Muon It on Over

While it's important to know what goes on inside a volcano, it's pretty darn difficult to get one to come by the doc's office for a checkup. That makes it tough to x-ray the thing, and although the Transportation Security Administration swears its scanner machines don't show your face to the people they let see you naked, volcanoes are apparently having none of that either.

So enter the muons. Literally. Muons are subatomic particles that pass through most things because they are so very small that even what we call solid objects are more like empty space to them. They're set free when cosmic rays strike other atoms and break them up -- which is not what Stan Lee and Jack Kirby told us that cosmic rays can do, but the real world sometimes just doesn't recognize a great idea when it sees one.

After being liberated from the oppressive power structure of their former atom (#OccupyNucleus), muons sail along their merry way until they strike another atom. As mentioned above, that doesn't happen very often because of the small size of the particles involved, but there are enough muons movin' on that they can be tracked and the rate of this interruption can be measured. Denser materials stop more muons (Washington, D.C. is pretty much a muon-free zone), so the muon detectors get a kind of a picture of what something looks like by imaging the denser and less dense areas. This is pretty much exactly how an x-ray machine works.

In volcanoes, the liquid magma is denser than the solid mountain because it is under pressure. Muon detectors can track more or less where the magma is inside the volcano and see if it is close to the surface or if it is flowing near weaker spots in the volcano's rock. If it is, then folks living nearby can be alerted to have their bags packed and fire insurance updated.