docOrigin of Lakes - Oregon State University
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Origin of Lakes - Oregon State University
Origin of Lakes Party Facts Lakes cover 2% of the earth's surface (2.5 x 106 km2) Largest purely freshwater lake is Lake Superior (83,300 km2) Laurentian Great Lakes A - 245,420 km2 V - 24,620 km3 Lake Baikal 20% of the world's fresh water World's deepest lake Maximum depth (zm) – 1620 m Mean depth (z) – 740 m V - 23,000 km3 Of 1200 species of animals and 600 species of plants found in Lake Baikal,over 80% of the taxa found in open water are endemic Tectonic basins Lakes formed by volcanic activity Lakes formed by landslides Lakes formed by glacial activity Solution lakes Lakes formed by fluvial action Lakes formed by wind Lakes associated with shorelines Lakes formed by organic accumulation Lakes formed by behavior of higher organisms Lakes formed by meteorite impact Tectonic Basins Depressions formed by movement of the earth's crust (e.g. warping, fracturing, faulting, thrusting). Does not include volcanic activity. Fort Rock Single fault displacement (orogenesis) Broken fault blocks which may become slightly and irregularly tilted Examples – Abert Lake, OR – Walker lake, NV – Lake Winnemucca, NV Walker Lake Downfaulted troughs or grabens (orogenesis) Elongated area is depressed and lake lies in bottom depression Often difficult to distinguish between single fault deplacement and grabens – Tule Lake and Lower Klamath Lake are single fault displacement basins but are surrounded by lake sediments deposited in Pleistocene graben lakes Tule Lake Downfaulted troughs or grabens Examples – Lake Tahoe, CA Zm - 501 m – Lake Lahonton Complex of fault troughs – Lake Baikal – Lake Tanganyika Lake Tanganyika Uplifted basins (epeirogenesis) Marine depressions uplifted Examples – Lake Okeechobee, FL Lake Okeechobee Uplifted basins (epeirogenesis) Uplifted plains Examples – Great Salt Lake – Lake Victoria – Lake Titicaca Altiplano was raised 4000 m during the formation of the Andes during the Tertiary Lake Titicaca Lake Titicaca Great Salt Lake Uplifted basins (epeirogenesis) Subsidence basins – Often formed by earthquakes – Often porous, therefore dry Examples – Reelfoot Lake, TN Reelfoot Lake Reelfoot Lake Lakes formed by Glacial Activity Pleistocene glaciation produced more current lakes than any other process of lake formation Four major episodes in Northern Hemisphere – Wisconsin glacier began to retreat 17,000 years ago and stopped 10,500 years ago Glaciers begin in mountain ranges and extend in ice sheets across flatter topography (piedmont glaciers) Glacial Lakes Glaciers Pleistocene Glaciers Morainal Deposits Lakes associated with active glaciers Lakes form on, within, beneath, and below thawing glaciers Examples – Laurentian Great Lakes Lakes on Glaciers Ice scour lakes Ice moving over fractures removes rubble along fracture Examples – Diamond Lake, OR – Crescent Lake, OR – Waldo Lake, OR – Odell Lake, OR Waldo Lake Odell Lake Cirque lakes (or tarns) Formed in upper portions of glaciated valleys of mountainous areas by repeated freezing and thawing action Amphitheatre-shaped Water held behind rock or morainal sill Generally small and relatively shallow (<50m) Often one above another - "hanging" lakes Examples – Grinnel Lake in Glacier National Park – Bull Run Lake, OR – Aneroid Lake, OR Cirque Lakes Cirque Lakes Upper Bull Run Lake Lakes below snow line Paternoster lakes – Corrosive action of ice forms chains of rock basins within glacial valley Examples – Glacier National Park – Yosemite National Park – Bighorn Mountains, WY Glacial Trough Paternoster Lakes Lakes below snow line Fjord lakes – Low elevations – Long, narrow lakes in deep, steep-sided valleys Examples – Kootenay Lake, B.C. – Lake Okanagan, B.C. – English Lake District Fjord Lakes Fjord Lake Loch Ness Loch Ness Lakes below snow line Piedmont lakes – Low elevation – Glacial scouring in weak areas of parent geologic material Examples – Great Slave Lake – Great Bear Lake – Great Lakes of St. Lawrence drainage Lakes formed by morainal deposits Lateral morainal dams – Moraine deposited across the mouth of tributaries – More V-shaped – Examples Finger Lakes of New York Finger Lakes Finger Lakes Finger Lake Lakes formed by morainal deposits Terminal morainal deposits – Moraine left behind retreating glacier with corrosion – More U-shaped – Examples Wallowa Lake, OR (also associated with lateral moraines) Flathead Lake, MT Wallowa Lake Wallowa Lake Lakes formed in ground moraine Deposition of meltwater outwash Drift left behind with blocks of ice mixed in Kettle lakes form where ice blocks melted – Very irregular in shape, slope, and topography – Generally shallow (<50 m) – Examples Walden Pond Trout Lake Walden Pond - Kettle Lake Morainal Deposits and Kettle Lakes Kettle Lake Forming Lakes formed from effects of permafrost Cryogenic lakes - formed by effect of frozen ground coalesce and forms larger lakes - thermokarst lakes Volcanic Activity Granitic or basaltic nature of parent material causes low concentrations of nutrients and, therefore, low productivity Crater Lakes Cinder cones – Small, conical lakes Examples – Crater Butte Lake in Mount Lassen National Park, CA Maars Created by explosive eruption of lava coming in contact with groundwater or degassing of magma – Circular and very deep – Small - b< 2km Examples – Lakes in Eifel district of Germany – Big Soda Lake, NV Calderas Created by subsidence of the roof of a partially emptied magma chamber Usually larger than maars Examples – Crater Lake, OR Second deepest lake in North America Seventh deepest lake in the world Collapse of peak of Mount Mazama in 4500 B.C. A - 64 km2 Zm - 608.4 m Crater Lake Crater Lake Lava Flow Lakes Coulee Lakes - Depression formed by collapse when overlying layers of a lava flow hardens and underlying layers continue to flow and leave voids Irregular lava flows – Examples Yellowstone Lake Damming by lava flows – Examples Clear Lake, OR Yellowstone Lake Yellowstone Lake So What? Does this stuff make any difference?
