What do volcanoes do when they are not busy erupting? Researchers from Italy and Ecuador have recently discovered that these huge buggers are really composing music, much in the vein of Iannis Xenakis. Honestly, these scientists are just tired of looking at numbers and graphs all the time, so they turned seismographic patterns into musical scores and then play them using a cheap MIDI interpreter. There are two volcanoes to compare here, Mt. Etna (MP3 sample) in Italy and Tungurahua (MP3 sample) in Ecuador. Domenico Vicinanza, the guy who started the whole thing, then got carried away and remixed one of the Etna composition for synthesizer (MP3). There is a little more background on this website.
You can also listen to some Alaskan volcanoes on-line, though these are only pitch-shifted original volcano rumblings, not transformed into MIDI synth splendor.
The scientific term for the whole process is sonification, and if you are bored or looking for grant money, you can really sonify any data set, be it radiation intensity (MP3 sample) or web server activity (MP3 sample).
Best of all, volcano sonification is a fail-proof indicator of imminent eruptions: If your next-door volcano starts to sound like Liberace, you better start moving.