I don't understand what in the earth's crust causes volcanoic
activeity. And what in the world is the differance between intrusive and
extrusive?
Greenboa
Hi Greenboa,
Intrusive refers to igneous rocks that solidify beneath the surface of the
earth, and extrusive refers to those igneous rocks that manage to make it
to the surface. As you can imagine, intrusive rocks tend to cool and
solidify slowly since they're down where it is hot. Thus they tend to
have larger mineral grains (such as granite and gabbro). On the other
hand, extrusive rocks rather suddenly find themselves out on the surface
where it is relatively cool. They thus cool quickly and tend to have
small mineral grains, sometimes so small that your eyes can't see them.
Basalt is a good example of this.
As for volcanic activity from the crust, I'll send you an answer to an
almost identical question from a couple days ago. I hope you don't mind a
used answer.
Sincerely,
Scott Rowland
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