Midterm Exam Questions with Solutions - Volcanoes and Civilization | GEOSCI 111, Exams of Geology

Download Midterm Exam Questions with Solutions - Volcanoes and Civilization | GEOSCI 111 and more Exams Geology in PDF only on Docsity! Version B 1 Name __________________________________ Geology 111 - Midterm Exam KEY November 7, 2007 25% of the exam Part 1: Short Answer. Note the word "short". You can use an outline form, noting just a few points; these are not essay questions. Confine your answer to the space provided. If I cannot read it, they will not be graded. A) What is the evidence that Yellowstone will eventually produce another large "super eruption", although probably not in the near future. Three eruptions in the last 2.1 m.y. occurred about every 600,000 to 700,000 years, and the last one was 600,000 to 700,000 years ago. In addition, there is clearly molten rock/magma in the upper mantle and deep crust beneath Yellowstone, reflecting the presence of a mantle plume/hot spot that is still active. B) What is the difference between pyroclastic and Hawaiian calderas? Pyroclastic caldera: violent collapse into the evacuated magma chamber from a large Plinian eruption. Hawaiian caldera: draining of a lava lake, usually by starting a flank eruption. C) Contrast the release of gas in basalt and rhyolite volcanoes, and how this relates to explosiveness. Basalt: slow, continual gas release during magma ascent allows only minimal build-up of over pressure, so basalt eruptions are not very explosive. Rhyolite: gas escape is hindered by the high viscosity of the rhyolite magma, which causes a great over-pressure of gas to build up as the magma ascends toward the surface, causing very explosive eruptions. D) The loss of life in the 1980 Mt. St. Helens eruption was much less than it could have been. What factors helped keep the loss of life relatively low? The eruption occurred on a Sunday morning: there were no loggers in the closed area as there would have been on a weekday (M-F). Also, a group of homeowners were on their way up the mountain - if the eruption had occurred ~1 hour later, they would have been killed. Version B 2 25% of the exam Part 2: Short Essay (Confine your answer to the space provided - more will NOT be read!) E) In 1991, pyroclastic flows on Mt. Unzen killed nearly 50 people, including several famous volcanologists. What exactly killed them? Why would they have thought they could have been safe? Be specific in terms of the various components of pyroclastic flows and how they are generated in the first place. Write neatly. They were killed by asphyxiation by a pyroclastic surge. The pyroclastic flows at Unzen were generated by a dome collapse. Pyroclastic surges are the light, gas-rich part of a pyroclastic flow that can separate from the denser part of the flow as it flows down the volcano. The dense parts of the pyroclastic flows travel down valley's, and people thought they were safe on the ridge. But pyroclastic surges can jump ridges.