Mount St. Helens erupted 40 years ago today.*
That makes it sound like the mountain went from 0 to 60 on May 18, 1980, which is not true at all. The USGS had measured earthquakes in the area since March of that year, and steam often erupted into the sky
This geologic warning was fortunate for the people who lived near this picturesque place. Most of them evacuated, and although they were anxious to go back to their homes, the evacuation order had not been lifted when the mountain erupted for real**.
At 8:32 on May 18, 1980, a 5.1 earthquake shook Mount St. Helens loose. Moments later, the north side of the mountain collapsed, causing a lateral explosion that released superheated gases and magma. A glowing cloud of gas and debris sped down at nearly supersonic speeds, killing everything out to eight miles. A shockwave knocked trees down for another 19 miles. Trees beyond that still stood but were now lifeless. Nearly 230 square miles were destroyed by the blast force.
But Mount St. Helens wasn’t done. After the lateral blast, a vertical explosion rose more than 12 miles up from the summit. About 540 tons of ash settled over seven states in the next few days.
The third punch came from ice and glaciers. The heat of the eruption melted what remained, and the water mixed with debris. A volcanic mudflow, called a lahar, raced down the mountain at speeds up to 90 mph, destroying and burying everything in its path.
Fifty-seven people died, including some scientists. Entire habitats were destroyed, and human infrastructure was disrupted. Damage costs were estimated at more than a billion dollars. The eruption of Mount St. Helens is considered the worst volcanic event in U.S. history.
And yet, it began to recover almost immediately. Roads were repaired, rivers were revived. Animals began to return to the area as early as the next spring. New growth emerged from the ash.
Forty years later, it is a grand place to visit and learn about our ever-changing planet. There are many active volcanoes in the northwest and around the world. By studying the eruptions of the past, we can prepare for the future.
*OMSI is hosting a virtual event to celebrate the anniversary of the eruption. Click here for details.
**Thanks to the anniversary of the eruption, there are many useful articles online. I like this one from LiveScience.