A mountain of numbers

A grab bag of facts about Southwest Washington's resident volcano


  1. The volcano lost its top 1,313 feet on May 18, 1980, shedding a total volume of 3.7 billion cubic yards of material. That’s enough to cover the entire state of Washington in a half-inch of mountaintop; instead, it buried 14 miles of the Toutle River Valley to an average depth of 150 feet.
  2. The volcano ejected 1.4 billion cubic yards of ash. The nine-hour eruption unfurled a 15-mile-high cloud of ash that turned day into night across Eastern Washington. Captured in prevailing west-to-east jet streams, the plume drifted across the United States in three days. In 15 days, it circled the globe.
  3. Mount St. Helens, whose once-conical top earned it the reputation as the Fuji of America, now is 8,363 feet tall.
  4. Uncorked by the biggest landslide in recorded history, a deadly cloud of rock, ash and gas spread to the north and west at an average speed of 450 mph with an internal temperature of 660 degrees. It devastated 230 square miles of alpine forests, meadows and lakes.
  5. In a matter of minutes, the eruption toppled 4 billion board feet of timber. That’s enough to build 300,000 two-bedroom homes.
  6. Twenty-seven bridges and almost 200 homes were damaged or destroyed in a fast-moving mudflow rolling down the Toutle River. The outflow choked the Columbia River’s 40-foot-deep shipping channel with 26 feet of mud, stranding 31 deep-draft ships between Portland and Longview.
  7. Remnants of the magma reservoir continued pulsing out of the mountain’s crater in a series of eruptions between 1980 and 1986, eventually building a lava dome measuring 876 feet tall, 3,500 feet across, and 97 million cubic yards in volume.
  8. A new lava dome grew in a 40-month eruption between 2004 to 2008, producing about 125 million cubic yards of lava — enough to pave seven freeway lanes three feet thick from Vancouver to New York City.