Beaches of Glacial Beaches of Glacial Lake AgassizLake Agassiz

Ben HuffmanBen Huffman

Ashley RussellAshley Russell

AppearanceAppearance

Old beaches are traceableOld beaches are traceable Continuous, smoothly rounded ridgeContinuous, smoothly rounded ridge Most lie 3-10 feet above till side, and 10-20 Most lie 3-10 feet above till side, and 10-20

above lake sideabove lake side Variations in height are due to unequal currents Variations in height are due to unequal currents

and wave powerand wave power Some beaches are cut through from old Some beaches are cut through from old

streamsstreams Marked by gravel and sand sloping into water Marked by gravel and sand sloping into water

level and tilllevel and till Provide strong evidence for the existence of Provide strong evidence for the existence of

glacial lakesglacial lakes

AppearanceAppearance

FormationFormation Storm waves moved gravel and sand from Storm waves moved gravel and sand from

erosion of till deposits transported into erosion of till deposits transported into Lake AgassizLake Agassiz

Fines settled to the middle of the lakeFines settled to the middle of the lake Interactions with wind, waves, and Interactions with wind, waves, and

currents formed bars, spits, hooks, loops currents formed bars, spits, hooks, loops and terracesand terraces

Best preserved on moderate slopes.Best preserved on moderate slopes. Successions of beaches can mark pauses Successions of beaches can mark pauses

in uplift after ice retreat, subsidence with in uplift after ice retreat, subsidence with outlet erosion, and lowering of lake levels outlet erosion, and lowering of lake levels with new discharge routeswith new discharge routes

These locations marked in red have well preserved beach ridges from many stages ofLake Agassiz.

Beach ridges can be described through Minnesota, North Dakota,and Manitoba.

Beach SuccessionsBeach Successions

There are many beaches that describe the There are many beaches that describe the levels of Agassiz through time.levels of Agassiz through time.

The main ones are as follows (starting with The main ones are as follows (starting with the oldest and highest):the oldest and highest):– Herman BeachesHerman Beaches– Minnesota BeachesMinnesota Beaches– Norcross BeachesNorcross Beaches– Tintah BeachesTintah Beaches– Campbell BeachesCampbell Beaches– McCauleyville BeachesMcCauleyville Beaches

Associated with southoutflow

Beach Successions (cont.)Beach Successions (cont.)– Blanchard BeachesBlanchard Beaches– Hillsboro BeachesHillsboro Beaches– Emerado Beaches Emerado Beaches

(2 main series)(2 main series)– Ojata Beaches Ojata Beaches

(2 main series)(2 main series)– GladstoneGladstone– BurnsideBurnside– OssowaOssowa– StonewallStonewall– Niverville Niverville

(2 main series)(2 main series)

The amount of beach ridges associated with each The amount of beach ridges associated with each set varies from place to place.set varies from place to place.

Associated with LakeAgassiz northeast outlet

Herman BeachesHerman Beaches

Uppermost beachesUppermost beaches Doubles in northern part of AgassizDoubles in northern part of Agassiz Gravel with pebbles 2-3 inches in diameterGravel with pebbles 2-3 inches in diameter Highest stand of Agassiz at 1,055 feet Highest stand of Agassiz at 1,055 feet

above sea levelabove sea level Some places show the Milnor stageSome places show the Milnor stage

– Stands about 20 to 30 feet above the HermanStands about 20 to 30 feet above the Herman– Records that the River Warren outlet was Records that the River Warren outlet was

higher for a short timehigher for a short time

Associated with South OutletAssociated with South Outlet Minnesota, Norcross, Tintah, Campbell, and Minnesota, Norcross, Tintah, Campbell, and

