2000-degree lava hits 70-degree air on top and sides, and 70-degree rock on the bottom, when the lava first flows out of the volcano, so the lava tends to freeze on all sides. Often, though, the lava will flow downhill away from the volcano fast enough that the leading edge will break as rapidly as it chills, and thus the end won’t get plugged, allowing the sort of lava flow seen in II. Stop the supply of melted rock to the volcano end of the tube, the tube drains out, and a cave is left, such as the beautiful one seen in II. , Points Earned:, 1/1 Correct Answer:, A Your Response:, A 12., Earthquakes can be caused in many different ways. The best interpretation of the planet’s earthquakes is that:, A., The rare, deepest ones are caused by “implosion” as minerals in downgoing slabs of subduction zones suddenly switch to a denser arrangement, whereas common shallower ones are caused by elastic rebound of bent rocks when a fault breaks. B., They are caused by Pepsi machines exploding after being kicked by Coke drinkers.C., Human-made atomic-bomb testing is responsible.
D., The deepest ones are caused by elastic rebound of bent rocks when a fault breaks, whereas shallower ones are almost all caused by collapse of natural caves such as Mammoth Cave.E., They are caused by Coke drinkers kicking the Pepsi machines in Penn State buildings. “Implosion” is the currently favored idea. As subduction zones take rocks deeper where pressure is higher, the building blocks tend to reorganize to take up less space, shifting from, say, a one-on-top-of-another pattern to a fit-in-the-space-between-those-below pattern. Sometimes, this seems to be delayed and then to happen all at once (I can’t move until my neighbor does…), giving an implosion. The biggest, deepest earthquakes happen where temperatures and pressures are so high that we don’t think rocks can break. Humans have never made a hole anywhere nearly as deep as the deeper earthquakes. We have mostly quit testing atomic bombs. And, a big earthquake is way bigger than a big atomic bomb. Penn State students, being naturally even-tempered, don’t kick hard enough to actually explode Pepsi machines. And Penn State basements are not deep enough to account for the deeper earthquakes. , Points Earned:, 1/1 Correct Answer:, A Your Response:, A 13., Volcanic eruptions cause many hazards to humans, and many geologists are employed to study these hazards and warn people. For a single, large, explosive volcanic eruption such as Mt. St. Helens, which of the following is not a worry that these volcanic-hazards geologists would warn people about?
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