Understanding Glaciers: Types, Movement, and Formation

1 3-1 Assignment: Glaciers Southern New Hampshire University PHY-103 Earth System Science Glaciers are accumulations of ice and snow, along with sediment and rock that form on land and slowly moves down a slope due to gravity and the weight of the ice. . Though it does not seem like it, glaciers are constantly moving. The ice that forms a glacier builds up, compacts, and recrystallizes until it becomes a thick mass ( What is a Glacier? n.d). Approximately three

2 quarters of Earth’s freshwater is stored in glaciers. Glaciers differ from sea ice and accumulated snowfall. As mentioned, glaciers are formed on land and are comprised of accumulated ice and snow, while sea ice is frozen seawater that is found floating on the surface of the ocean ( Sea ice n.d). Sea ice expands and contracts. The Artic Ocean is covered in sea ice. Accumulated snowfall is just that, snowfall that has piled up. Unlike glaciers, accumulated snowfall does not move and melts with the rise of the temperature. Glaciers can both advance and retreat subject to their glacial budget. Glacial budget is the balance or imbalance between accumulation of ice at the upper portion of the glacier and loss of ice at the lower portion. If the accumulation of ice is greater than the wastage, the glacier will advance until it is balanced again. Glaciers advance in two ways. The first is plastic flow. This is movement that occurs within the glacier itself. Once the pressure on the ice increases above a weight equivalent of about 165 feet, the glacier starts to flow downward. Glaciers also advance when the entire mass begins to flow and slips across the ground (Lutgens et al., 2016). Glaciers retreat due to rising temperatures and lack of snowfall. The glaciers front edge will recede if the glacial ice on the lower portion melts and the upper portion does not receive adequate accumulation. There are various types of glaciers found on earth. Alpine, also called valley glaciers are glaciers that are found in mountainous regions that are high in elevation. They are usually found in areas where streams once flowed. As alpine glaciers flow downward, they erode the surrounding landscape. Alpine glaciers are generally longer than they are wide. Hubbard Glacier in Alaska is an example of an alpine glacier. When an alpine glacier arrives at the end of a valley and is able to expand, it becomes a piedmont glacier. Piedmont glaciers are expansive sheets of ice and can cover huge areas. Malaspina Glacier in Alaska is an example of a piedmont glacier

3 (Lutgens et al,. 2021). Tributary glaciers are glaciers that flow into a larger main glacier. They are smaller and do not cause as much erosion as bigger alpine glaciers. Ice sheets spread for thousands of miles and cover the landmasses beneath them. Ice sheets are found in Greenland and Antarctica. Like ice sheets, ice caps cover the terrain below. Unlike ice sheets, ice caps only cover small areas (Lutgens et al., 2021). When a glacier reaches the sea it becomes a tidewater glacier. Tidewater glaciers stay in place in shallow water. In deeper water they float and become ice shelves. Ice shelves stay attached to the land on at least one side. Antarctica has ice shelves surrounding the majority of the continent. Outlet glaciers have tongues that flow from ice caps or sheets, through mountain terrains to the sea. Glaciers are made up of two zones. The zone of accumulation and the zone of wastage. In the zone of accumulation, snow builds up, increasing the weight of the glacier, which in turn causes it to move downward. The zone of wastage is the area where accumulated snow from previous winters, along with glacial ice melts, evaporates or breaks off (Lutgens et al., 2021). Glaciers erode the terrain through two main processes. The first process is plucking. Plucking occurs when a glaciers melt flows into cracks in the underlying rock. The meltwater then freezes, causing rocks and sediment to dislodge. As the glacier moves it picks up pieces of rock and integrates them into the ice. The second erosional process is abrasion. The glacier and the rock it has incorporated moves across the bedrock, polishing the rock as it goes. Glacial striations form from abrasion with large rocks. When a glacier flows across bedrock carrying small sediment the rock below is polished rather than scratched. Glacial striations can be studied to determine the direction that the glacier flowed (Lutgens et al., 2021). Glacial erosion creates many different landforms. As glaciers move, they will follow the routes of existing waterways. Valleys with streams are generally V-shaped due to downcutting. As a glacier moves through the

