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Colorado Hiking  
Alpine glacial features                              

The mountains in Colorado bear a strong imprint from the erosional and depositional affects of alpine glaciation. These occurred in several episodes over the last two million years, with the last ending 12,000 to 15,000 years ago. Glaciers form when more snow falls in an area during the winter, than melts in the summer. As it accumulates, the snow weighs down and compacts lower layers into ice. The thickness of the ice in alpine glaciers could be  thousands of feet, nearly filling up the valleys we see today.  Ice is a solid, but with that much weight on it, it becomes ductile and can flow downhill under the force of gravity.

As ice moves it mechanically works on the rock around it, scraping, grinding, wrenching and breaking it up. Glaciers carry a lot of rock and ground up sediment in them both from their own erosional work, and from rocks falling and avalanching down onto them from valley sides. The rocks a glacier carries act as tools in grinding against intact rocks, and against others carried in the glacier's load. The net effect is that glaciers excavate, transport, breakdown and deposit huge volumes of rock and sediment. In doing that, they change the terrain and create some characteristic features.

Some common erosional and depositional features formed by alpine glaciers. 

U-shaped valleys are created by glaciers because the U-shape provides less   frictional resistance to the moving ice than other shapes.    

Cirques are bowls or amphitheaters eroded out at the head of a glacier.   

Aretes are created when two glaciers on opposite sides of a mountain erode back toward each other far enough to leave a narrow ridge. 

Horns are created by several glaciers eroding back different sides of the same mountain. 

Hanging Valleys form when the main glacier deepens its valley more than the smaller tributary glaciers can erode theirs. When the glaciers melt, the tributary troughs or valleys are left stranded above the main valley floor, and cascading waterfalls can develop.

Moraines consist of glacial load rock and finer sediments deposited when the glacier melts.  Ground  moraine is deposited under a glacier. A lateral moraine is created by glacial erosion and avalanche from the valley wall onto the edge of a glacier. A terminal moraine consists of an accumulation of glacial debris pushed forward by the glacier. A secondary terminal moraine is deposited during a temporary glacial standstill, as debris laden ice moves from the higher reaches of the glacier to its terminus. Moraines usually have enough fine material to create good soil that soon gets vegetated.

Glacial lakes can be created by scouring out a depression, sometimes augmented by moraines  acting as dams. At the head of a glaciated valley a "tarn" lake may occur in the bottom of cirque.  Glacial scouring further  down valley can produce a series of stair step lakes (aka. paternoster lakes).

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