Glacial Valley - Formed by the movement of glaciers Shaped like the letter “u”
Glaciers An Introduction to a Powerful Force That Has Shaped the Earth.
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Transcript of Glaciers An Introduction to a Powerful Force That Has Shaped the Earth.
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GlaciersGlaciers
An Introduction to a Powerful Force That Has Shaped the Earth.
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Glaciers Have Sculpted the Earth Around You….
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How Do Glaciers Shape the Earth?
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What Is a Glacier?• A mass of
moving ice created from accumulation of snow over many years that compresses into large, thickened ice masses
• A glacier moves like a very slow river eroding and shaping the land beneath it
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What’s important about Glaciers?• Glaciers are the second largest reservoir of
water on earth.
• A 5o C increase in global average
temperature would likely cause all glaciers to melt, raising sea level by 50-70 m.
• Glaciers represent permanent ice (does not melt each summer) - so they reflect climatic conditions, not variations in weather.
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What’s important about Glaciers?• Glaciers are an important agent of
erosion and formed much of the landscape of Michigan.
• Form deposits of sediment that have distinctive characteristics (drift and till).
• Most recent glacial period culminated at the end of the Pleistocene, about 15,000-20,000 years ago.
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How do Glaciers form?• Starts with abundant winter snowfall that
doesn’t melt away (snowline - altitude above which snow is permanent)
• Snow is converted to glacial ice under overlying weight of accumulating snow
• 2 Major requirements:– Low Temperatures– Adequate amounts of snow
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FIRNFIRN•Grainy ice created from the partial melting and refreezing of snow crystals.
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Requirements for Glacier
Formation:
•Temperatures low enough to retain snow year round (High Altitude and High Latitude).
•Sufficient Snow: Some polar climates are very dry, so glaciers do not •develop.
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A Brief Overview of Glacier Formation
• Select this button to access the story of a Glacier….
Loading the web site may take a moment, please be patient….
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Types of GlaciersCategorized
by:• Size• Where they
formed
Two Types:• Valley Glacier• Continental
Glacier or Ice Sheet
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VALLEY GLACIER• A Glacier
formed in mountainous areas when ice moves down a valley. It produces a long, narrow, wedge-shaped mass of ice.
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Continental GlacierIce Sheets
• A Glacier covering a large land mass (millions of square
kilometers). The type of Glacier occurring during the ice age and in present day Greenland and Antarctica.
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Movement of Glaciers• When ice accumulation is thick enough
it will begin to flow.
• Speed and Amount of flow depends on slope and weight.
• Two Movement Types:– Basal Slip– Internal Plastic Flow
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Basal Slip• The weight of overlying ice exerts
enough pressure to melt some ice at the base of the glacier.
• The melting ice creates a slippery surface for the overlying glacier to slide over.
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Internal Plastic Flow• Solid ice crystals throughout the glacier
slipping over each other
• Creates a slow forward motion
• Like a river, not all parts of the glacier flows at the same speed. Where would it flow fastest? Slowest? And Why?
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Valley Glacier Landforms
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Cirque and AretesCirqueCirque• A bowl shaped
depression
Aretes ‘Spine’Aretes ‘Spine’• Sharp, jagged
ridges between cirque
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Horn
•Several Aretes joined to form a sharp, pyramid peak
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Hanging Valley
• A small tributary glacial valley suspended on a higher portion of a mountain.
• Ice melt flows over the cliff as a waterfall.
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U-Shaped Valley• As the valley
walls and floor are scraped away by a glacier, the original V-shape valley is changed into a U-shape.
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Moraine•Landforms
made from glacial till
•Ridges of unsorted rock material on the ground or on the glacier
Photo depicts a ground moraine.
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Lateral Moraines• Strips of dirt
and rock that flow with the ice along the sides of valley glaciers.
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Medial Moraines• When a
segment of the glacier merges into a larger ice mass, the lateral moraines create debris in the middle of the larger flow.
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Continental Glacier Landforms
• Erode by leveling existing landforms, producing relatively smooth, rounded landscapes.
• Features are exposed as the glacier retreats.
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Moraine•Landforms
made from glacial till
•Ridges of unsorted rock material on the ground or on the glacier
Photo depicts a ground moraine.
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Ground Moraine• A mantle of
till deposited underneath the ice
• Often very rocky
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Ground Moraine• Farmers and
people putting in a new yard uncover the many rocks deposited from the last ice age.The soil of Ohio west to Montana and North
to Canada is ground moraine
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Terminal Moraine• Hilly ridges
composed of a mixture of rock, sand, and clay
• Marks the farthest advance of the ice.
•Cape Cod and Long Island are examples of Terminal Moraines
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Till• The result of
glacial drift
• Contain various sizes of sediment that is not sorted or layered
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Outwash
• Glacial till that has been transported, sorted and deposited by glacial meltwater
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Kame• Small hills
of sand and gravel
• Formed from outwash.
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Esker• Long, narrow
ridges of sand and gravel in the middle of ground moraine
• They wind for kilometers roughly parallel to the direction the ice moved.
•Form from melt water streams flowing in tunnels along the bottom of the melting glacier.
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Gravel Pits• Today, Kames
and Eskers created during the last ice age are frequently exploited as gravel pits.
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Erratic• A large boulder
deposited by a glacier.
• Typically a different rock type than the material in which it is deposited.
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Kettle • The result of a very large block of ice being left behind as a glacier recedes. The melting ice forms potholes which are sometimes filled with water in a glacier, till, or outwash plain. Vegetation may grow up around kettles. A Kettle Lake
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Drumlins• Long, low, tear
shaped mounds of till
• The long axes of the drumlins are parallel to the direction of glacial movement
Drumlins have the shape of an inverted spoon
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Roches Moutonnees
• Rounded knobs of rock created by a glacier
• The glacier polishes and smooths out the top of existing rock as it passes over
The glacier plucks chunks of the rock out as it passes by creating a rough surface on the side
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Dangers of GlaciersIcebergs
Crevasses
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Iceberg• Pieces of ice that
break off of a glacier.
• The ice sheet on Greenland is the primary source of icebergs in the North Atlantic.
• Create a hazard for ships.
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Crevasses• Large cracks
formed in the surface of a glacier
• Often covered with snow and extending 30 m downward
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The Ice Age• A long period
of climatic cooling during which continental ice sheets cover large areas of the earth’s surface.
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The Ice Age• It is believed
that the world has gone through several periods of glacial ice age advancement and retreat.
• It will occur again….
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Causes for an Ice Age
• Small, regular changes in earth’s orbit and tilt which cause changes in the amount of solar energy reaching earth’s surface
MilankovitcMilankovitch h
TheoryTheory
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Causes for an Ice Age
3 Periodic Changes3 Periodic Changes
• A more elliptical orbit
• Tilt ranging from 21.50 - 24.50
• Circular motion of precession
MilankovitcMilankovitch h
TheoryTheory
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http://www.asf.alaska.edu:2222/how_form/glacier_form_begin.html
Useful web sites for Glaciers
http://www.uwsp.edu/geo/faculty/lemke/alpine_glacial_glossary
http://www.davison.k12.mi.us/bentley/glaciers.html
http://nsidc.org/glaciers/story/page1.html
http://wrgis.wr.usgs.gov/docs/parks/glacier/uvalley.html
www.nps.gov/olym/edglac.html
http://www.eoascientific.com/interactive/glaciers/glaciers.html