The Mount St. Helens volcanic eruption is the most famous volcanic eruptions in US history. The eruption and ensuing pyroclastic flow killed 57 people and dropped the elevation of the summit more than 1300 feet. The amount of ash debris was almost 1 cubic mile in volume. Imagine a box a mile on each side? That's alot of material. A look at Mount St. Helens before the eruptions.
What about the phrase "pyroclastic flow". What does this mean? It is term describing the flow of hot gas and collective material from the volcano that flows down the side of the mountain. It can reach speeds of 450 miles per hour and temperatures of close to 2000 degrees and has been know to cross bodies of water for miles. Its these pyroclastic flows that cause the majority of the damage in volcanic eruptions. A look a year after the eruption. Notice the crater in the middle.
A satellite timelapse over the last 30 years showing the evolution of the mountain since the eruption.
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