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UNIT 9 (Chapter 14) GLACIERS – WHEN THE EARTH TURNS COLD Study Guide

(Revised 9/12) UNIT 9 HOMEWORK WEB HIT HOMEWORK - part 1: ONE WRITTEN PARAGRAPH from any selected unit web hit site VIDEO WEB HIT HOMEWORK – part 2: ONE WRITTEN PARAGRAPH from any selected unit video site For any Unit Web Hits and Unit Web Videos, go to the “DMC HOME” website; in Search box –type “Geology”, select “Vernon Kramer”, scroll down to GEOL 1303, select “Syllabus”, select “Web Hit Links”, later then the select “Video Web Hits”, click on icon of interest for web sites OR: go to DMC Home website, select “Degrees, Certificates, Courses”, scroll down to Natural Sciences and select “Geology”, select “Faculty Listings”, select “Walter Vernon Kramer”, find “Geol 1303”, select “Syllabus”, and there you can find the” web hit links” click on icon of interest for web sites and then to “Web video hits”, click on icon of interest for video site [IF NONE OF THE WEB SITES COME UP, YOUR COMPUTER PROBABLY NEEDS TO BE REBOOTED (RESTARTED)

Introduction - No event in recent geologic history has had such a profound effect on Earth as the Last Great Ice Age. - With the retreat of the giant glaciers due to global warming and related climate change, large portions

of the Earth’s continents went from having large lakes and vast grasslands into deserts. - The giant glaciers never reached Texas, with the closest glacier reaching Kansas. - The Chihuahuan Desert began forming only 8,000 years ago when most of the giant glaciers had

melted (post ice-age geologic feature). - At the last Ice Age time, the GOM shoreline was almost 50 miles eastward of the present coast of

Corpus Christi (425 feet lower than today). Nueces Bay then was a wide river valley. - Mastodons, mammoths and other large mammals roamed over the area of what is now Del Mar

College. - The melting of the continental ice returned water to the oceans. Padre Island formed in steps (moving

landward) beginning about 18,000 years ago. The island reached its present location about 2,000 years ago (post ice-age geologic feature).

Continental glaciers over North America Diplomacy is the art of saying “nice doggie” until you can find a rock – Will Rogers

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Ice on Other Heavenly Bodies - Mars has a northern and southern ice cap with glaciers, just like Earth, except most of the ice on the

Mars ice caps is frozen carbon dioxide (dry ice). - The glaciers are comparable to those on Earth. Mars also appears to be undergoing a period of global

warming. - We find ice as a principle constitute on a number of moons that orbit the gas giant planets. - Jupiter alone has three moons Ganymede, Callisto and Europa (two larger than our moon) that are covered with water ice. All three moons have lower liquid oceans.

Ganymede Callisto Europa Corpus Christi and Snow - Corpus Christi largest snow in one day was in 1895 with 4.1 inches of snow - In 1973 Corpus Christi received 1.1 inches snow (February 8-9) - Christmas 2004 (it snow 2.3 inches Dec. 24 and 2.1 inches Dec. 25 for a total of 4.4 inches. - Corpus Christi receives at least a few snow flurries every 2 years, with the earliest being Oct. 31, 1993. General Terms - Flurry: a light snow with no accumulation - Sleet: frozen raindrops that do not stick to the ground upon impact, but bounce - Hail: pellet sized ice grains to large balls of ice formed within thunderstorms - Freezing rain: rain that falls on a surface that has temperatures below freezing which then forms a

coating of ice. This type of “rain” causes trees and power lines to collapse resulting in major problems. - Black ice: a layer of ice that coats roadways and makes it almost impossible to drive - Frost: a deposit of ice crystals formed when water vapor from the air condenses at a temperature below

freezing - Wind chill is based on the heat loss from exposed skin by combining the wind-cooling effect and the

actual cold temperatures. Sunshine all the times makes a desert – Arab Proverb Glaciers and the Sea - Glacier: system of moving (flowing) ice that forms where more snow and ice accumulates each year

than melts - Glaciers can extend into the sea which would then be called ice shelves - Sea ice does not form glaciers because the ice cannot get thick enough (lower-water “heat” cannot

escape above the ice). Because of this, submarines can break through the ice at the exact North Pole - Calving: masses of ice that break off a glacier into the sea (which then forms an iceberg)

