A useful fact sheet from the USGS on the wonders of volcanic ash. (Thanks to reader MG in Hawaii.) Graphic of the ash fall from the Mount St. Helens eruption thirty years ago, and likely ash patterns of past eruptions in the western United States:
On effects of the ash as it drifts down:
Volcanic ash can cause internal-combustion engines to stall by clogging air filters and also damage the moving parts of vehicles and machinery, including bearings and gears. Engines of jet aircraft have suddenly failed after flying through clouds of even thinly dispersed ash....Cars driving faster than 5 miles per hour on ash-covered roads stir up thick clouds of ash, reducing visibility and causing accidents.
Ash also clogs filters used in air-ventilation systems to the point that airflow often stops completely, causing equipment to overheat. Such filters may even collapse from the added weight of ash, allowing ash to invade buildings and damage computers and other equipment cooled by circulating outside air. Agriculture can also be affected by volcanic ash fall. Crop damage can range from negligible to severe, depending on the thickness of ash, type and maturity of plants, and timing of subsequent rainfall. For farm animals, especially grazing livestock, ash fall can lead to health effects, including dehydration, starvation, and poisoning.
Today's big-picture point: the reminder that a development no one would have included in a "problems to worry about" or "events that will shape the news" list for 2010 may end up having profound economic and other effects.
Update-update: An interesting hour-by-hour animation of the plume's initial dispersion, from the European Space Agency, here. Thanks to reader RG. Also my discussion yesterday with Guy Raz, on Weekend All Things Considered, here.