Glaciers
Ice that flows, and the landscape it leaves.
A glacier is a body of ice large enough to deform under its own weight and move. It forms where more snow falls each year than melts, so layers accumulate and compress — snow to granular firn to dense glacial ice, a process taking decades.
How ice flows
Movement happens two ways. Internal deformation is ice crystals sliding past one another under pressure, which happens in every glacier. Basal sliding is the whole mass sliding over meltwater at its bed, and it is much faster — which is why warm-based glaciers move far quicker than ones frozen to bedrock.
Landforms
| Feature | How it forms |
|---|---|
| U-shaped valley | Ice widens and deepens a former V-shaped river valley |
| Cirque | Bowl carved at the glacier's head by rotational flow |
| Arête | Sharp ridge left between two cirques |
| Moraine | Rock debris carried and dumped at the margins or snout |
| Erratic | Boulder transported far from its source rock |
Mass balance
A glacier advances or retreats according to mass balance: accumulation minus ablation. Retreat does not mean the ice stopped flowing — it still flows downhill, but melts back faster than it delivers. That distinction confuses a lot of reporting.