What remains to be discovered for future earth scientists what we (still) don't know about earth? What are the geological riddles that still lack answers - all questions are allowed - it could be a local anomaly, or a global phenomena, or something strange...(Naturally you can also include a possible answer to your problem).

Early scientists thought that volcanoes were the homes of gods, or passages to Hell, or conduits for a vast network of subterranean fires. (At left is Athanasius Kirchner's 1664 engraving of the interior of Mount Vesuvius, from his book Mundus Subterraneus. Image from Art.com.) These ideas have all fallen by the wayside, but volcanologists today are still trying to work out the details of volcano 'plumbing', as it's commonly called.
This is no easy task. For one thing, there are many different kinds of volcano; it stands to reason that they're not going to have similar plumbing systems or structures. For another, if you're interested in what's going on inside an active volcano, it's understandably a little difficult to get close enough to the object in question to even begin to work on the question.
So how do volcanologists know anything at all about the interior of volcanoes - and how can they find out more?

Another way is to use geophysical or remote sensing methods. Volcano seismology (including 3D seismic tomography, sort of a CAT-scan for volcanoes) has been used for years to locate and define the shapes of magma chambers under volcanoes, as well as the dikes and conduits which feed eruptions. For smaller edifices, methods such as ground-penetrating radar can give some idea of the shallow structure. Some researchers in Japan (Miyamachi et al., 1987) have even used explosions from fireworks to image the interior of lava domes (using the shock of the fireworks explosions to take the place of seismic shocks). GPS, ground tilt, and other deformation measurements give volcanologists an idea of how a volcano changes shape and volume, and from that some idea of the internal workings of the volcano can be discerned.
One interesting study by researchers in Japan (Sakuma et al., 2008) details a project where volcanologists actually drilled into an active volcano - Mount Unzen, which last erupted in 1996 and produced a summit lava dome. The Japanese volcanologists found a conduit with several feeder dikes, showing that Unzen's eruption wasn't fed by a single tube but several, and possibly from many sources. Still, this is only a small part of the volcano, and it's a very expensive and tricky way of finding things out.

And hey, maybe I'm being pessimistic and someone will invent a whole-body-scan for a volcano. It could happen...
Additional reading:
Keating, G.N. et al., 2008, Shallow plumbing systems for small-volume basaltic volcanoes. Bulletin of Volcanology, v. 70, p. 563-582.
Miyamachi, H. et al., 1987, Seismic experiments on Showa-Shinzan lava dome using firework shots. Pure and Applied Geophysics, v. 125, no. 6, p. 1025-1037.
Poland, M.P. et al., 2004, Patterns of magma flow in segmented silicic dikes at Summer Coon Voclano,Colorado; AMS and thin section analysis. Earth and Planetary Science Letters, v. 219, p. 155-169.
Sakuma, S. et al., 2008, Drilling and logging results of USDP-4; penetration into the volcanic conduit of Unzenvolcano, Japan. Journal of Volcanology and Geothermal Research, v. 175, p. 1-12.
4 comments:
As I started reading your post, I was wondering if seismic tomography had been used on volcanoes. I'm sort fascinated to read that it has. Is the resolution fine enough to get the kind of detail volcanologists want?
Well, you can't really see things like dikes or small magma pockets - it seems to work best for big hot things, like magma chambers. But there's some touchy math involved, and it's hard to resolve images even when things are big...
Wait, did Gordon Keating leave LANL and move to Buffalo? (I went to college with him. Great guy.) Or is one of the co-authors (hidden in the "et al.") your advisor?
Nope, but one of his colleagues (Greg Valentine) did. Greg's on my committee, and we got to see lots of Keating collaborations in the volcanology class that he co-taught last year.
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