide), and cut ver-tically into soft laminated sediments. Nodisplacement is observed. A parallel set ofN–S-trending fissures also occurs 1.3-kmnortheast of Sand Point (Figure 2C). Far-ther south along this trend, the fissuresappear to have well-developed hydrother-mal vent craters, although investigationswith the submersible show only weak orinactive vent fields in the central basin.Examination of the high-resolution mag-netic intensity map of this area shows alinear zone of relatively lower magneticintensities that spatially coincides with thefissures and graben (Figures 1C, 2B, 2D).

Observation of the features east ofStevenson Island (Figure 2C), using thesubmersible ROV, indicates that small,well-developed hydrothermal vents coa-lesce along northwest-trending fissures. Alarge hydrothermal vent at the south end ofthe northernmost set of aligned vents, inthe deepest part of Yellowstone Lake, at133 m (Plate 3B), emits hydrothermal flu-ids as hot as 120°C.

Finally, east–west seismic reflectionprofiles across the down-dropped blocknorth of Stevenson Island reveal a north-northwest-trending graben structurebounded by normal faults. This graben,referred to as the Outlet graben, was iden-tified by previous investigations, but ourstudies, using differential GPS navigation

and high-resolution seismic and bathy-metric data, provide the first accurateinformation on location and displacementof this important structure. Measured dis-placements along the two bounding faultsare variable, but displacement along thewestern boundary is generally ~6 m,whereas that along the eastern normal faultis ~2 m. The eastern bounding fault cutsHolocene lake sediments, indicating recentmovement. Seismic profiles across thegraben indicate that it projects (or strikes)toward Lake Village (Figures 1B, 2C),posing a potential seismic hazard in thatarea.

Another incipient graben may be offsetfrom and forming to the south-southwestof the Outlet graben, where the north-northeast fissures are identified. This struc-ture is on trend with the Eagle Bay faultsystem.

The sublacustrine fissures and faultsrevealed by the high-resolution bathyme-try are related to the regional tectonicframework of the northern Rocky Moun-tains, variable depths to the brittle-ductiletransition zone, and the subcaldera magmachamber and play important roles in shap-ing the morphology of the floor of Yel-lowstone Lake. Many recently-identifiedfeatures along the western margin of thenorthern and central basins, such as theactive fissures west of Stevenson Islandand the active graben north of it, are ori-ented roughly north–south, and are proba-bly related to a regional structural featurein western Yellowstone Lake on strikewith the Neogene Eagle Bay fault zone(Figure 1B). Seismicity maps of the Yel-lowstone region show concentrations ofepicenters along linear north–south trendsin the northwestern portion of the lake.

Landslide deposits.

Multibeam bathymetric data revealhummocky, lobate terrain at the base ofslopes along the margins, especially alongthe northeast and east of the lake basin(Figure 2A, Plate 2). Seismic reflectiondata indicate that the deposits range inthickness from >10 m at the eastern edgeof the lake, and are recognizable as thin(<1m) units extending up to 500 m intothe interior of the lake basin. We interpretthese as landslide deposits. The thickness


of the lacustrine-sediment cap depositedabove the landslide deposits is variable,and suggests that the landslides were gen-erated by multiple events. We suggest thelandslides were triggered by ground shak-ing associated with earthquakes and (or)hydrothermal explosions. The easternshore of Yellowstone Lake, near wheremany of these landslide deposits occur,marks the margin of the Yellowstonecaldera and abuts steep terrain of theAbsaroka Mountains to the east, both pos-sible factors contributing to landslide

events. The volume of material identifiedin these deposits would result in a signifi-cant displacement of water in the lake, andmay pose a potential hazard on shore.

Submerged shorelines.

Several submerged former lake shore-lines form underwater benches in the WestThumb and northern basins of Yellow-stone Lake (Figures 2A, B, and C). Thesubmerged, shallow margins (depth <15-20 m) of the northern basin are generallyunderlain by one-to-three relatively flat,

discontinuous, postglacial terraces thatrecord the history of former lake levels.Correlation of these submerged shorelineterraces around the lake is based primari-ly on continuity inferred from multi-beambathymetric data and shore-parallel seis-mic reflection profiles. These data indicatethat lake levels were significantly lower inthe past. An extensive bench occurs southof Steamboat Point and along the westernshore of the northern basin south of GullPoint (Figure 2C). In Bridge Bay, sub-merged-beach pebbly sand 5.5 m below

lake level

Temperature, oC

10 11562.5

110 110

90 90

70 70

50 50

30 30

10 10

1000 m

100 m

mm/yr

7C

10 11562.5

110

90

9070

7050

5030

30

10

10

mm/yr50

50

lake level

100 m

1000 m

Temperature, oC

lake level

7B

7A

fractured lava flow

sediments with no capping lava flow

0.5

0.5

100 m

1000 m

7Elake level

7D

Temperature, oC

10 11060

13090

90

90

50

50

10

10

mm/yr

50

50

fractured basal unit

impermeable lava flowhydrothermal vents in northern Yellowstone Lake

1 km

large gas cavities

upper vitrophyreshrinkage

jointssheeting joints

hydrothermal explosion crater

hot springs

hot springs

rhyolitic lava flow

lake sediments

120-150o

ROV

swath sonar

basal flow breccia

basalvitrophyre

near-ventpyroclastic deposits

feeder dikes

focused fluid flow throughbasal breccias and fractures

hot springs

hot springs

Spring 2003 29

the present lake level yielded a carbon-14date of 3,835 years. Well-developed sub-merged shoreline terraces are present inWest Thumb basin, especially along itssouthern and northern edges.