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- Pieces of ice that break free and float in the sea are called icebergs; - 7/8th of an iceberg mass is found hidden below water. - Surprisingly, glaciers can have many colors including blue. - There are signs of icebergs remaining under a cover of dust on Mars - There are many similarities between the moon Europa “icebergs” and the icebergs around our poles.

An iceberg Snow and Ice - To create glaciers, we must have a lot of snow that accumulates in ever-increasing thickness - Whiteout: an ice fog -Blizzard: a severe snow storm - Generally it takes from 10” to 12” of snowfall to equal one inch of rainfall. -Thicknesses of fresh snowfall on the ground generally contain 90% air. -Snow crystals become granular ice by:

1. Surface thawing and freezing 2. Compaction by burial “Melt water” will combine ice granules to form ice crystals (the snow metamorphoses).

- Firn (or Neve): Snow crystals that change to granular ice and are recrystallized - Glacial ice is really a metamorphic rock. The compaction (pressure) caused by the great thicknesses of

ice can change sediment (snow) into a metamorphic rock (ice); this process can take from 25 to 100 years to from glacial ice.

Glacier Types - Two classifications of glaciers: 1) Valley (Mountain or Alpine) Glaciers and 2) Continental Glaciers - Valley (Alpine or Mountain) Glacier: ice “streams” confined to canyons and valleys of mountainous

terrains (much smaller than continental glaciers) - Piedmont glacier: a valley glacier(s) that leaves a valley and coalesces at the base of a mountain - Tidewater glacier: a valley glacier that reaches the sea - Continental Glaciers (also known as ice sheets): Huge sheets of ice that are spread out over a large part

of Earth’s land mass, commonly with central thicknesses of 10,000 feet to 15,000 feet. Today’s examples are those continental glaciers on Greenland and Antarctica.

- Smaller (continental glaciers) ice sheets are termed “ice caps”.

Valley glaciers Continental glacier

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Glacier Movements - Ice on a mountain does not alone make a glacier - To be a glacier, the accumulated ice and snow must move as a unit. - When “mountain ice” reaches a critical thickness of about 60 feet, the mountain ice will begin to

deform and flow as a glacier. - Internal Movement: glaciers move non-uniformly, just like a river, with the slowest flow on the bottom

and sides (basal slip) and the faster flow at the center and top of the glacier (plastic flow). - [With ice skating, the pressure of the thin skate-blade “melts” the ice, whereby you actually skate on a

thin film of water.] - Basal slip or basal movement: glacial movement accompanied by melting and thawing of the ice near

its basal contact with bedrock (just like with ice skates) - Plastic flow: movement of the ice without actual “fracturing” - Glacier rate: average movement of 400 feet to 800 feet per year (faster than most groundwater

movements)

Glacier Components and Terms - External components of a glacier: - Zone of accumulation: Zone of a net gain of ice where snow is changed into ice and accumulation

exceeds melting. - Almost all the snow and ice that form a glacier will be derived from this zone of accumulation! - Zone of wastage: zone where net total ice leaves the system (net loss) by melting, calving or

evaporation (sublimation) - Firn Limit (Snow Line): “boundary” between the two above zones - Moraines: mounds or ridges of sediment and rocks pushed and deposited at the leading edge of a

moving glacier - Stagnant glacier: a glacier in equilibrium that is neither expanding nor shrinking - Crevasse: cracks or openings on top of glacier where it descends over extremely steep slopes or curves.

