Volcanic ash is as soft as baby powder, if baby powder were made of microscopic shards of glass. I was living in Portland, Oregon, in 1980, when Mt. St. Helens erupted. The first belch from the mountain sent all of its force and flotsam north and east, away from Portland; the second caught a westerly wind, and the ash drizzled down on the city. The day of the second eruption, I was at the Portland Art Museum, watching the epic, gloomy seven-hour Hans-Jürgen Syberberg film "Hitler: A Film...