Glaciated Landscapes SG3b Flashcards
During what ice age did the Laurentide Ice Sheet exist?
The Pleistocene
Where was the Laurentide Ice Sheet centred?
What is now Hudson Bay
Were the four names given to the glaciations of the LIS?
Nebraskan, Kansan, Illinois, Wisconsin
What was the last glacial period in North America called?
Wisconsin Ice Stage
When was the LIS at its maximum extent?
21,000 years ago
At its maximum extent, what area did the LIS cover?
13,000,000km2
At its maximum extent, how far south did the LIS reach?
37 degrees N
How thick was the LIS?
2-3km
What were the four ice domes that made up the LIS?
Greenland Ice Sheet, Cordilleran Ice Sheet, Keewatin Sector, Labrador Sector
Where was the Labrador Sector centred?
Over Hudson Bay
Define Ice Dome
Where accumulation started and flowed outwards, Thickest bit of ice
How did the LIS impact mountains?
Massive erosional impact wore down many of the mountains
How high are the highest peaks now?
500m - 700m
What is the highest natural point in Minnesota with an elevation of 701m?
Eagle Point
Define Ellipsoidal Basin
Huge lake basins created by erosion where the ice sheet gouged out deep depressions in the bedrock
What is the largest ellipsoidal basin created by the LIS?
Hudson Bay
What is the area covered by Hudson Bay today?
1,230,000km2
What are the five Great Lakes?
Huron, Ontario, Michigan, Erie, Superior
What were the Great Lakes formed by?
The advancing and retreating of ice lobes produced smaller ellipsoidal basins
Define Ice Lobes
Tongue shaped glaciers extending from the margins of the main LIS
What dammed the Great Lake basins?
Rock bars made from harder rock which wasn’t eroded, Deposited glacial till
What was the geology of the Great Lakes area?
Mainly sedimentary (e.g. limestones, shales and sandstone) with some outcrops of resistant igneous rock (e.g. Canadian Shield an area of granite and gneiss)
Where is an example of striations?
The shore of Lake Superior
How do striations form?
Subglacial debris scratches the bedrock as the LIS moved over it
Define Mega Scale Lineations (MSL)
Valley like features formed due to erosion and scouring of the bedrock as a result of ice streams within LIS
How long can MSLs be?
100s of km
How deep can MSLs be?
100s of m
How wide can MSLs be?
100s of m
What are the four ice lobes of the LIS which deposited material as till sheets and moraines?
Wadena, Rainy, Superior, Des Moines
Where did the Wadena Lobe advance from?
The North
What till did the Wadena Lobe deposit?
Red and sandy till derived from the red sandstone and shales to the North and North East
Where did the Rainy and Superior Lobes advance from?
The North East
What till did the Rainy and Superior Lobes deposit?
Coarse textured till of basalts, gabbro, granite, iron formation, red sandstones, slate and greenstone strewn across the north-eastern half of Minnesota
Where did the Des Moines Lobe advance from?
The North West
What till did the Des Moines Lobe deposit?
Fine-textured till coloured buff to tan and is clay rich and calcareous due to shale and limestone rocks at its source
How many drumlins are in the New York swarm?
10,000
What are the erratics in south-western Minnesota?
Three Maidens
What is the composition of the Three Maidens and the country rock of where they were deposited?
Three Maidens = Pink and grey granite
Country Rock = Sioux quartzite
Define Proglacial Lake
A body of water impounded in front of a glacier/ice sheet
What is an example of a proglacial lake?
Lake Missoula
Why did Lake Missoula form?
500 cubic miles of meltwater was trapped behind a wall of ice
How many mega-floods did the Lake Missoula cause?
100 floods over 2,000 years
