Crevasses form because of differences in glacier velocity. Longitudinal crevasses form semi-parallel to flow where a glacier expands laterally. This involved navigating the glacier (which was scattered with more crevasses) and the moraines below. The two fell 2000 feet onto and over crevasses on Elliot Glacier. The crossing of glaciers is potentially hazardous because of the potential for crevasses. Despite a fear of crevasses, they decided to approach the summit by the glacier. Intersecting crevasses can create isolated peaks in the ice, called seracs. The slopes surrounding the classical route to Elbrus from the South contain large crevasses. Lichen physically weather rocks by penetrating the rock's small crevasses with their rhizoids. This included removing of surface rocks and filling any crevasses. Marginal crevasses are largely transverse to flow. The first order cause of calving is longitudinal stretching, which controls the formation of crevasses. Plucking and shattering can be seen here by those exploring the crevasses. Many animals fall into the crevasses opened by the eruption. Most crevasses show an ice thickness of approximately .