Introduction

    "Glaciers are a thick mass of ice resulting from compact ion and recrystallization of snow" (Johnston, 65).  Glaciers form over time and then change the appearance of the land by erosion.  There are two types of glacial erosion.  The first is caused by continental ice sheets, and the second results from mountain glaciers.  "Continental ice sheets cover the land and can be very large whereas mountain glaciers are only on slopes of mountains and in the valleys" (Johnston, 66).  An ice sheet, or continental glacier, ..."is a glacier that covers an area of 50,000 square kilometers or more" (Thompson, 314).   Glaciers that are on mountains are called mountain glaciers or alpine glaciers.  When the glaciers erode away they form many different topographic features.

Glacial Erosion

    There are many types of glacial erosion and one that occurs at the base of the glacier is plucking.  Plucking is the process of particle detachment by moving glacial ice. (Landforms)  A flowing glacier scrapes areas of bedrock and erodes the land, and water is also seeping in cracks in the bedrock under the glacier and freezing, this loosens pieces and mixes in with the ice. (Thompson, 319)  The glacier than carries the rocks and fragments with it.  The ice itself can not break up the rocks under it, but the rocks picked up and carried along by the glacier are what breaks the rocks and creates different land features.  This process of erosion is known as scouring. (Landforms) As the glacier moves along the rocks in it scrape the land under it leaving groves that are parallel, which are known as glacial striations. (Thompson, 320).  The striations can show the direction in which the glacier was moving.

Erosional Landforms Created by Alpine Glaciers

    Glaciers travel long distances and create new landforms through erosion.  The glacier slowly moves off the mountain and leaves behind new features on the mountain.  A huge depression on the mountain side may be left after the glacier is gone and this is referred to as a cirque.  A cirque is formed where the snow accumulates and packs down.  A cirque starts to develop when the ice sheet starts to move and plucking begins to erode a small depression in the side of the mountain.  When the erosion and weathering continues over the years the cirque grows larger.  Once a cirque is formed a smaller depression may be left in the bottom.  This depression can then fill up with water, creating a small lake called a tarn. (Thompson, 321)

    If the glacier erodes three or more cirques on different sides of the mountain, a peak will begin to form.  The peak may be a steep pyramid shaped rock, which is known as a horn.  The Matterhorn in the Swiss Alps is a well known horn. (Thompson, 321)  A picture of the Matterhorn is shown below.  If two glaciers move along opposite side of the mountain, they erode both sides of the ridge, forming a narrow arete between valleys. (Thompson, 321)

This was taken from a photograph dating from 1894, WDC-A for Glaciology, University of Colorado, Boulder, Colorado, off of the National Snow and Ice Data Center, How do glaciers affect the land?

Landforms from Glacial Deposits

    When the glacier starts to melt and leaves behind all the sediments that it collected earlier it leaves behind many deposits forming new land features.  The sediments that the glacier has collected, and then leaves behind when the glacier melts or retreats, is called till. (NSIDC)  A moraine is a mound of till deposited by a glacier. (Thompson, 324)  There are many types of moraines.  One is the end moraine, this is when the glacier is not moving and the sediments pile up at the end of the glacier.  An end moraine that forms when the glacier is at its best, before beginning to retreat is known as a terminal moraine.  A ground moraine is formed when the glacier retreats and the end of the glacier moves at an even rate and the till is spread over a large area of land.  If a glacier has been moving and then stops and the end of the glacier is in the same place for years, this is a recessional moraine.  The recessional moraine is formed in the same way as the terminal moraine.  A lateral moraine is formed when the glacier scrapes the sides of the mountains picking up sediments, and then when the glacier melts the sediments are left behind, forming the moraine.  When two glaciers collide and combine to form one, any sediments on the colliding side are pushed together.  This forms a line of sediments in the glacier and when the glacier melts a line of till is left behind on the land the glacier covered, this is known as a medial moraine. (Thompson, 324-325)

This is a picture of an eroded moraine in the Rhone Valley, Switzerland. The photograph dates from 1894 (WDC-A for Glaciology, University of Colorado, Boulder, Colorado, off of the National Snow and Ice Data Center, How do glaciers affect the land?

    Conclusion

    Glaciers had a great impact when sculpting the land.  Without glaciers we wouldn't have some of the features on the mountains, and some of the lakes that the glaciers helped carve.  Glaciers have played a very big role in shaping different parts of the land.  There are many more types of landforms that glaciers have helped form including some lakes.  Without the glaciers some of the biggest lakes would not exist and the mountains would not have as many features on them.  Glaciers have sculpted some of the earth's surface creating new landforms that we would not have had under other conditions.
 

Works Cited

4(k) Landforms of Glaciation

Johnston, Paul, Susan Ward Aber, and Hengchun Ye.  Introduction to Earth Science Lab. (Burgess International Group, Burgess Publishing) p. 65-68.

NSIDC Publications:  Glaciers:  How do Glaciers Affect the Land?

Thompson, Graham R PhD. and Jonathan Turk, PhD.  Earth Science and the Environment.  (Saunders College Publishing, Harcourt Brace College Publishers, 1995) p. 314-325.
 
 

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This page was last updated May 4, 1998.

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