Snow surveys and Mount Saint Helens

On March 27, 1980, the first tephra eruption in approximately 123 years dusted the snowpack of Mount St. Helens, Washington. Within two weeks, special snow surveys were being conducted to assess the effects of tephra deposits on the snow. Preliminary evidence indicated there were substantial changes in snowmelt characteristics as a result of varying tephra thichnesses. On May 18, 1980, a catastrophic explosive eruption destroyed much of the residual spring snowpack. The snowpack outside the devastated area, and at higher elevations, was blanketed by a thick layer of tephra. The effect was a substantial reduction in snowmelt rates. Automated snow measuring equipment recorded preblast melt rates, the accumulation of tephra on the pack, and the subsequent rate of melt. During the fall of 1980, one destroyed data site was reestablished and three new sites installed. Now a total of seven snow monitoring sites automatically monitor snowpack conditions on the watersheds around the volcano. The data from these snowpack measuring sites are used in forecasting snowmelt volumes and streamflow rates for agricultural and power generation use, as well as flood warning.