Alan Hovhaness - Symphony No.50 ("Mount St. Helens")
Alan Hovhaness (1911-2000) was an Armenian-American composer, whose works often have exotic influences. His rather conservative style, combined with a large number of compositions (e.g. 67 symphonies), have not made him popular with critics, but there are many gems in his repertoire. My favourite is the Symphony No.50 ("Mount St. Helens"), op.360, from 1982. It was inspired by the 1980 eruption of that mountain. Relevant links below.