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Beaches of Glacial Lake Agassiz Ben Huffman Ashley Russell.

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1 Beaches of Glacial Lake Agassiz Ben Huffman Ashley Russell

2 Appearance  Old beaches are traceable  Continuous, smoothly rounded ridge  Most lie 3-10 feet above till side, and 10-20 above lake side  Variations in height are due to unequal currents and wave power  Some beaches are cut through from old streams  Marked by gravel and sand sloping into water level and till  Provide strong evidence for the existence of glacial lakes

3 Appearance

4 Formation  Storm waves moved gravel and sand from erosion of till deposits transported into Lake Agassiz  Fines settled to the middle of the lake  Interactions with wind, waves, and currents formed bars, spits, hooks, loops and terraces  Best preserved on moderate slopes.  Successions of beaches can mark pauses in uplift after ice retreat, subsidence with outlet erosion, and lowering of lake levels with new discharge routes

5 These locations marked in red have well preserved beach ridges from many stages of Lake Agassiz. Beach ridges can be described through Minnesota, North Dakota, and Manitoba.

6 Beach Successions  There are many beaches that describe the levels of Agassiz through time.  The main ones are as follows (starting with the oldest and highest): –Herman Beaches –Minnesota Beaches –Norcross Beaches –Tintah Beaches –Campbell Beaches –McCauleyville Beaches Associated with south outflow

7 Beach Successions (cont.) –Blanchard Beaches –Hillsboro Beaches –Emerado Beaches  (2 main series) –Ojata Beaches  (2 main series) –Gladstone –Burnside –Ossowa –Stonewall –Niverville  (2 main series)  The amount of beach ridges associated with each set varies from place to place. Associated with Lake Agassiz northeast outlet

8 Herman Beaches  Uppermost beaches  Doubles in northern part of Agassiz  Gravel with pebbles 2-3 inches in diameter  Highest stand of Agassiz at 1,055 feet above sea level  Some places show the Milnor stage –Stands about 20 to 30 feet above the Herman –Records that the River Warren outlet was higher for a short time

9 Associated with South Outlet  Minnesota, Norcross, Tintah, Campbell, and McCauleyville beaches  Hard to match with northern beaches due to the progression of Agassiz to the north.  Campbell stage is the most conspicuous below the Herman –Shows Agassiz at a much lower level –Sand and gravel swept southward from the Pembina Delta  McCauleyville beaches show that the outlet from Agassiz eroded below Lakes Traverse and Big Stone




13 Associated with NE outlet  14 total shorelines  Lie below the McCauleyville  River Warren was no long receiving drainage from ice, and thus Agassiz obtained a lower NE outlet  Beach sets are separated by 10-45 ft.  Blanchard stages are the oldest –Show three levels or three pauses in uplift  Hillsboro beaches show spits formed from currents associated with the fall of lake level  Emerado beaches are very traceable, and only have one beach in MN and ND, and two beaches in Manitoba  Niverville Beaches show 2 or 3 stages, caused by northward uplifting of land.


15 Timing and Epeirogenesis  Epeirogeny - Uplift or depression of the Earth's crust.  Relationship –Lake levels are associated with the outlet level –Rebound contributed to outlet shifts

16 Epeirogenic Dependence  It has been estimated that the lake bottom of Lake Winnipeg may have only been about 100 feet above sea level.  Now it is ~ 600ft above sea level  Elevation changes were affecting lake outlets.  Talk overlap.

17 Timing





22 (Morris Phase)

23 Epeirogenic Dependence  Today we see shorelines that must have been level at one time, but now display vertical changes in elevation.  South to North  Elevation change show some latitude dependents

24 Equal Postglacial Lift lines

25 Elevation Change Table

26 Take away  Beaches are dependent on Lake level which are dependent on outlet elevation.  Epeirogenesis was a driving factor is shifting lake outlets  Measurements of uplift can be attained by measuring vertical change in beaches

27 Sources  Teller, J.T., and Clayton, L., 1983, Glacial Lake Agassiz, The Geological Association of Canada, Special Paper 26.  Thorleifson, L.H., 1996, Review of Lake Agassiz History, Geological Survey of Canada.  Upham, W., 1895, Glacial Lake Agassiz, U.S. Geological Survey, Monographs XXV.

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