A crack in a glacier is called a crevasse. These are deep fissures or openings that form in the ice, often presenting significant hazards in glacial environments.
Understanding Crevasses
Crevasses are a fundamental feature of glaciers and ice sheets. They are essentially deep cracks that can vary greatly in size, from a few centimeters wide to several meters across, and can extend tens of meters deep into the ice.
How Crevasses Form
Glaciers are not static; they flow and move under their own weight, albeit very slowly. This movement is not uniform. As a glacier flows over uneven terrain, changes in slope, or constrictions in its valley, the ice can be subjected to immense tensional stress. When this stress exceeds the strength of the ice, it fractures, creating crevasses.
Key factors influencing crevasse formation include:
- Changes in Slope: As a glacier moves from a flatter area to a steeper one, the upper layers of ice stretch and pull apart, forming cracks.
- Curvature of Flow: When a glacier flows around a bend in a valley, the outer edge moves faster and stretches, leading to crevasse formation.
- Varying Speeds: Different parts of a glacier can move at different speeds (e.g., faster in the center, slower at the edges due to friction), creating shear forces that lead to cracks.
- Icefalls and Seracs: In areas of extreme steepness, glaciers can break into chaotic blocks of ice (seracs) separated by numerous, often unstable, crevasses, forming an icefall.
Types of Crevasses
Crevasses are typically categorized based on their orientation relative to the glacier's flow:
| Type of Crevasse | Description | Formation Context |
|---|---|---|
| Transverse | Perpendicular to the direction of ice flow. | Form where the glacier accelerates, such as over a convex slope. |
| Longitudinal | Parallel to the direction of ice flow. | Form where the glacier widens or experiences lateral shear stress. |
| Marginal | Angled upstream from the glacier's edges towards the center. | Caused by friction with the valley walls, slowing the edges. |
| Bergschrund | A large crevasse at the head of a cirque glacier. | Separates the moving glacier ice from the stationary ice or rock of the cirque wall. |
| Splaying | A network of cracks fanning out from a central point. | Often found at the snout (terminus) of a glacier where it spreads. |
Dangers Associated with Crevasses
Crevasses pose significant dangers, particularly to hikers, climbers, and anyone traversing glaciated terrain. The primary risks include:
- Falls: The most immediate danger is falling into a crevasse. Their depths can be hundreds of feet, making falls potentially fatal or leading to severe injuries and hypothermia.
- Hidden Crevasses: Often, crevasses are not visible, especially after fresh snowfall. Snow bridges can form over them, appearing solid but collapsing under weight. These hidden traps are especially perilous.
- Difficulty of Rescue: Rescuing someone from a crevasse requires specialized skills, equipment, and often considerable time, adding to the danger in remote areas.
Safety Precautions on Glaciers
Given the inherent risks, proper precautions are crucial when traveling on glaciers:
- Roping Up: Always travel roped together with partners. If one person falls into a crevasse, the others can arrest the fall.
- Proper Equipment: Carry essential gear, including ice axes, crampons, harnesses, ropes, and crevasse rescue equipment (pulleys, ascenders, prusiks).
- Route Planning: Study maps and reports to identify known heavily crevassed areas. Choose routes that minimize exposure to danger.
- Snow Bridges: Be extremely cautious of snow bridges. Test them carefully or avoid them if possible. Travel early in the morning when snow bridges are stronger due to colder temperatures.
- Crevasse Rescue Training: Undertake specific training in crevasse awareness, avoidance, and rescue techniques before venturing onto glaciated terrain.
- Travel with Experienced Guides: If inexperienced, travel with a certified mountain guide who possesses extensive knowledge of glacial travel and rescue.
Understanding crevasses is vital for anyone engaging in activities on or near glaciers, ensuring safety and respect for these dynamic natural formations.
