ponse:, E /// , 13 Points Missed , 2 Percentage , 87% 1. , Which of the following is commonly expected near a “textbook” subduction zone (that is, near a subduction zone that is so perfect and free of confusing complications that you would use it in a textbook to teach students)? , A., Slide-past (or transform, with horizontal but not vertical movement) earthquakes and faults, such as occur along the San Andreas Fault. B., Andesitic stratovolcanoes, such as Mt. St. Helens. C., Pull-apart earthquakes and faults, such as occur in Death Valley. D., Basaltic mid-ocean-ridge-type volcanoes, such as are found at undersea spreading ridges. E., Basaltic hot-spot-type volcanoes, such as at Hawaii Volcanoes. Pull-apart earthquakes and faults often occur at pull-apart basaltic mid-ocean ridges, which are not subduction zones. Slide-past also occurs on the planet, but not primarily at subduction zones, which also are not hot spots. But subduction does lead to layered thick-lava-flow/blown-up-bits stratovolcanoes of andesitic composition. , Points Earned:, 1/1 Correct Answer:, B Your Response:, B 2., Volcanoes occur above the downgoing slab of a subduction zone. Why?
of heat, but not too much; the downgoing slab makes the nearby mantle colder than normal, not warmer. And nature tends to separate regions where something is flowing one way from regions where the flow is reversed; if the flows are too close together, one will drag the other along and change its direction. Hot spots occasionally ride along on spreading ridges, because both involve
- Fall '08
- Earthquakes, Correct Answer, Volcano, St. Helens, Points Earned