Relief on these terraces is as much as2–3 m, a measure of post-depositional ver-tical deformation. Documentation of thesubmerged terraces adds to a database ofas many as nine separate emergent terracesaround the lake. Changes in lake level overthe last 9,500 radiocarbon years haveoccurred primarily in response to episodicuplift and subsidence (inflation and defla-tion) of the central part of the Yellowstonecaldera. Holocene changes in lake levelrecorded by these terraces have been vari-ably attributed to intra-caldera magmaticprocesses, hydrothermal processes, cli-mate change, regional extension, and (or)glacioisostatic rebound.

DISCUSSION

Do the newly discovered features inYellowstone Lake pose potential geo-logic hazards?

The bathymetric, seismic, and sub-mersible surveys of Yellowstone Lakereveal significant potential hazards exist-ing on the lake floor. Hazards range frompotential seismic activity along the west-ern edge of the lake, to hydrothermalexplosions, to landsliding associated withexplosion and seismic events, to suddencollapse of the lake floor through frag-mentation of hydrothermally-altered caprocks. Any of these events could result ina sudden shift in lake level, generatinglarge waves that could cause catastrophiclocal flooding. Ejecta from past hydrother-mal explosions that formed craters in the

floor of Yellowstone Lake extend severalkilometers from their crater rims andinclude rock fragments in excess of sever-al meters in diameter. Deposits from theIndian Pond hydrothermal explosion eventextend as much as 3 km from its crater andare as thick as 3–4 m. In addition, thethreat of another large explosion eventmay exist, as indicated by the abundanceof hydrothermal venting and domal struc-tures observed, especially in the northernbasin, where heat-flow values and temper-atures are extremely high. The area cov-ered by the “Inflated Plain” is very com-parable in scale to its neighboring featureto the east, the 800-m-diameter, 8.3-kaElliott’s hydrothermal explosion crater(Figure 2B, 4A).

The combination of active and vigor-ous hydrothermal vents, the plume of finesediments in the lake subsurface, thestrong, locally-sourced H2S scent, and theevidence for silicification of lake sedi-ments merit detailed monitoring of the“Inflated Plain” as a potential and serioushazard and possible precursor to a largehydrothermal explosion event. The “Inflat-ed Plain” area was resurveyed in 2002 inorder to compare any changes from the1999 survey; these analyses currently areunder investigation. In addition to hazardsaffecting humans, hydrothermal explo-sions are likely to be associated with therapid release into the lake of steam and hotwater, possibly affecting water chemistryby the release of potentially toxic tracemetals. Such changes could have signifi-cant impact on the fragile ecosystem ofYellowstone Lake and vicinity.

Do rhyolitic lava flows control

hydrothermal activity?

One of the basic observations from oursurveys is that a close spatial relationshipexists between the distribution ofhydrothermal vents, explosion craters, andsublacustrine rhyolitic lava flows. Does thepresence of fully-cooled lava flows in asubaqueous environment affect the distri-bution of hydrothermal vents? Could theidentification of rhyolitic lava flows beused as a tool to help predict where somehydrothermal activity may occur in thefuture?

The relationship between sublacustrinehydrothermal features and the areas ofhigh relief, interpreted here as rhyoliticlava flows, can be seen in Figures 1B, 2A,and 7D. Based on our observations of theabundant, present-day distribution ofhydrothermal vents, we infer that fully-cooled rhyolitic lava flows exert a funda-mental influence on subsurface hydrologyand hydrothermal vent locations. We spec-ulate that upwelling hydrothermal fluidsare focused preferentially through rhyoliticlava flows, whereas hydrothermal fluidsconducted through lake and glacial sedi-ments tend to be more diffuse (Figure 7).In addition, convective flow moves later-ally away from thicker, more impermeablesegments of the rhyolite flow toward thefractured flow margin, where the majorityof hydrothermal activity is observed (Fig-ure 7E).

