Minnesota case study

Question 1

when did the ice sheet cover Minnesota?

Answer 1

during the Quaternary period
2 million years ago

Question 2

what was the name of the ice sheet that covered Minnesota?

Answer 2

Laurentide ice sheet

Question 3

describe the Laurentide ice sheet.

Answer 3

over 1km thick
advanced and retreated many times due to climatic changes
reached southwards during colder periods

Question 4

what are rocks in Minnesota like?

Answer 4

lie in alternating belts
made out of volcanic and sedimentary rocks, while granite lies inbetween

Question 5

how old and where is the metamorphic gneiss?

Answer 5

3.6 billion years old
crops out along Minnesota River Valley

Question 6

when did sedimentary rocks start their formation in minnesota?

Answer 6

2.7 billion years ago

Question 7

how are faults formed?

Answer 7

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

Question 8

how do faults appear today?

Answer 8

mountains that are several of kilometres high

Question 9

how did the erosional impact of the ice sheet effect mountains?

Answer 9

worn down from several kilometres to just 500-700m

Question 10

what did the erosional impact of the ellipsoidal basin cause?

Answer 10

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

Question 11

what is an example of evidence of erosion which can evidence direction of ice movement, and where is it found?

Answer 11

striations
bare rock outcrops of gneiss and greenstone

Question 12

judgement: how much of an erosional impact did the ice sheet in Minnesota leave behind?

Answer 12

large impact, but did not leave behind the impressive and immense landforms that valley and alpine glaciers do

Question 13

what did the Wadena lobe of the ice sheet deposit?

Answer 13

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

Question 14

what did the final advancements of the Rainy and Superior Lobes leave behind?

Answer 14

coarse, textured till, containing fragments of
basalts, granite, gabbro, red sandstone, slate, greenstone

Question 15

where is this coarse textured till from the rainy and superior lobes found?

Answer 15

strewn across the north-eastern half of Minnesota to South of twin cities

Question 16

what did the Des Moines Lobe deposit?

Answer 16

tan coloured till, which is clay rich calcareous because of shale and limestone rocks

Question 17

how deep are till deposits in Minnesota?

Answer 17

100m thick
160m deep

Question 18

how are proglacial lakes formed in Minnesota?

Answer 18

lobes the extend off the end of the ice sheet naturally dam and drain the area

Question 19

what is the largest proglacial lake called?

Answer 19

Lake Agassiz

Question 20

how big is Lake Agassiz?

Answer 20

covered 440,000km2

Question 21

how was the river Lake Agassiz formed?

Answer 21

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

Question 22

what did the high amount of discharge form Lake Agassiz form?

Answer 22

helped the adjacent Mississippi river form a very large valley in south-eastern Minnesota

Question 23

what was left behind when the lake drained?

Answer 23

left fertile silt deposits , producing the rich farmlands of the Red River Valley

Question 24

what is the river that drained from lake agassiz called?

Answer 24

glacier river warren

Question 25

why does the Southeast Minnesota have an irregular landscape?

Answer 25

was not covered extensively by the ice sheet
it has steep hills, deep valleys, tributary rivers