Minnesota case study Flashcards
when did the ice sheet cover Minnesota?
during the Quaternary period
2 million years ago
what was the name of the ice sheet that covered Minnesota?
Laurentide ice sheet
describe the Laurentide ice sheet.
over 1km thick
advanced and retreated many times due to climatic changes
reached southwards during colder periods
what are rocks in Minnesota like?
lie in alternating belts
made out of volcanic and sedimentary rocks, while granite lies inbetween
how old and where is the metamorphic gneiss?
3.6 billion years old
crops out along Minnesota River Valley
when did sedimentary rocks start their formation in minnesota?
2.7 billion years ago
how are faults formed?
rock formations formed by volcanic debris (much of which has metamorphosed into Greenstone) settled onto the sea floor.
these rock formations folded due to high tectonic activity forming faults
how do faults appear today?
mountains that are several of kilometres high
how did the erosional impact of the ice sheet effect mountains?
worn down from several kilometres to just 500-700m
what did the erosional impact of the ellipsoidal basin cause?
left behind thousands of lakes that lie deeply in eroded shales, especially in Arrowhead region due to rapid erosion of shale rocks eg Upper and Lower Red Lakes
what is an example of evidence of erosion which can evidence direction of ice movement, and where is it found?
striations
bare rock outcrops of gneiss and greenstone
judgement: how much of an erosional impact did the ice sheet in Minnesota leave behind?
large impact, but did not leave behind the impressive and immense landforms that valley and alpine glaciers do
what did the Wadena lobe of the ice sheet deposit?
deposits till that is red and sandy as it is derived from the red sandstone and shales
deposited Alexandria moraine and formed drumlin fields spanning across a vast area
Itasca ground moraine
what did the final advancements of the Rainy and Superior Lobes leave behind?
coarse, textured till, containing fragments of
basalts, granite, gabbro, red sandstone, slate, greenstone
where is this coarse textured till from the rainy and superior lobes found?
strewn across the north-eastern half of Minnesota to South of twin cities
what did the Des Moines Lobe deposit?
tan coloured till, which is clay rich calcareous because of shale and limestone rocks
how deep are till deposits in Minnesota?
100m thick
160m deep
how are proglacial lakes formed in Minnesota?
lobes the extend off the end of the ice sheet naturally dam and drain the area
what is the largest proglacial lake called?
Lake Agassiz
how big is Lake Agassiz?
covered 440,000km2
how was the river Lake Agassiz formed?
formed as ice sheet melted
glaciers to the north blocked the natural northward drainage of the area, caused the proglacial lake to develop to the south of the ice. The water overflowed at browns valley, cut through the Traverse gap and cut the present Minnesota river valley
what did the high amount of discharge form Lake Agassiz form?
helped the adjacent Mississippi river form a very large valley in south-eastern Minnesota
what was left behind when the lake drained?
left fertile silt deposits , producing the rich farmlands of the Red River Valley
what is the river that drained from lake agassiz called?
glacier river warren
why does the Southeast Minnesota have an irregular landscape?
was not covered extensively by the ice sheet
it has steep hills, deep valleys, tributary rivers
