Glacial Advance and Retreat
Glaciers lose ice mass every year, to melting and sublimation. They are dynamic systems. Glaciers grow (advance) and shrink (retreat) as a result of precipitation, melting and sublimationall while slowly sliding down their valleys. Local and global climate changes cause the changes this dynamic system.
As precipitation adds more mass to a glacier than melting and sublimation remove, the total volume of the glacier increases. As a result, the glacier grows, extending farther down the valley than it did previously. This is called an advance.
When glaciers melt faster than they are replenished by precipitation, the total volume decreases. The glacier shrinks. This is called a retreat. The glacier is not actually retreating, or physically moving up the valley. It just appears to do so, since the glacier does not extend as far down the valley as it did previously.
Currently, a few glaciers around the world continue to advance, but many are retreating, and some at rates much faster than previously recorded. Some scientists believe this is an sign of fast global climate change caused by human impact on Earth's Systems.
Next: Glacial Impact on Lithosphere