On this day in 1980, Mount St. Helens volcanically erupts in a major geologic event still holding various records for severity. Located in Skamania County, in the State of Washington, the eruption (a VEI 5 event) was the most significant volcanic event to occur in the contiguous 48 US states since the 1915 eruption of Lassen Peak in California.
It has often been declared as the most disastrous volcanic eruption in US history. The eruption was preceded by a two-month series of earthquakes and steam-venting episodes, caused by an injection of magma at shallow depth below the volcano that created a large bulge and a fracture system on the mountain’s north slope.
Following an earthquake at 8:32:17 a.m. PDT (UTC−7) that Sunday the 18th, the entire weakened north face slid 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.
The eruption column rose 80,000 feet, or 15 miles into the atmosphere, and deposited ash in 11 states and British Columbia. 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.
Upwards of 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 a billion US dollars in damage ($3 billion in 2018 dollars), thousands of animals were killed, and Mount St. Helens was left with a crater on its north side. Owned by Burlington Northern Railroad at the time of the disaster, the area was later preserved, as is, in the Mount St. Helens National Volcanic Monument as a parcel of the US Forestry Service.
Since New Years Day 2018, Mount St. Helens has experienced 40 earthquakes within its vicinity as aftershocks continue every few hours. The most powerful earthquake January 3 had a magnitude of 3.9 that occurred around midnight west coast time about 5 miles from Mount St. Helens and 23 miles from the town of Morton.
On a less optimistic note, St. Helens and the region sit in the Cascadia Subduction Zone, a fault line deep in the belly of the planet under the Pacific Ocean. It’s gargantuan size and potential power amaze earthquake experts, who say it could cause the worst natural disaster in the history of North America. If the Cascadia were to experience a large-magnitude earthquake and rupture, the temblor and resulting tsunami could kill more than 13,000 people, injure more than 26,000, and displace or disrupt nearly 3 million, according to one FEMA model.
So there’s that.