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How do glaciers affect land? | National Snow and Ice Data Center
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How do glaciers affect land?
Glaciers not only transport material as they move, but they also sculpt and carve away the land beneath
them. A glacier's weight, combined with its gradual movement, can drastically reshape the landscape over
hundreds or even thousands of years. The ice erodes the land surface and carries the broken rocks and soil
debris far from their original places, resulting in some interesting glacial landforms.
Glacial erosion
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Common all over the world, glaciated valleys are probably the most
readily visible glacial landform. Similar to fjords, they are troughshaped, often with steep near-vertical cliffs where entire
mountainsides were scoured by glacial movement. One of the most
striking examples of glaciated valleys can be seen in Yosemite
National Park, where glaciers literally sheared away mountainsides,
creating deep valleys with vertical walls.
Fjords, such as those in Norway, are long, narrow coastal valleys that
were originally carved out by glaciers. They are often “U-shaped,”
with steep sides and rounded bottoms, giving them a trough-like
appearance. Once the glaciers receded, seawater covered the floor of
the glacial trough to create fjords.
The famous Matterhorn in Switzerland displays three types of glacial
erosion:
The Matterhorn in Switzerland was
carved away by glacial erosion. Zmutt
Glacier occupies the large cirque on the
west face of the mountain, and to the
far left, a hanging glacier clings
precariously to the side of the peak. —
Credit: Photograph by Harry Fielding
Reid. 1894. Zmutt Glacier: From the
Glacier Photograph Collection.
Boulder, Colorado USA: National
Snow and Ice Data Center. Digital
media.
Cirques are created when glaciers erode the mountainside,
scouring into it and creating rounded hollows with steep uphill
faces, shaped like tilted bowls. A cirque is often more visible
after the glacier melts away and leaves the bowl-shaped
landform behind.
Arêtes are jagged, narrow ridges created where the back walls of two glaciers meet, eroding the ridge
on both sides.
Horns are created when several cirque glaciers erode a mountain until all that is left is a steep,
pointed peak with sharp, ridge-like arêtes leading up to the top.
Glacial landforms
Fjords, glaciated valleys, and horns are all erosional types of
landforms, created when a glacier cuts away at the landscape. Other
types of glacial landforms are created by the features and sediments
left behind after a glacier retreats.
When glaciers retreat, they often deposit large mounds of till: gravel,
small rocks, sand, and mud. It is made from the rock and soil that was
ground up beneath the glacier as it moved.
Material a glacier picks up or pushes as it moves forms moraines
along the surface and sides of the glacier. As a glacier retreats, the ice
literally melts away from underneath the moraines, so they leave long,
narrow ridges that show where the glacier used to be. Glaciers do not
always leave moraines behind, however, because sometimes the
glacier’s own meltwater washes the material away.
Streams flowing from glaciers often carry some of the rock and soil
debris out with them. These streams deposit the debris as they flow.
Consequently, after many years, small steep-sided mounds of soil and
gravel begin to form adjacent to the glacier, called kames.
Kettle lakes form when a piece of glacier ice breaks off and becomes
buried by glacial till or moraine deposits. Over time, the ice melts,
http://nsidc.org/cryosphere/glaciers/questions/land.html
An eroded moraine juts above the
landscape in the Rhone Valley,
Switzerland. Giant boulders stud some
of the pinnacles, left behind by a
retreating glacier. A small tunnel has
been cut through the moraine, seen near
the upper left of the photograph. —
Credit: Photograph by Harry Fielding
Reid. 1902. From the Glacier
Photograph Collection. Boulder,
Colorado USA: National Snow and Ice
Data Center. Digital media.
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leaving a small depression in the land, filled with water. Kettle lakes are usually very small, more like ponds
than lakes.
Glaciers leave behind anything they pick up along the way, and
sometimes this includes huge rocks. Called glacial erratics or erratic
boulders, these rocks might seem a little out of place, which is true,
because glaciers have literally moved them far away from their source
before melting out from underneath them.
Drumlins are long, tear-drop-shaped sedimentary formations. What
caused drumlins to form is poorly understood, but scientists believe
that they were created subglacially as the ice sheets moved across the
landscape during the various ice ages. Theories suggest that drumlins
might have been formed as glaciers scraped up sediment from the
underlying ground surface, or from erosion or deposition of sediment
by glacial meltwater, or some combination of these processes. Because
the till, sand, and gravel that form drumlins are deposited and shaped
by glacier movement, all drumlins created by a particular glacier face
the same direction, running parallel to the glacier's flow. Often,
hundreds to thousands of drumlins are found in one place, looking
very much like whale backs when seen from above.
Meltwater flows out from under the
terminus of Forno Glacier in this
photograph from 1899. —Credit:
Photograph by Harry Fielding Reid.
1899. Forno Glacier: From the Glacier
Photograph Collection. Boulder,
Colorado USA: National Snow and Ice
Data Center. Digital media.
These cirques on Disko Island in Greenland exhibit the circular bowl shape, and are
separated by an arête. —Credit: Ole Mikkelsen, CC BY-NC-SA 4.0
See Also
NSIDC's Glacier Glossary - Search and browse terms related to glaciers in NSIDC's comprehensive
cryospheric glossary.
NSIDC Glacier Photograph Collection - NSIDC archives a Glacier Photograph Collection of historical
photos, which includes both aerial and terrestrial photos for the 1880s to 1975. The photos are primarily of
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Alaskan glaciers, but coverage also includes the Pacific Northwest and Europe.
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