C) Is a medium-to-high-silica andesitic volcano, different from the lower-silica basaltic volcanoes of Hawaii. D) Is a broad, flat flood basalt, different from the steep stratovolcanoes of Hawaii. E) Is a broad, flat shield volcano, different from the steep stratovolcanoes that are seen above sea level in Hawaii. Feedback: Melt a little basaltic sea floor with some water and sediment, and you get silica-rich andesite feeding explosive, subduction-zone stratovolcanoes such as Mt. St. Helens. Hot spots and spreading ridges make low- silica, basaltic volcanoes, which don’t explode powerfully. Mt. St. Helens is a stratovolcano, but stratovolcanoes are steep, not broad and flat like the above-sea-level parts of the basaltic (lower-silica) Hawaiian volcanoes. Mt. St. Helens was the most active of the Cascades volcanoes even before its big 1980 eruption, and the volcano has erupted many times since the big eruption, just as Hawaiian volcanoes have numerous eruptions. 10. Extra polymerization of silica in some lavas makes them lumpier than typical. Ways to increase this polymerization of silica to make the lava even lumpier include: Points Earned: 1.0/1.0 Correct Answer(s): D Points Earned: 1.0/1.0 Correct Answer(s): C
Feedback: The silicon-oxygen tetrahedra link up to make lumps, so anything that gets in the way of this linking will oppose lumping. Iron, water, carbon dioxide, or high heat that shakes the lumps apart can all oppose the lumping of polymerization. 11. In the picture above, the pink and yellow arrows in front of Dr. Alley point to two rather different deposits from an eruption of the Hawaiian Volcano Kilauea. As described in the class materials, these materials are: under the faulted materials as melted intrusions. followed the violent eruptions. faulted materials as melted intrusions. Feedback: Mt. St. Helens and similar volcanoes make giant explosive eruptions that throw bus-sized blocks, but Kilauea in Hawaii usually doesn't (although rarely, water flashing to steam may move some big things!). Dr. Alley showed you the gravel-sized pieces of glass at the end of the pink arrow, and the frozen "waterfall" of lava at the end of the yellow arrow.
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- Fall '08
- Correct Answer, Volcano, St. Helens, Basalt, GEOSC 010, Quiz, RockOn #3, 3