Marine Benthic Ecosystems

Take it Further: What are Glaciers?

ROVWilkins Ice Shelf
Photo credit: British Antarctic Survey
One-tenth of the earth's exterior is covered by glaciers hugging the earths surface (Walker, 1990). They exist in places like Antarctica as well as Greenland, Iceland, Canada, the Soviet Union and Alaska. Holding 75 percent of the world's fresh water supply, glaciers form in places where snow rarely melts and temperatures stay consistently cold. Even in the Antarctic summer, temperatures toggle around the freezing point and this is ideal for protecting the largest sheets of ice around the world. In fact, Antarctica has the largest ice sheet on Earth covering 30 million km³ or roughly the size of the U.S. state of Connecticut.

Glaciers form when snow and ice accumulate over time. The amount of snow that falls in a given year must be more than the amount of glacier ice that has melted. This is the only way a glacier can increase its size. For something to be called a glacier, the snow must first turn into ice and then the ice must move. The weight of the snow and ice creates pressure and over time that pressure flows outward and downward. Many factors influence the movement of glacier ice like thickness, weight, the steepness of the earth's surface, and the surrounding temperatures and gravity.

Fun Fact:
Northern hemisphere icebergs are fractured off the glacial edge and tend to have jagged tops. Southern hemisphere icebergs have about 60 to 90 meters of ice above the sea and are flat on top because they fractured from flat top ice shelves which project over the southern ocean.
Sometimes these massive ice sheets rest on land, but in West Antarctica they can also extend 2,500 meters below sea level. In some cases the ice sheet begins to float over the ocean forming ice shelves - much like the Larsen B. If large pieces of ice break away from the shelf they become icebergs. In situations where the air temperatures rise or the sea water becomes warmer, the ice shelf can melt, adding cold fresh water to the ocean.

When glaciers like the Larsen B in Antarctica melt, does that impact sea levels where I live? First, watch this video segment on the Antarctica Ice Sheet (part one) from the Teachers' Domain, Earth System: Ice and Global Warming, 2005. Then, explore the concept of ice sheets thinning and melting by watching this quick simulation.

Write your hypothesis down and include supporting evidence for your theory.

Sea level rise will impact everyone, especially those living in low lying coastal regions. If all of the glaciers on the Western Antarctic melt, sea level will increase 20 feet along every coastline in the world. Small sea level changes can have major impacts during storm surges, where the winds pile up water along the coast, pushing them inward over coastal plains with little effort. Since the majority of Earth's population live near the coast, these people will be directly impacted and forced to relocate to higher ground. That relocation would impact everyone.

View the effects of sea level rise where you live. Or try manipulating the sea level viewer created as a joint project between the Jet Propulsion Laboratory (JPL) and California Institute of Technology.


(Modified from the National Snow and Ice data Center)

cryosphere: The perennially frozen regions of the planet, including land-ice, sea-ice, permanent snow cover and permafrost. Another definition suggests it is the frozen water part of the hydrosphere (all the water on Earth) and includes continental and sea ice.

calving: the removal of ice from a glacier by melting.

flow: Glacial ice flows in two ways. (a) Ice behaves as a brittle solid until the pressure is equal to the weight of 50 meters (165 feet) of ice; then it becomes plastic and flow begins. (b) The whole mass of ice can slip along the ground, or along shear planes in the ice.

glacier: A large, long-lasting accumulation of snow and ice that originates on land and moves because of its weight and because of gravity.

glacial ice: Compact ice crystals with a density greater than 0.84. glacial retreat The backwards movement of the snout of a glacier when more snow is lost than is replaced each year.

icebergs: Floating chunks of ice which calved off a glacier. Five-sixths of the berg is typically underwater and one-sixth of the berg above the water. Icebergs can occur in fresh or salt water.

ice shelf: A large flat-topped sheet of ice attached to land along one side extending out into the ocean or lake.

ice sheet: a mass of glacier ice greater than 12 million acres.

sea ice: At temperatures of -2° C (28.5° F), sea ice freezes directly from ocean water to a thickness of five meters (15 feet). retreat a glacier where melting succeeds the accumulation of snow causing the it to recede.

snow density: New fallen snow density is near or less than 0.1. Old snow (corn snow) is up to 0.55. Firn density (snow that has survived one melt season) is 0.55 up to 0.82 and begins to compress.