SUMMARY AND CONCLUSIONS

This mapping of Yellowstone Lakeallows the lake basin to be understood inthe geologic context of the rest of the Yel-lowstone region. Rhyolitic lava flows con-tribute greatly to the geology and mor-phology of Yellowstone Lake, as they do

Figure 7. (facing page). (A) Schematic diagram showing physical features of a rhyolitic lava flow. (B) Two-dimensional fluid-flow model withsimple glaciolacustrine sedimentary aquifer (no cap rock), which results in low flow velocities, recharge at the surface, and lateral flow out ofboth ends of the model aquifer. Subsurface temperatures never exceed 114°C, as indicated by contours and color map. Fluid flow rates arelow (<0.7 mm/y), as indicated by velocity vectors. (C) Fluid-flow model with a fully-cooled rhyolitic lava flow acting as cap rock. The under-lying sedimentary aquifer and heat flow are exactly the same as in the previous model. The addition of a 200-m-thick fractured crystallinerock cap strongly focuses the upward limb of an intense convection cell under the cap rock. In this model, fluid temperatures reach 140°C,and flow velocities are as high as 150 mm/yr. (D) Locations of hydrothermal vents on the lake floor mapped using seismic reflection. Lavaflow boundaries are based on high-resolution bathymetry and aeromagnetic data. (E) Fluid flow model that includes a basal breccia zonebeneath an impermeable lava flow. In this case, the lower sedimentary unit is overlain by a thin, fractured lava flow unit (20-m-thick) thatextends the entire width of the sedimentary prism. Above the more permeable basal unit is a 170-m-thick, low-permeability, unfractured lavaflow. Flow vectors indicate strong upflow under the lava flow, with maximum subsurface temperatures of ~150°C and flow rates up to 160mm/y. Upflow is deflected laterally within the 20-m-thick "basal" fractured zone toward the flow edges, resulting in hydrothermal venting onthe lake floor near the margins of lava flows.


to the subaerial morphology of theYellowstone Plateau. We infer fromour high-resolution bathymetry andaeromagnetic data that Stevenson,Dot, and Frank Islands are underlainby large-volume rhyolitic lava flows(Figure 2A). Mapped late Pleistoceneglaciolacustrine sediment deposits onthese islands merely mantle or blanketthe flows. Similarly, the hydrother-mally-cemented beach depositsexposed on Pelican Roost, located ~1km southwest of Steamboat Point(Figure 2C), blanket another sub-merged large-volume rhyolite flow.The margin of the Yellowstonecaldera passes through the central partof the lake and northward along thelake’s eastern edge (Figure 1). Similarto most of the rest of the topographicmargin of the Yellowstone caldera(Figure 1A), we suggest that post-col-lapse rhyolitic lava flows are presentalong much of the caldera marginbeneath Yellowstone Lake and con-trol much of the distribution of thesublacustrine hydrothermal vents.Many potential hazards have beenidentified in our mapping effort. Nextsteps will include hazard assessmentsand methodologies to be employed inmonitoring these potentially danger-ous features under the aegis of theYellowstone Volcano Observatory.

ACKNOWLEDGMENTS

We thank Kate Johnson, EdduBray, Geoff Plumlee, Pat Leahy,Steve Bohlen, Tom Casadevall, LindaGundersen, Denny Fenn, Elliott Spik-er, Dick Jachowski, Mike Finley, JohnVarley, Tom Olliff, and Paul Doss forsupporting this work. We thank DanReinhart, Lloyd Kortge, Paul Doss,Rick Fey, John Lounsbury, AnnDeutch, Jeff Alt, Julie Friedman, BrendaBeitler, Charles Ginsburg, Pam Gemery,Rick Sanzolone, Dave Hill, Bree Burdick,Eric White, Jim Bruckner, Jim Waples,Bob Evanoff, Wes Miles, Rick Mossman,Gary Nelson, Christie Hendrix, and TimMorzel and many others for assistancewith field studies. We thank Bob Chris-tiansen, Karl Kellogg, and Geoff Plumleefor constructive reviews that substantially

improved the manuscript. We are gratefulto Coleen Chaney, Debi Dale, Joan Luce,Marlene Merrill, Mary Miller, VickyStricker, Sandie Williamson, and RobertValdez for their skillful assistance withproject logistics. This research was sup-ported by the U.S. Geological Survey, theNational Park Service, and the Yellow-stone Foundation.

SOURCES

Space constraints prevent us from list-ing the numerous citations and sourcesincluded in this article as originally sub-mitted. For a complete list, please [email protected].

Lisa Morgan (foreground) is a research geologist for the USGS. Her focus for the past 23 yearshas been the geology and geophysics of volcanic terrains, including that of the eastern SnakeRiver Plain and Yellowstone Plateau, Cascades, Hawaii, Japan, and other areas. With Ken Pierce,Morgan developed major concepts and a model for the Yellowstone hot spot. Her currentresearch focuses on the Yellowstone Plateau, mapping and interpretation of the geology andpotential geologic hazards in Yellowstone Lake, and physical processes associated with large-vol-ume caldera-forming eruptions and hydrothermal explosions.

Pat Shanks (right) is a research geochemist with the USGS. He has extensively studied seafloorand sublacustrine hydrothermal vents and mineral deposits on the mid-ocean ridges and in Yel-lowstone Lake, using stable isotopes and aqueous geochemistry as primary tools. His currentresearch includes hot spring geochemistry, hydrothermal explosion deposits, hydrothermal alter-ation processes in volcanic rocks, and the geochemistry of metals in the environment related tosites of past mining activities.

