High School Earth Science: Erosion and Deposition - Glacial Erosion and Deposition — Flashcards

Depositional Features of Glaciers    
Glaciers can carry rock particles of any size, from giant boulders to silt. The sediments can be carried for many kilometers over long durations of time. Melting glaciers deposit the sediments they are carrying in a jumble of particle sizes. The unsorted deposits are called glacial till. Many deposits of glacial till have a linear shape. Linear deposits are called moraines. Geologists study moraines to figure out how far glaciers advanced and how long it took them to recede.

Moraines are named for their location relative to the glacier.    

- Lateral moraines form at the edges of an alpine glacier from material that drops onto the glacier from erosion of the valley walls.    
- A medial moraine forms where the lateral moraines of two tributary glaciers join together in the middle of a larger glacier.    
- Ground moraines form from sediment underneath a glacier that is deposited as the glacier melts. Deposits of ground moraine may improve soil fertility.    
- Terminal moraine forms in a long ridge at the farthest point a glacier reaches.    
- End (recessional) moraines form wherever a glacier stops long enough as it recedes to deposit a ridge of sediment.    

After glaciers dump unsorted sediments, glacial meltwater can pick up, transport, and re-deposit the sediments.    
As meltwater moves through unsorted glacial till, it leaves behind the larger particles and takes away the smaller particles, especially silt and sand. The meltwater flowing beneath a glacier may deposit some of the sediments it is carrying in a winding ridge called an esker. As the sediments settle out of meltwater, the larger particles settle first, followed by layers of increasingly smaller sediments. These stratified layers are called stratified drift. A broad area of stratified drift from meltwater at the end of a receding glacier is called an outwash plain.