Individual crevasses on top of a glacier are usually open only for a short period of time. Nature does nothing uselessly - Aristotle

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Parts of a mountain glacier Erosion and Glaciers - A glacier is an agent for erosion, transportation and deposition. - Glacial Erosion: Regolith can fall on top of the glacier and be transported to the eventual “end” of the glacier to help

form the moraine. Glacial Plucking: the lifting out and removal of fragments of bedrock at the bottom of the glacier This sediment is pushed to the front of the glacier to form “terminal moraines”. Abrasion: grinding by the plucked rock which is a trademark of a glacier

Glacial Erosion

Moraines: ridge of sediment deposited at the leading edge of a glacier Glacial Polish: grinding bedrock to a “polish” by the fine grains found at the bottom of a glacier Glacial Striations: everything from small to large scratches and grooves that have been abraded

into the bedrock. These scratches are caused by grinding rocks trapped at the base of an advancing glacier. Glacial striations indicate the direction that the glacier moved!

Rock Flour: clay and fine silt caused by glacial abrasion. This sediment is generally transported by streams; and later by winds to become loess deposits.

Most present day loess deposits found in agricultural areas are actually wind-blown deposits of soil that was derived from an Ice Age glacier outwash of rock flour.

-Components of Alpine (valley) glaciers: individual glaciers can merge with other valley glaciers, yet maintain individual identity (piedmont glaciers).

Glacier Landforms - There are numerous Erosional landforms associated with Alpine (valley) glaciers; - [We will concentrate on just three of these landforms.]

1) Alpine glaciers produce U-shaped valleys. These valleys are scraped out by the bottom of the glacier leaving behind a “rounded” valley (rivers leave V-shaped valleys in mountain areas).

2) Cirque: a bowl-shaped depression produced by glacial plucking at the head of a mountain valley.

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3) Horns: pyramid mountain produced by three or more cirques. A famous example of a horn is the Matterhorn in the Alps of Switzerland.

Continental Glaciers - Continental glacier: Huge sheets of ice that are spread out over a large part of Earth’s land mass - Continental ice needs to be more than 120 feet thick (40 meters) to flow as a glacier. - Greenland and Antarctica continental glaciers currently contain 95% of all glacial ice on Earth, which

could raise sea level about 200 ft (if all were to melt). - The weight of this ice is so heavy that the surfaces of Antarctica and Greenland (in some places) are

6,000 feet below the current sea level - Entire mountain ranges are buried by these glaciers. - This ice can be 10,000 feet to 15,000 feet thick. - Ice at parts of Antarctica exists from snowfalls more than 120,000 years ago to 500,000 years ago. Continental Glacier Landforms - Erosion, transportation and depositional processes also apply to continental glaciers. - These glaciers produce numerous landforms but we will concentrate on two (2) forms. - Kettle lakes: lakes formed from depressions left by large blocks of detached ice (continental

glacier) that later melted (Minnesota is famous for this type of lake.) - Erratics: large boulders, lying free on the surface. These rocks were deposited or left behind by

melting, retreating glaciers. These rocks were can be transported great distances (hundreds of miles) from their original location.

Kettle lakes Erratics To different state of mind within us – the world is either a hell or a heaven, it is still the same world

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Ice Ages - Ice Ages: periods when a large portion of Earth’s land surface was covered by ice. - Earth is about 4.56 billion years old and it has been noted that widespread glaciation is a fairly rare

event. - There have been only five periods of widespread continental glaciation. - The last widespread glaciation only began about 2 million years ago.

Timing of ice ages on Earth (note logarithmic scale) Notice five major Ice Ages shown above!

Human lineages “Lucy” Neanderthal - It was during this time period (the current 1.6 - 2 million year old Ice Age) that (fossil) evidence

indicates a series of “advanced” humans making their appearance on earth. Near the end, there were only two species of man.

- Neanderthal man’s existence ended about 35,000 – 28,000 years ago during a period of intense continental glaciers. Most likely, Homo sapiens eliminated that species.

