Glaciers

• Glacial ice represents ~84% of earths fresh water - Glacial deposits account for large areas of fertile soil in the Northern US and southern Canada

A glacier is an accumulation of snow and ice thick enough to flow under its own weight

• Valley glacier • Ice sheet • Ice caps

Are long, narrow glaciers confined to bedrock valleys that flow from high elevations to low elevations like a stream

Are unconfined glaciers larger than 50,000km squared. There are two ice sheets on earth in Greenland and the Antarctica

Are unconfined glaciers that are smaller than ice sheets. Both ice sheets and ice caps exhibit radial flow

They form where snow persists year-round • High altitudes where temperatures are cooler than the surrounding country side • Snowline where the elevation above which snow persists throughout the year • High altitudes where seasons are colder

They are commonly 50-300 meters thick

The Antarctic ice sheet is as thick as 4km and contains 29 million km cubes of glacial ice

Snow is a mineral that metamorphoses at temperatures and pressures close to Earth’s surface

• Snowflakes turn to rounded ice grains and become more compact • Rounded grains recrystallize as contacting grains transfer molecules from one to another, diminishing air space • The result is interlocking crystals with a density of ~0.9gm/cm cubed

In Alaska, hard ice has been found at 15m which are 3-5 years old

Freeze/thaw cycle

They move faster in the middle and slower at the edges

They flow from the zone of accumulation to the zone of wastage due to mass increase in the zone of accumulation

They move downslope whether they are in advance or retreat at their toe

The ratio of accumulation to wastage

Sliding and sliding is related to erosion

Cohesion and friction

The weight of the overlying ice

Nearly equal to the weight of the ice which substantially reduces friction by lifting the glacier off of the underlying rock

Think of glaciers as “rivers of ice” they share similarities to rivers - They flow downhill, erode sediment and transport it

Along the base, especially upslope where the ice is actively flowing downward, and along the valley walls

the base, within the ice, and atop the glacier due to mass wasting along the valley walls and by sediment exposure by thawing