Minnesota Case Study - Ice Sheet Flashcards
When was the present landscape of Minnesota formed roughly?
In the Quaternary period, 2 million years ago to now.
What was the name of the ice sheet, and where was it centred?
Laurentide ice sheet, centred in Hudson Bay.
How thick was the sheet in the Pleistocene Epoch?
More than 1 km thick.
What is the pattern of rock in Minnesota?
Alternating bands of volcanic and sedimentary rocks, with granitic rock between belts.
Where is the metaphoric gneiss rock in Minnesota, and how old is it?
Along the Minnesota River valley, it is 3,600 million years old.
How long ago did the volcanic and sedimentary rocks begin formation?
2,700 million years ago.
How did tectonic activities affect the landscape?
They created faults and high mountains, which were eroded down to approximately 500-700m.
What have some volcanic rocks metamorphosed into?
Greenstone.
What exists in the ellipsoidal basin?
Thousands of lakes, such as Upper and Lower Red Lakes in northern Minnesota.
What is important in the Arrowhead region of the ellipsoidal basin?
It is particularly deep as previous tectonic activity caused tilting, exposing weak shale rocks which were eroded faster than the surrounding volcanics.
Where did the Wadena Lobe extend to and from?
From the north-east of Canada to south of Minneapolis.
What are the characteristics of the till from the Wadena Lobe?
It is red and sandy, from red sandstone and shales in the north and north-east.
What is the name of the first and last moraine from the Wadena Lobe?
The Alexandria moraine and the Itasca moraine.
Where are the drumlin fields formed by the Wadena Lobe?
Spanning Otter Tail, Wadena and Todd counties.
What are the characteristics of the ground moraine at St Cloud?
Reddish, iron-rich sediments from St Cloud northeastwards, with fragments of basalts, gabbros, granite, red sandstone, slate and greenstone.
Which two cities are known as the ‘Twin Cities’?
Minneapolis and St Paul.
What colour was the till deposited by the Des Moines Lobe?
Tan, calcareous due to shale and limestone at source.
What is the name of an end moraine formed by the Des Moines Lobe?
Prairie Coteau, in the south-west.
What depth have boreholes been dug into till from the Des Moines Lobe?
160m, and not yet reached bedrock.
What is a proglacial like?
Lakes formed by the edge of the giant ice sheet dammed the natural drainage of the area, forming many lakes.
What is the largest proglacial lakes?
Lake Agassiz.
How much land did the Lake Agassiz cover at its largest?
440,000 km squared.
What is the name of the river that drains Lake Agassiz?
The Glacial River Warren.
What is left behind after proglacial lakes have drained?
Fertile silt, producing rich farmland of the Red River valley.
