Question

which occurs just before a volcanic eruption?
lava flows onto the sides of the volcano.
the expanding gases push magma through the pipe.
a pocket of magma forms beneath the volcano.
new rocks are formed as lava hardens.

Explanation:

• Lava flowing onto the sides of the volcano occurs during an eruption, not just before.
• When a pocket of magma forms beneath the volcano, it is an earlier stage in the process of magma accumulation, not the immediate precursor to eruption.
• New rocks forming as lava hardens is a post - eruption process.
• Just before a volcanic eruption, the expanding gases (which build up pressure as magma rises) push magma through the volcanic pipe (the conduit that connects the magma chamber to the surface).

Answer:

The expanding gases push magma through the pipe.