Dave Lovalvo (left) is the founder and owner of Eastern Oceanics. For 30 years, He has filmedand supported underwater research projects in just about every major ocean and many of theworld's major inland lakes. Dave has spent 15 years exploring, filming and now mapping Yel-lowstone Lake, and continues to support projects in Yellowstone and many other locationsaround the world. He has been a manned submersible pilot of the Deep Submergence Vehicle(DSV), Alvin, and a pilot and member of the design team for the unmanned DSV, Jason 2. Hecurrently operates Eastern's unmanned DSV Oceanic Explorer. His latest projects have been thesearch and discovery of the PT-109 with Bob Ballard and the National Geographic Society, andthe government-sponsored exploration of the new underwater volcano off Grenada called "Kick-em Jenny." Dave resides in Redding, Connecticut.

Spring 2003 31

Predators and Prey at Fishing Bridge

by Paul Schullery

For more than thirty years now, I’ve watched Yellowstone cutthroat trout rise in the slow waters at the outlet ofYellowstone Lake. Their reliable presence, their abundance, and their easy familiarity with gawkers like me, all madeit seem like this was something I could get around to photographing someday, but didn’t have to do right now. Afterall, the only thing I really wanted was some beautiful overhead shots of these golden fish, sinuously distorted and glow-ing against the mottled greens of the river bottom.

Last summer, I finally started taking the pictures. About noon on a very hot, bright early July day, I walked out onFishing Bridge and discovered that quite a few fish were feeding steadily on small mayflies and stoneflies. Eagerlyrising trout are as exciting to me as the sight of a grizzly bear, and I was immediately caught up in the scene. Ratherthan looking for a fish tastefully holding over just the right color of bottom so I could get my artful trout picture, I spentthe next hour on the bridge or along the shore, banging away at these eager risers. Even as I was taking the pictures,I wondered if my autofocus camera and 300 mm lens were up to the challenge of stopping the action, and what I mightfind when I could finally examine the pictures.

What I found was as exciting as watching the risers. In that first hundred or so images, a surprising number of whichweren’t just blurry splashes, the camera stopped the action at many distinct stages of the rise and take. What was justa quick flash of action when I watched it was revealed as much, much more. The more I looked, the more I saw. Themore I saw, the more I needed to go back and take more pictures.

Each subsequent visit to the bridge led me back into the angling literature and (more fruitfully) into the scientif-ic literature on the physiology of feeding fish. I would look through each new batch of pictures, notice something new,think about it until I wondered about something else, then look through the pictures again, and again, and again. I’m


still not done looking, and the moreI find the more I realize I’m a longway from being done taking pic-tures, too.

If you’ve watched many naturefilms on television, there’s a pow-erful image you will almost cer-tainly remember. The scene is atropical reef—some colorful sub-merged landscape replete withcoral forests, sponges, and otherexotica. The whole thing is nearenough to the surface for sunlightto dapple its happy, travel-postercommunity of plants and animals.But off to the side (sinister sound-track here), you see the snout, oreven the whole head, of some dark-ly porcine, heavy-jawed fish, shad-owed patiently amidst the undulat-ing vegetation.

1. A Yellowstone cutthroat trout with one of the many thousands of mayflies it will eat each summer. In all these photographs, wildYellowstone cutthroat trout were photographed feeding naturally; neither trout nor flies were interfered with or manipulated in anyway.

2. Something about an individual mayfly has sparked something in the brain of an individual trout, which turns to investigate. Thefly has tipped over and a wing is pinned against the water surface. Perhaps the trout's interest was triggered by the panicky motion ofthe insect's struggles.

ALL P

HO

TO

S PA

UL S

CH

ULLE

RY

Spring 2003 33

Then a new camera angle reveals aninnocent little creature—a tiny fish, acrusteacean, some other tidbit of biolog-ical mobility—going about its day(peppy, cheerful soundtrack here, toevoke additional sympathy).

You know what’s going to happen,but it’s always startling anyway, becauseit happens so fast. The innocent little tid-dler comes doodling along until it’sdirectly in front of the big fish, then it’ssuddenly gone and the fish, which hasn’tleft its place, is closing its mouth (onlythe tackiest of producers put a smallburp on the soundtrack at this point, butsome do succumb to a little ascendingpennywhistle toot, to signify the hastysucking in of the prey).

It’s a great nature film gimmick,always good for a startled chuckle. It’salso terrifically interesting predatorybehavior. It’s evolution making the most

3. Even in the cleanest, clearest water, the trout must pick its food from a distracting assortment of flotsam in the surface film, caughthere when the camera chose to focus on it rather than on the trout below.

4. The trout has a kind of visual lock on this drifting mayfly. The fly is now well within the range of the fish's suction. The tiny "lens"of distorted surface just above the trout's head indicates that the trout has already begun to create a "rise form," though whether ornot the fish will take the fly is uncertain.


of the animal’s tools and environ-ment. It’s predation without thechase. It’s always dramatic, and forall its staginess and comic effectit’s also a little scary. It looksalmost like magic.

