The Mississippi River currently makes up the western boundary of the state of Illinois. However, the Ancient Mississippi River Valley once flowed through the center of the state,
cutting off one-quarter of the state from its modern boundaries. How did the Mississippi River shift from its ancestral location to its present one? How did it end up staying in its current location? Explain.
What will be an ideal response?
Answer: During the Illinois Episode Glaciation, the advancing glacial lobe from the Lake Michigan basin spread westward across the state. This process diverted the river into modern eastern Iowa, where the river flowed along the margin of the ice and created the curved streambeds of the lower Cedar and Wapsipinicon Rivers. At the end of the glaciation, the glacier retreated, and the Mississippi resumed its ancestral course. However, during the Wisconsin Episode Glaciation, meltwater from the Lake Michigan Lobe deposited large outwash plains in central Illinois, filling the ancestral streambed, and the Mississippi was diverted to its current location.
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How does the lithosphere differ from the asthenosphere?
A) The lithosphere is stronger than the asthenosphere. B) The asthenosphere is stronger than the lithosphere. C) The asthenosphere is part of the core, while the lithosphere is part of the mantle. D) The asthenosphere is less dense than the lithosphere.
Fine-grained igneous rocks (grains < 1.0 mm) that have small grains cooled rapidly and are likely to be ________.
A. reclusive B. obtrusive C. intrusive D. preclusive E. extrusive
The percentage by which a population grows in years is called the
A) doubling time. B) crude birth rate. C) natural increase rate. D) total fertility rate. E) life expectancy.