Volcanoes

Question 1

Describe the distribution of volcanoes globally

Answer 1

Generally, volcanoes are located along plate boundaries, with a high concentration (90%) on the pacific rim e.g Indonesia. An anomali is Hawaii, located in the middle of Pacific plate.

Question 2

Describe decompressional melting

Answer 2

1) Convection currents pull the plates apart
2) Crust & upper mantle becomes thinner due to tensile stress
3) Mantle that is already at melting point, is under less pressure, so melts
4) Less dense and rises through weakensses created in the crust.

Question 3

Describe heat addition

Answer 3

In a mantle plume, which is formed by an abnormally warm sections of the outer core. This pushes the mantle way past its melting point

Question 4

Describe volatile addition

Answer 4

• Volatile compounds are gases e.g: CO2, SO2 H2O

As subduction occurs, sedimentary rocks release volatiles into the crust
- Melting point decreases (e.g water decreases to 800*C at 100km)
- Crust melts and mixes with mantle (Crustal assimilation)
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Question 5

What factor causes volcano explosivity?

Answer 5

Silica content (highest with Rhyolytic) (65%)