Minnesota: action of ice sheets (glaciation)

Question 1

location

Answer 1

state in the upper midwestern region of the US
bordered by canadian Manitoba and Ontario

Question 2

landscape shaped by

Answer 2

the Laurentide Ice Sheet
advancing and retreating numerous times in the quaternary

Question 3

geology

Answer 3

-oldest rocks lie in alternating belts of volcanic and sedimentary rocks
-tectonic compression created a range of mountains several km high in N Minnesota

Question 4

lobes

Answer 4

-around 75000 years ago a series of lobes or tongues of ice extended from the main laurentide ice sheet and spread across minesota
-advanced and retreated a number of times transporting and depositing till
-over 1km thick in some places

Question 5

last glacial maximum

Answer 5

-ice sheet covered 13 million km^2
-lasted over 800000 years and eroded extensivly
-ice radiated outward from two high points
-changes in climate and precipitation caused these domes to shift periodically changing the direction of ice flow

Question 6

glacial landforms: ellipsoidal basin

Answer 6

the ice eroded high mountains so a large ellipsoidal basin was created and is now studded with thousands of lakes such as Upper and Lower Red lakes

Question 7

glacial landforms:striations

Answer 7

the lobes of ice abraded striations in the bare rock outcrops

Question 8

glacial landforms:moraines

Answer 8

-Wadena alone advance from NE canada and the till deposited by this is red & sandy from being derived from red sandstone & shales
-it deposited the Alexandria moraine forming the drumlin fields spanning Ottertail, Wadena and Todd counties
-formed the Itasca Morraine

Question 9

glacial landforms:end morraine

Answer 9

Prairie Coteau

Question 10

glacial landforms:periglacial lakes

Answer 10

-the edge of the giant ice sheet damned the natural drainage of the area creating a number of periglacial lakes
-eg Lake Agassiz-300000 sq km

Question 11

glacial landforms:knocks and lochans

Answer 11

the areal scouring associated with this ice sheet resulted in thousands of low lying knocks and intervening lochans

Question 12

glacial landforms:River Warren

Answer 12

water from the glacial Lake Agassiz drained southward from this lake in glacial River Warren
this raging river created the large valley in which the Minnesota river now flows

Question 13

change over time:sediments

Answer 13

-sediments during this time that were deposited mask nearly all of minnesotas previous geological history

Question 14

change over time:mountains

Answer 14

-the high mountains were eroded down so they are now 500-700 m

Question 15

change over time:lakes

Answer 15

-when the Lake Agassiz finally drained it left behind fertile silt deposits producing the rich farmland of the Red River Valley
-as the ice retreated for the last time the variable topography left behind resulted in numerous lows that filled with water becoming the “1000” lakes seen today

Question 16

change over time:by 1000 years ago

Answer 16

by 1000 years ago it was mostly ice free however the Rainy Lobe and the St. louis sun lobe were still present