The public was shocked by the extent of the eruption, which had lowered the elevation of the summit by , destroyed of woodland, and spread ash into other states and Canada. The lateral blast that killed Johnston started at a speed of and accelerated to . Even USGS scientists were awed. With a Volcanic Explosivity Index value of 5, the eruption was catastrophic. More than 50 people were killed or missing, including Johnston, mountain resident Harry R. Truman, photographer Robert Landsburg, and "National Geographic" photographer Reid Blackburn.