GlaciersGlaciers

An Introduction to a Powerful Force That Has Shaped the Earth.

Glaciers Have Sculpted the Earth Around You….

How Do Glaciers Shape the Earth?

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

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.

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.

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

FIRNFIRN•Grainy ice created from the partial melting and refreezing of snow crystals.

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.

A Brief Overview of Glacier Formation

• Select this button to access the story of a Glacier….

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Types of GlaciersCategorized

by:• Size• Where they

formed

Two Types:• Valley Glacier• Continental

Glacier or Ice Sheet

VALLEY GLACIER• A Glacier

formed in mountainous areas when ice moves down a valley. It produces a long, narrow, wedge-shaped mass of ice.

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.

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

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.

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?

Valley Glacier Landforms

Cirque and AretesCirqueCirque• A bowl shaped

depression

Aretes ‘Spine’Aretes ‘Spine’• Sharp, jagged

ridges between cirque

Horn

•Several Aretes joined to form a sharp, pyramid peak

Hanging Valley

• A small tributary glacial valley suspended on a higher portion of a mountain.

• Ice melt flows over the cliff as a waterfall.

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.

Moraine•Landforms

made from glacial till

•Ridges of unsorted rock material on the ground or on the glacier

Photo depicts a ground moraine.

Lateral Moraines• Strips of dirt

and rock that flow with the ice along the sides of valley glaciers.

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.

Continental Glacier Landforms

• Erode by leveling existing landforms, producing relatively smooth, rounded landscapes.

• Features are exposed as the glacier retreats.

Moraine•Landforms

made from glacial till

•Ridges of unsorted rock material on the ground or on the glacier

Photo depicts a ground moraine.

Ground Moraine• A mantle of

till deposited underneath the ice

• Often very rocky

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

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

Till• The result of

glacial drift

• Contain various sizes of sediment that is not sorted or layered

Outwash

• Glacial till that has been transported, sorted and deposited by glacial meltwater

Kame• Small hills

of sand and gravel

• Formed from outwash.

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.

Gravel Pits• Today, Kames

and Eskers created during the last ice age are frequently exploited as gravel pits.

Erratic• A large boulder

deposited by a glacier.

• Typically a different rock type than the material in which it is deposited.

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

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

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

Dangers of GlaciersIcebergs

Crevasses

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.

Crevasses• Large cracks

formed in the surface of a glacier

• Often covered with snow and extending 30 m downward

The Ice Age• A long period

of climatic cooling during which continental ice sheets cover large areas of the earth’s surface.

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….

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

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

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