The Physics of Glaciers, 4th edition : Academic Press. Ice streams as the arteries of an ice sheet: their mechanics, stability and significance. Earth-Science Reviews , 61, What controls the location of ice streams? Earth-Science Reviews , , Greenland flow variability from ice-sheet-wide velocity mapping. Journal of Glaciology , 56, Ice flow of the Antarctic ice sheet. Science , , Quaternary Science Reviews , , Evaluating Younger Dryas glacier reconstructions in part of the western Scottish Highlands: a combined empirical and theoretical approach.
Boreas , 34, A theoretical approach to glacier equilibrium-line altitudes using meteorological data and glacier mass-balance records from southern Norway. The Holocene , 13, The southernmost Quaternary niche glacier system in Great Britain. Journal of Quaternary Science , 30, Climate Climate controls the annual temperature cycle of a region as well as the amount of precipitation that falls as snow.
Photo: M. The Alps mountains above Chamonix, France, not only rise to a high enough altitude that glaciers can exist there due to the cold conditions, but the very steep slopes running away from Mont Blanc top left dictate the form and flow of Glacier des Bossons front and Glacier de Tacconaz behind.
Photo: S. The snowline is marked by the boundary between bare ice grey and black and snow white. Photo: NASA. Ice streams of Antarctica draining the ice sheet interior. From: Rignot et al. Image: NASA.
Note in the upper reaches that the glacier has several cirque basin tributaries that feed the main glacier trunk. Photo: D. Notice the tributary glaciers feeding the main trunk of Columbia Glacier centre. GoogleEarth image of the Spitsbergen island of the Svalbard archipelago, showing transection glaciers. Conversely, if ice shelves break down continental glacier flow can speed up.
Alpine glaciers aka valley glaciers originate high up in the mountains, mostly in temperate and polar regions Figure The flow of alpine glaciers is driven by gravity, and primarily controlled by the slope of the ice surface Figure Alpine glaciers grow due to accumulation of snow over time.
In the zone of accumulation , the rate of snowfall is greater than the rate of melting. In other words, not all of the snow that falls each winter melts during the following summer, and the ice surface in the zone of accumulation does not lose its annual accumulation of snow cover over the course of the year. In the zone of ablation , the rate of melting exceeds accumulation. The equilibrium line marks the boundary between the zones of accumulation above and ablation below Figure Above the equilibrium line of a glacier, winter snow will remain even after summer melting, so snow gradually accumulates on the glacier over time.
The snow layer from each year is covered and compacted by subsequent snow, and it is gradually compressed and converted to firn Figure Firn is a form of ice that forms when snowflakes lose their delicate shapes and become granules due to compression.
With more compression, the granules are squeezed together, and air is forced out. Downward percolation and freezing of water from melting contributes to the process of ice formation. The equilibrium line of a glacier near Whistler, BC, is shown in Figure Below this line is the zone of ablation. Above this line the ice is still mostly covered with snow from the previous winter.
The position of the equilibrium line changes from year to year as a function of the balance between snow accumulation in the winter, and snow and ice melt during the summer. If there is more winter snow and less summer melting, this favours the advance of the equilibrium line down the glacier and ultimately increases the size of the glacier.
Cool summers promote an increase in glacier size, and thus lead to advance of the equilibrium line. Warm summers promote melting, and retreat of the equilibrium line. Alpine glaciers move because they are heavy, and the force of gravity acts on the ice in the glacier to pull it down the slope of the mountains where they form. The movement of the glacier generates stress in the ice, which is proportional to the slope of the glaciers surface features of the underlying rock surface, and to the depth within the glacier.
As shown in Figure Stresses are greater in areas where the ice surface is relatively steep. Like rock, ice behaves in a brittle fashion under low pressure conditions shallow depths in the glacier , and plastically at higher pressures deeper in the glacier. Stress also affects how ice deforms; at high stress ice will either break or deform plastically ductile deformation depending on the pressure conditions.
Under brittle deformation conditions low pressures, shallow depths in the glacier , stress is released when the ice cracks, so does not build up to high values. Within the upper 50 — m of ice above the dashed red line, in Figure Under ductile deformation conditions higher pressures deeper in the glacier , stress can accumulate, and the ice will flow plastically in response to that stress. Ice deforms plastically if deeper than about m in the glacier, and in this region stress levels can accumulate to high values kilopascals or greater, Figure When the lower ice of a glacier flows, it moves the upper ice along with it.
