Reliving the eruption of Mount St. Helens 30 years later

Print
Email
|

by KING5.com

KING5.com

Posted on May 17, 2010 at 10:26 AM

Updated Wednesday, May 19 at 9:35 AM

Thirty years ago this month, Mount St. Helens made history. On May 18, 1980, the volcano erupted in a massive explosion.

Before its devastating eruption, Mount St. Helens was considered to be one of the most beautiful and most frequently-climbed peaks in the Cascade Range. The peak's symmetric cone earned it the title of the "Fuji of North America" and nearby scenic Spirit Lake was a vacation area offering hiking, camping, boating, and fishing.

About 20 seconds after 8:32 a.m. on May 18, 1980, apparently in response to a magnitude 5.1 earthquake about 1 mile beneath the volcano, the bulging, unstable north flank of Mount St. Helens suddenly began to collapse, triggering a rapid and tragic train of events that resulted in widespread devastation.

USGS volcanologist David A. Johnston had radioed in the message "Vancouver! Vancouver! This is it!" Seconds later, the USGS volcanologist was engulfed in the volcano's gigantic lateral blast.

The mountain's bulge and surrounding area slid away in a gigantic rockslide and debris avalanche - the largest landslide ever recorded - releasing pressure and triggering a major eruption of ash and pumice. Thirteen hundred feet of the peak collapsed or blew outwards laterally.

The eruption reduced the elevation of the mountain from 9,677 feet to 8,353 feet, a difference of about 1,314 feet.

The lateral blast ripped through the debris at 300 miles per hour and at temperatures of 660 degrees Farenheit, scorching 14 to 17 miles of land from the crater.

As a result, 24 square miles of valley was filled with avalanche debris, 250 square miles of recreation, timber and private lands were damaged by the lateral blast, and an estimated 200 million cubic yards of material was deposited directly by volcanic mudflows into river channels.

Fifty-seven people were killed, including Johnston, whose body was never found.

The blast and lahars destroyed more than 185 miles of highways and roads and 15 miles of railways. Countless animals died, including 7,000 big-game animals such as elk and deer.

In less than three minutes, 230 square miles of forest lay flattened. 86,000 square acres of trees were mowed down, the equivalent to 4 billion boards of timber enough to build 300,000 homes. Some scientists estimated the power of the blast to 1,000 atomic bombs.

The eruption produced a column of ash and gas that rose 15 miles into the atmosphere in 15 minutes. Over the course of the day, 520 million tons of ash covered 22,000 square miles. It spread across the U.S. in three days and circled the Earth in 15 days.

The eruption lasted nine hours and by the following morning, major eruptive activity had ceased and the landscape appeared to be a gray wasteland.

Five more explosive eruptions of Mount St. Helens occurred in 1980 after the May 18 eruption. One eruption on July 22 sent pumice and ash 6 to 11 miles into the air, and was visible in Seattle.

 

 

Print
Email
|