If there is more accumulation than ablation, the glacier will advance. If there is more ablation than accumulation, the glacier will recede. Think of it as a large conveyor belt, continually moving ice and rocks toward the toe of the glacier. This glacier has lost much of the ice that was previously present. Yosemite Valley, California.
Glaciers leave abundant clues.
Among them, the presence of debris from lateral, medial or terminal moraines is a good indicator of the existence of a glacier. Glaciers also carve very distinctively-shaped valleys. In fact, Bridalveil Falls tells us exactly how much ice used to fill the valley. Modern Bridalveil Creek is all that is left of a tributary glacier to the main Yosemite Valley glacier. This former tributary entered the valley above the top of Bridalveil Falls.