Kolka is fed by avalanches and collapses of firn and ice all year round. Diffusion within the firn layer causes other changes that can be measured. In temperate glaciers, snow repeatedly freezes and thaws, changing into granular ice called firn. The island surface is mainly covered by a central ice cap and firn. Firn resembles caked sugar and is very resistant to shovelling. Over a period of years, layers of firn undergo further compaction and become glacial ice. By summer's end, the result is firn.