Open and closed lakes refer to the major subdivisions of
lake
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
s – bodies of water surrounded by land. Exorheic, or open lakes drain into a river, or other body of water that ultimately drains into the ocean.
Endorheic basins
An endorheic basin (; also spelled endoreic basin or endorreic basin) is a drainage basin that normally retains water and allows no outflow to other external bodies of water, such as rivers or oceans, but drainage converges instead into lakes ...
fall into the category of endorheic or closed lakes, wherein waters do not drain into the ocean, but are reduced by evaporation, and/or drain into the ground.
Open lake
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 usually
fresh water
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
: dissolved solids do not accumulate. Open lakes form in areas where
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
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
The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...
' water flows into the
St. Lawrence River
The St. Lawrence River (french: Fleuve Saint-Laurent, ) is a large river in the middle latitudes of North America. Its headwaters begin flowing from Lake Ontario in a (roughly) northeasterly direction, into the Gulf of St. Lawrence, connecting ...
and eventually the
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
.
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
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...
s, is referred to as exorheic (from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
''exos'', outside and ''rhein'', to flow).
Closed lake
In a closed lake (see
endorheic drainage), no water flows out, and water which is not evaporated will remain in a closed lake indefinitely. This means that closed lakes are usually
saline, though this salinity varies greatly from around three parts per thousand for most of the
Caspian Sea
The Caspian Sea is the world's largest inland body of water, often described as the world's largest lake or a full-fledged sea. An endorheic basin, it lies between Europe and Asia; east of the Caucasus, west of the broad steppe of Central Asia ...
to as much as 400 parts per thousand for the
Dead Sea
The Dead Sea ( he, יַם הַמֶּלַח, ''Yam hamMelaḥ''; ar, اَلْبَحْرُ الْمَيْتُ, ''Āl-Baḥrū l-Maytū''), also known by other names, is a salt lake bordered by Jordan to the east and Israel and the West Bank ...
. 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
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
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
The Aral Sea ( ; kk, Арал теңізі, Aral teñızı; uz, Орол денгизи, Orol dengizi; kaa, Арал теңизи, Aral teńizi; russian: Аральское море, Aral'skoye more) was an endorheic basin, endorheic lake lyi ...
, 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 is 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 Corangamite
Lake Corangamite , a hypersaline endorheic lake, is located near Colac in the Lakes and Craters region of the Victorian Volcanic Plains of south-west Victoria, Australia. The lake's salinity levels have increased dramatically as the lake level ...
in southern
Victoria
Victoria most commonly refers to:
* Victoria (Australia), a state of the Commonwealth of Australia
* Victoria, British Columbia, provincial capital of British Columbia, Canada
* Victoria (mythology), Roman goddess of Victory
* Victoria, Seychelle ...
, when a succession of wet years during the 1950s caused the level of the lake to rise so much that it almost overflowed. There is a great deal of evidence that Lake Corangamite was an open lake prior to the end of the
Little Ice Age
The Little Ice Age (LIA) was a period of regional cooling, particularly pronounced in the North Atlantic region. It was not a true ice age of global extent. The term was introduced into scientific literature by François E. Matthes in 1939. Ma ...
- some evidence says it was an open lake for much of the
Holocene
The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...
due to a wetter climate.
It is 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, also known as Lake Nyasa in Tanzania and Lago Niassa in Mozambique, is an African Great Lake and the southernmost lake in the East African Rift system, located between Malawi, Mozambique and Tanzania.
It is the fifth largest fre ...
in
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
. It is known that in very dry periods, outflow from the
Shire River
The Shire is the largest river in Malawi. It is the only outlet of Lake Malawi and flows into the Zambezi River in Mozambique. Its length is . The upper Shire River issues from Lake Malawi and runs approximately before it enters shallow Lake Malo ...
— 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
The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent.
Ice sheets covered much of Northern North America, Northern Eur ...
and other similarly dry periods.
Apart from
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
and
Southern Africa
Southern Africa is the southernmost subregion of the African continent, south of the Congo and Tanzania. The physical location is the large part of Africa to the south of the extensive Congo River basin. Southern Africa is home to a number of ...
, 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 (; es, Lago Titicaca ; qu, Titiqaqa Qucha) is a large freshwater lake in the Andes mountains on the border of Bolivia and Peru. It is often called the highest navigable lake in the world. By volume of water and by surface area, ...
, the largest lake in South America, has historically been a semi-open lake with very limited outflow, but recent
glacial retreat
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. Deglaciation occu ...
has reduced inflows so much that some believe it could become a completely closed lake in the future. In
North Dakota
North Dakota () is a U.S. state in the Upper Midwest, named after the Native Americans in the United States, indigenous Dakota people, Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north a ...
Devils Lake, historically a closed lake, is known to have been an open lake during the
Medieval Warm Period
The Medieval Warm Period (MWP), also known as the Medieval Climate Optimum or the Medieval Climatic Anomaly, was a time of warm climate in the North Atlantic region that lasted from to . Proxy (climate), Climate proxy records show peak warmth oc ...
.
Since 1999, possibly due to
global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
, Devils Lake has overflowed into another terminus called
Stump Lake, which could overflow into the
Red River of the North
The Red River (french: rivière Rouge or ) is a river in the north-central United States and central Canada. Originating at the confluence of the Bois de Sioux and Otter Tail rivers between the U.S. states of Minnesota and North Dakota, it fl ...
if present wet conditions in the region continue.
Also, the former
Tulare Lake
Tulare Lake () (Spanish: ''Laguna de Tache'', Yokuts: ''Pah-áh-su'') is a freshwater dry lake with residual wetlands and marshes in the southern San Joaquin Valley, California, United States. After Lake Cahuilla disappeared in the 17th century ...
in California was known to have overflowed its basin in some years but not others, switching between an open and closed lake.
References
{{DEFAULTSORT:Open And Closed Lakes
Bodies of water
Lakes