An incursion of dust in the southwestern United States from April 1980 eruptions of Mount St. Helens

An intrusion of volcanic dust occurred over the northern Mojave Desert, one month before the explosive eruption of 18 May 1980. Visibility was reduced to 15 to 30 miles during meteorological conditions that should have yielded a visibility in excess of 100 miles. This intrusion was documented by particle size distributions, scanning electron microscope analysis of Nuclepore filter samples, insolation measurements, observations by Navy and NASA aircraft, and meteorological data. No further incidents have been observed to date because of a lack of simultaneous volcanic activity with the particular wind patterns that existed in April. Therefore, under certain meteorological conditions, the desert of the southwestern United States could be significantly affected by volcanic ash from an eruption of Mount St. Helens.