Why doesn't the lava melt through the sides of the volcano?
Bnunn
Hi Bnunn,
Flowing lava actually can melt through the sides of a volcano but it is a
very very slow process. The main reason is that the volcano itself is
(of course) also made of lava (and ash). The important thing is that the
lava has to melt the solid form of itself. If the lava was super super
hot, meaning that it was way above the melting point of rock, then it
would be easy to melt through. Actually, rock has a melting RANGE rather
than a melting POINT. That is because it is made up of more than one
mineral, each with a different melting point (in truth each of them has a
melting range as well, but that's getting too far from the point).
Anyway, because it gets cooled as it rises to the surface, erupted, and
flows across the ground, lava is almost always within its melting range
rather than above it. That means that it may be able to melt some of the
minerals in the pre-existing rock (the volcano) that it is flowing over,
but probably not all of them. Only if the lava flows in the same place
for days to weeks (such as in a lava tube or channel), will it be able to
heat the underlying rock to the point that it starts to soften.
I guess you might be able to demonstrate this yourself, but I've never
tried this. Ice is frozen water so you might think of water as the lava
and ice as the solid volcano. If you pour hot water over ice it will cut
a channel easily, but that is cheating. Try pouring ice water over a big
block of ice--that will be closer to the lava-flowing-over-rock
situation. I think you'll find that if it starts to cut a groove at all,
it will happen very slowly.
Hopefully this will help to answer your question. It is a question that
lots of people ask and also one that is not easy to answer.
Sincerely,
Scott Rowland
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