glaciated landscape MINNESOTA (ice sheet)

Question 1

geology of Minnesota

Answer 1

• situated in the north of the USA
• part of the Laurentian shield
• Minnesotas oldest rocks lie in alternating belts in the northern half of the state and much of the Minnesota valley.
• volcanic formations lie throughout Minnesotas portion of the laurtenide shield.

Question 2

glaciation of Minnesota

Answer 2

• around 75,000 years ago a series of lobes or tongues of ice extended from the main Laurentide ice sheet and spread across Minnesota.
• these lobes advanced and retreated a number of times, transporting and depositing across a wide area.

Question 3

erosional impact

Answer 3

• The laurtentide ice sheet is over 1km thick in places, and its lopes had a massive erosional impact on the landscapes.
• the high mountains wore down
• a large ellipsoidal basin was created by this erosion and is now studded with thousands of lakes
• As the lobes advanced they abraded striations in bare rock outcrops on gneiss and greenstone, their alignment indicating the direction of ice advance
• the erosional impact of the Laurentide ice sheet wad therefore considerable and shaped the overall landscape.

Question 4

depositional impact

Answer 4

• the wadena love advanced from northeast Canada several times and reached just south of Minneapolis.
• the till deposited by this lobe is characteristically red and sandy.
• the wadena lobe first deposited the Alexandira moraine, formed the drumlin fields and finally formed the Itasca moraine.
• the glaciers produced formed a set of terminal moraines.
• The Des Moines lobe deposited till that is coloured tan to buff and is clay rich and calcareous because of shale and limestone rock at its source to the northwest.

Question 5

proglacial lakes

Answer 5

• the edge of the giant ice sheet and its associated lobes also dammed the natural drainage of the area. this created a number of proglacial lakes.
• glaciers to the north blocked the natural northward drainage of the area. as the ice melted, a proglacial lake developed south of the ice.
• the water overflowed the watershed t browns valley drained through the traverse gap and cur the present Minnesota river valley.