Erosion by Glaciers
In what ways is this glacier creating distinctive landforms?
This glacier is modifying the landscape it's flowing through. Glaciers erode and
deposit telltale landforms. They show the direction a glacier flowed and how far it
advanced. They create fantastic and unique features in mountain areas. Did glaciers
leave clues where you live? If you live in the northern part of the United States,
you might be able to find some. Would you know what to look for?
Erosion by Glaciers
Like flowing water, flowing ice erodes the land and deposits the material
elsewhere. Glaciers cause erosion in two main ways: plucking and abrasion.
• Plucking is the process by which rocks and other sediments are picked up by a
glacier. They freeze to the bottom of the glacier and are carried away by the
flowing ice.
• Abrasion is the process in which a glacier scrapes underlying rock. The
sediments and rocks frozen in the ice at the bottom and sides of a glacier act
like sandpaper. They wear away rock. They may also leave scratches and
grooves that show the direction the glacier moved. These grooves are called
glacial striations.
Valley Glaciers
Valley glaciers create several unique features through erosion.
• As a valley glacier flows through a V-shaped river valley, it scrapes away the
sides of the valley. It carves a U-shaped valley with nearly vertical walls
(Figure below).
The glacier on the left is carving out the sides of a valley. The U-shaped valley on the right is what will be
left when the glacier melts away.
• A hanging valley was cut off from the main valley by a larger glacier (Figure
below).
The waterfall on the right flows through a glacial valley. A larger glacier carved the valley the water falls
into. There is a waterfall because this is a hanging valley.
• A cirque is a rounded hollow carved near the top of a mountain by a glacier
(Figure below). This is where the glacier begins. The highest cliff of a
cirque is called the headwall.
On the left, there are several cirques where glaciers are originating. A glacier melted and left behind
cirques in the mountains on the right.
• An arête is a jagged ridge that remains when cirques form on opposite sides of a
mountain. A low spot in an arête is called a col.
• A horn, like the one pictured below (Figure below), is a sharp peak that is left
behind when glaciers erode all sides of a mountain.
The Matterhorn in Switzerland is the classic glacial horn.
Summary
• Glaciers are incredibly powerful agents of erosion.
• Valley glaciers create very distinctive landforms like horns, cirques, and hanging
valleys.
Glaciers pluck rocks from valley walls. This turns a V-shaped river valley into a Ushaped glacial valley.