We don’t hear much about thissort of thing with trout, especiallytrout rising to feed near or on thesurface. Their fastidious little “riseforms” (the spreading rings of rip-ples that follow each feedingepisode) hint of a greater refine-ment, as if trout have better tablemanners than to go around actinglike a starship with an overactivetractor beam.

In fact, fishing writers havetended to describe the trout’s feed-ing behavior as quite passive, moreor less like this: When the trout

5. The same stage of the process as the previous pictures, but with a different fish photographed from a different angle. The trout'smouth is slightly open, with the fly perfectly suspended across the gap. The lower jaw, seeming a bit underslung, appears to be fillingout already as the fish begins to create the suction that will pull the fly in.

6. The decision to take the fly has been made. The fly, this time a mayfly "spinner," has barely begun to tip into the opening mouth ofthe trout (the spinner, with its wings extended flat across the surface, is the last life stage of the mayfly). Suction has also begun; thebeginning of the suction trough is passing over the head of the trout.

Spring 2003 35

sees a fly gliding toward it, the fishsimply rises to the surface, opensits mouth and gills, and lets the riverrun through its head, carrying thefly in. The fish keeps the fly andlets the extra water flow on, rightout the gills.

But trout use precisely the samesuction forces as the big reef fishdescribed earlier. In a process that islikewise too quick for us to observefrom the bank, or even from a fewfeet away, they take their food in bymeans of a complexand forceful seriesof valve-like motions of surprisingpower and elegant efficiency.

Let’s follow a mayfly to itsdoom in a trout’s mouth, startingwith the fly, poised on the surface,riding the current downstream. Thetrout sees it, and moves in to inves-

tigate. Forget for the moment thatin that one sentence is a world ofengaging wonders to do with thetrout’s visual acuity, its ability toidentify prey, the refraction of lightin a stream and how that affects thetrout’s “window,” and a host ofother subjects that many writershave capably explored. Right nowwe’re only concerned with thechallenges the fish faces in eatingthis fly.

Anglers have spent centurieswatching fish feed. Vincent Mari-naro’s beautiful book In the Ringof the Rise (1976), with its series ofphotographs of trout rising, gaveanglers their first close look at theways in which trout conduct theirinspection of a prospective meal.Water is a much thicker and poten-tially clumsier “atmosphere” than

7. The mouth is now as open as it gets. A mayfly is in it, and two more drift by to the left.

8. It isn't enough to get the fly over the lip. It must be pulled deep into the fish's mouth, and the powerful suction is now doing that.The suction trough is clearly visible around the fish's head as down-curving distortion lines. The trough is likewise revealed in itsshadow on the river bottom—a twin-lobed circle encompassing the trout's head.


air. A fish that simply charges up to itsprey is likely to push it away with its own“bow wave.” But depending upon thespeed of the trout as it approaches the fly,and the care it exercises, it may approachquite closely. Fish routinely get their littlefaces right up close to the insect, and seemto lock it in place right there in front ofthem as it drifts long.

I wonder about this stage in theprocess. Marinaro showed us, in his pho-tographic series depicting what he calledthe “compound rise” and the “complexrise,” the way a trout noses right up to a fly,then drifts backwards along with the flyas it continues on its way downstream. Thetrout concentrates on the fly, and keeps itright there, just off the end of its snout.

This behavior is certainly agonizing forthe angler, and who knows what the flymust make of it?

But here is what I find most curiousabout it. The whole time this is going on,often for several feet or even yards of drift,the fly is well within the suction range ofthe fish (rainbow trout in one study, feed-ing under the surface, rarely applied suc-tion toward food that was much more thana head-length away). I wonder if while thetrout is eyeing the fly from this close, if itisn’t also applying some subtle little out-ward or inward currents to the fly, testingit in some way? Animals take every evo-lutionary advantage that comes along.Maybe the trout is only toying with the flya little (trout are known to “play” withtheir food more toward the end of an insecthatch, when they are presumably sated,than at the beginning). Or maybe suchmanipulation, jostling the fly around a lit-tle, would somehow help in the decision ofwhether or not to eat it. Imagine being thefly at this point.

That’s all speculation, of course. Whathappens next is vividly real. If all goeswell with the inspection, it’s time to feed.

9. The same process, with another fish viewed from another angle. Again the trough is revealed in the surface distortion around themouth, and again the two-lobed shadow stands out on the river bottom. The twin-lobed shape is probably the result of the trout's"chin" dividing the suction trough. At this stage, though the gills may be partly open, they are not fully expelling water.

10. Though the fish is somewhat obscured by the distortion of the water, this is the busiest of the pictures in the sequence. The lowerjaw is still distended; notice how the cutthroat markings stand out. Both gills are now open wide, and the trout's right gill is clearlyexpelling a strong current of water. Water is almost certainly also exiting the left gill, but the light is from the right (as the off-centershadow of the suction trough, on the river bottom, shows), and the distortion of light on that side is probably lost under the fish.

