Earth & Space Science: Session 6
A Closer Look: Glacial Landforms
What are examples of landforms created by glacial erosion?
As a glacier moves, it picks up rock pieces from the landscape. Debris of all sizes that is stuck in the glacial ice can scour and erode the land. From this action, valleys can become wider and deeper, forming u-shaped (or trough) valleys. Glaciers can carve bowl-shaped depressions, called cirques, into a mountainside. A tarn is a lake that forms by ice melting in a cirque. An arête is the steep ridge that forms between two adjacent cirques. A col is a low spot on an arête. A horn is a peak formed when three or more adjacent cirque glaciers carve away the side of a mountain.
Continental glaciers scour linear finger lakes out of pre-existing stream channels. Paternoster lakes are a series of lakes that form in the low spots of a u-shaped valley; a stream that flows through the valley links them.
What are some landforms created by glacial deposition?
A glacier will deposit rock chunks along the sides and the front of it. Moraines are created when a glacier pushes or carries along this rock debris as it moves, and then deposits it. Moraines can form in front of a glacier (terminal or end moraine) marking the furthest position of advance of an ice sheet; along the side of a glacier (lateral moraine); or under a glacier (ground moraine). When two glaciers flow next to each other they deposit lateral moraines between them called medial moraines. Long Island, New York and Cape Cod, Massachusetts are examples of terminal moraines of the ice sheet that covered New England and eastern Canada during the last ice age.
Drumlins are elongated hills formed of till (an unsorted mixture of mud, sand, pebbles and rock deposited by a glacier) with a distinctive streamline shape that results from having been overridden by a glacier or modified by meltwater. The long axis of a drumlin indicates the direction of glacier flow. Eskers are the deposits of rivers and streams that flowed on, in, or under a glacier. They form mounds or hills that meander across a landscape roughly parallel to the path of the original glacial river. Kettle holes are formed by blocks of ice that separate from the main glacier. Under the right conditions the ice blocks will melt and leave behind holes or depressions that fill with water to become kettle ponds or kettle lakes.