seracs

Seracs are large blocks or pinnacles of ice that form on a glacier, typically above crevassed zones or near icefalls. They develop where crevasses propagate through the glacier and the broken ice blocks accumulate, sometimes stacking on one another as flow concentrates and surface fractures reopen. Seracs are most common on high-altitude or heavily crevassed glaciers and in areas of intense vertical shear.

The appearance of seracs varies: individual blocks can be slender towers, massive blocks, or sheets with overhanging lips. They may be isolated or part of a larger, unstable icefall. Sizes range from small columns to substantial walls, and the configuration can change with weather, sun exposure, and meltwater.

Seracs are dynamic features. They shift as the underlying glacier moves, and wind, temperature, and melting can alter their stability. Undercutting at the base, hidden crevasses, and the pressure of overlying ice can cause seracs to collapse without warning, generating icefalls and avalanches that pose serious hazards to climbers and expeditions. Wind can tilt or topple blocks, while new crevasses can separate blocks from the main mass.

In glaciology and mountaineering, seracs indicate areas of rapid ice flow and fragmentation. They are considered major cautions in route planning and glacier travel, often prompting the use of rope teams, safe spacing, and avoidance of typical icefall zones.