Pedogenesis in Andisols of Craters of the Moon National Monument and PreserveKaren L. Castenson1, Paul A. McDaniel1, and Dave Hoover2

1University of Idaho, Moscow; 2Natural Resource Conservation Service, Boise, Idaho.Recent volcanic activity at Craters of the Moon National Monument andPreserve, in southern Idaho, has provided the ideal location to observe earlysoil formation. Eight volcanic periods have been documented in this areabetween 15,000 and 2,000 years B.P., regularly occurring no more than 2,000years apart. Lava flows, cinder cones, and a variety of tephra, including ash,pumice, and cinders comprise the landscape. Weathering of this tephra resultsin the classification of these soils as Andisols, which are distinguished fromother soils on the basis of their unique chemical, physical, and mineralogicalproperties. Many of these properties have important edaphic implications in thehigh-desert environment of the Eastern Snake River Plain. Samples of the iron-rich-basaltic tephra were taken from five of the eight known eruptive periodsranging from 12,000 to 2,000 years B.P. Acid oxalate extractable iron andaluminum were measured on the samples to determine the relative amountand rate of weathering of tephra in a climate with an aridic moisture regime.The NaF pH of samples collected from various aged deposits ranged from 9.5to 10.9, indicating an abundance of amorphous iron and aluminum. Soilmoisture content was measured in profiles with varying amounts and types oftephra. It appears that the abundance, amount of weathering, and type oftephra have significant effects on the soil moisture and therefore, theestablishment of particular vegetational communities.Objectives1. Determine the extent and distribution of tephra in the Craters of the Moon area.2. Identify the major the sources and elemental compositions of tephra.3. Assess tephra weathering and resultant secondary mineral phases.4. Examine the influence of tephra on ecologically important soil properties such aswater-holding capacity and nutrient sorption.

Classification of volcanic glass identified at Craters of the Moon(adapted from Dahlgren et al., 1993)

Clear62.8 - 75.6%Rhyolitic, dacitic, and andesite.1.49-1.51Non-colored

Light brown, red, & dark brown.48.1 - 59.6%Basaltic andesite and basalt.>1.52Colored

Glass ColorsSilica ContentParent Rock CompositionRefractive IndexType of glass

NaF pH v ersus AOD Al + 0.5Fe

y = 0.4188x + 8.9365R2 = 0.4973

7.0

7.5

8.0

8.5

9.0

9.5

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10.5

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11.5

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pH

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Low Total Cover

0 cm

25 cm

50 cm

High Total Cover

Landscape displaying the unique vegetation patternobserved on some cinder cones. The limber/antelopebitterbrush (high total cover) community is on the left andthe cinder garden (low total cover) community is on theright.

Soil Formation on Cinder Cones and Cinder Gardens:Cinder fragments, or scoria, eject from an erupting volcano and are deposited on the surroundinglandscape. A number of soils have formed in these materials resulting in the followingclassifications:

•Ashy-skeletal over fragmental or cindery, aniso, glassy Xeric Vitricryands•Medial-skeletal, amorphic, frigid Lithic Vitrixerands•Medial, amorphic Xeric Vitricryands•Medial, amorphic, frigid Typic Vitrixerands

Unique vegetation patterns have been observed on cinder cones and cinder gardens. Areasdominated by limber/antelope bitterbrush (high total cover) are composed of large, block type lavaremnants interspersed with cinder gardens (low total cover).

NaF pH relationship with poorlycrystalline minerals (oxalate-extractableAl + 0.5Fe (%)) in soils sampledthroughout the Preserve. (Soil SurveyStaff, 1998). NaF pH measured rangedfrom 8.5 to 10.9.

0 10 20 30 405Kilometers

LegendCOM Data Points% Alox + 0.5 Feox

0.23 - 0.400.41 - 1.001.01 - 2.002.01 - 3.69

¯

0 10 20 30 405Kilometers

¯

Legend

COM Data PointsNaF pH

7.00 - 9.009.01 - 9.409.41 - 10.9

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Ammonium oxalate-extractable Al, Fe, and Si with depth at (a) site 1 low total cover, (b) site 1 high total cover, (c)site 2 low total cover, and (d) site 2 high total cover.

Preliminary data suggests that andic soilproperties are more abundant in thenorthern portion of the Great Rift that runsthe length of Craters of the Moon. (a) NaFpH values greater than or equal to 9.4indicate an abundance of poorlycrystalline minerals and are assumed tobe influenced by volcanic ash (Fieldesand Perrott, 1966). (b) Oxalate-extractable Al + 0.5Fe (%) is used todetermine the presence of amorphous Aland Fe. Depending on percent volcanicglass, soils with oxalate-extractable Al +0.5Fe (%) greater than 0.4 may beclassified as andic soil materials (SoilSurvey Staff, 2003). Due to the severeterrain, a representative sample of alllandscapes in the Preserve has yet to becollected. Electron microprobe data for Ca, K, and Fe (sum=100%) in glass shards from soil sampled (a) in

an aspen grove on a south aspect within the northern park boundary and (b) on a cinder cone inthe northern part of the Preserve. Unlabeled points are tephra from unidentified events.

100% Fe

100% Ca

100% K

CaO

K2 O

Fe2O3

0%

100%

0%100%

0%

100%

Tephra fromlocal source

Tephra fromCascade range

(a)

100% Fe

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Tephra fromlocal source

CaO

K2 O

Fe2O3

0%

100%

0%100%

0%

100%

(b)

Maps showing (a) the state of the Idaho outlining Craters of the Moon lava flows, (b) closer Landsatimage of Craters of the Moon, and (c) Craters of the Moon National Monument and Preserveboundaries.

References

Dahlgren, R., S. Shoji, and M. Nanzyo. 1993. Mineralogical characteristics of volcanic ash soils. P.101-143. In S. Shoji et al. (eds.) Volcanic ash soils –Genesis, properties, and utilization. Elsevier, Amsterdam.

Fieldes, M., and K.W. Perrott. 1966. The nature of allophane in soils. Part 3. Rapid field and laboratory test for allophane. N.Z. J. Sci. 9:623–629.

Soil Survey Staff. 2003. Keys to soil taxonomy. 9th ed. U.S. Gov. Print. Office, Washington, DC.

ID

MT

Soil Formation on Lava Flows:

Lithic Torrifolists have been described on lava flows thatsurround the cinder cones in the northern part of thePreserve. These soils are found under woody vegetationthat have been able to root deep into the cracks in the lava.Organic material accumulates at the base of these plantsand aids in the collection of wind-blown mineral material.

Weathered volcanic ash with NaF pH of 10.3-10.7 wasfound on a lava flow with a radio carbon age of 2,076 yearsBP. The amount of time necessary for this ash to weatheris greater than the age of the lava flow. It is hypothesizedthat this material has been deposited by wind afterweathering elsewhere. The ash is protected from furthertranslocation by a desert pavement of basalt that coversthe soil surface. Volcanic ash protected under pieces of

Blue Dragon lava.

Organic materials accumulating below alimber pine growing on a recent lavaflow. Black line measures 20 cm.

Colored volcanic glass from soillocated on Broken Top, a cindercone in Craters of the Moon.

25µm 25µm