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GLACIERS CHAPTER 11 GEOLOGY
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Top 10 glacier facts 10. Approximately 10 percent of the Earth is covered by glaciers; during the last Ice Age, they covered one-third of the Earth’s surface. 9. Glacier ice is the largest reservoir of fresh water on the planet, storing an estimated 75 percent of the world’s supply. 8. Glaciers are found in 47 countries. 7. A glacier can range in length from the equivalent of a football field to more than 100 miles. 6. The Antarctic ice sheet is actually a glacier and has existed for at least 40 million years. If it were to melt in its entirety, sea levels would rise 210 feet worldwide, according to the U.S. Geological Service.
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5. Though it sits on the equator, Mount Kilimanjaro is glaciated.
4. On steep slopes, a glacier can be as thin as 50 feet. 3. Mountain valleys are typically “V” shaped before being taken oven by a glacier; during glaciation, the valley widens and deepens and thus becomes “U” shaped. 2. A single glacier ice crystal can grow to be as large as a baseball. 1. Alaska is estimated to have more than 100,000 glaciers. Most remain unnamed
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World glaciers
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a thick mass of moving ice
What is a glacier? a thick mass of moving ice
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Glaciar Perito Moreno, in Santa Cruz province, Argentina
Glaciar Perito Moreno, in Santa Cruz province, Argentina. It hasn’t happened since 1988 and it is said to be one of the most extraordinary natural events in the world. - Roberto Cerrudo
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Trans Labrador Highway
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Snow to firn to glacial ice
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How do glaciers erode the surface?
Plucking –freeze/thaw process lifts particles into ice Striations- parallel scratches made from rocks in ice scraping against bedrock
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Kelly’s Island Glacial grooves
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Glacial polish
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TYPES OF GLACIERS Alpine (Valley)Glaciers – glaciers that form at high elevation in mountain valleys Ice sheets or Continental Glaciers form in polar regions such as Greenland and Antarctica.
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Cirque A bowl-shaped depression located where a glacier begins to form
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Horn A tall, pointed rock peak left at the top of a mountain
Kinnerly Peak - Glacier National Park A tall, pointed rock peak left at the top of a mountain
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The most famous horn in the Alps… The Matterhorn
Located on the boundary between Switzerland and Italy, the Matterhorn’s summit is 1500 feet above sea level.
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Arete – spines or ridges of rock that separate glacial valleys
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U-shaped Valley - Yosemite National Park
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V-shaped valleys become U-shaped valleys as glaciers move through them…
Step 2 Step 1 A typical river valley Over time, running water cuts a deeper V-shape. Step 3 Glacier fills valley, widening and straightening the channel Step 4 Glaciers melt leaving a U-shaped valley
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VALLEY GLACIER
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Glaciers pick up lots of sediment as they advance over the land.
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TYPES OF GLACIAL DRIFT (Sediments)
TILL- unsorted; deposited by ice STRATIFIED DRIFT- layered; deposited by meltwater streams OUTWASH- sorted sand; deposited by meltwater
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till outwash
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Erratics Boulders carried great distance by the glacier
Don’t match surrounding rock “strange rock”
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Erratics along Lake Michigan Shoreline
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TYPES OF GLACIERS Alpine (Valley)Glaciers – glaciers that form at high elevation in mountain valleys Ice sheets or Continental Glaciers form in polar regions such as Greenland and Antarctica.
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MORAINES Deposited along edge of glacier during melting Ridges of till
Terminal- very end of glacier Lateral- side of glacier Recessional- progresses behind terminal
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MORAINES MADE OF TILL
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terminal moraine – unsorted sediments deposited at the edge of the melting glacier
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Ground Moraine- flat till deposits between recessional moraines
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Moraine Deposits = unsorted sediments
Moraines are made of unsorted sediments. Only mass movements and glaciers deposit unsorted sediments. Since there are no large hills or mountains in Michigan for this sediment to fall down, it must have been deposited by the glaciers.
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Drumlins Hills of sediment deposited by the glacier- till
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Boyne, Nubs Nob, Irish Hills are drumlins in MI
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MI Drumlins
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KAMES Cone shaped deposits Deposited at end of meltwater streams
Stratified drift
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Mt. Holly is a kame
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ESKERS Meandering ridges of stratified drift
Deposited by meltwater streams Mined for gravel
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Mt. Brighton Mason esker
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Kettle Lakes Made from ice blocks Deep inland lakes rocky
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Kettle Lakes Kettle lakes form when blocks of ice break off the front edge of a glacier, become buried by sediment. The ice melts leaving a hole which fills with water creating a lake.
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Outwash plain From melt water (lake) in front of ice Flat; sandy
Contains outwash and often kettle lakes
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Pleistocene Epoch “Ice Age” 2my- present
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1.5 mya
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mastodon
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Mammoth Bigger than mastodon Curvy tusk
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When the climate cooled…
Ice advanced over the land, moving southward from Canada over the Great Lakes Region.
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Each of the Great Lakes began as a river.
Image from Earth Science, Tarbuck and Lutgens, 2003
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As the climate cooled… The rivers froze.
Glaciers moved through the river valley – widening and deepening them to form today’s lake bottoms.
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Why do scientists believe that glaciers once covered Michigan?
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Moraine Deposits =unsorted sediments
What can deposit unsorted sediment? Mass movement? ice
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Moraine Deposits have the same shape as the Great Lakes.
Michigan moraines run parallel to the shoreline. The same process that formed the moraines formed the Great Lakes.
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3 ice lobes
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When the climate began to warm, the glaciers began to melt and retreat.
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The Glacial History of Michigan
The depth of the lake is determined by the thickness of the ice at the time of glaciation. The farther north the lobe of ice, the thicker it was. Consequently, the lakes get more shallow in the southern Great Lakes region. LAKE: GREATEST DEPTH: Superior = 1,333 ft. Michigan = ft. Huron = ft. Ontario = ft. Erie = ft.
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The fresh water from the melting glaciers filled in the deep U-shaped valleys that they had carved and turned them into the lakes we have today.
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What other evidence do we have that glaciers once covered our state?
Depositional features such as drumlins and kettle lakes. Kalkaska, Michigan
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Isostatic (crustal) rebound land is rebounding up from weight of glacier about 53 cm/ century
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Pictured Rocks
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Kettle Lakes
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Why do scientists believe that glaciers once covered Michigan?
Michigan is covered with till The moraine deposits follow the outline of Great Lakes Erratics Striations Isostatic rebound
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What glacier evidence do we see in Grosse Pointe?
Erratics Old beach ridges Ridge road Mack avenue Till
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Resources http://cse.cosm.sc.edu/erth_sci/Erosion/plucking.jpg
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