Glacial Geomorphology

• Ice has advanced and retreated across continental land many times throughout geologic history. The processes and the evidence are the basis for this lecture.

NA Glaciation – The Pleistocene

The Basics

• More snow falls than melts. As depth of snow increases, the weight of the overlying snow creates ice. The pressure plus influence of gravity causes the ice to move.

• The glacier ends at the point melting exceeds rate of supply.

• Think of how a conveyor belt moves material in one direction.

Snow to Ice

• Snow piles up during the winter and if it does not all melt, it can accumulate from year to year.

• To become ice, you must have 150-200 feet of snow compressing itself, squeezing out the atmospheric gases to form ice.

• Ice is a crystalline substance, in essence it is a rock.

Glacier motion – caused by Gravity

Rate of motion – thickness of the ice and slope of the land surface

Continental and Alpine Glaciers

• Continental glaciers formed over large regions like the Hudson Bay and grew to great depths and extended for miles in all directions.

• Alpine glaciers formed in mountain ranges. Extent was a function of the valley system around each glacier.

• In both systems, advance and melt (retreat) are totally controlled by climate and associated characteristics.

Glaciers Impact the Surface

• Ice is a geomorphic agent – forms of erosion and deposition are evident after ice has moved over the surface.

• Some evidence is subtle, striations left in bedrock, whereas U-shaped valleys and moraines are features easily observed.

• >14,000 ft. of ice exerts tremendous pressure on the surface. Bedrock is depressed by the weight and rebounds when the ice is removed.

Snowball Earth

• 750,000,000 years ago Earth was totally covered by ice!

• Remember, continents were in very different positions than today.

• Evidence proves that ice covered all land.

• Impact on plants and animals???• Can it happen again???

Land 750,000,000 years ago

Evidence – Erosion by Ice – U Shaped

Huerfano River, CO

NorwayWyoming

Evidence – grooves and erosion

Svartisen Glacier, Norway

A Groove Caused by Ice

Glacier du Bosson, France – 15K feet down to 3K – a river of ice!

Glaciers and People

• The European Alps are accessible to many people for skiing, hiking, and climbing. Glaciers are dangerous because they are in constant motion. Steep slopes in the Alps mean ice can fall long distances. Alpine Institute in Grenoble plot on maps where people die if their bodies are not recovered.

Key Terms• Erosion – U-shaped valley; arete –

knife-like ridge between two glacial valleys; col, tarn and horn also .

• Deposition – rock debris is called till; the landform composed of till is a moraine.

• A moraine can be lateral (side), terminal (end), medial (in the middle –formed when two glaciers merge), or ground. Till is the term that describes the material in the moraine.

Till – rock material of different texture

Colorado

FranceAlaska

Alpine Glaciation – Teton Glacier

• The remnant of the Teton Glacier, WY is fast disappearing. The U shape is a col, meaning that the ice moved over this ridge in two directions. The glacier once descended to the Snake River plain.

Debris on the Teton Glacier – contributed by freeze-thaw activity

Views on the Teton Glacier

Mt. Moran, Teton N.P., WY

Grinnell Glacier – about 20 years of ice left

Grinell Glacier, Lake and Moraine, G.N.P.

Patterns in Snow over Moving Ice

Snow and Ice, G.N.P., MT

Snow and Ice, G.N.P., MT

Iceberg Lake in a Cirque, G.N.P., MT

Iceberg Lake, G.N.P., MT

Snow, Ice and Rock in G.N.P.,

MT

Snow, Ice, Crevasses in G.N.P., MT

Snow, Ice, Moraine in Glacire N.P. MT

Medial Moraine, Glacier N.P, MT

Goats along trail in

Glacier N.P.

Uinta Mts, Utah

Evidence of glacial erosionand deposition of talus.

Mt. Rainier, WA

Nisqually Glacier

Nisqually Glacier, Mt Rainier, WA

• The ridge of rock debris is the moraine left as the glacier disappears.

• A volcanic event can convert this glacier into a huge debris flow.

• Position of the ice has been monitored for years.

The Nisqually Glacier – In Retreat

Terminus is noted on Maps: Nisqually Glacier, Mt. Rainier, WA

Debris transport varies by glacier.

• The Svartisen glacier in Norway is relatively clean ice because it once covered the entire upland and rock fall onto it was minimal.

Remove Ice – Deposits Left Behind

• From the sediments deposited, geomorphologists can recreate the past.

Continental Glaciers Covered the Landscape

• Acadia National Park in Maine was over-ridden by ice many times. The rounded topography reflects erosion and the stepped topography represents plucking.

Moraines – landforms of deposition

• Fremont Lake, WY reveals a stepped moraine formed as ice melted.

• The size of boulders in till can vary tremendously.

Hummocky Landscape

• As glaciers melted, rock debris once incorporated into the ice is left behind. Most of the deposits are not sorted by size, a key indication of deposition by ice.

• (Ex. from So. Dak.)

Direction of Ice Movement

• Drumlins are streamlined shaped forms that indicate direction of ice movement.

Moraine – once worthless land

• This moraine in NW Indiana was not suitable for crops, hence worthless. But with expressways to Chicago, commuters now live on wooded acreage.

Variability from the Presence of Ice

Iowa

Illinois

France

Glacial Deposits

• Maps abound about the deposits and how they impact human activity.

Glacial Ice

• The future – may reflect the past in that glaciers can expand beyond current limits.

• The future is linked to natural climatic change.

Antarctica – The Ice Continent

Antarctic Peninsula – Ice Melting

Ernest Shackleton – 1914-1916 Explorer Read “Endurance” for his story.

South Georgia – a glaciated islandPopulation 20 people

Ice and snow dominate the South Georgia Landscape

A River of Ice to the sea – South Georgia

Melting Glacier – rock debris on top and a beach full of penguins and seals.

King penguins and chicks (fed by parents for 18 months)

Elephant seals 2,000 pounds and more dominate the beach.

Antarctic Peninsula dominated by glaciers

Glaciers – from land into the sea; Antarctic Peninsula

Glaciers reach the sea and form icebergs – fantastic colors and shapes.

Ice, crevasses rocky slopes and contact with the sea. Ice is dynamic!

Crevasses indicate downslope motion as the ice is pushed into the sea.

Classic crevasse pattern on moving glacial ice.

Glaciers represent an accumulation of snow over millenia, or longer. With

changing temperatures on Earth, glaciers can grow or recede depending

upon what is occurring in the local environment. Do not confusion Global Warming with every place warming. Antarctica is getting more ice on the

main landmass.

In Conclusion:

• Glaciation has modified the surface again and again. If Snowball Earth happened, it can happen again.

• Evidence to support a quick return to glaciation is lacking.

• The next advance of ice is unknown at this time.