Why are plug dome volcanoes considered dangerous? ...

[frankwu]

Why are plug dome volcanoes considered dangerous?

Question 2

What is the main factor that determines whether a volcanic eruption is explosive or effusive? How does that factor affect eruptions in this way?

[phuda]

Answer to Question 1

Plug domes form where extremely viscous silica-rich magma pushes up into the vent of a volcanic cone but does not flow further. Great pressures build up, producing the potential for extremely violent explosive eruptions, including pyroclastic flows.

Answer to Question 2

Viscosity is the main factor. Magma viscosity influences the explosiveness of a volcanic eruption through its effect on the dissolved gas content of the magma, which tries to escape the magma as the magma rises closer to the surface. Gases are not vented easily from more viscous magmas, allowing gas pressure to build.

[frankwu]

Excellent

[gcook]

Gracias!