Video: 'Photographing a Catastrophic Explosion at Mt. St. Helens'

(Sunday, May 18, 1980, 8:32:17 a.m. PDT; during the 1980 eruption of Mount St. Helens) — The Mount St. Helens volcano in southwestern Washington state exploded this morning, blowing the top off the mountain and killing 57 people.

An earthquake caused the entire weakened north face to slide away, creating the largest landslide ever recorded. This allowed the partly molten, high-pressure gas- and steam-rich rock in the volcano to suddenly explode northwards toward Spirit Lake in a hot mix of lava and pulverized older rock, overtaking the avalanching face.

An eruption column rose 80,000 feet into the atmosphere and deposited ash in 11 U.S. states and significant ash in two Canadian provinces.

Video: 'Minute by Minute: The Eruption of Mount St. Helens' (May 18, 1980, at 13:36)

At the same time, snow, ice and several entire glaciers on the volcano melted, forming a series of large lahars (volcanic mudslides) that reached as far as the Columbia River, nearly 50 miles to the southwest.

Approximately 57 people were killed directly, including innkeeper Harry R. Truman, photographers Reid Blackburn and Robert Landsburg, and geologist David A. Johnston.

Hundreds of square miles were reduced to wasteland, causing over $1 billion in damage (equivalent to $3.4 billion in 2019), thousands of animals were killed, and Mount St. Helens was left with a crater on its north side.