For most mountaineers, the primary goal of glacier travel is not to reach the summit, but rather to not fall in along the way. Crevasses are notorious for swallowing even highly skilled travelers. Yet looking into the abyss of a deep crevasse is also one of the great thrills of glacier travel. A little knowledge in rope rescue techniques and in how crevasses form can help make glacier travel safe.

Crevasses form because the glacier is flowing over a rough uneven surface. Frozen water, as you know, does not easily pour. Thus as the thick sheet of ice moves down the mountain cracks open up in the brittle ice sheet. The depth of these cracks on a glacier like the Blue can reach 30 meters or more while the width can vary from a few centimeters to tens of meters. The main reason crevasses present such a hazard to climbers is that snow bridges often obscure them. Winter snow accumulation regularly covers the openings. As ablation increases, these bridges become thinner and thinner. The most common mountaineering accident occurs when a climber pops through a thin snow bridge into a hidden crevasse. Climbing parties rope up in three or four person teams so that others can stop someone from falling to the bottom.

The patterns crevasses make on the glacier surface reveal much about the glacier’s flow. On Blue Glacier two types of crevasses—transverse and marginal—are easy to recognize. The rows of parallel crevasses pointing up glacier along the edges of the glacier are marginal crevasses. This pattern develops when friction from valley walls actually slows or stops the flow along the edges of the glacier. The ice is also relatively thin in these areas. Transverse crevasses span the width of the glacier and are found anywhere there is active movement. Their concave up glacier shape is due again to the faster center flow. Transverse crevasses are often of great assistance to mountaineers following the standard climbing route on Mount Olympus. In a whiteout they simply travel parallel to the cracks across the glacier towards home. Blue Glacier also features a unique patch of tic-tac-toe crevasses at the base of the icefall. This small spot where sets of parallel cracks run perpendicular to one another is formed by a high spot in the bedrock that the ice must flow over.


intro | terminology | accumulation | firn | blue | ablation | water | equilibrium | massbalance | movement | crevasse | structure | algae | moraine | debris | erosion
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Benjamin Drummond 2002