Crevasses are among the most striking and potentially dangerous features of glacial landscapes. These deep, open cracks in glacier surfaces are often hidden beneath snow, making them a serious hazard for mountaineers and explorers. But beyond their threat lies a fascinating natural process rooted in the dynamics of ice flow and geological forces. Understanding how a crevasse forms not only reveals the inner workings of glaciers but also contributes to broader knowledge about climate change, glacial movement, and Earth’s polar environments.
The Nature of Glaciers
What is a Glacier?
A glacier is a massive, slow-moving body of ice formed from compacted layers of snow. Over time, as snow accumulates and compresses under its own weight, it transforms into dense glacial ice. These ice bodies flow like very slow rivers due to gravity and internal pressure. This movement is key to understanding crevasse formation.
Glacier Movement and Stress
Glaciers are not rigid structures. While they appear solid, they are constantly in motion. This movement occurs at varying speeds across different parts of the glacier. The center typically moves faster than the edges, and the upper ice layers can move differently from the deeper sections. These varying movements create tension and stress within the glacier, which is essential in forming crevasses.
The Formation of a Crevasse
Stress and Fracture
Crevasses form when the stress within a glacier exceeds the ice’s ability to deform plastically. The upper layers of a glacier are more brittle, and when they are pulled apart due to tension or shearing forces, they crack open. This fracture in the ice surface becomes a crevasse.
Depth and Shape
Most crevasses form within the upper 50 to 60 meters of the glacier where the ice behaves as a brittle solid. Below this depth, the pressure increases, and the ice flows instead of breaking. As a result, crevasses usually do not extend beyond this limit. The shape and depth of a crevasse depend on the glacier’s speed, slope, and internal ice structure.
Influencing Factors
Several environmental and geological conditions contribute to the formation of crevasses
- Glacier SlopeSteeper slopes create greater tension and faster flow, increasing the likelihood of fractures.
- ObstaclesWhen a glacier flows over uneven bedrock or around curves, it experiences bending and stretching that can lead to crevasse formation.
- Speed VariationsChanges in glacier velocity from one section to another introduce stress, causing the ice to split.
- TemperatureColder ice is more brittle and more likely to fracture under stress than warmer, more flexible ice.
Types of Crevasses
Transverse Crevasses
These are the most common type, running across the glacier perpendicular to its flow. They usually form when a glacier moves over a steep incline or accelerates quickly, creating tension that splits the ice.
Longitudinal Crevasses
Running parallel to the glacier’s flow direction, longitudinal crevasses occur when the glacier spreads outward, such as in wide valley glaciers. They are usually not as deep as transverse crevasses.
Chevron Crevasses
Also known as splaying crevasses, these form at the glacier’s terminus or snout, where ice movement fans out. They appear at angles and create a distinctive pattern on the ice surface.
Marginal Crevasses
Located along the sides of a glacier, marginal crevasses form due to friction between the ice and the valley walls. The center moves faster than the edges, creating stress that leads to fracturing near the margins.
Bergschrund
This unique type of crevasse forms where a moving glacier ice mass separates from the stagnant ice above. Often found at the head of glaciers, bergschrunds can be extremely deep and are common in mountain glaciers.
Seasonal and Climatic Influences
Summer vs. Winter Conditions
Crevasse formation is not uniform throughout the year. In summer, surface meltwater can seep into existing cracks, deepening and widening them through lubrication and refreezing processes. In winter, snow accumulation can conceal crevasses, creating hazardous conditions for travel but slowing their formation.
Climate Change Impact
As global temperatures rise, glaciers are melting and retreating faster than before. This can increase crevasse formation in some areas due to unstable movement and added meltwater. Changes in glacier volume and pressure gradients may also lead to more frequent fracturing near glacier margins and icefalls.
Crevasses and Glacier Health
Indicators of Glacier Dynamics
Scientists use crevasse patterns and frequency to study glacier behavior. A glacier filled with numerous crevasses may be accelerating, retreating, or flowing over rough terrain. By analyzing their orientation and location, researchers can infer how internal stress is distributed across the glacier.
Role in Meltwater Flow
Crevasses can serve as important conduits for surface meltwater to reach deeper layers or even the glacier base. This process affects glacier sliding and can increase the speed at which the glacier flows, especially during warm seasons. It also influences the formation of subglacial lakes and tunnels.
Crevasse Hazards and Safety
Risks for Climbers and Researchers
Falling into a crevasse is one of the greatest dangers in glacier travel. Crevasses may be hidden by thin snow bridges, making them nearly invisible. A fall can result in injury or death from impact or hypothermia. Because of this, mountaineers often rope together and use probes or GPS mapping to detect hidden crevasses.
Crevasse Rescue Techniques
In the event of a crevasse fall, quick and proper rescue techniques are essential. Teams are trained to use ice screws, pulleys, and harnesses to lift a victim out safely. These rescues require detailed knowledge of crevasse structure and glacier behavior to avoid worsening the situation.
Scientific Exploration and Mapping
Remote Sensing and Drones
Modern technology has improved how scientists map and study crevasses. Drones equipped with high-resolution cameras or lidar sensors can safely fly over glaciers to create detailed maps of crevasse fields. This technology is especially valuable in regions like Antarctica or Greenland, where ground access is limited.
Glaciology and Future Study
Crevasses provide a window into the movement and structure of glaciers. By studying them, scientists gain a better understanding of how ice masses evolve, respond to climate changes, and interact with their environment. Continued research helps predict sea-level rise and informs conservation strategies for polar and alpine regions.
The formation of a crevasse is a natural response to the immense stress and movement within a glacier. Influenced by slope, speed, temperature, and terrain, these deep fractures reveal much about glacial dynamics and environmental change. Whether viewed as hazards or research opportunities, crevasses are vital to our understanding of Earth’s icy landscapes. Knowing how a crevasse forms not only enhances glacial exploration but also deepens our awareness of the forces shaping our planet’s coldest regions.