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The goal of the trout is to cre-ate enough suction to ensurethat the fly is drawn well intothe mouth. To increase theforce of that flow beyond itsown physical capacity to cre-ate suction, the trout willoften move forward as ittakes, its speed adding a littlemore umph to the currentflow it is creating with suc-tion. As it does that, it createssuction with its mouth. Thereare now three distinct forcesspeeding the fly into thetrout’s mouth: the down-stream flow of the current,the upstream movement ofthe trout, and the suction ofthe trout’s mouth.

The trout creates the suc-tion by enlarging its mouthcapacity, which it does byopening and extending itsjaws, and dropping the floorof the lower jaw, deepeningthe mouth cavity. This isfacilitated by those pleatlike

structures that run the length ofthe bottom of the lower jaw (acutthroat trout’s “cutthroat”marks are partly hidden inthose pleats until they stretchopen).

The photographs capturethe effect of this suction clear-ly. The surface-feeding fish, insucking down the fly, actuallypulls a shallow hole in thewater surface—a little feedingdepression, or trough. Theinsightful British anglingwriter G.E.M. Skues recog-nized the evidence of thisprocess eighty years ago in TheWay of a Trout with a Fly. Hedescribed the initial stage ofthe take as “a faint hump on thesurface, often accompanied bya tiny central eddy caused bythe suction with which thetrout has drawn in the fly.”

Now the fish’s mouth hasopened, the oral cavity hasdeepened, and the fly is eitherin or on its way into the mouth.

11. In this revealing photograph, the trout has closed its mouth, and the suction trough is sliding back over its head. Most important,the rapid closing of the mouth and the contraction of the floor of the mouth is expelling water from the gills with such force thatsome of it also escapes in strong little spurts from the sides of the fish's mouth. This startling process occurred with more than one ofthe photographed trout.

12. The trout inadvertently inhales air along with any fly taken from the water's surface. This air is then expelled out the gills with thewater. Here, the first bubble of air emerges from the trout's gill and reaches the surface as the fish turns down from its take.


The gills are already in play, as somewater is moving out of them, but thefish is dealing with some involvedphysics at this point. If it simplydrops the floor of its lower jaw andopens its mouth and gills all withequal force and at the same time,there will still be a lot of suction, butwater may be pulled in from bothends—into the mouth and in throughthe gills (the latter, if it happens toodramatically, is apparently not anespecially pleasant experience forthe trout). This could defeat the realgoal of the suction. The trout needsto keep the suction going mostly oneway, into the mouth, to have the bestchance of capturing the fly. Thatsaid, even when the trout does thisright, there may be a modest back-

wash into the gills, but notenough to interfere withthe capture of the fly.

Now that the suctionhas been successful, thetrout has the fly in itsmouth. But recall whatanglers dread at this stage:that the fish will reject, or“spit out” the fly. Theyactually do this—ptui!—and the reason they cando it so quickly and soforcefully is that they justreverse the process thatpulled the fly in. They canjust contract that lowerjaw expansion, collapsethe large oral cavity, andthe fly spurts back out. Ifthe trout was operatingonly a passive, flow-through system, it wouldhave no capacity for suchabrupt and decisivechanges of plan, and we’dcatch a lot more of them.

But let’s assume thatthe trout approves of the

fly. It closes its mouth (a good bitmore quickly than it opened it),flushes the water out the gills, andthe fly is retained, presumably eitherin the throat or against the gill rak-ers—those hard arching structures towhich the gills are attached.

There is one lovely lingeringaftereffect in the take of a trout, firstnoted by the angling writer Skues.Perplexed by rising trout whose preyhe could not see, Skues needed away to determine if a fish was risingto floating flies, or feeding rightunder the surface. He reasoned that afish feeding beneath the surfacewould inhale only water when takinga fly, but a fish feeding on the sur-face, especially if taking anupwinged insect like an adult

mayfly, would necessari-ly engulf a fair amount ofair with the water and thefly. That air would beexpelled out the gills withthe water, and would beevident as bubbles in theresultant rise form. A fishfeeding on insects thatwere under the surface ofthe water, such as mayflynymphs or drownedadults, might cause a sur-face disturbance thatlooked like any other riseform, but it couldn’t havebubbles in it because thefish had no air to eject.The photographs showthis too.

Setting aside what allthis observation and pho-tography and reading hastaught me about fishing,it has given me a deep-ened respect for trout—creatures I alreadythought I admired prettythoroughly. Perhaps most

13. More bubbles have appeared, and are drifting back over the trout as the fish settles back into its holding position. But one last finestream of small bubbles can be seen, still underwater, as they emerge from the trout's right gill.

14. The serendipitous beauty of a complete rise: as the trout turns down from a successful take, another mayfly eases past, caught bythe camera as it passes over the pectoral fin.

Spring 2003 39

important, I admire them much more asindividuals than I used to. The feedingprocess is so full of opportunities for vari-ation, not only in one fish but from fish tofish, that I am much less likely than beforeto make assumptions about one fish basedon what the fish next to it has been doing.We fishermen have joked for so long abouthow we’re made fools of by these simplelittle creatures that we have begun tobelieve not only that we’re fools but thattrout really are simple. They may not be asindividual as humans, but I’m now con-vinced they’re a lot closer to it than I usedto think.

