Guide to Geologic Hazards in Alaska

Volcanic gas
Volatile matter, released during a volcanic eruption, that was previously dissolved in the magma. (Neuendorf, K.K.E. and others, 2005)
Volcanic vents often emit steam and gases, including hydrogen sulfide and carbon dioxide, in concentrations that are potentially harmful to humans. Lava flows and pyroclastic flows also emit large amounts of steam and gas. Dangerous invisible, odorless volcanic gases can collect in low-lying areas near fumaroles, making it inadvisable to descend into craters, caves, or fissures occupied by fumaroles." href="/pubs/id/7042">(RI 2004-3)