But, some other hot spots, while clearly coming up from below, don’t seem to start quite as deep. , Points Earned:, 1/1 Correct Answer:, E Your Response:, E 7. , What is accurate about a typical volcano formed by eruptions from a hot spot?
, A., The lava of the volcano is mostly andesitic in composition, with gradual sides where the volcano projects above sea level, but steeper sides on undersea portions. B., The lava of the volcano is andesitic in composition, and the volcano itself is shaped like a Pepsi can, with vertical sides below sea level. C., The lava of the volcano is mostly andesitic in composition, and the volcano itself has steep sides where projecting above sea level, but less-steep sides on undersea portions. D., The lava of the volcano contains less silica than basalt has, and thus is like the mantle in composition because the melt comes from the mantle, and the volcano itself has uniformly sloping sides like the beautiful peak of Mt. St. Helens before the 1980 eruption. E., The lava of the volcano is mostly basaltic in composition, with gradual sides where the volcano projects above sea level, but steeper sides on undersea portions. The rising hot rock of hot spots feeds volcanoes. Both sea floor and hot-spot volcanoes come from melting a little of the very-low-silica mantle, pulling out the melt, and freezing it, and so are basaltic (low-silica) volcanoes. Note, though, that a few hotspots (such as Yellowstone) are not basaltic, because the basalt has been altered in getting through the continent. The melt probably started out as something that would make basalt, and indeed, the Yellowstone hot-spot track includes basaltic lavas such as those at the glorious Craters of the Moon National Monument. The hot-spot lavas are runny, and spread easily under the air to make volcanoes with gradual slopes, unlike the steep stratovolcanoes, although the slopes of hot-spot volcanoes are steeper under water because the water cools the lava so rapidly that it can’t spread far. , Points Earned:, 1/1 Correct Answer:, E Your Response:, E , 8. , Look at the picture above. What happened here? , A., A giant glacier used to sit here, and water flowing into a hole on the surface fell to the bed and hollowed out a great pothole, seen here.
B., An immense marmot named George, shown here, dug the hole.C., A sharp bend in a river created a whirlpool that carved the hole now filled by a lake.D., A great volcanic explosion occurred, spreading material across the landscape and leaving a hole. E., Death-Valley-type faulting dropped the bottom, making space for the lake; during the Ice Age, Death Valley looked like this, too. Nature has many ways to make holes, and many other ways to make mountains. Part of this class is learning to read the clues, just as geologists do. We saw at Death Valley that the faults tend to make straight lines. Streams on glaciers are not nearly this big, nor are river bends. And while George is cute, he could never dig such a hole. This is the aftermath of the eruption of Mt. St.
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