Helping Aubie this week is Dr. Robert B. Cook, a professor of geology at AU.

Dear Addison,

     Everyone who has seen a videotape of a volcanic eruption, or better yet, witnessed one in person knows that there is an enormous amount of heat involved.  Volcanoes occur where there is an unusual amount of heat relatively near the earth’s surface. This heat is enough to melt rock producing what is called “magma,” the lava of an eruption. This molten rock does not reach the surface by virtue of its heat alone. There is pressure involved, a very large amount necessary to push what are commonly huge masses of rock material upwards.  This pressure is related to the formation of large amounts of steam by the vaporization of water at high volcanic temperatures. It is this steam, seeking a lower pressure environment such as the earth’s surface that forces the magma upwards, ultimately causing the eruption. So, that smoke we see associated with volcanic eruptions is usually not smoke from something burning but actually steam, usually containing tiny pieces of ash. The temperature of the magma, the size of the underground chamber containing it, its closeness to the surface, the amount of available water, the type of channel to the surface, and many other factors determine the type of eruption. These can vary dramatically from those that are relatively quiet and little more than the slow, but persistent flow of magma outward from a crack, or vent to those that are explosively violent.

      The most important questions of all are why volcanoes occur where they do and what the source of all that heat is.  Geologists know that they occur most frequently where broken fragments of the earths crust, commonly known as plates, meet one another. Such a boundary is that generally forming rim around the Pacific Ocean. This region is known as the ring of fire because of the many volcanoes located there.  The source of the heat is still debated by scientists with explanations that are usually related to heat produced by decay of naturally occurring radioactive isotopes such as those of uranium.  Volcanoes are fun to study and for students contemplating a career as an earth scientist, a worthy target for specialization.    

Thanks for your question!

Aubie and Dr. Cook