Glacial retreat created other features of the landscape. Materials deposited by a glacier as it retreats are called ground moraines. The jumble of rock, gravel, and dirt making up ground moraines is called till. Much of the fertile soil in the Great Plains of North America was formed from layers of till left by ancient ice sheets. Glacial valleys exist on almost every continent.
These valleys are scooped out as a glacier scrapes through them. There are no glaciers in Australia, but Mount Kosciuszko still has glacial valleys from the last Ice Age. Distinctive mountain formations called aretes and horns are the result of glacial activity. Glacier National Park in the U. These tall, singular landforms are also called pyramidal peaks. Roche moutonnee is a smooth, rounded rock formation created as a glacier crushes and rearranges rocks in its path.
Roche moutonnee is visible in many hilly areas as outcroppings of flat rock. In contrast to alpine glaciers, ice sheets do not create landscape features as they spread. They tend to smooth out the land beneath them. Glaciers provide people with many useful resources. Glacial till provides fertile soil for growing crops. Deposits of sand and gravel are used to make concrete and asphalt.
The most important resource provided by glaciers is freshwater. Many rivers are fed by the melting ice of glaciers. The Ganges is the most important source of freshwater and electricity in India and Bangladesh.
Electricity is created by dams and hydroelectric power plants along the Ganges. Some companies link glacial water to clean, fresh taste. Because water has been trapped in the glacier for so long, many people believe it has not been exposed to pollutants that liquid water is exposed to. The dramatic, diverse landscape of Yosemite Valley, California, was sculpted entirely by glaciers during the last Ice Age. Threats to Glaciers The processes that remove snow, ice, and moraine from a glacier or ice sheet are called ablation.
Ablation includes melting, evaporation, erosion, and calving. Glaciers melt when ice melts more quickly than firn can accumulate.
Glaciers are important indicators of global warming and climate change in several ways. Melting ice sheets contribute to rising sea levels. As ice sheets in Antarctica and Greenland melt, they raise the level of the ocean. Tons of fresh water are added to the ocean every day. Large icebergs created by such an event create hazards for shipping. Large additions of fresh water also change the ocean ecosystem.
Organisms, such as many types of corals, depend on salt water for survival. Some corals may not be able to adjust to a more freshwater habitat. The loss of glacial ice also reduces the amount of fresh water available for plants and animals that need fresh water to survive. Glaciers near the Equator , such as those on the tropical island of Papua or in South America, are especially at risk.
The residents below Chacaltaya Glacier in Bolivia, for instance, depended on the glacier for almost all of their fresh water and electricity. In , Chacaltaya Glacier melted entirely.
A few glaciers may actually be benefiting from global warming. Glaciers are growing quickly there. Less precipitation also affects some glaciers. This reduction is the result of few heavy snowfalls. Why So Blue? Some glaciers and icebergs are blue, for the same reason water is blue. The chemical bond between oxygen and hydrogen in water absorbs light in the red end of the visible light spectrum.
Blue glaciers and icebergs are not blue for the same reason the sky is blue. The sky is blue due to atmospheric scattering of light Raleigh scattering , a different phenomenon. Siachen Glacier is the worlds highest area of conflict. Although India controls Siachen, both India and Pakistan claim the area as part of their country. Siachen Glacier is the site of the worlds highest helicopter landing pad, which India built for military and emergency use. Icefall Glaciers are called "rivers of ice.
Ice flows down the icefall just like water falls down a waterfall. The Khumbu Icefall is one of the most difficult terrains on Mount Everest. Paleoclimatology Paleoclimatology is the study of the Earth's atmosphere in prehistoric times.
Paleoclimatology depends on ice and bubbles in glaciers and ice sheets. Scientists extract long tubes of ice, called ice cores, from thick ice sheets, usually in the Antarctic. Ice cores are layered, with the deepest ice having the oldest information. Wide bands indicate a heavy snowfall. Darkly colored bands indicate smoke or other chemicals in the atmosphere.
Ice cores can measure the state of the atmosphere as far back as 80, years. For instance, cores from ice sheets from the year contained chemicals from the massive eruption of Krakatoa, a volcanic island in Indonesia.
Ice cores showed those chemicals drifted from the South Pacific to Antarctica and Greenland and stayed in the atmosphere for many years afterward. Also called the Ganga. Also known as a pyramidal peak. The last ice age peaked about 20, years ago.
Also called glacial age. Sea level is determined by measurements taken over a year cycle. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
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