Mount St. Helens Volcano, Cascade Range, Southern Washington, U.S.A. (46.20°N, 122.18°W). All times are local (GMT-7 hours). The devastating May 18th eruption of Mount St. Helens was followed by explosions on May 25 and June 12 that were much smaller but produced substantial ashfalls over wide areas of Oregon and Washington. A series of explosions ejected tephra from Mount St. Helens during the evening of July 22, nearly 6 weeks after the June 12 activity. Eruption cloud heights were similar to those of May 25 and June 12, but ashfall thicknesses were significantly less.