Question

Which of the following is a true statement about lava that contains large amounts of dissolved gases? Lava that produces violent explosions is very viscous, which prevents the gases from escaping. When the lava does erupt, the dissolved gases escape to produce a violent eruption.
a) Lava of this type would not produce a violent eruption.

b) Lava of this type would not be viscous so the gas can escape.

c) The dissolved gases produce a violent eruption as they escape.

d) Both B and C

Answer 1

Answer:

The dissolved gases produce violent eruption as they escape.

Explanation:

Magma contains dissolved gases and these dissolved gases induce vapor pressure on the magma. The magma is able to remain in the dissolved state itself without erupting because this vapor pressure is less than the confining pressure of the rock surrounding the magma.

One the vapor pressure exceeds this confining pressure the dissolved gases begin to  expand and forms small gas bubbles.

The density of these gas bubbles called vesicles is less than the density of magma and thus naturally tries to push out. When the gas bubbles escape the magma is also pushed out. Thus greater amount of dissolved gases result in violent eruptions.

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