Starvation (glaciology)
Encyclopedia
In glaciology
, starvation occurs when a glacier retreat
s, not because of temperature
increases, but due to precipitation
so low that the ice flow downward into the zone of ablation exceeds the replenishment from snowfall. Eventually, the ice will move so far down that it either calve
s into the ocean
or melts.
When starvation does occur, however, it can almost always be reversed by slight changes in precipitation, such as are brought about by mountain
ranges. Thus, even if glaciers do not cover a lowland due to low precipitation, glaciation is almost certain to occur at higher elevations.
in many areas of Canada
and the West Siberian Plain
.
It is thought that, after the end of the Eemian Stage, continental ice sheets first formed near or beyond their northern margins (that is, in the extreme northwest of Siberia
and the Yukon Territory
, Northwest Territories
and Nunavut
in North America
). However, as an ice sheet advances, precipitation at its centre (known as a dome) tends to become very low because high-pressure systems form due to the very cold temperatures above the ice. This meant that at the northern edge of the ice sheets, there was almost no replenishment of the ice, and as it fell to lower elevations, even if it did not melt, it was not being replaced.
Thus, as the continental ice sheets of Quaternary
glaciations advanced south according to each Milankovitch cycle
, their northern edges were starved and it is believed that starvation caused them to retreat substantially southward by the time the southern limits of maximum glaciation were approached. Of course, in areas such as the Russian Far East
, eastern Siberia and Beringia, glaciers were, in effect, starved before they could form at all.
Some have also argued that starvation, as well as increasing temperatures, played a significant role in the decay of continental ice sheets after the LGM. The argument is that as fresh water from the melting edges of the ice sheet reached the sea, the flow of warm water which fed the ice sheets was stopped and deglaciation during the summer accelerated. This, however, is a highly controversial position.
Starvation of glaciers is believed to have occurred during the Little Ice Age
in parts of Alaska
, the Himalayas and the Karakoram
. This is because these glaciers do not follow the general global patters of glacial advance during warm periods and retreat during cold periods, which would imply that their size is controlled by the amount of precipitation they receive, for temperatures are so low that the increases deemed like from, say, global warming
would fail to melt them to any degree whatsoever.
Glaciology
Glaciology Glaciology Glaciology (from Middle French dialect (Franco-Provençal): glace, "ice"; or Latin: glacies, "frost, ice"; and Greek: λόγος, logos, "speech" lit...
, starvation occurs when a glacier retreat
Glacier retreat
Glacier retreat or glacial retreat is discussed in several articles, depending on the time frame of interest, and whether the climatological process or individual glaciers are being considered. Articles on these topics include:...
s, not because of temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
increases, but due to precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
so low that the ice flow downward into the zone of ablation exceeds the replenishment from snowfall. Eventually, the ice will move so far down that it either calve
Ice calving
Ice calving, also known as glacier calving or iceberg calving, is a form of ice ablation or ice disruption. It is the sudden release and breaking away of a mass of ice from a glacier, iceberg, ice front, ice shelf, or crevasse...
s into the ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
or melts.
When starvation does occur, however, it can almost always be reversed by slight changes in precipitation, such as are brought about by mountain
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...
ranges. Thus, even if glaciers do not cover a lowland due to low precipitation, glaciation is almost certain to occur at higher elevations.
Occurrences
Starvation of continental ice sheets is known to have occurred during the period before the Last Glacial MaximumLast Glacial Maximum
The Last Glacial Maximum refers to a period in the Earth's climate history when ice sheets were at their maximum extension, between 26,500 and 19,000–20,000 years ago, marking the peak of the last glacial period. During this time, vast ice sheets covered much of North America, northern Europe and...
in many areas of Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
and the West Siberian Plain
West Siberian Plain
The West Siberian Plain is a large plain that occupies the western portion of Siberia, between the Ural Mountains in the west and the Yenisei River in the east, and by the Altay Mountains on the South-East. Much of the plain is poorly drained and consists of some of the world's largest swamps and...
.
It is thought that, after the end of the Eemian Stage, continental ice sheets first formed near or beyond their northern margins (that is, in the extreme northwest of Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
and the Yukon Territory
Yukon
Yukon is the westernmost and smallest of Canada's three federal territories. It was named after the Yukon River. The word Yukon means "Great River" in Gwich’in....
, Northwest Territories
Northwest Territories
The Northwest Territories is a federal territory of Canada.Located in northern Canada, the territory borders Canada's two other territories, Yukon to the west and Nunavut to the east, and three provinces: British Columbia to the southwest, and Alberta and Saskatchewan to the south...
and Nunavut
Nunavut
Nunavut is the largest and newest federal territory of Canada; it was separated officially from the Northwest Territories on April 1, 1999, via the Nunavut Act and the Nunavut Land Claims Agreement Act, though the actual boundaries had been established in 1993...
in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
). However, as an ice sheet advances, precipitation at its centre (known as a dome) tends to become very low because high-pressure systems form due to the very cold temperatures above the ice. This meant that at the northern edge of the ice sheets, there was almost no replenishment of the ice, and as it fell to lower elevations, even if it did not melt, it was not being replaced.
Thus, as the continental ice sheets of Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
glaciations advanced south according to each Milankovitch cycle
Milankovitch cycles
Milankovitch theory describes the collective effects of changes in the Earth's movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković, who worked on it during First World War internment...
, their northern edges were starved and it is believed that starvation caused them to retreat substantially southward by the time the southern limits of maximum glaciation were approached. Of course, in areas such as the Russian Far East
Russian Far East
Russian Far East is a term that refers to the Russian part of the Far East, i.e., extreme east parts of Russia, between Lake Baikal in Eastern Siberia and the Pacific Ocean...
, eastern Siberia and Beringia, glaciers were, in effect, starved before they could form at all.
Some have also argued that starvation, as well as increasing temperatures, played a significant role in the decay of continental ice sheets after the LGM. The argument is that as fresh water from the melting edges of the ice sheet reached the sea, the flow of warm water which fed the ice sheets was stopped and deglaciation during the summer accelerated. This, however, is a highly controversial position.
Starvation of glaciers is believed to have occurred during the Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...
in parts of Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, the Himalayas and the Karakoram
Karakoram
The Karakoram, or Karakorum , is a large mountain range spanning the borders between Pakistan, India and China, located in the regions of Gilgit-Baltistan , Ladakh , and Xinjiang region,...
. This is because these glaciers do not follow the general global patters of glacial advance during warm periods and retreat during cold periods, which would imply that their size is controlled by the amount of precipitation they receive, for temperatures are so low that the increases deemed like from, say, global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
would fail to melt them to any degree whatsoever.