Lake Origins

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Lake Origins
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Freshwater

• Water in lakes streams - 0.02 of water on
  earth
• Covers lt2 of worlds land area
• Most water found in just 20 deep (gt400 m) lakes
  throughout world

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Lake Baikal

• Contains 20 of all freshwater

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Other Lakes

• N.A. Great Lakes
• African rift lakes
• Malawi
• Victoria
• Canadian great lakes
• Great Bear
• Great Slave
• Athabasca

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Most Lakes

• Most lakes are much smaller, shallower (lt20 m)
• Lakes can be formed in many ways
• Two general categories
• Catastrophic
• Non-catastrophic

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Catastrophic Formation

• Most lakes have catastrophic origin
• Developed as result of some violent activity
• Tendency to be clustered together in lake
  districts

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Types of Catastrophic Lakes

• Glacial lakes
• Erosion and deposition by glacial ice movements
• Most important lake-forming process
• Most numerous in Northern Hemisphere

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Glacial Lakes

• Some exist only when in contact with existing
  glaciers
• Pools of water on or beneath glacier
• Streams dammed by tongues of ice

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Glacial Scour Lakes

• Glaciers widened and deepened existing valleys or
  scoured out huge basins
• Fjords - may connect with ocean or remain
  isolated (Loch Ness)

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Glacial Scour Lakes

• Smaller lakes in amphitheater-shaped area at snow
  line
• Cirque lakes - at upper end of glacial-scoured
  valley

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Glacial Scour Lakes

• Non-mountainous area with soft or cracked
  geology
• Great Slave Great Bear
• Great Slave - deepest lake in North America (600
  m)

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Glacial Scour Lakes

• Scour played large role in development of Great
  Lakes, especially Lake Superior
• Other origins as well

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Lakes in Glacial Outwash or Moraine

• Detached, isolated ice blocks in glacial outwash
  or moraine melt, leave water-filled pit
• Form irregular kettle lakes

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Morainal Damming

• Terminal or lateral moraines impounded valleys,
  filled with water
• Lake Mendota, WI
• Finger Lakes, NY

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Tectonic Lakes

• Lakes formed by faulting, folding, warping of
  earths crust (non-volcanic)
• Most common form - graben
• Depressed block between adjacent highlands

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Tectonic Lakes

• Lake Tahoe
• Lake Tanganyika
• Lake Baikal
• Great Salt Lake

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Tectonic Lakes

• Uplift basins - elevated above sea by slow,
  moderate geologic activity
• Caspian Sea
• Lake Okeechobee
• Very shallow

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Tectonic Lakes

• Earthquake lakes - basins formed by earthquake
  activity
• Reelfoot Lake, KY/TN
• Overnight formation (?) after earthquake produced
  lowlands, filler with water from Mississippi River

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Volcanic Lakes

• Crater lakes
• Calderas - collapse of magma chambers
• Maars - explosion craters
• Crater Lake, OR
• A caldera
• Deepest U.S. lake - 608 m

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Volcanic Lakes

• May also be formed by lava flows damming valleys

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Volcanic Lakes

• Landslide lakes
• Stream impoundment by rock slides, mud flows
• Often short-lived
• Mountain Lake, VA is long-lived example

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Non-catastrophic Lakes

• Solution lakes
• Wind-formed lakes
• River lakes
• Shoreline lakes
• Lakes formed by organisms

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Solution Lakes

• Bodies formed when water dissolves soluble rock
  formations - karst
• Limestone sinks
• FL, MI, KY, IN, TN
• Cenotes
• Yucatan Peninsula

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Solution Lakes

• Salt-collapse basins
• Sodium chloride, calcium sulfate
• Bottomless, Lake, NM

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Wind-formed Lakes

• Dry climates
• Dunes with depressions or damming of streams
• Common in TX, NE, E shore of Lake MI
• May be very short-lived

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River Lakes

• Ponding by deltas
• Levee or lateral lakes
• Parallel to river, filled by flooding

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River Lakes

• Oxbow lakes
• River meanders cut off from main river flow

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River Lakes

• Plunge pools formed beneath waterfalls

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Shoreline Lakes

• Bays cut off from main lake by longshore wave
  action and sand bars

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Lakes formed by Organisms

• Beaver dams
• Human reservoirs
• Sphagnum dams