Ask A Scientist General Science Archive

Question:  One of my 3rd graders asks, What makes a Volcano erupt?
 david ptasnik

Answer:  I'm no geologist, but I'll try to answer.
The part of the earth we walk on is a thin sort of "skin"
called the crust (like an ant might walk on the skin of
a peach, we walk on the crust of the earth). Underneath the crust
there are pools of hot, liquid rock. This is because the inside
of the earth is VERY HOT and some of that heat melts rock, which
can be forced to ooze up near the crust.  When too much hot,
liquid rock (called magma) pours into one place below the
earth, the pressure has to be released. If the crust near
that point is weak, the pressure forces the magma up through the earth
and it explodes upward. The magma comes oozing out of the hole and
(and we call the hot liquid rock "lava" when it's up on the surface)
and eventually cools and solidifies. When this happens many times,
eventually a mountain of the cooled rock forms with a hole
at the top where the magma keeps coming out; this is a volcano.
And every time the pressure builds up below and forces magma up
through the top of the volcano, we say that it has erupted.

Hope this answers your question -

-dr topper