McCauleyville beachesMcCauleyville beaches Hard to match with northern beaches due to the Hard to match with northern beaches due to the

progression of Agassiz to the north.progression of Agassiz to the north. Campbell stage is the most conspicuous below Campbell stage is the most conspicuous below

the Hermanthe Herman– Shows Agassiz at a much lower levelShows Agassiz at a much lower level– Sand and gravel swept southward from the Sand and gravel swept southward from the

Pembina DeltaPembina Delta McCauleyville beaches show that the outlet from McCauleyville beaches show that the outlet from

Agassiz eroded below Lakes Traverse and Big Agassiz eroded below Lakes Traverse and Big StoneStone

Associated with NE outletAssociated with NE outlet 14 total shorelines14 total shorelines Lie below the McCauleyvilleLie below the McCauleyville River Warren was no long receiving drainage from ice, and River Warren was no long receiving drainage from ice, and

thus Agassiz obtained a lower NE outletthus Agassiz obtained a lower NE outlet Beach sets are separated by 10-45 ft.Beach sets are separated by 10-45 ft. Blanchard stages are the oldestBlanchard stages are the oldest

– Show three levels or three pauses in upliftShow three levels or three pauses in uplift Hillsboro beaches show spits formed from currents Hillsboro beaches show spits formed from currents

associated with the fall of lake levelassociated with the fall of lake level Emerado beaches are very traceable, and only have one Emerado beaches are very traceable, and only have one

beach in MN and ND, and two beaches in Manitobabeach in MN and ND, and two beaches in Manitoba Niverville Beaches show 2 or 3 stages, caused by northward Niverville Beaches show 2 or 3 stages, caused by northward

uplifting of land.uplifting of land.

Timing and Epeirogenesis Timing and Epeirogenesis

Epeirogeny - Uplift or depression of Epeirogeny - Uplift or depression of the Earth's crust. the Earth's crust.

RelationshipRelationship– Lake levels are associated with the Lake levels are associated with the

outlet leveloutlet level– Rebound contributed to outlet shifts Rebound contributed to outlet shifts

Epeirogenic DependenceEpeirogenic Dependence

It has been estimated that the lake It has been estimated that the lake bottom of Lake Winnipeg may have bottom of Lake Winnipeg may have only been about 100 feet above sea only been about 100 feet above sea level. level.

Now it is ~ 600ft above sea levelNow it is ~ 600ft above sea level Elevation changes were affecting Elevation changes were affecting

lake outlets. lake outlets. Talk overlap.Talk overlap.

Timing Timing

(Morris Phase)(Morris Phase)

Epeirogenic DependenceEpeirogenic Dependence

Today we see shorelines that must Today we see shorelines that must have been level at one time, but now have been level at one time, but now display vertical changes in elevation.display vertical changes in elevation.

South to NorthSouth to North Elevation change show some latitude Elevation change show some latitude

dependentsdependents

Equal Postglacial Lift linesEqual Postglacial Lift lines

Elevation Change Elevation Change TableTable

Take awayTake away

Beaches are dependent on Lake level Beaches are dependent on Lake level which are dependent on outlet which are dependent on outlet elevation. elevation.

Epeirogenesis was a driving factor is Epeirogenesis was a driving factor is shifting lake outletsshifting lake outlets

Measurements of uplift can be Measurements of uplift can be attained by measuring vertical attained by measuring vertical change in beacheschange in beaches

SourcesSources

Teller, J.T., and Clayton, L., 1983, Glacial Teller, J.T., and Clayton, L., 1983, Glacial Lake Agassiz, The Geological Association Lake Agassiz, The Geological Association of Canada, Special Paper 26.of Canada, Special Paper 26.

Thorleifson, L.H., 1996, Review of Lake Thorleifson, L.H., 1996, Review of Lake Agassiz History, Geological Survey of Agassiz History, Geological Survey of Canada.Canada.

Upham, W., 1895, Glacial Lake Agassiz, Upham, W., 1895, Glacial Lake Agassiz, U.S. Geological Survey, Monographs XXV.U.S. Geological Survey, Monographs XXV.