May 18, 1980, was a remarkable day for me and almost every geologist I know. We identified with David A Johnston, the geologist killed in the volcanic event. The explosion and subsequent landslide of the north face of Mt. St. Helens in Washington state, USA, was top news throughout that day and ensuing weeks and months.
The USGS put together still photos to create this video of one of the largest (if not the largest) landslides ever on earth.
Individual trees in the direct path of the blast were charred. . .
Downed logs still remain as in this 2012 photograph:
An earthquake at 8:32 a.m. local time on Sunday, May 18, 1980, caused the entire weakened north face to slide away. This suddenly exposed the partly molten gas- and steam-rich rock in the volcano to lower pressures. The rock responded by exploding a hot mix of lava and pulverized older rock toward Spirit Lake so fast that it overtook the avalanching north face.
An eruption column rose 80,000 feet into the atmosphere and deposited ash in 11 U.S. states. A USGS friend brought back vials of varying sized ash collected after the explosion.
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.
and trees were caught up in the mudflows.
What are your memories of that day? Were you nearby, perchance?
Steph
