What is a Lake & How are They Formed?

Lakes can be found in every country on planet Earth, yet no two lakes will ever be found to be the same. There are many ways that a lake can be formed, although the two major classes are either man-made or as a result of a natural occurrence.

What is a Lake?

A lake is ‘a body of water that is completely surrounded by land’. The Encyclopedia notes that the majority of lakes are also of some considerable size.

How are Lakes Formed?

There are a number of ways that lakes can be formed with examples cited below to illustrate the forms taken.

Man-Made Lakes

Man-made lakes are created by damning watercourses such as rivers and large streams to form service-specific reservoirs known as lakes. The Ord River Scheme in Western Australia is one such scheme that has seen the damning of the Ord River engineered to create a service-specific lake. The lake is said to be 9 (nine) times the volume of Sydney Harbour. The scheme has changed the social and economic face of the northern reaches of Western Australia and has been instrumental in opening up the area to farming and agriculture the like of which would never have been possible had the building of the lake not been undertaken.

Natural Lakes

There are a number of ways that natural lakes have been created that include the use of extinct volcanoes, known as Crater Lakes, to Glacial Lakes and Coastal Lakes. Through to Flood Plain Lakes, Playas, and Oxbow Lakes.

Crater Lakes

Extinct volcanoes have become lakes, a reservoir or water storage unit, made available by the eruption and subsequent extinction of an active volcano. Some of these volcano lakes can be of significant depth as have been found in the lake system in Mt Gambier in Victoria. The Blue Lake as it is commonly known as has been used extensively as a diving area, where experienced divers tackle the subterranean caves that are a part of the lake system.

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Unfortunately, the Blue Lake and some of the lesser-known diving lakes have claimed the lives of divers who have become disorientated, losing their way than running out of the air before they could surface. Lake Taupo on the North Island of New Zealand is another Crater Lake as is Billy Mitchell Crater Lake on the island of Bouganville, Papua New Guinea. Whilst the majority of volcanic crater lakes are round in configuration the same cannot be said for the vast majority of other natural lakes.

Glacial Lakes

Lakes have evolved as a result of glacial shift that has resulted in the lake taking on the topographical shape of the contours of the indentation. A glacial lake is formed is as a result of a shift and movement of a glacier when the glacier leaves a large indentation in the earth’s crust that overtime is filled with water. These glacial lakes can be extremely large in relation to the megalitres of available water storage space and they can also be very deep. Lake St Clair in Tasmania is just such a lake it was formed by a glacier and is Australia’s deepest lake. Lakes Te Anau and Wanaka on New Zealand’s South Island are other examples of just such glacial shifts.
Coastal Lakes

Coastal areas also have vast lake systems that have developed as a result of sand bars near the mouth of a river slowly shifting to close of the water escape route to the sea. The sand bars act as seals, isolating the waters and forcing them back up the riverways and overflowing into low lying areas. Lake Macquarie on the central coast of New South Wales is an example of a coastal lake dammed by encroaching sands. The Gippsland Lake system in Victoria is another example. The only time that a coastal lake can be breached is when an exceptionally high tide penetrates the sand dams.

Flood Plain Lakes

Flood plain lakes only occur when the river systems, swollen by flooding waters spill over into the topographical depressions that in drought times would not be considered as ever having the capacity to become inland lakes. There are a number of natural depressions within Australia’s inland, only observable during flood times. Many of these lakes are unnamed as they come and go according to the season.

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Playa or Dry Lake

However, Lake Ayre in South Australia has retained the name ‘Lake’ due to it’s being both a salt-pan in drought time and a wildlife mecca when the floodwaters come coursing down from Northern Queensland and Western New South Wales. Lake Ayre is a Playa or dry lake that only contains water on an infrequent basis. The shallow lake though not deep is large in circumference as it sits in a shallow depression in what is considered in most cases to be desert.
Oxbow Lake

Another lesser-known type of lake is what is known as an Oxbow Lake. These Oxbow lakes are formed in tropical areas along very winding rivers. The increased volume of fast-flowing water resulting from heavy tropical monsoon or cyclonic rains creates a build-up of silt that cuts off a loop of the river and isolating a portion of the river. When the waters slow and drop the isolated spur of water becomes an Oxbow Lake. The Fly and the Sepik River in Papua New Guinea and Arnhem Land in the Northern Territory are all situated in tropical areas where very heavy rains occur. They are examples of rivers that follow along and very contorted courses and have on occasion become an Oxbow Lake system. Billabongs (an aboriginal name for waterholes) are similar though smaller versions of the Oxbow lakes. They are formed to become small waterholes after the main body of water has dried up or recede far upstream from the billboard.

As noted above there are a variety of ways that a lake can be created. There are also lakes that once made are seldom used as water storage systems. There are lakes that are relatively round such as the crater lakes and there are lakes that are extremely complex in their topographical size. Lakes that are deep and lakes that are shallow. The one constant factor noted in Vol.10 of the Australian and New Zealand Encyclopedia ‘ A lake is a body of water, usually of considerable size, surrounded by land’.

Reference: Australian New Zealand Encyclopedia Vol 10

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