minnesota Flashcards
what is the main ice sheet which effected minnesota
laurentide ice sheet
where is minnesota
northern USA
describe geology in minnesota in three points
consits of;
- belts of volcanic and sedimentary rock
- metamorphis gneiss that crops out alongside the minnesota river valley
- many volcanic rocks have metamorphised to greenstone
describe glaciation over minnesota
-a series of lobes or tongues from the laurentide ice sheet spread across minnesota in repeated advance and retreat
what are the four lobes from the laurentide ice sheet that occupied minnesota
rainy lobe, wadena lobe, superior lobe, des moines lobe
name three main erosional impacts on minnesota from the laurentide ice sheet
- high mountains were worn down such that the highest peaks today are only 500-700m
- a large ellipsodal basin was created that is now studded with thousands of lakes today such and the upper and lower red lakes in northern minnesota
- as lobes of ice advanced they abraded striations into the gneiss and greenstone, their alignment indicating the direction that the ice was moving.
review the effect of ice sheets on a landscape in comparison to valley glaciers
the landforms produced by ice sheets are of such a large scale that they do not produce the spectacular imagery of the effects of alpine, warm based glaciation.
describe the depositional impacts from the wadena lobe with one specific example
- till is red and sandy
- first deposited the alexandra moraine which formed the drumlin fields over the otter tail, wadena and todd counties.
describe the depositional impacts of the rainy and superior lobes in two points
- coarse textured till containing fragments of rock such as basalts, grabbo and greenstone
- deposits can be found across the north eatern half of minnesota
why did proglacial lakes form in minnesota
-glaciers to the north blocked the natural northward drainage of the landscape
what was the largest proglacial lake and its maximum size
lake agassiz, at its maximum was 440,000km2.
