Physiography of Lakes and Reservoirs - Freshwater Ecology: Concepts and Environmental Applications - page 96

Ways That Lakes Form and Essential Characteristics of Each Type a TABLE 6.3

Lake type Formation process Essential characteristics and examples

Tectonic Basin formed by movement of Earth's Can be very old and very deep; Lake

crust: graben, a block slips down Baikal, Asia, and Lake Tanganyika,

between two others; horst, diagonal Africa

slippage

Pothole or kettle Formed when ice left from retreating glacier Small lakes/wetlands; prairie pothole

is buried in till (solid material deposited region in Alberta and North and

by glacier) and then melts South Dakota

Moraine Glacial activity deposits a dam of rock Narrow, fill valley

and debris

Earthslide Movement of earth dams a stream or river Similar to reservoirs; Quake Lake,

Montana

Volcanic—caldera Volcanic explosion causes hole that is filled Often round and deep; Crater Lake,

with water Oregon

Dissolution lake Limestone dissolves and lake forms Small, steep sides

Oxbow River bend pinches off, leaves lake behind Shallow, narrow, may be seasonally

flooded

a Many more types are possible (Hutchinson, 1957).

Glacial activity is responsible for the formation of many lakes in the
temperate regions and for the formation of more lakes than any other process
(Fig. 6.5). Several processes associated with glacial activity lead to lake for-
mation. Glaciers scour as they move down valleys. The ice flow of these glac-
iers creates basins. Lakes occur where glaciers have scoured more deeply,
leading to the formation of cirque (also called tarn lakes) lakes in the “am-
phitheaters” at the heads of the valleys. The glacier forms chains of pater-
noster lakes as it flows further down the valleys (Figs. 6.7 and 6.8). Glacial
scour can lead to formation of extremely large lakes. The Great Slave Lake
in Canada was carved to a depth of 464 m below sea level by the massive
weight of the continental ice sheet and is the deepest lake in North America.
The Laurentian Great Lakes of North America (e.g., Superior, Huron, and
Erie) were partially formed by glacial action. Fjord lakes such as Loch Ness
(the home of a legendary creature) are long glacial lakes formed in steep val-

FIGURE 6.4 Diagrams of two modes of lake formation associated with tectonic processes:
(A) graben, a block drops below two others; and (B) horst, blocks tip and a lake forms along
a single fault line.