Cold climates are known for many distinct types of landforms. These landforms are associated with freezing and subfreezing temperatures along with the presence of water. Cold climate processes are often linked to frost action. During the last major ice age, ice covered nearly one-third of the Earth's surface. The Northern Hemisphere was buried under a massive ice sheet up to 2 miles (3.2 km) thick in places. The ice extended from the North Pole southward to southern Illinois. Greenland was buried under ice, as was much of northern Asia and northern Europe. As seen in earlier chapters, this was not the only time this happened. The Earth has been subjected to multiple advances and retreats of ice sheets throughout its history. Each ice age that occurs leaves its unique mark on the geology of the landscape. Landforms of cold climates are very distinct and, as such, can be identified and dated. They have proven to be one of the prime tools that has allowed climatologists to be able to piece together the climatic history of the Earth.
Even when glaciers are not involved, cold temperatures act on the ground. Repeated freezing and thawing of the ground acts to move and sort earth. If there is a slope present, it causes the soil to begin to slowly flow, or creep, downhill. This is a process called solifluxion. This churning activity within the ground causes the larger rocks to rise to the surface, while the smaller particles settle into the open gaps beneath that are created after the freezing action has caused the soil to expand. Giant wedges of ice can form in the ground. Over time, as this process continues, it creates an odd, distinct pattern on the ground when seen from above. It creates a polygonal patterning of wedges and circles of stones called patterned ground. When geologists see this, they know a cold climate existed there at one time. If the ground is in the tundra and drainage is poor, this process eventually forms a series of hills called pingos. Pingos can reach 98 feet (30 m) high.
There are several distinct glacial landforms that climatologists use to identify past glaciation. Glacial moraines are formed from the deposition of material eroded by a glacier. Where rock, soil, debris, and other matter is scoured off canyon walls and carried along, the material builds up as the glacial ice carries the heavy load like a conveyor belt. As soon as the ice melts, huge sinuous deposits are left along the glacier's sides and at its terminal end.
Drumlins are asymmetrical, egg-shaped hills composed of till. Till is unstratified material of various sizes consisting of a mixture of clay, silt, sand, gravel, and boulders. The steeper side of the hill is the uphill side and can range from 50 to 165 feet (15-50 m) in height. The downward slope is much gentler and can extend up to 0.6 miles (1 km) in length. Drumlins usually form in groups, making them a distinctive depositional landform.
Eskers are long snakelike ridges formed by networks of streams that run under glaciers. As the rivers flow, they pick up and carry material, such as rock fragments. When the matter falls out of the water and is deposited along the channel, it forms an esker. Once the glaciers have melted, these features look like worms traveling across the landscape. Eskers can be 330 feet (100 m) tall and travel for 65 miles (100 km).
Larger pieces of rock deposited randomly on the ground's surface are called erratics. Erratics can range in size from pebbles to huge chunks of rock. They can be moved large distances when carried by the ice. Deposits of erratics help climatologists determine where ancient glaciers traveled.
Before an area is glaciated, mountain valleys are typically V-shaped because they have been carved by the erosive power of rivers. During glaciation, however, these narrow valleys deepen and widen under the erosive power and weight of the ice. The moving ice slowly grinds away at the canyon walls, weathering it smooth and creating distinctive U-shaped valleys, another strong indicator of climate change.
When a glacier first forms high up on a mountain, the initial bowl where the snow collects and begins the glacial cycle is called a cirque. A
Glaciers flowing out of canyons carve out a characteristic U-shape, as shown in this photo. Note also at the lower left corner, the large granite boulders strewn along the ground. They were carved by the glacier farther up the canyon, carried downhill, and deposited at the mouth of the canyon as glacial erratics.
cirque glacier is a small glacier that occupies a cirque or rests against its headwall. If a mountain peak has more than one cirque and is eroded from more than one cirque at a time from different directions (such as back to back) at its peak, it can form an arête. An arête is a narrow crest with a sharp, knifelike edge. If three or more arêtes converge, it forms a pyramid-style peak called a horn. One of the more famous of these glacial features is the Matterhorn in Switzerland.
Kame and kettle topography is another easily identifiable glacial landform. Kettles are depressions in the ground. They occur where large blocks of ice are caught in the glacial deposits. After the ice melts, large holes are left in the sediment. Kettles can vary in size, but most average about 1.2 miles (2 km) in diameter and 33 to 165 feet (10-50 m) deep. Kames are upraised deposit features that look like mounds or columns. Kames form when meltwater deposits sediments through openings inside the glacial ice.
Glaciers are responsible for many distinct landforms, such as eskers, drumlins, moraines, kettles, and arêtes.
Another signal that glaciers have passed over an area is glacial stri-ations. These are etched parallel grooves in rocks cut when a glacier drags material (such as rocks) over the rock it is sliding across, scratching the base rock as it passes over. These parallel etchings, or furrows, in the rock not only clue climatologists in to the fact that glaciers once existed in a particular area but also indicate which direction the glacier was traveling.
When these types of cold environment landforms are present in a landscape, climatologists look at past glaciation and reconstruct past climates. This is valuable information that can be used in climate modeling on computers.
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