Glaciers & Ice Ages

Davidson Glacier near Haines, Alaska

Glaciers Glacier: a large, long-lasting mass of ice, formed on land that moves under the influence of gravity and its own weightGlacier: a large, long-lasting mass of ice, formed on land that moves under the influence of gravity and its own weight Glaciers form by accumulation and compaction of snowGlaciers form by accumulation and compaction of snow –Packed snow becomes firm –Then refreezes to ice

Formation of Glacial Ice from Snow

Types Of Glaciers Valley Glaciers: found in mountain regionsValley Glaciers: found in mountain regions Continental Glaciers: exists where a large part of a continent is covered by glacial ice - cContinental Glaciers: exists where a large part of a continent is covered by glacial ice - cover vast areas

Types of Glaciers

Types of Glaciers– Valley Glacier Mount Edith Cavell, Jasper National Park, Canada

Types of Glaciers – Valley Glacier Tongas National Forest, Alaska

Types of Glaciers – Icecap and Continental Sentinal Range, Antarctica

More on Glaciers Gain snow in zone of accumulation Lose ice in zone of ablation

A Glacier’s Budget Summer Rain Year round Snow Note that a glacier is a river. Even if the terminus doesn’t advance, still flows

Iceberg Calving – Hubbard Glacier, Wrangell-St. Elias National Park, Alaska

Erosion by Glaciers Abrasion –Rocks embedded in glacier’s base make linear scratches and grooves in bedrock Plucking –Glacier breaks off and removes large blocks of rock

Glacial Abrasion in Bedrock Source: Tom Bean

Glacial Erosion Yosemite NP, California

Landforms created by Glaciers Horn Cirque U-shaped valley Kettle lake Fiord Moraine

Alpine Glacial Erosion

Valley Glacial Erosion Origin of Hanging Valley

Yosemite Falls

Valley Glaciers Erode a large quantity of bedrock and sediment Convert V-shaped stream valleys into U- shaped glacial valleys.

U-Shaped Valley in Tracy Wilderness, Southeastern Alaska

Seawater Flooded U-Shaped Valleys: Fjords Bela Bela Fjord, BC

Erosion by Continental Glaciation Erosional Landforms much larger in scale than alpine glaciers – Huge U-shaped troughs, including: Finger Lakes, Great Lakes, Puget Sound, and Loch Ness were all once valleys excavated by glaciers

Erosion of Preglacial Lowlands (Finger Lakes)

Erosion of Preglacial Lowlands (Great Lakes of North America) Source: U.S. Dept. of Interior, USGS Eros Date Center

Glacial Deposits or Drift Glacial Till: unsorted, unstratified sediments deposited by melting ice. –May contain glacial erratics –Often accumulate at glacier’s terminus as a Moraine: hills of sediment left by a glacier’s retreat.

Advance & Retreat: Moraines

Large Granite Erratics

Medial Moraines – Kennicott Glacier

Effects of Glaciation Change Climate – increased precipitation Drop in sea-level: alter coastlines Form continent-wide Dams –Divert streams – Ohio and Missouri rivers

Lowered Sea-level - Landbridge

Lowered Sea-level exposed continental shelf

Giant Ripples of the Missoula Flooding

Causes of Ice Ages Plate Tectonics Moves Continents to Poles Raises mountains above snowline Orbit Distances, Axis Tilt and Wobble –Moderates solar radiation past 65° N –Croll-Milankovitch Cycles ~ 100,000 years –Low summertime radiation causes glaciers to expand

Glacier Distribution 20,000 ya Approximate Maximum

Milankovitch Cycles 100,000 years

41,000 years

Earth’s Past Ice Ages PreCambrian Glaciation –750 mya ice flowed from poles to tropics Late Pennsylvanian & Permian Glaciation –covered South Africa, South America, India, Australia Pleistocene Glaciation –most recent, ended about 10,000 years ago

Pleistocene Glaciation started 1.6 mya -30 advances and retreats Latest retreat ended 10,000 years ago “Little Ice Age” occurred 700 to 150 years ago, paralyzed Europe Next glaciation period - ???

Sustained warming since 1850 Athabaska Glacier, Columbia Icefield, W. Canada

End of Glaciers