The day the sky darkened: Mount St. Helens erupted in Washington State 45 years ago

Yahoo

18-05-2025

On May 18, 1980, the United States experienced the deadliest and most destructive volcanic eruption in its history. After more than two months of rumbling, Washington State's Mount St. Helens erupted with a force equivalent to as much as 50 megatons of TNT.
The massive blast and subsequent landslides, flooding and ash cloud killed 57 people, caused more than $1 billion in damages, destroyed at least 200 homes and was heard more than 200 miles away.
The resulting scorching ash cloud reached as high as 16 miles into the atmosphere, darkening the sky and causing homes and businesses as much as 300 miles away to close. A massive wave of melted snow, ice, ash and pumice raced down the sides of the mountain, reaching up to 60 miles away and crushing homes, forests, bridges and roadways in its path.
Once known as the Mt. Fuji of America, the eruption came after the majestic cone-shaped volcano had lain dormant for 123 years. The eruption, observed in detail by hundreds of geologists, volcanologists and ecologists, added immensely to human knowledge about vulcanism, a silver lining to the devastation it caused.
It led to better preparation in volcanic areas, significant new scientific study and awareness of volcanic systems and the creation of five USGS volcano observatories in volcanically active portions of the United States – Alaska, California, the Cascade mountains (Washington, Oregon, Idaho) and Hawaii.
Here's how the eruption unfolded:
Scientists observed magma building inside the volcano, creating a visible bulge on its northern side. A series of small earthquakes began on March 16, reaching several hundred by the end of the month. On March 27, the volcano experienced its first major eruption since the mid-1800s. A steam explosion blasted a 250-foot wide crater through the ice cap on the summit, covering the snow-clad southeastern portion of the mountain with dark ash. A 15-miles radius around the area was evacuated and roadblocks put in place.
By April 22, more than 10,000 earthquakes had occurred on the mountain and the northern flank bulged out by 450 feet, growing six-and-a-half feet per day, as molten magma rose up inside the volcano.
At 8:32 a.m., a magnitude 5.1 earthquake shook the mountain, setting off an enormous landslide on the volcano's northern flank. An estimated 3.3 billion cubic yards of material sloughed off the mountain, the largest debris avalanche in Earth's recorded history, according to the U.S. Geological Survey. With the loss of all that material, the boiling, highly pressurized magma underneath was released.
As NASA put it, "When the mountain collapsed, it was like uncorking a bottle of champagne: hot rocks, ash, gas, and steam exploded upward and outward to the north."
Within 15 minutes, a cloud of tephra (ash, rocks and cooling magma) rose more than 15 miles into the atmosphere.
The blast, avalanche and pyroclastic flows destroyed more than 230 square miles of forest. A total of 57 people died, most from asphyxiation after inhaling hot ash. They included locals who refused to leave despite warnings as well as residents, volcanologists and journalists who thought they were observing from a safe distance.
Avalanches of hot ash, pumice and gas as well as volcanic mudflows from all the melted snow and ice spread for miles, destroying 27 bridges, more than 200 homes, 185 miles of roads and 15 miles of railway. River valleys were smothered and the path of the Toutle River was altered. To this day it remains full of sediment.
The area was so completely devastated that when viewing it, then-President Jimmy Carter said, "Someone said this area looked like a moonscape. But the moon looks more like a golf course compared to what's up there."
Communities hundreds of miles away were covered in ash from the eruption. The corrosive ash, composed of rock, mineral crystals and volcanic glass, snarled air travel, closed airports, shuttered schools and businesses and damaged machinery and automobiles. People wore bandanas over their mouths when outside to avoid breathing it in. When they tried to wash it off their cars, it scraped the paint.
Within two weeks, the thinning ash cloud had circled the globe.
A new lava dome, recorded by USGS and NASA, began to rise in the middle of the crater formed by the 1980 eruption. Earthquake activity renewed in September. Swarms of small earthquakes shook the mountain and small steam and ash explosions were observed in 2005. By 2008 millions of cubic yards of lava had erupted onto the crater floor, refilling about 7% of the crater. By the end of 2008 the mountain had once again calmed down.
The aftermath of the 1980 eruption continued. Warm weather and melting snow led to a landslide of volcanic debris that washed out the Spirit Lake Outlet Bridge and damaged portions of State Road 504 in Washington, blocking access to the Johnson Ridge Observatory, which remains closed.
This article originally appeared on USA TODAY: Mount St. Helens erupted 45 years ago: Here's what happened