GL27 Laurentide Introduction Flashcards
What is the Laurentide ice sheet?
The Laurentide ice sheet was a vast ice sheet that covered much of Canada and Northern USA during the Quaternary period. It was up to 4km thick and advanced and retreated many times due to changes in climate.
What was the most recent advance of the Laurentide ice sheet called?
The most recent advance of the Laurentide ice sheet was called the Wisconsin glaciation and started around 100,000 years ago.
What is the bedrock geology of Minnesota?
The bedrock geology of Minnesota consists mainly of gneiss and greenstone.
How did the lobes of the Laurentide ice sheet affect Minnesota?
During the Wisconsin glaciation, four ice lobes from the Laurentide ice sheet advanced and retreated across Minnesota, transporting and depositing large quantities of glacial till across the state. The different origins of the lobes resulted in tills with different characteristics and materials, making it possible to determine where each lobe flowed.
What is a proglacial lake?
A proglacial lake is a large feature that forms as glaciers retreat and release large amounts of meltwater, which may be trapped by an ice or moranic dam.
What was the largest proglacial lake formed in Minnesota by the Laurentide ice sheet?
The largest proglacial lake formed in Minnesota by the Laurentide ice sheet was Lake Agassiz. The edge of the ice sheet and its associated lobes dammed the natural drainage of the area, blocking meltwater from its northward passage to the sea.
What are striations in outcrops of gneiss and greenstone?
Striations are scratches and grooves left on the bedrock by the movement of the ice. They are preserved in outcrops of gneiss and greenstone and indicate the former direction of flow of the ice lobes.
What was the Pleistocene climate?
The Pleistocene climate was characterized by periods of repeated glaciations and interglacial periods over the last 2 million years.
How did the Laurentide ice sheet change the landscape of Minnesota?
The Laurentide ice sheet and its associated lobes advanced and retreated across Minnesota, depositing large quantities of glacial till and forming proglacial lakes. The ice sheet and its meltwater also eroded the landscape and created a variety of landforms.
