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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.
Common all over the world, glaciated valleys are probably the most readily visible glacial landform. Similar to fjords, they are trough-shaped, 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:
- 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.
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, 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.
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 Alaskan glaciers, but coverage also includes the Pacific Northwest and Europe.