Why does the differential stress increase downwards in the brittle crust?
What will be an ideal response?
Answer: Because it is more difficult to fracture a rock under confining pressure than an unconfined rock. The deeper down in the upper crust, the more stress can build up before it fractures (yields). Thus the strength increases downwards through the brittle crust, until crystal-plastic mechanisms kick in at the brittle-plastic transition.
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Each number on this figure refers to a location depicting groundwater in a subsurface material that is consistent in character across the entire figure. Of these locations, which one would have groundwater flowing to the left?
A) 1
B) 2
C) 3
D) 4
E) 5
How many Category 5 hurricanes have made landfall in the U.S. between 1900 and 2005?
A) 2 B) 3 C) 5 D) 10
Over time, which of the following has happened to Niagara Falls?
A) They have become rapids. B) They have migrated several kilometers upstream. C) They have migrated several kilometers downstream. D) They have drained away most of Lake Ontario's water. E) They have evolved into the world's most famous example of stream capture.
During the second wave of U.S. environmental policy, in 1872, Congress designated Yellowstone as the world's first __________.
- national forest - national park - wilderness area - wildlife refuge