Mt St Helens 1980

USGS were monitoring Mt. St. Helens in the lead up to its eruption. A magnitude 4.2 earthquake on March 20, 1980 provided the first indication that Mt. St Helens was becoming active (Tilling, 1984). Several hundred earthquakes were recorded in the days following. Intermittent steam and ash eruptions occurred from the 27th March and through to April and on the 3rd April the Governor of Washington, Dixy Lee Ray, declared a state of emergency.

Appropriate evacuation decisions were made for 35 locals in the settlement at Spirit Lake and an exclusion zone formed (Wilson et al., 2012a). On April 30th, geologists monitoring the lava dome bulge formation noted a landslide could trigger a lateral blast eruption. On the 18th May, an earthquake on the northern flank induced a colossal landslide traveling north, directly into the path of the USGS observation post and killing a USGS volcanologist David Johnston.

Ash removal was a monumental endeavor. It was estimated 900,000 tons of ash was removed from highways and airports in Washington alone. It costs $2.2 million USD and took 10 weeks to complete ash removal in Yakima, Washington.

Ash disposal sites were selected based on proximity and ability to clean up ash as quickly as possible. Some areas used old quarries, while others using existing dumps. To prevent remobilization of this stored ash, topsoil and grass were placed on top.