As the title suggests, this piece is programmatic and is supposed to portray the large volcano in Italy of the same name.
The introduction don't consist of traditional melodies but contains a mixture of separate motives by certain instruments that occur at different times. This immediately gives the piece a feeling of disorginization that one would associate with a volcano.
The main melodic theme of this song is wonderful. The time signature is in 9/8 but rather than being in a triple meter, it is in a mixed meter that sounds like 4/4 with an extra eighth note on the second beat. This gives the piece a very unsteady yet funky feel.
The piece then proceeds into woodwind solos which are most likely trying to evoke some sort of sound associated with the ancient Greeks. It sounds to me like it has a pentatonic or modal feel rather than traditional harmonies. This part does sound really pretty and is probably meant to be the calm before the eruption.
Then when the fast section comes back in, the main melody is elaborated by, or should I say interrupted by woodwind sixteenth note runs and ratchet which adds to the unsteadiness and gives the feeling that an explosion is happening. After this, Ticheli takes two of the earlier melodies and puts them together to create a polyphonic structure that adds more tension.
After going back to another section of separate instrumental motives mixed together, the piece reaches a very beautiful fugue of the main melody that is at least 5 instruments deep. In addition to the number of instruments, it is also interesting to note that each new instrument enters at the beginning of the fourth bar of the eight bar phrase rather than the expected fifth. The fugue is a wonderful way to build up complexity and make a great crescendo.
A timpani solo leads into the final hoorah, which has the interuppted melody again which is followed by another crescendo into brass glissandos first on the quarter notes and then on quarter note triplets, followed by high woodwind trills and one last rhythm enforcement of the melody to the end.
The appeal of this piece is the excitement and the instability. The rhythmic meter and instrument separation contribute a lot to this, but it's the fugue which really makes this piece stand out.