Minnesota Ice Sheets
- Created by: AlexMaltby
- Created on: 20-02-21 17:54
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- Minnesota Ice Sheets
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- Canada-USA border, west of Lake Superior
- Cold base glacier, but with warm characteristics because increasing temp
- landscape is result of quaternary glaciation
- gigantic Laurentide ice sheet advanced and retreated with climate changes
- Laurentide Ice Sheet
- Covered millions of km. Up to 2 miles thick in Canada + USA
- ice sheet had signif impact on geology
- gouged out the great lakes
- Geology
- oldest rocks lie beneath alternating volcanic/sedimentary belts in North
- between these belts lie granitic rock materials
- volcanic and sedimentary rocks formed 2.5bil years ago when lava escaped sea floor
- Gneisses (metamorphic granite+sedimentary rocks) were established (failed to form mountain ranges)
- oldest rocks lie beneath alternating volcanic/sedimentary belts in North
- Glaciation
- 75k years ago, 4 main lobes extended from Laurentide ice sheet and spread across Minnesota, depositing widespread till
- Land sculpted by ice over 2 mil years
- Different origins of lobes resulted in tills with diff. characteristics + materials
- Erosional Impact
- massive, wore down many mountains, highest peaks are 500-700m, highest Eagle mountain (701m)
- created ellipsoidal basin containing many lakes
- particularly deep in arrowhead region due to weak sedimentary rock
- early tectonic tilting exposed less resistant shales, forming lakes
- glacial striations due to abrasion beneath ice
- most steep hills + valleys in Minnesota are result of fluvial processes
- Depositional Impact
- Wadena ice lobe deposited drumlins + glacial drift in Wadena county + central Minnesota
- drumlin field has fanlike form with long axis tending southwest, suggests ice movement from NE
- ground moraines with reddish iron
- drumlin field has fanlike form with long axis tending southwest, suggests ice movement from NE
- rich sediments characteristic of red sandstone and shales from N Minnesota
- Rainy and Superior lobes left coarse texture till with fragments of basalt, gabbro, red sandstone, slate and greenstone
- reflects shale and limestone rocks lobe passed over, till deposits up to 160m depth
- Des Moines lobe deposited tan/buff till -> clay rich
- Wadena ice lobe deposited drumlins + glacial drift in Wadena county + central Minnesota
- Pro-glacial Lakes
- meltwater is released during interglacial periods
- results in formation of proglacial lakes
- edge of Laurentide ice sheet dammed natural drainage of area blocking meltwater from natural northward passage to sea
- thereby creating pro-glacial lakes (ie Lake Agassiz, covered 440k km and 400m deep)
- edge of Laurentide ice sheet dammed natural drainage of area blocking meltwater from natural northward passage to sea
- results in formation of proglacial lakes
- meltwater is released during interglacial periods
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