Points Earned: 1/1 Correct Answer: E Your Response: E 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? A. Pyroclastics, including bus-sized pieces that could fall on people’s heads and kill them. B. Tsunamis, or giant waves, that could drown people, if the volcano is in the ocean or a very large lake and the eruption moves a lot of water out of the way. C. Climatic warming, with the volcano causing a sudden heat wave that would harm people living in big cities. D. Mudflows and landslides that could bury people and buildings. E. Poisonous gases, that could kill people who breathe them in. This is one of those interesting cases where “slow” and “fast” are different. Volcanoes release carbon dioxide, and carbon dioxide warms. But carbon dioxide stays up a long time, and no single volcanic eruption puts up enough carbon dioxide to make a detectable difference to the concentration in the air and the temperature of the Earth. However, a single big eruption can put enough material into the stratosphere to block enough sunlight to cool the Earth by a degree or two for a year or two. So the climatic hazard from a single big volcanic eruption is cooling, not warming. Explosive volcanoes are often large and steep, and may have huge glaciers. As heat melts the ice, and as melted rock moving into the volcano bulges the sides, huge landslides and mudflows happen. Tens of thousands of people have been killed in single mudflows. Well over 100,000 people live on the deposit from one old mudflow from Mt. Rainier (and those who know about that Osceola Flow really hope it doesn’t happen again!). A tsunami is a big wave, caused by an earthquake, landslide, meteorite impact, or volcanic eruption that displaces sea water. Waves can be 100 feet high or more, and do incredible damage. A big eruption underwater can push a lot of water out of the way, making a tsunami. Pyroclastic flows are major volcanic hazards, and can kill lots of people quickly. Imagine a few-hundred- degree mixture of pulverized rock, glass and poison gas chasing you at a few hundred miles per hour! Volcanoes do put out poison gases, such as hydrogen sulfide or carbon dioxide (a little is good; too much is deadly!). When rocks melt a little, fluid- and gas- making materials preferentially end up in the melt rather than in the remaining rock, so eruptions commonly come with gases, and some of those gases are of types or in concentrations that are not good for nearby humans.
Points Earned: 0/1 Correct Answer: C Your Response: D 14. The pictures show famous volcanoes, that we discussed in the class materials.
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