What can cause water to separate from a water-bearing basaltic magma to drive an eruption?
A) Injection of dry rhyolite magma into the basalt magma chamber from below can cause water to separate.
B) A decrease in pressure as the magma rises can cause water to separate.
C) Water streaming up into the magma chamber from the Earth's mantle can cause this.
D) Once water gets into a basalt magma, it can't separate.
E) Basalt magmas only erupt as lava flows; water is irrelevant.

Question

Quizplus · Accepted Answer

A decrease in pressure as the magma rises can cause water to separate from the magma. This is because as pressure decreases, water's solubility in the magma decreases, causing it to separate out as bubbles. These bubbles can then provide the driving force for an eruption. The other options are incorrect because dry rhyolite magma would not introduce water to a basaltic magma chamber, water streaming up from the mantle would not cause water to separate from the magma, once water is in the magma it can separate out, and basaltic magmas can also erupt explosively and not just as lava flows.

What Can Cause Water to Separate from a Water-Bearing Basaltic