At 8:32 a.m. on May 18, 1980, a 5.1 magnitude earthquake struck under Mt. St. Helens. Within ten seconds, the bulge and surrounding area fell away in a gigantic, rock avalanche. The avalanche created a gap in the mountain, allowing the release of pent-up pressure that erupted laterally in a huge blast of pumice and ash. The noise from the blast was heard as far away as Montana and California; however, those close to Mt. St. Helens reported hearing nothing.
The avalanche, huge to begin with, quickly grew in size as it crashed down the mountain, traveling around 70 to 150 miles per hour and destroying everything in its path. The blast of pumice and ash traveled northward at 300 miles per hour and was a raging hot 660° F (350° C). The blast killed everything in a 200-square mile area. Within ten minutes, the plume of ash had reached 10 miles high. The eruption lasted nine hours.
Mt. St. Helens had been surrounded by a lush forest of coniferous trees and numerous clear lakes before the blast. The eruption felled entire forests, leaving only burned tree trunks all flattened in the same direction. The amount of timber destroyed was enough to build about 300,000 two-bedroom homes.
Logging companies have gathered many of the blown down trees, but mumerous trees are still laying all over the valley near the Johnston Ridge Observatory a stark reminder of the powerfull force that blew down and away all the trees, Johnston Ridge Observatory, Mt. St. Helens, Washington, USA