Case study - Minnesota

• What is the background on Minnesota ice sheet?

  It is a midwestern U.S. state bordering Canada and Lake Superior, the largest of the Great Lakes
• What has primarily shaped the landscape of Minnesota?

  Glacial activity throughout the Quaternary period (last 2 million years)
• What was the glacial activity like in the ice sheet?

  Over the last 2 million years, its retreated a lot - the Laurentide Ice sheet covered Hudson Bay and grew and retreated many times
• What is the name of the ice sheet that shaped the landscape of Minnesota?

  Laurentide ice sheet
• How has the underlying geology of the northern part of Minnesota contributed to the topography of the landscape?

  The folding of these rocks has made a more mountainous (hilly) landscape
• What is the name of the highest point in the state of Minnesota?

  Eagle Mountain - 701m
• What is the underlying geology of the southwestern portion of Minnesota?

  thick layer of sedimentary rock
• How thick was the ice sheet over most parts of Minnesota?

  1 km
• What is the large scale erosional feature found in northern Minnesota?

  an ellipsoidal basin
• What are the named features that are evidence of the ellipsoidal basin in northern Minnesota?

  Upper and Lower Red lakes; Mille Lacs Lake in Central Minnesota
• What are the unnamed features that are evidence of the ellipsoidal basin in northern Minnesota?

  Thousands of lakes studding the landscape
• What other evidence is there of the overwhelming erosional impact of the ice sheet on the Minnesota landscape?

  There are no high mountains in the state. The highest peaks are only between 500-700m.
• What small scale evidence of the erosional impact of the ice sheet is there on Minnesota?

  Striations found on bare rock throughout the state, indicating the direction of ice advance
• Which part of Minnesota was not covered by the ice sheet and how is this shown in the landscape?

  The south east of Minnesota. There are steeper hills and deeper valleys found here as a result of the action of rivers
• What is a summary of the erosional impact of the Laurentide ice sheet on Minnesota?

  The impact has been very considerable and shaped the overall landscape. However, it has not produced spectacular landforms associated with valley glaciers.​
• What are the names of the 4 main lobes that extended from the Laurentide ice sheet that spread across different parts of Minnesota?

  Wadena

  Superior

  Des Moines

  Rainy
• Which part of Minnesota did the Wadena lobe travel over?

  It advanced from NE Canada, covering the northwest part of Minnesota and reaching just south of Minneapolis
• Approximately when did the Wadena lobe retreat, leaving depositional features across the landscape?

  30,000 years ago
• What are the characteristics of the Wadena lobe till?

  red sandstone and shale rock in the north and the northeast of Canada (sandy)
• What are the two moraines called that have formed from the Wadena lobe?

  Itasca

  Alexandria
• Where are drumlin fields found from the Wadena lobe?

  Otter Tail and Todd counties
• Which part of Minnesota did the Rainy and Superior lobes travel over in Minnesota?

  It advanced from Canada to cover the North East part of Minnesota.
• When did the Rainy and Superior lobes retreat, leaving depositional features across the landscape?

  20,500 years ago
• What are the characteristics of the Rainy and Superior lobe till?

  Red coarse-textured till containing fragments of basalts, gabbro, granite, red sandstone, slate and greenstone.
• Where can the Rainy and Superior lobe deposits be found in Minnesota?

  Across the north-eastern half of Minnesota as far south as Minneapolis & St Paul​
• When did the Des Moines lobe retreat, leaving depositional features across the landscape?

  13,000 years ago
• Which part of Minnesota did the Des Moines lobe travel over in Minnesota?

  It advanced from North and South Dakota to spread over the south west part of Minnesota
• What are the characteristics of the Des Moines lobe deposits?

  Tan to buff coloured (yellowish brown) fine texture; clay-rich due to the shale & limestone at its source in the NE
• How thick are the Des Moines deposits?

  over 160m
• What is a named example of the terminal moraine features formed by the Des Moines lobe?

  Prairie Coteau
• What is the name of the proglacial lake formed by the Laurentide ice sheet?

  Lake Agassiz
• What is the name of the moraine dam in Minnesota that was finally overtopped by Lake Agassiz?

  Big Stone Moraine
• What was the name of the glacial river that was formed from the overtopped moraine dam?

  River Warren
• What is the name of present day river valley that now occupies the glacial river Warren valley?

  Minnesota river valley
• How wide the Minnesota river valley in places?

  5 miles
• What is the name of the valley where lake Agassiz overtopped the moraine dam?

  Brown's valley
• What is the name of the land between Brown's valley and the Minnesota river valley?

  Traverse Gap
• What impact did the glacial River Warren have on how the present day Red River Valley is used?

  It left behind fertile silt deposits that make it ideal for agriculture
• Describe the till in the Wadena lobe?

  Yellowish (Buff) brown colour - limestone, granite
• Describe the till in the Superior lobe

  Red colour - mixed rocks such as granite, basalt and gabbro