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a mudflow associated with a volcanic eruption.


1. What are the two types of volcano?

Effusive and Explosive


2. Why are volcanoes so hazardous?

1. Their EXPLOSIVE force
2. The harmful GASES they release
3. TSUNAMIS they create either during or between eruptions
4. The LANDSLIDES, FLOWS OR FALLS they can cause during and between eruptions


2. What controls the explosive nature of a volcano?

The explosive nature of a volcano is controlled by the amount of silicon in the silicate mineral 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) thereby creating high, potentially explosive pressures


4. During the 1980 eruption of Mt. St. Helens, in Washington State, geologists were not convinced the eruption was genuine at first. 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 Mt. St. Helens often emit gases, especially in late winter and early spring.

Harmonic tremors small earthquakes around the magma chamber also occur, so this wasn't uncommon.

As time passed however, 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 pressures inside the volcano had reached dangerous levels.


5. What is a flood basalt?

These are large, effusive outpourings of mafic lava that cover a very large area of the Earth's surface.

These eruptions can last thousands of years.


5. Why are flood basalts so hazardous?

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 pH (acidity) of ocean water.

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.


6. 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.

Mt. Vesuvius is a a stratovolcano 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 for 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.


7. How does a Tuya volcano form?

Formed beneath the ice after the glacier has formed.


Formed before glacation and have since been covered in ice.


8. What kind of hazard is associated with a tuya volcano?

force of the eruption
large flood of water that may result if the glacier melts

(may result in a lahar, a mudflow associated with a volcanic eruption.)


1. Explosive Volcano Characteristics (8)

Example: Mt. St. Helens
Type of Plate: Continental
Type of rock: Felsic
Lava Viscosity: High
Silicon Content: Higher
Amount of trapped gas: High
Frequency of eruption: Rare
Duration of eruption: Short


1. Effusive Volcano Characteristics (8)

Example: Hawaii
Type of Plate: Oceanic
Type of rock: Mafic
Lava Viscosity: Low
Silicon Content: Lower
Amount of trapped gas: Low
Frequency of eruption: Common
Duration of eruption: Long


Volcano defining factors (mark's table)

Type of Plate
Type of Rock
Lava Viscosity
Silicon Content
Amount of trapped gas
Frequency of eruption
Duration of eruption


Tuya volcano

A volcano in a mountainous area that is partially or completely enclosed by glacial ice.


Siberian Traps.

Huge flood basalt deposits at the end of the Permian Period.

Thought to be the cause of the largest mass extinction on Earth.