Ch 6. & 7 - Volcanoes Flashcards
(8 cards)
What are the two types of volcano?
- Example - Explosive: Mt St. Helens, Effusive: Hawaii
- Type of plate - Ex: Continental, Ef: Oceanic
- Rock type - Ex: Felsic, Ef: Mafic
- Lava viscosity - Ex: High (does not flow easily), Ef: Low (flows easily)
- Silicon content - Ex: higher, Ef: lower
- Amount of trapped gas - Ex: high, Ef: low
- Frequency of eruption - Ex: rare, Ef: common
- Duration of eruption - Ex: short, Ef: long
What controls the explosive nature of a volcano?
The explosive nature of a volcano is controlled by the amount of silicon in the silicate minerals in the rocks. The higher silicon content in felsic minerals such as quartz produces a high viscosity lava. When they melt, this thick, viscous lava traps a lot of gas (mostly water) there by creating high, potentially explosive pressures.
Why are volcanoes so hazardous?
Volcanoes are hazardous because of: 1. their explosive force, 2. the harmful gases they release, 3. the tsunamis they can create either during or between eruptions, 4. the landslides, flows or falls they can cause during and between eruptions.
During the 1980 eruptions of Mt. St. Helens, in Washington States, geologists were, at first, not convinced the eruption was genuine and that a major catastrophic event was imminent. What evidence was there to support this conclusion?
Mt St. Helen erupted May 18 1981. Cascade volcanoes, like St. Helen, often emit gases, especially in late winter and early spring when the snow on them begins to melt. Harmonic tremors, small earthquakes around the magma chamber also occur. In 1980 none of these caused any alarm yet. As time passed and more attention was paid to this volcano there were more and more signs that a major eruptions was likely. What eventually convinced authorities that a eruption could be expected was ash on the snow around the vent on top of the volcano. A) this confirmed a direct link between the surface and the magma chamber and that pressures inside the volcano had reached dangerous levels.
What is a flood basalt and why is it so hazardous?
Flood basalts are large, effusive out pouring of mafic lava that covers a very large area of the earths surface. These eruptions can last thousands of years. While this out pouring of lava is catastrophic for the immediate area there is a much greater hazard. The sustained release of volcanic gases, in particular CO2 in the atmosphere will raise air temperatures and the lowering of PH (acidity) of ocean water. This formation of Siberean Trops, huge flood basalts deposits at the end of the Permion period is thought to be the cause of the longest mass extinction on earth.
Discuss the problems associated with an actual or impending eruption of Mt. Vesuvius, Italy and the need to protect the civilian population who live in the area?
A strato volcano with a long, recorded history of very violent eruptions. Naples is a large, old city surrounding much of this volcano. Exposure is high, sensitivity is mixed. So vulnerability is higher than it should be. What makes Naples worse, like it does other older European cities, is the infrastructure. Old, less stable buildings, lack of streets, narrow streets and a lot of people crowded into a small area make evacuation before a catastrophe and response during one more difficult.
What is a “tuya volcano” and how is it formed?
Tuya volcano is a volcano in a mountainous area that is partially or completely enclosed by glacial ice. These volcanoes may form beneath the ice after the glacier has formed. They may also have formed before glaciation and have since been covered by ice.
What kind of hazard is associated with the tuya volcano?
The hazard associated with a Tuya volcano is not only the force of the eruptions but also the large flood of water that may result if the glacier melts. This may result in a lahar, a mud flow associated with a volcanic eruption.
