How does a glacier "retreat?"

Question

It would seem obvious to assume it slowly melts, but what about when it grows? The glacier itself doesn't actually move forward does it? Or where is the new glacier formed? Glaciers are pretty huge, so it wouldn't make sense that over time, as it got colder, stuff froze upward to produce the thick glaciers, so how does an advancing glacier...well...advance?

Thanks.... Just curious :)

Answer 1

Glaciers respond to climate in an attempt to achieve equilibrium. A glacier advances due to a climate cooling/snowfall increase that causes positive mass balance.  This advance increases the glaciers area at low elevation where ablation is highest, returning the glacier to equilibrium.  A climate warming/snowfall decrease leads to negative mass balances and glacier retreat.  To reestablish equilibrium a retreating glacier must lose enough of its highest ablating sections, usually at the lowest elevations, so that accumulation in the accumulation zone once again balances ablation, reestablishing equilibrium..  If a glacier cannot retreat to a point where equilibrium is established, it is in disequilibrium with the climate system.

Answer 2

Yes, glaciers do move.  Gravity slowly causes the glacier to move down a mountain,  Just like a mountain stream flows down hill.  Just as a mountain stream can evaporate and disappear before reaching a lake or the ocean, its upper parts do not stop flowing.  Same with a glacier, it can melt at its lowest part (the face), but the upper part can still be accumulating and flowing down the mountain.  If more snow falls and accumulates at the head of the glacier than melts at the face then the face will advance further down the mountain.