The Collaborative International Dictionary of English v.0.48:

Vulcanology \Vul`can*ol"o*gy\, n. [See Vulcan, and -logy.]
   The science which treats of phenomena due to plutonic action,
   as in volcanoes, hot springs, etc. [R.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

vulcanology
    n 1: the branch of geology that studies volcanoes [syn:
         volcanology, vulcanology]