Open and closed lakes
Encyclopedia
Open and closed lake
s refer to the major subdivisions of lakes - bodies of water surrounded by land.
An open lake is a lake where water constantly flows out under almost all climatic circumstances. Because water does not remain in an open lake for any length of time, open lakes are always fresh water
: dissolved solids do not accumulate. Open lakes form in areas where precipitation
is greater than evaporation. Because most of the world's water is found in areas of highly effective rainfall, most lakes are open lakes whose water eventually reaches the sea. For instance, the Great Lakes
' water flows into the St. Lawrence River and eventually the Atlantic Ocean
.
Open lakes typically have stable levels which do not fluctuate because input is always matched by outflow to rivers downstream. If more water enters an open lake than was previously leaving it, then more water will leave the lake. The drainage from an open lake, like that from ordinary river
s, is referred to as exorheic (from the Greek
exos, outside and rhein, to flow).
A closed lake (see endorheic drainage
) is exactly the opposite. In a closed lake, no water flows out, and water which is not evaporated will remain in a closed lake indefinitely. This means that closed lakes are always saline
, though this salinity varies greatly from around 3 parts per thousand for most of the Caspian Sea
to as much as 400 parts per thousand for the Dead Sea
. Only the less salty closed lakes are able to sustain life, and it is completely different from that in rivers or freshwater open lakes. Closed lakes typically form in areas where evaporation is greater than rainfall, although most closed lakes actually obtain their water from a region with much higher precipitation
than the area around the lake itself, which is often a depression of some sort.
The level of most closed lakes is unstable because if runoff into the lake is lessened, the water balance of a closed lake is altered, and the amount of water in the lake falls. This is what has caused the shrinkage of the Aral Sea
, formerly the world's second largest closed lake. Similarly, if runoff into a closed lake is increased, then the level will increase because evaporation is not likely to increase at all - let alone enough to stabilise the level of the lake.
Fluctuation in the level of closed lakes are therefore much more useful in paleoclimatology than are studies of open lakes which can reduce the level of outflow if inflow decreases.
in southern Victoria
, when a succession of wet years during the 1950s caused the level of the lake to rise so much that it nearly overflowed. There is a great deal of evidence that in fact Lake Corangamite was an open lake prior to the end of the Little Ice Age
- some evidence says it was an open lake for much of the Holocene
due to a wetter climate.
It is, of course, also possible that the inflow into an open lake could decrease so much that any outflow would dry the lake up completely — that is, the open lake would become a closed lake. The only lake that is currently an open lake for which there is any evidence of a closed lake existing in the same location in the past is Lake Malawi
in Africa
. It is known that in very dry periods, outflow from the Shire River
— Lake Malawi's only outlet — can drop precipitously, and it is strongly believed that during past dry periods outflow from Lake Malawi has ceased entirely and salt has accumulated in the lake, especially during the Last Glacial Maximum
and other similarly dry periods.
Apart from Australia
and Southern Africa
, it is rare for runoff variability to be high enough for these changes to take place on a useful time scale, and lakes forming in areas where conversions from closed to open or open to closed are likely are very rare. However, Lake Titicaca
, the largest lake in South America, has historically been a semi-open lake with very limited outflow, but recent glacial retreat
has reduced inflows so much that some believe it could become a completely closed lake in the future. In North Dakota
Devils Lake, historically a closed lake, is known to have been an open lake during the Medieval Warm Period
. Since 1999, probably due to global warming
, Devils Lake has overflowed into another terminus called Stump Lake, which could overflow into the Red River of the North
if present wet conditions in the region continue.
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
s refer to the major subdivisions of lakes - bodies of water surrounded by land.
An open lake is a lake where water constantly flows out under almost all climatic circumstances. Because water does not remain in an open lake for any length of time, open lakes are always fresh water
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
: dissolved solids do not accumulate. Open lakes form in areas where 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...
is greater than evaporation. Because most of the world's water is found in areas of highly effective rainfall, most lakes are open lakes whose water eventually reaches the sea. For instance, the Great Lakes
Great Lakes
The Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...
' water flows into the St. Lawrence River and eventually the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
.
Open lakes typically have stable levels which do not fluctuate because input is always matched by outflow to rivers downstream. If more water enters an open lake than was previously leaving it, then more water will leave the lake. The drainage from an open lake, like that from ordinary river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
s, is referred to as exorheic (from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
exos, outside and rhein, to flow).
A closed lake (see endorheic drainage
Endorheic
An endorheic basin is a closed drainage basin that retains water and allows no outflow to other bodies of water such as rivers or oceans...
) is exactly the opposite. In a closed lake, no water flows out, and water which is not evaporated will remain in a closed lake indefinitely. This means that closed lakes are always saline
Saline water
Saline water is a general term for water that contains a significant concentration of dissolved salts . The concentration is usually expressed in parts per million of salt....
