Lake Origins

1. Lake Origins

2. Freshwater • Water in lakes & streams - 0.02% of water on earth • Covers <2% of world’s land area • Most water found in just 20 deep (>400 m) lakes throughout world

3. Lake Baikal • Contains 20% of all freshwater

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

5. Most Lakes • Most lakes are much smaller, shallower (<20 m) • Lakes can be formed in many ways • Two general categories • Catastrophic • Non-catastrophic

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

7. Types of Catastrophic Lakes • Glacial lakes • Erosion and deposition by glacial ice movements • Most important lake-forming process • Most numerous in Northern Hemisphere

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

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

10. Glacial Scour Lakes • Smaller lakes in amphitheater-shaped area at snow line • Cirque lakes - at upper end of glacial-scoured valley

11. Glacial Scour Lakes • Non-mountainous area with “soft” or cracked geology • Great Slave & Great Bear • Great Slave - deepest lake in North America (600 m)

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

13. Lakes in Glacial Outwash or Moraine • Detached, isolated ice blocks in glacial outwash or moraine melt, leave water-filled pit • Form irregular kettle lakes

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

15. Tectonic Lakes • Lakes formed by faulting, folding, warping of earth’s crust (non-volcanic) • Most common form - graben • Depressed block between adjacent highlands

16. Tectonic Lakes • Lake Tahoe • Lake Tanganyika • Lake Baikal • Great Salt Lake

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

18. 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

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

20. Volcanic Lakes • May also be formed by lava flows damming valleys

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

22. Non-catastrophic Lakes • Solution lakes • Wind-formed lakes • River lakes • Shoreline lakes • Lakes formed by organisms

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

24. Solution Lakes • Salt-collapse basins • Sodium chloride, calcium sulfate • Bottomless, Lake, NM

25. 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

26. River Lakes • Ponding by deltas • Levee or lateral lakes • Parallel to river, filled by flooding

27. River Lakes • Oxbow lakes • River meanders cut off from main river flow

28. River Lakes • Plunge pools formed beneath waterfalls

29. Shoreline Lakes • Bays cut off from main lake by longshore wave action and sand bars

30. Lakes formed by Organisms • Beaver dams • Human reservoirs • Sphagnum dams