A glacier is a persistent body of dense ice that forms on land and moves constantly downhill under its own weight, acting like a slow-motion river of ice. This movement, driven by gravity and the weight of accumulated snow, causes intense stress and fracturing within the ice mass. Because they are dynamic and continually shifting, glaciers are inherently unstable environments that present significant hazards. Understanding the nature of the ice and its interaction with meltwater is the first step in managing the substantial risks associated with these powerful natural features.
Hidden and Structural Dangers on the Ice
The most immediate danger on a glacier’s surface comes from crevasses, which are deep fractures that form in the upper, brittle layer of the ice, often reaching depths of up to 150 feet. These cracks occur where the ice accelerates, slows down, or flows over uneven terrain, creating zones of tension. Transverse crevasses run perpendicular to the glacier’s flow, common where the ice flows over a convex slope, stretching the surface layer.
Longitudinal crevasses, running parallel to the direction of movement, appear where the glacier spreads out, such as when a valley widens. The greatest risk arises when these fractures are covered by a layer of snow, forming a deceptively sturdy-looking “snow bridge.” These bridges are particularly weak and hazardous during warmer periods, such as late spring and early summer, as meltwater erodes the snow from below.
Unstable, towering blocks of ice known as seracs pose another unpredictable threat, typically found in icefalls where the glacier flows steeply over a rock step. Seracs are large columns of ice created by the intersection of multiple crevasses in a highly fractured zone. They can be house-sized or larger, and their collapse, often without warning, triggers catastrophic ice avalanches.
Catastrophic serac failures have been responsible for major mountaineering tragedies. The constant flow of the glacier means that a route deemed safe one day can shift, opening new crevasses or destabilizing seracs overnight. Traveling on the ice requires continuous assessment of the ever-changing structural integrity of the glacier’s surface.
Hazards Related to Glacier Melt and Water
The presence of water, both liquid and frozen, introduces a separate category of hazards, especially near the glacier’s edges or terminus. Calving occurs when large pieces of ice break off the glacier’s front and crash into a lake or the ocean. This sudden displacement of water creates powerful, tsunami-like waves that can surge up to 15 feet high, posing an extreme threat to nearby boats and shorelines.
Calving events are often preceded by a loud cracking sound as the ice fractures. Another water-related danger is the jökulhlaup, an Icelandic term for a glacier outburst flood. These events occur when a meltwater lake, often dammed by ice or glacial sediment, suddenly breaches its boundary.
Jökulhlaups release massive volumes of water in a short period, capable of scouring valleys, destroying infrastructure, and depositing vast amounts of debris far downstream. On the glacier surface itself, vertical shafts called moulins form as meltwater bores its way down through the ice. Falling into these deep, fast-moving subsurface rivers presents a significant danger, as the water pressure and cold make survival nearly impossible.
Essential Safety Measures for Glacier Environments
Mitigating the inherent dangers of a glacier requires specialized equipment and strict adherence to proven travel protocols. For anyone unfamiliar with glacier environments, hiring an experienced, certified guide is the single most effective safety measure. Guides possess the route-finding knowledge to identify the most stable paths and safely navigate around crevasse fields.
Essential personal gear includes crampons, which are metal spikes that attach to boots, providing the necessary traction on slick ice and hard snow. An ice axe is used for balance and, most importantly, for self-arresting a slide down a slope. Roping up is the foundational safety practice for crevasse danger, requiring a team of at least two to three people tied into a rope at specific intervals.
The rope team functions as a mobile safety system: if one person falls into a crevasse, the others immediately drop to the ground to perform a crevasse rescue. Experienced teams use knots tied into the rope at regular intervals to help anchor the line against the crevasse lip in the event of a fall. Route planning is also paramount, involving studying satellite imagery or maps to identify potential crevasse zones and avoiding travel in flat light or whiteout conditions when hidden cracks are virtually invisible.