Glaciers Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Glaciers are thick masses of ice that originate on land from the accumulation, compaction, and recrystallization of snow. Glaciers make up the cryosphere, the frozen part of the hydrosphere. The frozen water is temporarily removed from the hydrologic cycle. Glaciers occur more commonly at places on earth where temperatures are such that the glacial ice remains frozen during a sufficient part of the year, preventing the glacier from melting completely. These cold places occur at high elevations and at high latitudes.

Glaciers fall into two broad categories: alpine or valley glaciers; and continental glaciers, ice sheets or ice caps. Alpine glaciers occur at high elevations, on mountain tops. Continental glaciers occur at high latitudes, close to the poles. Alpine and continental glaciers are actually two ends of a spectrum. Many glaciers have characteristics of both.

Alpine glaciers exist on the tops of mountains, and therefore are subject to the force of gravity, which constantly pulls the glacier down the slope. As the glacier slowly moves down the side of the mountain, new glacial ice forms on the mountain top (accumulation). As the glacier reaches the higher temperatures that occur on the lower parts of the mountain, the ice melts (ablation or wasting). This system is like a conveyor belt where the glacier forms in the area of accumulation, then constantly slides down the mountain to the area of ablation where it melts and becomes outwash streams. The downslope movement is due in part to flow within the glacier, and also to sliding over the ground surface. The sliding produces significant erosion resulting from the abrasion of bedrock and the transport of the eroded material to the area of ablation where it is deposited as a moraine.

The moraine may act as a natural dam resulting in a glacial lake. Alpine glaciers are common today in many mountain belts such as the Alps, the Northern and Canadian Rockies, the Andes, and the Himalayas. An alpine glacier exists on top of Mt. Kilamanjaro (19,340 feet), illustrating that glaciers can exist close to the equator if the ground elevation is high enough.

Continental Glaciers

Unlike alpine glaciers, continental glaciers are not dependent on high elevations. Continental glaciers occur at high latitudes, on relatively flat, widespread areas that may cover a major part of a continent, hence the term continental. Today, continental glaciers exist on Antarctica, Greenland, and a small ice cap in southeast Iceland. The movement of continental glaciers is driven by flowage and sliding of the glacier outward from the area where the accumulation is the greatest. If part of the glacier moves into an area of lower latitude, ablation will occur as the glacier melts and deposits its sediment as a moraine, and the water becomes outwash streams. If the water is trapped behind the moraine, a glacial lake may form. The Finger Lakes of New York are a prime example.

The budget of a glacier is a concept relating its volume to the rates of accumulation and ablation (wastage). During cooler intervals, the rate of accumulation may exceed the rate of ablation, and the glacier will expand or advance. During warmer intervals, the rate of ablation may exceed accumulation and the glacier will shrink or recede. The terms advance and recession relate only to an increase or decrease in the mass of the glacier. They do not imply movement of the glacier. Regardless of whether a glacier is advancing or receding, alpine glaciers always move downslope, and continental glaciers always move outward from the area of maximum accumulation.

Spectacular Landforms

Glaciers produce distinctive landforms and landscapes that can be quite spectacular and beautiful. Landforms typically associated with alpine glaciers include horns, U-shaped valleys, hanging valleys, cirques, aretes, and moraines (lateral, medial and end). Continental glaciers produce features such as drumlins, eskers, kettles, terminal and recessional moraines, and outwash plains. These landforms preserve the geologic record of ancient glacial conditions, and are used to reconstruct environmental conditions that existed during the Ice Age. The most recent Ice Age was first recognized in terms of the glacial landforms that are found in many places in the high northern latitudes, areas that are not glaciated today. As such, glaciers produce an important record of past climatic conditions on earth.

The occurrence and size of glaciers is directly dependent upon global temperatures. Today, glaciers cover about 10 percent of Earth’s land surface. During the past 2 to 3 million years, the globe was alternately cooler and warmer, producing what is referred to as glacial and interglacial episodes of the Ice Age. During glacial episodes, alpine glaciers existed at lower elevations, and ice sheets extended further toward the equator. Some of those ice sheets were about 3 times as extensive as today. During the warmer, interglacial episodes, glaciers receded to higher elevations and higher latitudes.

Glaciers play a major role in the water available to the hydrologic cycle. Glaciers today comprise 2.2 percent of earth’s total water budget, second only to the oceans, which comprise 97.2 percent. Changes in the volume of glaciers are compensated by change in the volume of seawater. During intervals of global warming, such as is occurring now, glaciers recede and sea-level rises. The opposite has occurred during times of global cooling.

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