Karteikarten
Minnesota
Karten in diesem Stapel (26)
- 1Ice sheet activityLaurentide ice sheet covered most of Minnesota (from north) + lobes extended down
- 2Wherecentred over Hudson bay
transformed landscape of Canada and northern USA
during colder periods extended southward across upper Midwest - 3Glacial activityQuaternary period
(2 million years ago to now)
Minnesota >
advance + retreat of several major successive periods of continental ice sheet activity - 4Glacials and interglacialsglacials 100,000 years average
interglacials 10-15,000
ice sheet grew + retreated many times with climatic changes - 5With each advance and retreat glacial till was transported and deposited across wide areasorigin of each resulted in till with different characteristics + materials
- 6Movement of ice sheet shaped by landscapehighlands diverted glacier into lobes of ice that advanced into lowland areas
- 7GEOLOGYpre-glacial
- 8Oldest rocks in northern part of the state and much of the Minnesota River valleyalternating belts of volcanic and sedimentary rock
between these belts - granitic rock materials - 9Formation volcanic + sedimentary rocks2700 million years ago
lava escaped through rifts in the sea floor
volcanic debris released into nearby seas settled onto sea floor forming massive layers of sedimentary rock - 10tectonic activityfolded many of these rock formations and formed faults
- 11Volcanic rocks metamorphosedgreenstone
- 12Rocks along Minnesota river valleymetamorphic gneiss crops (metamorphic granite and sedimentary rocks)
3600 million years - 13Tectonic compressionrange of mountains
several kms high
northern Minnesota - 14GLACIATION75,000 years ago
series of lobes (tongues of ice) extended from main ice sheet and spread across Minnesota - 15EROSIONAL IMPACTLaurentide ice sheet (over 1km thick in places) + its lobes had a massive erosional impact on the landscape
- 16High mountains worn downhighest peaks now only 500-700m (were several kms)
Eagle Mountain highest point
only 701m - 17Large ellipsoidal basinnow studded with thousands of lakes
Upper and Lower Red Lakes - northern Minnesota - 18EBin Arrowhead region of northeast erosional basin particularly deep
- earlier tectonic tilting of landscape exposed weak shale rocks which were eroded much more rapidly than resistant volcanic rocks around them
> lakes lie in deeply eroded shales - 19Striationslobes of ice abraded striations as they advanced
in bare rock outcrops of gneiss and greenstone
alignment indicates direction of advance - 20More varied landscapefar southeast
not extensively covered by ice sheet
retains varied landscape
> steep hills + deep valleys
most rivers draining this area tributaries of the Minnesota and Mississippi Rivers - 21Shaped overall landscapecontinental ice sheet erosion doesn't produce the spectacular landforms associated with valley glaciers and alpine glaciation
- 22DEPOSITIONAL IMPACT-
- 23Wadena lobefrom northeast Canada
reached just south of Minneapolis
till red + sandy (red sandstone + shale)
Alexandria moraine
drumlin fields e.g over Wadena
Itasca moraine - 24Rainy and superior lobesground moraine with reddish iron-rich sediments
- from St Cloud northeastward
set of terminal moraines
- from northwest St Cloud into the Twin Cities (Minneapolis + St Paul)
coarse-textured till
abundant fragments of basalts, gabbro, granite, red sandstone, slate and greenstone
> across northeastern half of Minnesota as far south as Twin Cities - 25Des Moines lobefrom northwest
till tan/buff coloured
clay-rich
calcareous - shale + limestone
southwest: Prairie Coteau terminal moraine - 26Till deposits in westborehole drilling >
more than 100m thick
southwest
160m deep still not bedrock
Informationen
- Beschreibung
- - Geography (Glaciers) Karteikarten am Minnesota, erstellt von Emily H am 03/01/2019.
- Erstellt von
- Emily H
- Aufrufe
- 3
- Bewertung
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