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4 V-shaped valley, the valley is eroded into a U-shaped glacial trough. Tributary glaciers that flow into the main alpine glacier do not cause the same extent of erosion due to their lack of size and weight. Because the main glacier has eroded more of the valley below it, the valley that the tributary glacier has left is much higher. This valley is called a hanging valley (Lutgens et al., 2021). Cirques are formed from the plucking action of an alpine glacier. Cirques have walls on three sides and an opening that faces the valley below it. Cirques are formed from frost wedging and plucking that occurs on the bottom and sides of a glacier. The glacier moves the material it has picked up out of the hole it has created. When the glacier melts, small lakes called tarns are often left behind. Glaciers can also create sharp ridges called arêtes or peaks called horns. Arêtes are formed as two glaciers flow in parallel lines. As the glaciers erode the valleys, narrow ridges are left behind (Fisher-Rohde, 2013). Horns are formed from several cirques around a peak. As the glacier removes rock from the cirques, a narrow, jagged peak is left behind. The Matterhorn in Switzerland is an example of a horn. Truncated spurs are triangular formations that are created when a glacier moves through a valley. They are essentially arêtes that are cut off by the glacier (Fisher-Rohde, 2013). Fjords are another landform that is left by glacial movement. Fjords are waterways that are created when a glacial trough filled with water after the Ice Age (Lutgens et al,. 2021). Just as glaciers erode the land as they move, they also deposit sediment. The depositional features left after a glacier moves through an area are moraines, kettles, drumlins, eskers, outwash plains, and kames. Moraines are ridges of glacial till left behind as a glacier melts. There are multiple varieties of moraines. Lateral moraines are found on the sides of a glacier, medial moraines are created when two glaciers meet and form a single mass. End moraines are created from glacial till that is deposited at the terminus of a glacier as it melts (Lutgens et al,.

5 2021). Kettles are areas where blocks of ice are caught in the glacial drift and subsequently melt. When the ice melts pits are left behind. Kettles generally fill with water to create ponds or lakes. Drumlins are composed of till and form irregular hills. They can be anywhere from 50 to 200 feet in height. and as long as a half mile in length. Eskers are winding ridges composed of sand and gravel. They are created from streams that ran through a glacial near the terminus (Lutgens et al,. 2021). Outwash plains are found in front of a melting glacier. Braided rivers can be found in them due to the large sediment load the meltwater is carrying ( Outwash Plains and Eskers n.d). Like eskers, kames are also composed of sand and gravel. Kames are steep hills formed by sediment that is caught in cavities in stationary glacial ice. Granite Creek Tarn (Wrangell-St. Elias National Park, Alaska) (U.S. Department of the Interior. (n.d.-a). Cirques) The photo above illustrates a cirque created by a glacier. The cirque is bowl shaped and has a tarn in the middle. Along the top of the cirque are arêtes created by the presence of another glacier along its outside edge. A truncated spur is also seen on the left side of the photo. Truncated spurs occur when a glacier cuts the mountain off through erosion.

6 Matterhorn, Swiss Alps The Alps’ Matterhorn shows how much even big mountains sway . Science News Explores. The Matterhorn pictured above is a prime example of a horn. Horns are formed from cirques that surround a mountain. As a glacier erodes, jagged peaks are left behind.

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7 Little Ice Age Moraine Grand Teton National Park (U.S. Department of the Interior. (n.d.-c). Terminal and recessional moraines) The photo above shows a terminal moraine. As the glaciers terminus stays in place, more sediment builds up, creating a larger moraine. If the glacier retreats quickly smaller moraines will form . Michigan Kettle Lakes (Kettle Lakes . Keweenaw Geoheritage. (n.d.)).

8 The kettle lakes shown above are the result of large blocks of glacial ice stagnating then melting. This causes large depressions that generally fill with water to create lakes.

9 References Fisher-Rohde, S. (2013, March 31). Alpine Glacier Basics . YouTube. https://www.youtube.com/watch?v=mspVqx3vgek Kettle Lakes . Keweenaw Geoheritage. (n.d.). https://www.geo.mtu.edu/KeweenawGeoheritage/Glaciers/Kettles.html Lopata, P. (2022, March 28). The Alps’ Matterhorn shows how much even big mountains sway . Science News Explores. https://www.snexplores.org/article/alps-matterhorn-big- mountains-sway Lutgens, F. K., Tarbuck, E. J., & Tasa, D. G. (2021). Foundations of Earth Science (9th ed.). Pearson Education (US). https://bookshelf.vitalsource.com/books/9780135851609 Sea ice . National Snow and Ice Data Center. (n.d.). https://nsidc.org/learn/parts-cryosphere/sea-ice U.S. Department of the Interior. (n.d.-a). Cirques (U.S. National Park Service) . National Parks Service. https://www.nps.gov/articles/cirques.htm U.S. Department of the Interior. (n.d.-b). Outwash Plains and Eskers (U.S. National Park Service) . National Parks Service. https://www.nps.gov/articles/outwashplainsandeskers.htm U.S. Department of the Interior. (n.d.-c). Terminal and recessional moraines (U.S. National Park Service) . National Parks Service. https://www.nps.gov/articles/terminalandrecessionalmoraines.htm

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10 What is a Glacier? . U.S. Geological Survey. (n.d.). https://www.usgs.gov/faqs/what- glacier#:~:text=A%20glacier%20is%20a%20large,its%20own%20weight%20and %20gravity.

Module 3 Assignment phy103

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