Lake Origins

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Lake Origins

• Water bodies may be classified by their origin.
• Gradual or catastrophic geological events form
  and/or destroy lakes, streams, wetlands and
  estuaries.
• Lakes are ephemeral in a geologic sense.
• The rate of aging can be measured.

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• Most lake basins are created by gradual events.
• glacial activity
• deformation of the earths crust

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• Rapid catastrophic geologic events
• earthquakes
• landslides (Mount St, Helens eruption triggered
  massive mudslides expanding Spirit Lake)
• volcanic eruptions

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Lake districts

• Lakes formed in one geographic area are generally
  created by some common natural event.
• In a lake district the lakes have similar
  characteristics
• but their water quality,
• basin morphometry and biological productivity may
  differ.

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Minnesota
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Non-geologically formed lakes

• Beavers dam up streams, shallow but extensive
  lakes.
• Humans create artificial lakes
• damming rivers and streams
• irrigation
• water storage
• hydroelectric power generation

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Tectonically formed lakes

• Shifts in the earths crust
• uplifting of mountains
• breaking and displacement of rock strata
• cause part of a valley to sink
• creating a depression that fills with water.
• Faulting Lakes may be associated with the
  movement of a single fault.
• depressions formed by tilting.

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• Grabens are lakes associated with the movement of
  multiple faults.
• Lake Tahoe depressed area between adjacent
  faults.

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Tectonic formation

• The size of the lake depends on the magnitude of
  the faulting and the amount of silting over the
  years since formation.
• Uplift of portions of sea floor created Lake
  Okeechobee, Florida
• area 1840 km2, the second largest surface area
  of freshwater lake in the United States.

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• Rift lakes One great fault forms a series of
  lakes.
• In eastern Africa
• Lakes Malawi, Tanganyika, Edward, Albert, and
  Turkana, and now marine Red Sea.

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Volcanically formed lakes

• Worldwide distribution
• Calderas (broad craterlike basin of a volcano,
  formed by an explosion or by collapse of the
  cone).
• Best known Crater Lake, Oregon 10 km across,
  gt600 meters deep.
• Lava flows may dam a valley to form a lake
• Snag Lake, in Mount Lassen National Park, CA.
• Differential cooling of lava forms lake basins
• Yellowstone Lake in Yellowstone National Park.

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Glacially formed lakes

• Glacial activity has been the most important
  lake-creating force over the last few millennia.
• Most of the worlds lake basins, including the
  Great Lakes,
• were formed during the Pleistocene Era
• when glaciers covered much of the earth.
• Lakes filled with water as glaciers melted and
  shrunk.
• Famous lake districts
• Great lakes, Wisconsin (land of a 1,000 lakes)
• English and Scottish, Ontario, Canada
• Scandinavian and Alpine Lakes (in general)

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Quebec
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• Cirque lake (French cirque, meaning semicircle or
  amphitheatergt
• Glacial rock-basin lake.
• Usually found at the head of glaciated valleys
  where the valley abuts the steep slope of a
  mountain.
• Deepest near the cliff and shallow near the
  outlet.
• The water is dammed at the outlet by a low
  barrier of glacial debris called a moraine.

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Cirque lake
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Glacial moraines may dam a stream and form a lake.
Moraine Lake
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Glacial valley lake
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• Rock is eroded by the slow downhill movement of
  the glacier
• aided by continual freezing and thawing activity
  that fractures the rock.
• A series of valley-rock-basin lakes like the
  beads on a rosary are called paternoster lakes.

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• Blocks of ice trapped in a glacial moraine,
• melts and a kettle lake is formed.
• Kettle lakes
• are very steep sided,
• may be meromictic (the bottom water never mixes
  with surface water,
• because of their small surface-to-volume ratio
• and the wind fetch is small.
• Walden Pond in Massachusetts

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Kettle Lake
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Kettle lakes
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Kettle lakes
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• Oxbow and scroll lakes are small lakes formed in
  the flood plains of rivers.
• Oxbow formed when the loop of a meandering river
  is cut off by silt deposition.
• Found in the flood plains of almost any river
  worldwide.

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Oxbow formation, erosion through meander neck
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• Scroll lakes a former river channel has moved as
  a result of sediment deposition at a bend.
• Flood plain lakes are connected to the river
  during high floods,
• and become a great habitat for fish.

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