glaciers

types of glaciers

The types of glaciers are: Continental glaciers are large ice sheets that cover relatively flat ground. These glaciers flow outward from where the greatest amounts of snow and ice accumulate. Alpine (valley) glaciers flow downhill from where the snow and ice accumulates through mountains along existing valleys. Ice caps are large glaciers that cover a larger area than just a valley, possibly an entire mountain range or region. Glaciers come off of ice caps into valleys. The Greenland ice cap covers the entire landmass.

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glacial growth

where are the glaciers

Nearly all glacial ice, 99%, is contained in ice sheets in the polar regions, particularly Antarctica and Greenland. Glaciers often form in the mountains because higher altitudes are colder and more likely to have snow that falls and collects. Every continent, except Australia, hosts at least some glaciers in the high mountains.

shrinking

Glaciers are melting back in many locations around the world. When a glacier no longer moves, it is called an ice sheet. This usually happens when it is less than 0.1 km2 in area and 50 m thick.

glacier national park

Many of the glaciers in Glacier National Park have shrunk and are no longer active. Summer temperatures have risen rapidly in this part of the country and so the rate of melting has picked up. Whereas Glacier National Park had 150 glaciers in 1850, there are only about 25 today. Recent estimates are that the park will have no active glaciers as early as 2020. This satellite image shows Grinnell Glacier, Swiftcurrent Glacier, and Gem Glacier in 2003 with an outline of the extent of the glaciers as they were in 1950. Although it continues to be classified as a glacier, Gem Glacier is only 0.020 km2 (5 acres) in area, only one-fifth the size of the smallest active glaciers.

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formation

Glaciers grow when more snow falls near the top of the glacier, in the zone of accumulation, than is melted from lower down in the glacier, in the zone of ablation. These two zones are separated by the equilibrium line. Snow falls and over time converts to granular ice known as firn. Eventually, as more snow and ice collect, the firn becomes denser and converts to glacial ice. Water is too warm for a glacier to form, so they form only on land. A glacier may run out from land into water, but it usually breaks up into icebergs that eventually melt into the water.

movement

Whether an ice field moves or not depends on the amount of ice in the field, the steepness of the slope and the roughness of the ground surface. Ice moves where the pressure is so great that it undergoes plastic flow. Ice also slides at the bottom, often lubricated by water that has melted and travels between the ground and the ice. The speed of a glacier ranges from extremely fast, where conditions are favorable, to nearly zero. Because the ice is moving, glaciers have crevasses, where cracks form in the ice as a result of movement. The large crevasse at the top of an alpine glacier where ice that is moving is separated from ice that is stuck to the mountain above is called a bergshrund. Crevasses in a glacier are the result of movement.

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glaciers as a resource

In regions where summers are long and dry, melting glaciers in mountain regions provide an important source of water for organisms and often for nearby human populations. Click image to the left or use the URL below. URL:

instructional diagrams

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questions

where are glaciers found?

a) antarctica and greenland only

-->  b) every continent except australia

c) every continent except antarctica and greenland

d) australia only

large glaciers that cover a larger area than just a valley, possibly an entire mountain range or region.

a) continental glacier

b) alpine glacier

-->  c) ice caps

d) valley glacier

a deep crack in the glacier that forms as a result of ice movement.

a) glacial breakage

b) crack

c) bergshrund

-->  d) crevasse

the lower part of the glacier where the amount of snow and ice that melts off is the

a) zone of accumulation

-->  b) zone of ablation

c) equilibrium line

d) none of these

when a glacier no longer moves, it is called an ice sheet.

-->  a) true

b) false

whether an ice sheet is a glacier depends on

a) the amount in the field.

b) how steep the slope is.

c) the roughness of the ground surface.

-->  d) all of the above.

how do glaciers move?

a) by plastic flow at the bottom where the pressure is high.

b) at the bottom where meltwater lubricates it.

c) from extremely fast to nearly no movement.

-->  d) all of the above.

glacier national park has lost many of its active glaciers because

-->  a) temperatures in that region have been rising.

b) plate tectonics is moving the region into a warmer location.

c) people are ruining them with their hiking and atv riding.

d) none of the above.

glaciers are a resource because

-->  a) they are a source of water in the summer.

b) they provide energy as the water turns from snow to glacial ice.

c) they cover up vast mineral resources that are exposed when they melt.

d) gold dust and other valuable minerals land on glaciers and can be mined.

gem glacier in glacier national park is no longer moving, but it is still a glacier.

a) true

-->  b) false

diagram questions

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