Accumulation Zone: Located at higher altitudes where temperatures remain low enough for snow to persist year-round, allowing it to compress into firn (or névé) and eventually glacial ice.
Ablation Zone: Found at lower altitudes where warmer temperatures cause ice loss to outpace snow gain; this area is often characterized by meltwater streams and debris.
Equilibrium Line: The critical boundary separating these two zones where accumulation and ablation are exactly equal; its position shifts annually based on climate conditions.
Unconstrained Glaciers: Large-scale ice masses like ice sheets (covering ) and ice caps that submerge the underlying topography and flow outward in all directions.
Constrained Glaciers: Smaller masses whose flow is restricted by valley walls or mountain hollows, such as valley glaciers, cirque glaciers, and niche glaciers.
Piedmont Glaciers: Formed when a valley glacier exits a mountain range and spreads out into a broad lobe on a flat plain.
| Feature | Accumulation Zone | Ablation Zone |
|---|---|---|
| Location | Upper part of the glacier | Lower part (snout) |
| Net Balance | Positive (Gain > Loss) | Negative (Loss > Gain) |
| Surface Type | Fresh snow and firn | Bare ice and rock debris |
| Primary Process | Snow compaction/Ice formation | Melting and calving |
The 'Retreat' Misconception: Always remember that even when a glacier is 'retreating,' the ice itself is still flowing downhill due to gravity; retreat simply means the snout is melting faster than the ice is being replaced.
Feedback Loops: Be prepared to explain positive feedback, such as how melting ice reduces the surface albedo (reflectivity), causing more solar radiation to be absorbed and further accelerating the melt.
Equilibrium Line Shifts: If an exam question asks about climate warming, explain that the equilibrium line will move to a higher altitude as the ablation zone expands upward.
