Guide to Geologic Hazards in Alaska

Ash cloud
A cloud of volcanic gases, with ash and other pyroclastic fragments (tephra), that forms by volcanic explosion; Syn: explosion cloud; ash cloud; dust cloud [volc]; volcanic cloud; volcanic plume. (Neuendorf, K.K.E. and others, 2005)
A principal hazard associated with explosive eruptions is the generation of clouds of pulverized rock debris, pumice, volcanic ash, and gas which are blasted high into the atmosphere and then drift away from the volcano with the wind. Ash-rich clouds produced during large eruptions can reach heights of 10 to 20 kilometers or more above the volcano. All aircraft should avoid flying near ash clouds, as contact with ash can damage aircraft windows and instruments, clog air vents, and shut down jet engines. (RI 2004-3)