Suncups on Challenger Glacier, Picket Range, North Cascades.

A familiar sight to climbers, this oddity occurs as snow on top of a glacier or snowfield dissipates unevenly due to dry, fair weather conditions which favor faster melting in the hollow of the suncup, and slower evaporation at the point. This differential causes the hollow to deepen faster than the point can melt away. Suncups can easily reach depths of two feet or more, and always establish a large pattern across a snowfield, rather than appearing as isolated depressions. August 30, 1972.