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Glacier Movement: Definition & Process

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  • 0:01 Glaciers
  • 0:35 Internal Plastic Deformation
  • 1:44 Basal Sliding
  • 2:19 Crevasses
  • 2:50 Glacial Flow Rates
  • 3:40 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Glaciers are mountains of ice that move. This movement is usually a combination of processes that include internal plastic deformation and basal sliding. Learn about these processes and factors that increase glacial flow rates.

Glaciers

Glaciers are basically ice mountains. But unlike typical mountains that are made of rock, these mountains can move. As they move across the Earth's surface, they act like a sculptor's tool, scraping against rocks and carving out basins. In fact, many of the most beautiful and rugged landscapes, as well as many of our lakes, have been shaped by moving glaciers. Glaciers move because they either get top-heavy or they slip on their base. We will discuss the processes by which glaciers move in this lesson.

Internal Plastic Deformation

Now, all glaciers start with snowfall that accumulates faster than it melts. As the years pass, layers of snow pile up, compressing the layers below into dense ice. This process continues until the mountain of ice becomes very heavy. It starts to move when the weight becomes too heavy to maintain the glacier's shape. Of course, if you stand next to a glacier, you probably would not see this movement because most glaciers only move a couple of centimeters to a couple of meters per day.

The movements they do make are typically a combination of processes, but the most common process is internal plastic deformation, or internal flow, in which the glacier's weight becomes too much to support itself. This results in the slippage of ice layers within the glacier, so the glacier moves downhill, as if it is being spread like a deck of cards with the top layers moving more quickly than the bottom layers. This spreading happens because the lower layers are subjected to friction due to contact with the land, which slows their movement.

Basal Sliding

Another process by which glaciers move is basal sliding. With basal sliding, we see the entire glacier moves as a single unit due to melting at its base. Pressure at the base of the glacier causes a thin layer of ice to melt. This reduces friction, allowing the entire glacier to slide downslope as a single mass, kind of like it's on a water slide. Basal sliding is greatest on steep slopes, where the reduction in friction allows the glacier to succumb to the pull of gravity.

Crevasses

The lowest levels of a glacier are under a lot of pressure due to the weight above. However, the upper layers are not subjected to the same forces and are therefore more brittle. This can cause the upper layers to split as the glacier below moves, forming huge crevasses, or ice cracks, on the surface of the glacier. Crevasses are what make walking on glaciers very dangerous because they get covered with fresh snowfall, making them invisible to hikers and mountain climbers.

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