A lake is a great extent of Eau, generally soft, surrounded by the grounds. Generally however, the lake runs out in direction of the Mer by a emissary River named . The deepest lake of the world is the Lac Baïkal (Siberia).
The definition of a lake is a rather vague concept in the current language: the local names given to the water levels by the population do not take account of the official definitions and it is often the size which was then taken into account. A lake is thus rather larger and deeper than a pond.
From the ecological point of view, if one must differentiate two types of great water levels one can obtain a distinction rather clear and less prone to discussion: we will have the not very major zones on lequelles the sun brings everywhere energy until the bottom: water then is heated and végétalisée: they are the ponds. And if the depth is more important, the sun does not reach all the zones and of the layers of cool water and not vegetalized set up themselves: it is then very an other ecosystem definitely oligotrophic (not very rich in organic matter) which is set up then. Indeed the size and especially the origin of the water level (artificial or not) have an influence definitely less important than the depth on the type of ecosystem which is set up.
It is noted whereas with the thousands of years which pass, the sediments settle at the bottom of the lakes, accumulate on meters or tens of meters and the lake ends up being filled almost and thus functioning like a pond, then it becomes a marsh, then a forest.
More the big lakes without maritime outlet are also named inland seas , following the example Caspian Sea, but the rule is fuzzy since one speaks about the Dead Sea and of the Big lake Salted. It is sometimes proposed to distinguish the seas from the lakes by the character salted of marine water and fresh water of the lakes.
Then a classification of the lakes can be done on the geological type of event which governed their formation:
- oceanic , like the Caspian Sea or the Sea of Aral;
- tectonic , due to the collapse of portions of the earth's crust, like the Lake Tanganyika, the Lake Malawi and the Lake Victoria;
- volcanic . A lake can be formed in a Caldeira or an active volcano (acid Lac):
- lakes of crater like the Lake Albano, the Lake Nemi or the Barombi-mbo;
- lakes polycratères or intercratères, like the Lake Bolsena or the Lake Bracciano;
- alluvial , when a river, for example the Brenta in Venezia, meets alluvial deposits on its course, thus forming the Lac of Levico and the Lac of Caldonazzo;
- glacial , due to the glacial erosion, like the lakes of the areas préalpines; it is the example of the Hundred lakes in Italy;
- proglacial , when the lake is located in front of and fed by a glacier;
- morainic , when the materials transported and deposited by the glaciers form stopping;
- karstic , due to phenomena of erosion in calcareous medium and often very small;
- of deflation , due to erosion by the winds, such those of the Languedoc;
- artificial , created by works built by the man, often of the Stopping S for the hydroelectric production, for example the Lake of Greenhouse-Ponçon.
The water mass of the lakes is not motionless. In addition to the currents created by the rivers, upstream or downstream, and the underground source S, it can occur swirls or waves due to various causes, among which the action of the wind at water surface. Moreover, the lakes are prone to a series of movements, true periodic displacements of water from one side to another of the basin, observable like real unevennesses from one part to another of the coast. In the Lake Bolsena, in spite of his relatively limited size, one thus recorded variations of level going up to 50 cm.
Displeased the water of the big lakes in the metropolitan cities are artificial lakes (cf lake of the park Chaumont hillocks), whose water does not go on the ground (source Bodo Groening, 2004, Madrid).
Finally the various layers of water move in-depth because of the differences in temperature according to the depth, of the day and the seasons.
Sports activitiesIn the lakes, in addition to the fishing, one practices many sports activities, among which the Canotage, the veil or the Planche with veil, of the walks in Barque or Bateau, and of the plunged. These activities are practiced rather the summer. Nevertheless, of many lakes belonging to the private Field, is used in winter and, more generally, for the period of closing of the First category) for the Pêche with the fly.
The lakes are relatively more dangerous than the maritime coasts, for various reasons: water is colder, it can have unexpected currents or swirls there, they are often without monitoring, small Bain nor equipment of rescue.
Thanks to new technologies of Géolocalisation (GPS and tools such as Google Earth), it is possible to reach hundreds of positions (Longitude, Latitude) and air images of lakes, for strolls or fishes, via Community sites of referencing like HTTP: /www.geo-peche.fr www.geo-peche.fr.
the study of the lakes is the Limnologie, science creates by François-Alphonse Forel
- One in the case of speaks about lake of lava some Volcan S of the basaltic type to fluid lava.
; General information
- List of the lakes of the world (Belgium, Canada, the United States, Ireland, Iceland, Italy, France, the Pyrenees, Senegal, Swiss)
- List of the lakes by size
- List of the lakes and inland seas
- List of the lakes of Western Europe by size
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