moraine

definition: 
A mass of rocks and sediment carried down and deposited by a glacier, typically as ridges at its edges or extremity.
sentence: 
It is also likely that mass movement is much more common during periods when glaciers are retreating; large moraines and steep valley sides are then unstable because they are no longer supported by the glacier.
difficulty: 
medium
toefl frequency: 
1
toefl classification: