Unmanned aerial sampling of a volcanic ash cloud

On September 17, 1992, Alaska's Mount Spurr erupted for the third time in 12 weeks. The eruption cloud drifted east and south across Canada and reentered U.S. airspace over the upper midwest (Figure 1). By the morning of September 20, the cloud had moved northeast out of U.S. domestic air corridors and had begun to disperse. Canadian aviators were advised of thecloud position by Transport Canada, and no damaging encounters with ash occurred. But upon reentering U.S. airspace, the cloud had a major impact on air traffic despite the 4000-km distance from the volcano.