As large glaciers retreat, the underlying ground surface is typically scoured of most materials, leaving only scars on the underlying surface.

Glacier retreat, melt, and ablation, result from increasing temperature, evaporation, and wind scouring. Ablation is a natural and seasonal part of glacier life. As long as snow accumulation equals or is greater than melt and ablation, glacier health is maintained.

In the northern half of North America, glacial remnants from the last ice age may be reincarnated as vegetated hillsides. Views from an airplane window over the midwestern states and provinces reveal lines of eskers and herds of drumlins dotting the landscape.

Throughout advance and retreat, glacial debris (till) is jostled in all directions. Till is thrust forward with the glacier, brushed aside as the glacier pushes past less mobile objects, such as a mountainside, or drawn along on the glacier's journey.

Over the past 60 to 100 years, glaciers worldwide have tended toward retreat. Alpine glaciers, which are typically smaller and less stable to begin with, seem particularly susceptible to glacial retreat. Whether this is due to a predictable climate trend or because of increased human impacts on global climate remains to be determined.

Photo, top: Glaciers carved many of the mountains and landforms seen in present-day Glacier National Park. A small glacier remained in the uppermost cirque (bowl-shaped hollow) in this photograph from 1925. (Army Air Corps/Captain A. W. Stevens photograph at the World Data Center for Glaciology, Boulder)

Photo, middle: Forno Glacier, from an 1896 photograph. Notice the small rocks and boulders scattered across the surface of the glacier, as well as the pile of till in front of the glacier. (H.F. Reid photograph, at the World Data Center for Glaciology, Boulder)

Photo, bottom two: Franz Joseph Glacier (Unattributed photographs at the World Data Center for Glaciology, Boulder)

The Franz Josef Glacier in New Zealand retreated rapidly over a 15 year period during the 1950s and 1960s.

The top photograph dates from 1951, and the lower photograph dates from 1964.