By Jael Edgerton | Kent State University
Lakes exist in a range of shapes and sizes that contribute to their beauty and uniqueness. A lake’s shape often directly results from the manner in which it was formed. Important natural lake-forming forces include glacial activity, movements of the Earth’s tectonic plates (tectonic movement), volcanic activity, river erosion, and other unique mechanisms. Human activity also creates many man-made lakes, including most intentionally created reservoirs.
Glacial lakes are common in North America as in other regions formerly traversed by the many glaciers of the last ice age. The grinding weight and pressure of encroaching and retreating ice sheets carved many depressions in the Earth’s surface, where melting ice then collected to form lakes. When ice sheets moved over flat rock surface with weakened areas of fissures, the rock could splinter and loosen to form the basin of “glacial scour lakes,” such as the Great Lakes in the U.S. and Canada1 (Figure 1). Glacial lakes are often surrounded by other geological evidence of glacial scour.
When glacial scour action has formed a circular depression in a mountain valley, this type of scour is termed a cirque lake or tarn (Figure 2). Occasionally, a string of cirque lakes will form in adjacent mountain valleys to create successive “paternosters lakes”2. These lakes are often extremely clear, cold, and sensitive to environmental disturbances.
Several other types of lakes can form by glacial action and rocky debris gathered by glacial movement. Lakes can form from depressions or dams generated by glacial concentration of rocks and soils; these are referred to as moraine lakes because they form from the rock piles, or moraines, generated by glaciers. When a large chunk of glacial ice is left behind as a glacier recedes the ice itself could create a depression and melt to fill it, creating a “kettle lake” (Figure 3). Kettle lakes are irregularly shaped in the manner of the original ice blocks that produced them2. Kettle lakes are also sometimes referred to as pothole lakes.
Glaciers and ice can create lakes in other unique ways. Periglacial lakes form when ice shapes part of a lake’s margins, restricting otherwise natural drainage of the landscape. Some lakes, such as Lake Vostok in Antarctica, are known as subglacial lakes because they are covered by a perennial ice sheet on their surfaces. Fjord lakes can also form from the action of glaciers carving steep fjord valleys and depositing rocks, boulders, and soils — moraine — at one end of the valley, forming a lake.
Another significant lake-forming force is movement of the tectonic plates that form the Earth’s crust. These lakes typically form at fault lines where plates meet and earthquakes are more common. When adjacent plates separate at fault lines, the steep, narrow gap between them can result in the formation of a graben. Some of the largest, deepest, and oldest lakes on Earth are graben lakes, where a long history and large size can host unique biological diversity. Perhaps the most famous graben lakes are Lake Baikal and the African rift valley lakes, including Lake Tanganyika. Lake Baikal (Figure 4), located in eastern Russia is the world’s oldest, deepest, and largest lake (by volume). Lakes may also occur at points of tectonic upwarping, where the edges tilt or rise to form a discontinuity in the landscape. These tectonic lakes are typically not as deep as graben lakes2.
Indirectly controlled by tectonic activity, volcanism can also create lakes. Ejected magma may leave behind a fissure that holds water in what is termed a maar lake (Figure 5). When the roof of a volcanic crater caves in, a larger caldera may form a crater lake, such as the aptly named Crater Lake in Oregon, U.S.A. (Figure 6). Both kinds of lakes are typically deep in relation to surface area, and drain a limited area. High concentration of volcanic minerals and few nutrients typically yield little productivity in these lakes, which means they are typically clear and deep blue in color.
Many lakes result from river movements of sediments that slowly create lakes over time. The force of water rushing along a riverine flowpath can be tremendous and lead to extensive erosion. Over time, eroded areas may become lake basins. When a lake forms at the foot of a waterfall, it is referred to as a plunge-pool lake (Figure 7).
As riverine erosion occurs, sediments are collected and deposited downstream in the process. Large rivers can deposit sediments in a manner that dams tributary streams and allows new lakes form as a result., These lakes are called lateral lakes. At river bends, turbulence and sediment deposition can build up. Occasionally, this sediment causes the river path to divide and may actually dam of a portion of the river bend entirely. The resulting water body is called an oxbow lake (Figure 8 )2.
Lakes may form on river floodplains when depressions in the floodplain remain filled as floodwaters recede. These lakes are called lateral levees or dish lakes when the ratio of length to width is less than five, or channel lakes when the ratio of length to width is greater than five. The billabongs of Australia are examples of lateral levee lakes2.
Lakes can also form at the mouths of rivers and on deltas. Lakes here form in a similar fashion as Oxbow Lakes, with the aggregation of sediments on a delta closing off otherwise natural water flow. These lakes are referred to as fluviatile lakes or alluvial fan dam lakes. Often, these lakes may be young in origin and disappear with floods and higher water flow.
Reservoirs and impoundments are man-made lakes that form through intentional or unintentional damming or other processes that lead to the pooling of water in one location. Examples include reservoirs that are constructed for drink water, power generation, fisheries, or other recreational activities.
Other types of man-made lakes include farm ponds, ornamental lakes, and quarry lakes, which form in quarry pits used to extract minerals and other resources.
Natural reservoirs can form from the activities of animals and plants such as beavers. Beavers often dam rivers, forming lake behind the dam. Given enough time, sediments can aggregate against the dam, forming a levee and a natural reservoir.
Erosive forces have the power to form other types of lakes. The action of waves along ocean shoreline can also lead to lake formation through erosion and damming of estuaries and river deltas. These lakes may be semi-saline brackish water lakes.
The force of wind is also capable of creating lake basins in coastal regions at the boundaries of large lakes by manipulating sand dunes to create temporary depressions where precipitation collects. Wind blowing across geographically flat regions can move or erode soil sufficiently that shallow lakes called deflation basins or playas result. Often these shallow lakes are endorheic, meaning they don’t drain to the ocean but instead only lose water through evaporation or seepage.
Certain bedrocks, particularly limestone, are easily eroded by even slightly acidic water and may dissolve to form lakes called solution lakes, cenotes, sinkholes, or karsts. Solution lakes may occur on the surface or below ground in caves; they are typically highly circular due to the even chemical erosion of the bedrock at their edges2.
Lakes in polar latitudes may result from freeze/thaw cycles. The action of permafrost in the Arctic causes raised, polygonal soil mounds in which water collects to form cryogenic lakes. When these ponds connect, or an area of permafrost melts, a larger thermokarst lake results. Interestingly, cryogenic and thermokarst lakes are becoming more common, probably as a result of global climate change and the consequent warming of the arctic.
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- Wetzel, Robert G. (2001). Limnology, 3rd ed. San Diego: Elsevier.
- Wayne Wurtsbaugh. American Society for Limnology and Oceanography online photo registry. 2010. Retrieved online at: http://www.aslo.org/photopost/showphoto.php/photo/625/title/cirque-lakechina-lakeidaho-/cat/502
- Midendian. Kettle lakes in the meadow below Fitz Roy, Santa Cruz, Argentina. 2010. Retrieved online at: http://www.flickr.com/photos/midendian/3448102248/
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- Open University Geological Society Mainland Europe. Thermokarst lakes. 2010. Retrieved online at: http://ougseurope.org/rockon/surface/thermokarst.asp