Minnesota

Question 1

What happened 75,000 years ago?

Answer 1

Series of lobes extended from main Laurentide ice sheet + spread across Minnesota. They advanced + retreated no. of times, transporting + depositing till across a wide area. Different origins of lobes = tills w different characteristics + materials = mixing of landscape

Question 2

What erosional features are there?

Answer 2

ice sheet -> over 1km thick in places. High mountains worn down, highest peaks now only 500-700m
Ellipsoidal basin -> now studded with thousands of lakes eg Upper and Lower red lakes. Weak shale rocks were eroded much more rapidly than resistant volcanic rocks around them
Striations -> lobes advanced abraded in bare rock outcrops of gneiss + greenstone

Question 3

What is the erosional impact of Laurentide ice sheet?

Answer 3

Considerable + shaped overall landscape => lobes had massive impact. However, continental ice sheet erosion does not produce landforms associated with valley glaciers + alpine placation

Question 4

What is the geology?

Answer 4

• belts of volcanic + sedimentary rocks; granitic rock materials lies in areas between the belts
• Metamorphic gneiss
• Volcanic formations, some buried beneath glacial deposits
• Volcanic debris released into seas -> huge layers of sedimentary rock -> tectonics folded rock formations = faults

Question 5

What depositional features are there?

Answer 5

Till -> deposited from Wadena Lobe, red + sand
Drumlin fields -> from Wadena lobe
Ground moraine -> made up of iron rich sediment
Till containing salts, gabbros, granite, red stone -> left from rainy + superior lobes

Many of the till deposits in W of Minnesota have found to be more than 100m thick

Question 6

What created a no. of proglacial lakes? and how are they formed?

Answer 6

Edge of ice sheet + associated lobes dammed natural drainage area. Largest = Lake Agassiz

Glaciers retreat + terminal moraine is left at the front so creates dam where it is formed

Glaciers to the N blocked natural drainage northward of the area. As ice melted, proglacial lake developed S of ice. At its max. Lake covered 440,000km2. Water overflowed the water shed at Brown’s valley. Minnesota cut the present Minnesota river valley = discharge was staggering