I also admire them more as predators.I don’t know what’s going on when a troutis nosing up against a fly, doing its equiv-alent of judging and deciding. But themore I stare at these pictures of fish staringat insects, the more I respect whatever it isthat the trout is going through (so far, I trynot to think much about what the insect is

going through). Like its physiologicalattainments, which result from millions ofyears of evolutionary engineering, thetrout’s cognition seems to me a spectacu-larly successful tool.

Over the years, I’ve spent a hugeamount of time watching Yellowstonepredators go about their work, makingtheir assessments, passing their fatefuljudgments, making their perfect moves.Trout are unmistakably members of thesame guild. Whatever rarified sphere ofconsciousness or even wisdom these crea-tures may inhabit, and whatever we mayeventually conclude about the primitive-

ness or sophistication of their brains, I aminfinitely more aware of their superioritiesthan I am of their limitations.

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Paul Schullery, a former editor of YellowstoneScience, is the author of many books, includingAmerican Fly Fishing: A History (1987) andLewis and Clark Among the Grizzlies (2002).This essay appeared in different form in theMay 2003 issue of Fly Fisherman magazine.

USFWS Reclassifies Some Wolves fromEndangered to Threatened

The U.S. Fish and Wildlife Service haschanged the status of gray wolves in thewestern Great Lakes states and northernRocky Mountains from “endangered” tothe less serious “threatened” designationunder the Endangered Species Act.

The reclassification rule also establish-es three “Distinct Population Segments”(DPS) for gray wolves under the Endan-gered Species Act. The three DPSsencompass the entire historic range of thegray wolf in the lower 48 states and Mex-ico, and correspond to the three areas ofthe country where there are wolf popula-tions and ongoing recovery activities.

Wolf populations in the Eastern andWestern DPSs have achieved populationgoals for recovery, and Advance Noticesof Proposed Rulemaking are being pub-lished concurrent with this reclassificationrule to give the public notice that the Ser-vice will soon begin work to proposedelisting these populations.

The threatened designation, which nowapplies to all gray wolves in the lower 48states except for those in the Southwest, isaccompanied by special rules to allowsome take of wolves outside the experi-mental population areas in the northernRocky Mountains. These rules provideoptions for removing wolves that causeproblems for livestock owners and otherpeople affected by wolf populations.Wolves in experimental population areasin the northern Rocky Mountains arealready covered by similar rules thatremain in effect.

The USFWS will now begin theprocess of proposing to remove graywolves in the western and eastern UnitedStates from the endangered and threatenedspecies list, once the agency has deter-mined that all recovery criteria for wolfpopulations in those areas have been metand sufficient protections remain in placeto ensure sustainable populations.

To delist the wolf, various recovery cri-teria must be met, in addition to reaching

population goals. Among those criteria arerequirements to ensure continued survivalof the gray wolf after delisting. This willbe accomplished through managementplans developed by the states and tribes.Once delisted, the species will no longerbe protected by the Endangered SpeciesAct. At that point, individual states andtribes will resume management of graywolf populations, although the Servicewill conduct monitoring for five years afterdelisting to ensure that populations remainsecure.

The final rule reclassifying the graywolf will be published in the Federal Reg-ister. For more information on the graywolf, visit the Service’s wolf website athttp://midwest.fws.gov/wolf.

Bison Capture Operations OutsideNorth Entrance

During the first week of March, bisonmigrated near Stephens Creek along thepark’s northern boundary, and captureoperations began at the Stephens Creek

NEWS notes


capture facility outside the North Entrancefor the first time since 1996. Under thefinal state and federal Records of Decision(ROD) for the Interagency Bison Manage-ment Plan (IBMP) that were signed inDecember 2000, and the December 2002IBMP Operating Procedures, when thebison population in late winter/early springis over 3,000 animals, and they are movingonto lands where cattle are being grazednear the North Entrance, they will be cap-tured in the Stephens Creek facility andsent to slaughter facilities. The Novemberpopulation estimate was approximately3,800. About 25 bison have died this yeareither by management actions west of thepark, natural mortality, or motor vehicleaccidents.

The IBMP and the IBMP OperatingProcedures use a variety of methods alongthe north and west boundaries of the parkto limit the distribution of bison and tomaintain separation of bison and cattle onpublic and private lands. It also allowssome bison on certain public lands wherecattle are not grazed.

The first response to bison approachingthe north boundary is to haze them to keepthem inside the park. However, afterattempts at hazing the bison become inef-fective and unsafe, it may become neces-sary to begin capturing the animals. Haz-ing occurred during the previous fewweeks on numerous occasions.

A total of 231 bison were captured atthe Stephens Creek facility and sent toslaughter facilities. Meat, headsand hides will be donated toNative American groups/individ-uals and other social serviceorganizations.

Spring Bear EmergenceReminder

The park’s Bear ManagementOffice has started receivingreports of bear activity withinYellowstone, indicating that bearsare beginning to emerge fromtheir winter dens.

