Located in Southern Washington state, Mount St. Helens is part of the Cascade Volcanic arc, a ring of mountains across the Pacific Northwest that contains nearly 20 active volcanos. Having been silent for almost 130 years, it was not considered to be much of a threat to the surrounding area. But all that changed in the early spring of 1980.
A series of earthquakes and steam venting had brought attention to the mountain and with it, fears that an eruption was eminent. Throughout the month of April, the north side of the mountain began to bulge and infrared photography indicated that lava was beginning to build in the throat of the volcano and that an eruption was possible. At one point, a blue flame of burning gases was seen in a crater near the summit!!
The State ordered evacuations and while most people complied, there were a few that insisted on staying, including Harry Truman (no, not the former President), owner of the Mount St. Helens lodge which stood on the shore of Spirit Lake at the base of the North side of the mountain. Also remaining in the area were several photographers and geologists.
On the morning of May 18th the unthinkable happened. At 8:32 AM an earthquake occurred just below the surface of the North face of the mountain causing the entire face to slide. The resulting landslide was the largest in recorded history. Traveling at 125 miles per hour, it temporarily displaced the water in Spirit lake and caused a 600 foot tall wave of water to crash into the north shore of the lake.
While that was happening, the magma inside the volcano was exposed to much lower pressure and a series of explosions occurred as super-heated gases, ash, pumice and rock were directed up and out of the landslide, following it down the face of the mountain. Commonly referred to as pyroclastic flows, they reached nearly 670 miles per hour and destroyed everything in their path. The sure-heated flow caused the water in Spirit lake to instantly flash into steam and cause a secondary explosion that was heard as far away as northern California.
Trees in the path were flattened. Here's a picture of what had been a rather majestic forest only a few days before...
Approximately 57 people were killed, including Harry Truman and the others that stayed on the mountain to record what happened. To this day, the mountain continues to vent steam and ash. It still has a large lava dome inside its crater and could erupt again.
Here's a picture of the mountain the day before the eruption...
And here's a picture from the same location after the eruption....
That's nearly 1,300 feet shorter in less than 2 minutes with a 2,100 feet deep crater left behind.
And here's a video of the actual eruption put together from still photos of it as it occurred...
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