, though this salinity varies greatly from around 3 parts per thousand for most of the Caspian Sea
Caspian Sea
The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...
to as much as 400 parts per thousand for the Dead Sea
Dead Sea
The Dead Sea , also called the Salt Sea, is a salt lake bordering Jordan to the east and Israel and the West Bank to the west. Its surface and shores are below sea level, the lowest elevation on the Earth's surface. The Dead Sea is deep, the deepest hypersaline lake in the world...
. Only the less salty closed lakes are able to sustain life, and it is completely different from that in rivers or freshwater open lakes. Closed lakes typically form in areas where evaporation is greater than rainfall, although most closed lakes actually obtain their water from a region with much higher 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...
than the area around the lake itself, which is often a depression of some sort.
The level of most closed lakes is unstable because if runoff into the lake is lessened, the water balance of a closed lake is altered, and the amount of water in the lake falls. This is what has caused the shrinkage of the Aral Sea
Aral Sea
The Aral Sea was a lake that lay between Kazakhstan in the north and Karakalpakstan, an autonomous region of Uzbekistan, in the south...
, formerly the world's second largest closed lake. Similarly, if runoff into a closed lake is increased, then the level will increase because evaporation is not likely to increase at all - let alone enough to stabilise the level of the lake.
Fluctuation in the level of closed lakes are therefore much more useful in paleoclimatology than are studies of open lakes which can reduce the level of outflow if inflow decreases.
Conversion between an open and a closed lake
If the amount of water entering a closed lake is increased beyond a certain level - for most closed lakes far more than would normally enter the lake - it is possible that the water level in the lake would rise so much that the lake would no longer be capable of absorbing it. This is rare but known conclusively in the case of Lake CorangamiteLake Corangamite
Lake Corangamite is Victoria’s largest natural lake, located near Colac in south-west Victoria, Australia in the Lakes and Craters region of the Victorian Volcanic Plains. The lake is hypersaline, and salinity levels have increased dramatically as the lake level has dropped in recent decades...
in southern Victoria
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....
, when a succession of wet years during the 1950s caused the level of the lake to rise so much that it nearly overflowed. There is a great deal of evidence that in fact Lake Corangamite was an open lake prior to the end of 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...
- some evidence says it was an open lake for much of the Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
due to a wetter climate.
It is, of course, also possible that the inflow into an open lake could decrease so much that any outflow would dry the lake up completely — that is, the open lake would become a closed lake. The only lake that is currently an open lake for which there is any evidence of a closed lake existing in the same location in the past is Lake Malawi
Lake Malawi
Lake Malawi , is an African Great Lake and the southernmost lake in the Great Rift Valley system of East Africa. This lake, the third largest in Africa and the eighth largest lake in the world, is located between Malawi, Mozambique, and Tanzania...
in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. It is known that in very dry periods, outflow from the Shire River
Shire River
The Shire is a river in Malawi and Mozambique. The river has been known as the Shiré or Chire River. It is the outlet of Lake Malawi and flows into the Zambezi. Its length is 402 km; including Lake Malawi and the Ruhuhu, its headstream, it has a length of about 1200 km...
— Lake Malawi's only outlet — can drop precipitously, and it is strongly believed that during past dry periods outflow from Lake Malawi has ceased entirely and salt has accumulated in the lake, especially during the Last Glacial Maximum
Last 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...
and other similarly dry periods.
Apart from Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and Southern Africa
Southern Africa
Southern Africa is the southernmost region of the African continent, variably defined by geography or geopolitics. Within the region are numerous territories, including the Republic of South Africa ; nowadays, the simpler term South Africa is generally reserved for the country in English.-UN...
, it is rare for runoff variability to be high enough for these changes to take place on a useful time scale, and lakes forming in areas where conversions from closed to open or open to closed are likely are very rare. However, Lake Titicaca
Lake Titicaca
Lake Titicaca is a lake located on the border of Peru and Bolivia. It sits 3,811 m above sea level, making it the highest commercially navigable lake in the world...
, the largest lake in South America, has historically been a semi-open lake with very limited outflow, but recent glacial retreat
Retreat of glaciers since 1850
The retreat of glaciers since 1850 affects the availability of fresh water for irrigation and domestic use, mountain recreation, animals and plants that depend on glacier-melt, and in the longer term, the level of the oceans...
has reduced inflows so much that some believe it could become a completely closed lake in the future. In North Dakota
North Dakota
North Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....
Devils Lake, historically a closed lake, is known to have been an open lake during the Medieval Warm Period
Medieval Warm Period
The Medieval Warm Period , Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region, that may also have been related to other climate events around the world during that time, including in China, New Zealand, and other countries lasting from...
. Since 1999, probably due to 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...
, Devils Lake has overflowed into another terminus called Stump Lake, which could overflow into the Red River of the North
Red River of the North
The Red River is a North American river. Originating at the confluence of the Bois de Sioux and Otter Tail rivers in the United States, it flows northward through the Red River Valley and forms the border between the U.S. states of Minnesota and North Dakota before continuing into Manitoba, Canada...
if present wet conditions in the region continue.