Soon after bears emerge fromtheir dens, they search for winter-killed wildlife and winter-weak-ened elk and bison, the primarysources of much-needed foodduring spring for both grizzlies

and black bears.Visitors are askedto be especiallycautious ofwildlife carcassesthat may attractbears, and to takethe necessary pre-cautions to avoidan encounter. Donot approach abear under anycircumstances.An encounterwith a bear feed-ing on a carcassincreases the riskof personal injury.Bears will aggressively defend a foodsource, especially when surprised.

The National Park Service is continu-ing the seasonal “Bear Management Area”closures in Yellowstone’s backcountry.The program regulates human entry inspecific areas to prevent human/bear con-flicts and to provide areas where bears canrange free from human disturbances.

Visitors are asked to report any sight-ings or signs of bears to the nearest visitorcenter or ranger station as soon as possible.Permits for backcountry camping andinformation on day hikes are available atvisitor centers and ranger stations.

For further information on spring con-ditions in Yellowstone National Park, callpark headquarters at (307) 344-7381.

Winter Use FSEIS Released for GrandTeton and Yellowstone National Parks

The Final Supplemental Environmen-tal Impact Statement for winter use wasmade available to the public on February20, 2003. There will not be a public com-ment period. National Park Service andNational Environmental Policy Act(NEPA) regulations call for a 30-day wait-ing period, but public comment is not cus-tomary on a final environmental impactstatement. A Record of Decision wasexpected to be signed near the end ofMarch 2003.

Five alternatives for winter visitor usein the three park units are evaluated in theFSEIS. Three of the alternatives, includingthe preferred alternative, are limitedspecifically to actions that allow snowmo-bile recreation to continue in the parks.The other alternatives include a no actionalternative that would implement the

NPS and Montana Department of Livestock personnel meet at theStephens Creek capture facility.

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Recent aerial photos taken in Hayden and Pelican Val-leys (left and below, respectively) show that bears havebegun their spring emergence.

Spring 2003 41

November 2000 Record of Decision to bansnowmobiles from the parks beginning the2003-2004 winter use season, and a sec-ond that would delay implementation ofthe November 2000 Record of Decisionuntil the 2004-2005 winter use season.

The preferred alternative strikes a bal-ance between phasing out all snowmobileuse—as required under the November2000 Record of Decision—and allowingfor the unlimited snowmobile use of thepast. Critical elements of the preferredalternative include: reduced numbers ofsnowmobiles through daily limits; imple-menting best available technologyrequirements for snowmobiles; imple-mentation of an adaptive management pro-gram; guided access for both snowmobilesand snowcoaches; a reasonable phase-inperiod; a new generation of snowcoaches;and funding to effectively manage the win-ter use program. Implementation of all thecritical elements will address the adverseimpacts identified in the November 2000Record of Decision.

Hard copies and CDs of the documentare available by writing: FSEIS, PlanningOffice, P.O. Box 168, Yellowstone Nation-al Park, Wyoming 82190. The documentcan also be found by accessingwww.nps.gov/grte/winteruse/winteruse.htm. The FSEIS is loaded in two volumes.Volume 1 is the main document and theappendices. Volume 2 is the public com-ments and their responses.

Happy 10th Anniversary, YCR!The Yellowstone Center for Resources

celebrated its 10th anniversary on March13, 2003. Created with the goal of central-izing resource research and management,YCR now includes the park’s Branches ofNatural and Cultural Resources, its SpatialAnalysis Center (GIS lab), and YCR’sown support branch (including theResource Information and PublicationsTeam, AKA the people who bring youYellowstone Science!). Although all majorundertakings, such as wolf restoration,represent cooperative efforts among thepark’s divisions, many such projects havebeen primarily directed out of the YCR.Highlights of the past ten years includewolf restoration; the lake trout eradication

program; initiation of thermophile sur-veys; successful bald eagle and peregrinefalcon recovery programs; meeting targetgoals for grizzly bear recovery; six bienni-al science conferences (planning for theseventh is underway!); the halting of theNew World Mine; initiation of a new Her-

itage and Research Center to house thepark’s library, archives, and photo andmuseum collections; strengthening of trib-al relations through the consultationprocess; completion of the interagencybison management plan and EIS; andacquisition of the Jack and Susan Daviscollection. Yellowstone Science also cel-ebrates 11 years this year, with a mailinglist that has grown to include more than2,100 individuals interested in Yellow-stone’s research and resources.

Lake Conference Proceedings Available

The proceedings from the Sixth Bien-nial Scientific Conference on the GreaterYellowstone, Yellowstone Lake: Hotbedof Chaos or Reservoir of Resilience? arenow available. Conference participantswill receive their copies in the near future.Others who would like a copy, pleasecontact Virginia Warner at [email protected] or (307) 344-2233.

NEWS notes

Above, YCR Director John Varley cuts the NPS arrowhead-shaped YCR birthday cake.

Below, Here from the start: original YCR employees Wayne Brewster, Kerry Gunther, MaryHektner, Mark Biel, Jennifer Whipple, Ann Rodman, Paul Schullery, Sue Consolo Murphy,John Varley, Joy Perius, and Melissa McAdam.

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