Proglacial lake
Encyclopedia
In geology
, a proglacial lake is a lake formed either by the dam
ming action of a moraine
or ice dam
during the retreat of a melting glacier
, or by meltwater trapped against an ice sheet
due to isostatic depression
of the crust around the ice. At the end of the last ice age
approximately 10,000 years ago, large proglacial lakes were a widespread feature in the northern hemisphere.
In some cases, such lakes gradually evaporated during the warming period after the Quaternary
ice age. In other cases, such as Glacial Lake Missoula
and Glacial Lake Wisconsin
in the United States, the sudden rupturing of the supporting dam caused glacial lake outburst flood
s, the rapid and catastrophic release of dammed water resulting in the formation of gorges and other structures downstream from the former lake. Good examples of these structures can be found in the Channeled Scablands
of eastern Washington, an area heavily eroded by the Missoula Floods
.
In Great Britain, Lake Lapworth
, Lake Harrison
and Lake Pickering
were examples of proglacial lakes. Ironbridge Gorge
and Hubbard's Hills
are examples of a glacial overspill channel created when the water of a proglacial lake rose high enough to breach the lowest point in the containing watershed.
The receding glaciers of the tropical Andes
have formed a number of proglacial lakes, especially in the Cordillera Blanca
of Peru, where 70% of all tropical glaciers are. Several such lakes have formed rapidly during the 20th century. These lakes may burst, creating a hazard for zones below. Many natural dams (usually moraines) containing the lake water have been reinforced with safety dams. Some 34 such dams have been built in the Cordillera Blanca
to contain proglacial lakes.
Several proglacial lakes have also formed in recent decades at the end of glaciers on the eastern side of New Zealand
's Southern Alps
. The most accessible, Lake Tasman, hosts boat trips for tourists.
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, a proglacial lake is a lake formed either by the dam
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
ming action of a moraine
Moraine
A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...
or ice dam
Ice dam
An ice dam occurs when water builds up behind a blockage of ice. Ice dams can occur in various ways.-Caused by a glacier:Sometimes a glacier flows down a valley to a confluence where the other branch carries an unfrozen river...
during the retreat of a melting glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
, or by meltwater trapped against an ice sheet
Ice sheet
An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...
due to isostatic depression
Isostatic depression
Isostatic Depression is the term used by geologists for the sinking of large parts of the Earth's crust into the asthenosphere. The sinking is caused by a heavy weight placed on the Earth's surface...
of the crust around the ice. At the end of the last ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
approximately 10,000 years ago, large proglacial lakes were a widespread feature in the northern hemisphere.
In some cases, such lakes gradually evaporated during the warming period after the 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...
ice age. In other cases, such as Glacial Lake Missoula
Glacial Lake Missoula
Glacial Lake Missoula was a prehistoric proglacial lake in western Montana that existed periodically at the end of the last ice age between 15,000 and 13,000 years ago...
and Glacial Lake Wisconsin
Glacial Lake Wisconsin
Glacial Lake Wisconsin was a prehistoric proglacial lake that existed from approximately 19,000 to 15,000 years ago, at the end of the last ice age, in the central part of present-day Wisconsin in the United States....
in the United States, the sudden rupturing of the supporting dam caused glacial lake outburst flood
Glacial lake outburst flood
A glacial lake outburst flood is a type of outburst flood that occurs when the dam containing a glacial lake fails. The dam can consist of glacier ice or a terminal moraine...
s, the rapid and catastrophic release of dammed water resulting in the formation of gorges and other structures downstream from the former lake. Good examples of these structures can be found in the Channeled Scablands
Channeled scablands
The Channeled Scablands are a unique geological erosion feature in the U.S. state of Washington. They were created by the cataclysmic Missoula Floods that swept periodically across eastern Washington and down the Columbia River Plateau during the Pleistocene epoch. Geologist J Harlen Bretz coined...
of eastern Washington, an area heavily eroded by the Missoula Floods
Missoula Floods
The Missoula Floods refer to the cataclysmic floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age. The glacial flood events have been researched since the 1920s...
.
In Great Britain, Lake Lapworth
Lake Lapworth
Lake Lapworth existed in England in the Ice Age when ice from Wales and the north blocked the outlet of the River Dee near the site of Chester. The Dee backed up, forming Lake Lapworth, until it overflowed southwards and cut the Ironbridge gorge, permanently diverting part of the Dee drainage into...
, Lake Harrison
Lake Harrison
Lake Harrison is the name given to a huge lake that in parts of the Ice Age covered much of the Midlands in England around Warwick and Birmingham and Leicester. It was formed when ice from Wales and the north blocked the drainage and trapped a lake between the ice front and the Cotswolds...
and Lake Pickering
Lake Pickering
Lake Pickering was an extensive proglacial lake of the Devensian glacial. It filled the Vale of Pickering between the North York Moors and the Yorkshire Wolds, when the ice blocked the drainage, which had hitherto flowed north-eastwards past the site of Filey towards the Northern North Sea basin...
were examples of proglacial lakes. Ironbridge Gorge
Ironbridge Gorge
The Ironbridge Gorge is a deep gorge formed by the River Severn in Shropshire, England.Originally called the Severn Gorge, the gorge now takes its name from its famous Iron Bridge, the first iron bridge of its kind in the world, and a monument to the industry that began there...
and Hubbard's Hills
Hubbard's Hills
Hubbard's Hills is an area of natural beauty directly to the west of Louth, Lincolnshire, England.It is popular for family picnics, school field trips and dog walking....
are examples of a glacial overspill channel created when the water of a proglacial lake rose high enough to breach the lowest point in the containing watershed.
The receding glaciers of the tropical Andes
Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...
have formed a number of proglacial lakes, especially in the Cordillera Blanca
Cordillera Blanca
The Cordillera Blanca is a mountain range in the Ancash Region of Peru. Part of the larger Andes range, it includes 33 major peaks over high in an area wide and long.-Overview:...
of Peru, where 70% of all tropical glaciers are. Several such lakes have formed rapidly during the 20th century. These lakes may burst, creating a hazard for zones below. Many natural dams (usually moraines) containing the lake water have been reinforced with safety dams. Some 34 such dams have been built in the Cordillera Blanca
Cordillera Blanca
The Cordillera Blanca is a mountain range in the Ancash Region of Peru. Part of the larger Andes range, it includes 33 major peaks over high in an area wide and long.-Overview:...
to contain proglacial lakes.
Several proglacial lakes have also formed in recent decades at the end of glaciers on the eastern side of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
's Southern Alps
Southern Alps
The Southern Alps is a mountain range extending along much of the length of New Zealand's South Island, reaching its greatest elevations near the island's western side...
. The most accessible, Lake Tasman, hosts boat trips for tourists.
See also
- List of prehistoric lakes
- Pluvial lakePluvial lakeA pluvial lake is a landlocked basin which fills with rainwater during times of glaciation, when precipitation is higher. Pluvial lakes that have since evaporated and dried out may also be referred to as paleolakes.-Geology:...
- Proglacial lakes of MinnesotaProglacial lakes of MinnesotaThe proglacial lakes of Minnesota were lakes created in what is now the U.S. state of Minnesota in central North America in the waning years of the last glacial period. As the Laurentide ice sheet decayed at the end of the Wisconsin glaciation, lakes were created in depressions or behind moraines...