The May 18, 1980 eruption of Mount St. Helens in Washington. Photo by USGS. Next year will be the 35th anniversary of one of the largest eruptions to occur on U.S. soil since the nation was founded: the May 18, 1980 eruption of Mount St. Helens. It always amazes me how much our coverage of volcanic eruption has changed in that time as there is not a single video or film of the eruption.