/ Mount St. Helens 25th Anniversary

02:45 PM PDT on Thursday, May 12, 2005

From KING5.com and USGS Reports

Before the devastating May 18, 1980 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.

On March 27, 1980, an explosion occured and a crater about 200 to 250 feet wide was reported near the summit. Frequent small explosions began at 3 a.m. the following day, lasting nearly two hours. A small cloud of ash and steam rose more than a mile above the volcano.

By mid-April, U.S. Geological Survey scientists became increasingly concerned over the growing instability of glaciers and rock on the north flank of the volcano. A Red Zone from 3 to 7 miles out from the peak was established on April 30, and access in this zone was restricted to scientists, law enforcement, and other officials. A Blue Zone further out was restricted during daylight hours to loggers and property owners with special permits.

A "bulge" developed on the north side of the volcano as magma pushed up within the peak. Scientists were extremely concerned that large avalanches of rock, snow and ice from the bulge high on the volcano could reach Spirit Lake and State Route 504 within a few minutes.

USGS / Austin Post

Thirteen-hundred feet of Mount St. Helens' peak collapsed or blew outwards. As a result, 24 square miles of valley was filled by a debris avalanche, 250 square miles of recreation, timber, and private lands were damaged by a lateral blast, and an estimated 200 million cubic yards of material was deposited directly by volcanic mudflows into the river channels.

On May 16, the north and northwest rims of the crater had abundant cracks that were partially filled with snow and ash. The National Weather Service predicted good weather for volcano watching for the upcoming weekend.

The mountain erupts

May 18, 1980, a Sunday, dawned bright and clear.

At 7 a.m., USGS volcanologist David A. Johnston, who had Saturday-night duty at an observation post about 6 miles north of the volcano, radioed in the results of some laser-beam measurements he had made moments earlier that morning.

Even considering these measurements, the status of Mount St. Helens' activity that day showed no change from the pattern of the preceding month. Volcanic data, such as seismic, rate of bulge movement, sulfur-dioxide gas emission, revealed no unusual changes that could be taken as warning signals for the catastrophe that would strike about an hour and a half later.

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

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 of the volcano. Thirteen hundred feet of the peak collapsed or blew outwards laterally.

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

While the eruption was heard as far as 690 miles away, thousands of witnesses said Mount St. Helens was wrapped in a cone of silence approximately 60 miles in every direction. The eruption also produced a bolt of lightning every second.

The eruption's devastation

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.

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 hot gas and magma melted the snow and ice that covered the volcano. The resulting floodwater mixed with the rock and debris to create concrete-like mudflows that scoured river valleys surrounding the mountain at speeds of 10 to 50 mph.

While the landslide and lateral blast were over within minutes, the eruption column, mudflows and pyroclastic flows continued throughout the day and following night.

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.

USGS/Lyn Topinka

86,000 square acres of trees were mowed down, the equivalent to 4 billion boards of timber enough to build 300,000 homes.

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 May 18. One eruption on July 22 sent pumice and ash 6 to 11 miles into the air, and was visible in Seattle, Washington.