Alpine glaciers begin high up in the mountains in bowl-shaped hollows called cirques. As the glacier grows, the ice slowly flows out of the cirque and into a valley. Several cirque glaciers can join together to form a single valley glacier. When valley glaciers flow out of the mountains, they spread out and join to form a piedmont glacier.
The ice in contact with the valley walls contains a lot of rock and sediment which makes the ice dark grey or brown. When several cirque glaciers merge into a single valley or piedmont glacier the ice has a striped appearance.
Zones of an alpine glacier:
- Truncated spur
- Hanging valley
Alpine glaciers pluck and grind up rocks creating distinctive U-shaped valleys and sharp mountain peaks and ridges.
An arête is a sharp ridge of rock that is left between two adjacent glaciers.
Truncated (cut off) ridges and hanging valleys form when small valley glaciers merge with a single large valley glacier.
Sometimes a small lake called a tarn will form at the bottom of the cirque. There are three tarns in a small area of Cumbria, UK, on the geological map below, they are the black shapes.
Horns are steep mountain peaks that form when a mountain has been surrounded by cirque glaciers, such as the Matterhorn in Switzerland.
Glaciated valleys that are flooded with sea-water are called fjords. Some fjords are over 1 km deep.