Crevasse

A crevasse is a deep crack found in a glacier or an ice sheet.

These features are essential to the study of glaciology, which is the science of glaciers and ice. Crevasses provide important information about how ice moves and reacts to its environment. They often feature vertical or near-vertical walls. These icy walls can melt over time to create unique formations like arches or seracs. Sometimes, the walls of a crevasse expose different layers of ice. These layers represent the stratigraphy, or the historical layering, of the glacier.

Crevasses form because of the movement and stress within the ice. Glaciers move over a layer called a plastic substrate. This substrate is a soft, pliable material underneath the ice. Crevasses occur when two semi-rigid pieces of ice move at different rates. This difference in speed creates shear stress between the pieces. The intensity of this shear stress eventually causes the ice to break along its faces.

The presence of liquid water can also change how these cracks form and grow. Water can increase how deep a crevasse penetrates the ice.

Water plays a major role in the movement of a glacier. Water-filled crevasses can reach all the way to the bottom of an ice sheet. This creates a direct hydrologic connection between the surface and the glacier bed. In the summer, significant melting occurs on the surface of the glacier. This water travels down through the cracks to the bottom. This process can moisten and lubricate the bed of the glacier. This lubrication can actually accelerate the flow of the ice. Some direct drains of water from the top of a glacier are known as moulins.

There are three distinct types of crevasses based on how they form. Transverse crevasses are the most common type. They form in a zone of longitudinal extension. In this zone, the principal stresses are parallel to the direction of the glacier flow. This creates extensional tensile stress that stretches across the glacier. These usually form where a valley becomes steeper.

Splaying crevasses appear along the edges of a glacier. They result from shear stress at the margin and longitudinal compressing stress. These are concave up and make an angle of less than 45 degrees with the margin.

Longitudinal crevasses are the third type. These form parallel to the direction of the ice flow. They develop in areas of tensile stress, such as when a valley widens or bends. These crevasses are typically concave down. They form at an angle greater than 45 degrees with the margin.

Understanding these different shapes helps scientists map the movement of the ice. Each type tells a story about the shape of the land beneath the glacier.

Navigating glaciers can be very dangerous due to these cracks.

A crevasse may be covered by a snow bridge. These bridges are made from snow drifts and previous years of snow accumulation. A snow bridge can make a crevasse completely invisible to someone walking on the ice. This makes them potentially lethal to anyone navigating the glacier. Falling into a deep crevasse can cause fatal injuries. For example, the Khumbu Icefall on Mount Everest contains very deep crevasses. Hypothermia is a frequent cause of death for those who fall into them.

Climbers use specific methods to minimize these risks. One common method is to travel in a rope team. This means multiple climbers are tied together with a rope. They also use friction knots to help secure themselves.

These tools and techniques are vital for safety in glacial environments. By working together and using proper equipment, climbers can better manage the hazards of the ice.