What is a lake

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What is a lake?

• A depression filled with water
• Not salty (usually)
• Permanent (usually)
• Not too big

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Depression the lake BASIN
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Origin of lake basins

• 168 pages in Hutchinsons Treatise on Limnology
  76 ways lake basins are formed

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I. Tectonic basins

• Earthquakes
• Reelfoot Lake, TN 1811

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Graben Lakes
Depressions between tectonic plates Located in
areas of seismic activity Typically long and
narrow and deep Graben grave
Lake Tahoe, CA (502 m deep) Lake Baikal, Russia
(1,741 m deep) Lake Tanganyika, Africa (1,435 m)
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I. Tectonic basins

• Changes in sea level uplift lakes
• 1. Lake Okeechobee, FL (4 m deep)
• Lake Drummond, VA (Dismal Swamp)
• Typically very shallow

Lake Okeechobee
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II. Volcanic origin

• A. Filling of a caldera
• 1. Crater Lake, OR (610 m deep)
• Small watershed
• Very clear
• Secchi depth 60-70 m
• 2. Ecuadorian lake

Volcano Crater Lake (2) Ecuador lake
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II. Volcanic origin

• B. Lava dam or mud flow
• 1. Lava dam (Oregon)
• 2. Spirit Lake, OR (Mt. St. Helens)

lava dam (2) Spirit Lake (2)
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III. Lakes formed by ice

• (Mostly Pleistocene glaciation)
• A. Morainic Impoundment river valley dammed by
  the gravel till left at the end of glacial advance

Lateral moraine
Terminal moraine
Glacial advance
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A. Morainic impoundments

• Lake McDonald, MT
• Waterton Lake, Canada
• New York Finger Lakes

McDonald (3) Waterton NY
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More morainic impoundments

• Tarn -- a small morainic impoundment, usually
  high in the mountains, at the base of a glacier
  or in the cirque where a glacier was.
• Paternoster lakes -- a series of morinic
  impoundments formed by the advance and retreat of
  a glacier

Avalanche Lake Siyeh Pass
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Paternoster Lakes
Someone thought they looked like prayer beads
hence paternoster (Our Father )
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B. Kettle Lakes (or prairie potholes)

• Formed from chunks of ice left behind by the
  glaciers
• Typically small and shallow
• Many have been filled in by the process of
  natural eutrophication

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C. Glacial scour lakes

• Great Lakes (though very complex tectonic
  processes also involved)

Slide of Great Lakes
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D. Cryogenic lakes

• Formed by freezing and thawing in areas of
  permafrost
• Typically small and shallow
• Often oval and oriented with long axis
  perpendicular to the prevailing summer wind

Slide of tundra lakes
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IV. Solution basins

• Formed by the dissolution of bedrock in an area
  of carbonate rock (e.g., limestone) when a
  sinkhole connects to underground water.

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IV. Solution basins

• Montezuma Well, AZ
• Silver Springs, FL

Montezuma Well (2) Silver Springs
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V. Landslides

• Landslide dams up a valley -- often temporary
• Gros Ventre River, WY, 1925
• Lake San Cristibol, Slumgullion landslide
• Mountain Lake

San Cristibol (2) Mnt. Lake (2)
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VI. Fluviatile lakes

• Lakes formed by rivers
• Ponding by tributary sediments
• Lake Pipin, WI, where Chippawa R. joins
  Mississippi R.
• Oxbow lakes -- in floodplain

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VII. Deflation basins

• Lakes formed by wind
• Usually small
• Usually temporary

Oregon coast slide
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VIII. Meteoric origin

• Meteor Crator, AZ
• Carolina Bays, SE U.S.
• 500,000
• Shallow
• NW-SE orientation

AZ (3) Carolina (2)
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Carolina Bays

• Meteor shower
• Deflation basins
• Schooling fish (whale wallows)
• Solution basins
• Burning of peat

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IX. Animal origin

• Beaver dams
• Pre-European 60-400 million in NA
• Killed 10,000/y in CN and MA in 1620-1630
• Killed 80,000/y in Hudson R. in 1630-1640
• 3rd leading export from Virginia at one time
• Almost extinct by 1900
• Now 6-12 million

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Reservoirs

• Human impoundment
• For over 4000 y
• Farm ponds to massive (Aswan -- 3.8 km)
• 12,000 in U.S. over 15 m high
• Typically dendritic
• Downstream effects

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