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Effects of the Last Ice Age - We will have five (5) recent stages of glaciation in North America, depending upon various studies;

but remember that we are still in our fifth overall ice age. - Europe may have had seven (7) glaciation stages during this same time frame. - Earth’s last widespread glacial period of large continental glaciers began 115,000 years ago (global

cooling) and lasted to about 18,000 years ago (start of global warming) - Looking at the last 160,000 years, Earth has gone through two (2) stages of glaciation and two (2)

stages of global warming or interglaciation

- Interglaciation: periods of shrinking ice sheets and glaciers (not absence of glaciers but the presence of

shrinking glaciers). This represents a period of global warming. - The previous “Sangamon” interglacial period (global warming) had sea levels 10 feet higher than

today. - These interglacial warm periods generally last 20,000 – 30,000 years of duration (and we have been in

this one for 18,000 years) - At 18,000 years ago, a huge ice sheet covered most of the northern portion of North America, and the

tall mountains in the west were covered with alpine glaciers. - At that time (18,000 years ago), the North American continental ice started to melt (global warming) to

form our current interglacial period. - About 9,000 years ago, a huge freshwater lake – Lake Agassiz formed. Its former lakebed is now part

of the agriculture belt for the Dakotas and Canada.

- Much of our sea water was tied up in glaciers. The North American Indian ancestors took advantage

of this shallow water “Bering Straits land bridge” and migrated to the Americas from Asia.

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- The “last” Ice Age caused sea levels to drop (Eustatic sea level) more than 300-400 feet to near the edge of the continental shelf.

Giant ripples - Scablands of Montana: A giant “ice dam” broke, releasing the water of the very large Lake Missoula

(greater than the size of some of our current Great Lakes). The expelled water created a temporary giant river that was +1,000 feet deep and moved at 65 mph. The entire lake emptied in two days. That river “scoured” hundreds of square miles removing topsoil (creating the Scablands) and formed giant sand ripple marks.

- The “last” Ice Age continental glacier on North America created today’s Great Lakes (10,000 years

ago), which holds USA’s largest single surface fresh water supply. These lakes were created by the immense weight of this glacier and by some gouging by the roots of the glaciers. The bottoms of these lakes are “rebounding” upward at a rate of one inch a year.

-All that remains of the “last” Ice Age glacier that covered a large part of North America is the “Barnes

Icecap” found in Canada. - The end of “last” Ice Age helped create today’s Mississippi River drainage basin. - Pluvial lake: a former lake currently found in arid areas that was created by the melting of Alpine

glaciers, especially in Nevada and Utah - Lake Bonneville or the Great Salt Lake began as a giant fresh water pluvial lake (evaporation resulted

in its salty water).

Pluvial lakes

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Extinctions - The “last” Ice Age contributed to mass extinctions of many species of plants and animals in the Corpus

Christi area including: mammoths, rhinos, camels, horses, saber-tooth tigers, ground sloths, giant armadillos, etc.

Begin FYI only: Proposed causes for glaciation:

1) Since the dinosaurs died, C02 has decreased dramatically, but this decrease shows no direct relationship with widespread glaciation.

2) Changes in the sun’s energy output: (not likely, sun is getting hotter) 3) Meteorite impact (not likely, an ice age did not arise with the Chicxulub impact) 4) Increased volcanic activity: (short period only, had major volcanism without ice ages) 5) Sun and Earth passing through a spiral arm of our galaxy and nearby supernovas (still testing) 6) Location of continents (maybe) 7) Changing ocean currents (not likely)

End FYI only: Proposed causes for glaciation:

Cycle To Know: - Milankovitch cycles: changes in Earth’s orbit and axis tilt and precession (pointing to North Star) that

may affect incoming solar radiation (heating); may help explain the last ice ages - Our present day “global warming” may slightly postpone the next Ice Age. A student who changes the course of history is probably taking an exam! MORE ABOUT GLOBAL WARMING OR GLOBAL COOLING WITH OUR LAST LECTURE