Chapter 6 and 7 Flashcards
Review Questions
What are the two types of Volcano
Explosive / Effusive
Feature Explosive Effusive
Type of plate Continental Oceanic
Rock Type Felsic Mafic
Lava Viscosity High Low
(Does not (flows easily)
flow easily)
Silicon Content High Low
Amount of
Trapped gas High Low
Frequency
of eruption Rare Common
Duration of
Eruption Short Long
What controls the explosive nature of a volcano
The amount of silicon in the silicate minerals of the rocks.
The higher silicon minerals such a quarts produces a high viscosity lava (does not flow easily) when they melt. This thick, viscous lava traps a lot of gas (mostly water) there by creating high, potentially explosive pressure.
Why are Volcanoes so hazardous
Their explosive force.
The harmful gasses they release.
The tsunamis they can create either during or between eruptions.
The landslides, flows or falls they can cause during or between eruptions.
During the 1980 eruption of Mt. St Helen’s, in Washington States, geologists were, at first, not convinced the eruption was genuine. Why not? As time went by, they became convinced the eruption was genuine and that a major catastrophic event was imminent. What evidence was there to support this conclusion?
Cascade volcanoes, like St.Helen often emits gases especially in late winter and early spring, when snow on them begins to melt. Harmonic tremors, small earthquakes around the magma chamber also occur. In late 1990, 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 eruption was likely. What eventually convinced authorities that an eruption could be expected was ash on the snow around the vent on top of the volcano.
This confirmed a direct link between the surface and the magma chamber and that pressure inside the volcano had reached dangerous levels.
What is a flood basalt and why is it so hazardous?
Large, effusive out pourings of mafic lava that covers a very large area of the earth’s surface. These eruptions can last thousands of years.
While this outpouring of lava is catastrophic for the immediate area, there is a much greater hazard.
The sustained release of volcanic gases, in particular CO2, can change the atmosphere and oceans.
Increased CO2 in the atmosphere will raise air temperatures and the lowering of PH of ocean waters.
The formation of the siberian traps, huge flood basalt deposits at the end of the permian period, is thought to be the cause of the largest 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?
Exposure is high. Sensitivity is mixed. Vulnerability is higher than it should be.
What makes Naples worse, like it does other older European cities, is infrastructure.
Old less stable buildings, lack of streets, narrow streets, and lots 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?
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 in ice.
What kind of hazard is associated with a tuya volcano?
The force of the eruption as well as the large flood of water that may result if the glacier melts. This may result in a lahar, a mudflow associated with volcanic eruption.
