Facts about Mount St. Helens and the history of eruptions there.
MOUNT ST. HELENS
— The mountain is 8,364-feet tall.
— It's surrounded by a national forest about 100 miles south of Seattle.
— The closest structure is the Johnston Ridge Observatory, about five miles from the crater.
— After the furor of the eruption in 1980, the volcano continued to erupt until 1986, violently at first, then quietly building a lava dome.
— Thick pasty lava eruptions oozed out, each one piling on top of the next. The lava dome is now 920 feet high.
— Each year thousands of climbers make the journey to the crater rim. Permits are required above 4,800 feet year-round.
THE 1980 BLAST
— The most devastating blast in recent history at Mount St. Helen came at 8:32 a.m., May 18, 1980.
— The eruption was prompted by an earthquake measuring 5.1 on the Richter scale.
— The north face of the mountain collapsed in a massive rock debris avalanche.
— In a few moments this slab of rock and ice slammed into Spirit Lake, crossed a ridge 1,300 feet high, and roared 14 miles down the Toutle River.
— The avalanche rapidly released pressurized gases within the volcano. A tremendous lateral explosion ripped through the avalanche and developed into a turbulent, stone-filled wind that swept over ridges and toppled trees.
— Nearly 230 square miles of forest was blown over or left dead and standing.
— The eruption blasted away the mountain's top 1,300 feet, spawned mudflows that choked the Columbia River shipping channel, leveled hundreds of square miles of forests and paralyzed towns and cities more than 250 miles to the east with volcanic ash.
— A mushroom-shaped column of ash rose thousands of feet in the sky, then covered much of eastern Washington state with a dark, gray ash.
— Fifty-seven people were killed.
— In 1982 the President and Congress created the 110,000-acre National Volcanic Monument for research, recreation, and education. Inside the Monument, the environment is left to respond naturally to the disturbance.