On Vadret da Morteratsch, 2160 m.a.s.l.: In the glacier's ablation area [1] all snow from the previous winter melts, as well as some glacier ice. At this altitude the glacier may lose an ice layer 5 meters thick per year. If enough ice flows from the accumulation area [2] to the ablation area, and replaces the ice loss, the glacier tongue will maintain a constant size. If the ice loss is bigger, the tongue will retreat after a certain time, or - if the ice loss is smaller - it will advance.

The ice loss (ablation) on the glacier tongue is here illustrated by melt water streams [3] and a glacier table [4]: The boulder protects the underlying ice [5] from the sun's radiation, so that after some time the ice surface around the bolder gets lower and lower and forms the table.