We've seen some news footage the past couple of days showing folks in Alaska cleaning up ash deposited in the wake of eruptions by the Redoubt volcano there, and it can not be any fun to deal with that (imagine the worst of our pine pollen season, but sometimes inches thick and considerably more abrasive!).

Another major volcanic ash issue is how it can affect aircraft in flight. The effects can range from abrading the outside of the aircraft to clogging instrument intakes, to being ingested in the engines and causing total loss of power. I can remember briefing Air Force pilots on the expected locations of plumes when I was a military forecaster, and apprising aircrews and flight planners of locations to be avoided remains a very important function to this day.

To accomplish that mission, the entire world is covered by a system of Volcanic Ash Advisory Centers, made up of components of several of the world's national meteorological organizations. Each center is responsible for a portion of the earth that is subject to volcanic eruptions, and uses surface observations, satellite imagery and computer modeling to apprise their users of the geographical locations and altitudes of volcanic plumes.

The attached link to the Australian Bureau of Meteorology's Darwin VAAC includes a nice write-up on the hazards of volcanic ash to aviation, and a clickable map with links to all the worldwide VAACs. I also included a link to a National Oceanic and Atmospheric Administration / Air Resources Laboratory site, where you can find hypothetical plots that answer the question "where would the plume from Volcano "X" go if it erupted today?" with a series of maps showing calculated plume projections. Finally, the image you see is a satellite photo from a few days ago that illustrates how high that Redoubt cloud was (it cast a very long shadow on other clouds below).