Mt. St. Helens1980 Eruption

Before, During and After

Where is Mt. St. Helens

The Cascade Range is a volcanic chain stretching from Northern California to British Columbia

Mt. St. Helens is part of this range

Mt. St. Helens, the smallest of five major volcanic peaks in Washington state had an elevation of 9677

feet before the eruption of May 1980.

Mt. Adams (12,286) in the distance

First Evidence of Activity Initial ice

fractures on March 27, 1980

3/28- First phreatic (steam) eruption

The vent: 250 ft in diameter

March 29, 1980 Second Crater Crater appeared

on the NE side of the first crater

The new vent was 75ft. Wide and 30-60ft deep

3/31 the two craters joined together

March 30, 1980 Ash Darkens Slopes

Ash came from rock pulverized by the explosively-expanding, high-temperature steam and other gases- No new rock produced

Mt. Rainier in the background

Steam Explosion -4/10/80

Bulge Forms on N-NE Flank

Bulge first detected on 4-23

End of April the bulging area was one mile long and 0.6 mile wide

Maximum uplift 320 feet

Some areas of uplift - 5 feet a day!

Another View of the Bulge April 27,1980

Steam Eruption Prior to 5-18-80

Typical phreatic (steam) eruption in early May

Eruptions reached 13,000 feet in elevation

This activity was followed a two week quiet period

On may 18th 1980 at 8:32… Geologist David

Johnston was taking measurements on a ridge just 5 miles NW of the summit when he radioed “Vancouver! Vancouver! This is it! Moments later he was vaporized by the cloud of hot gas, ash, rock, ice and trees that hit him

For more than nine hours, the eruption continued. People that escaped had to drive

80+mph on old logging roads to escape

May 18th 1980

8:32 AM PDT a magnitude 5.1 shook Mt. St. Helens

The bulge and surrounding material slid away in a gigantic landslide and debris avalanche

Computer Version of Landslide The initial earthquake

and eruption triggered one of the largest landslides in recorded history.

The slide traveled 110-155mph

Hit a 1150ft high ridge about 6 miles north. Some of the slide spilled over the ridge

Most of the slide moved 13 miles down the North Fork of the Toutle River filling its valley up to 600 ft deep

The initial May 18th Eruption View From Less Than Three Miles

The cloud rose to more than 12 miles in 10 minutes

The cloud generated its own lightning

Ash rained down initially in an area that extended 25-30 miles to the north and east

Later, ash covered parts of eleven states

From an airplane that barely made it back!

For over nine hours, a vigorous plume of ash erupted reaching 12-15 miles above sea level

The plume moved eastward at an average speed of 60 mph with ash reaching Idaho by noon

Many cities had to use snowplows to remove the several inches of ash accumulation

Eleven States Had Ash Fallout

View from the NE on June 19, 1980

This area was completely forested prior to the May 18, 1980 eruption

Helicopters were deployed to try and save survivors. Few were found

Some people were found with their arms calmly folded or a camera held to their eye. The hot gasses killed them as they stood. It is believed that some people and vehicles were instantly incinerated

The total volume of ash as approximately .26 cubic mile or enough ash to cover a football field to a depth of 150 miles

The initial blast flattened over four billion board feet - Enough

to build over 150,000 homes.

Nearly 135 miles of river channels surrounding the volcano were affected

by the lahars.

Note the “mud line” on the trees and the person in the picture

The remains of Spirit Lake, once surrounded by lush forest

Mt. Rainier, 14,410ft in the distance

After the May 18,1980 eruption, Mt.St. Helens’ elevation was only 8364 feet and the volcano had a one-mile wide horseshoe-shaped crater

Craters were formed when water and hot ash came together making large steam explosions

Reid Blackburn, a National Geographic Photographer’s car

Ried Blackburn along with Volcanologist David A. Johnston were never found

The “U” shaped basin formed by the landslide and 5/18/80 eruption

June 4th 1980 - Mudflows are visible in the picture

Mt. St. Helens erupted often between 1980 and 1986

An explosive eruption on 3/19/82 sent pumice and ash 9 miles into the air and resulted in a lahar

Pyroclastic flow from August 7,1980 eruption

During the 5/18/80 eruption, at least 17 separate pyroclastic flows descended the flanks of the mountain

Pyroclastic flows typically move at speeds of over 60 mph and reach temperatures of over 800 degrees

October 24, 1980 a new dome started growing. This October dome was 112ft high and 985 feet wide making it taller than a nine-story building and wider than the length of three football fields

Mt. St. Helens soon after the 5/18/80 eruption from Johnston’s Ridge

Taken September 10, 1980

USGS Scientist Explore Pumice Blocks from a Pyroclastc flow

October 17, 1980

Geologists install a seismic station near the dome.

An increase in seismicity is often the first precursor to an approaching eruption

5/19/82- Plume from Harry's Ridge

Plumes of steam, gas, and ash often occurred at Mt. St. Helens in the early 1980’s. On clear days, they could be seen from Portland Oregon, 50 miles to the south

Harry's Ridge Was Named After Harry Truman of Spirit Lake

Measuring magnetic field in crater 6/18/84

Geologist measured the strength of the magnetic field surrounding the dome. The strength of the field increased as the dome cooled and magnetic minerals formed. During the eruptions, the strength usually changed rapidly as magma heated and deformed the dome

USGS scientists survey the dome 5/26-84

April 18, 1988 USGS Deformation Monitoring on the

Dome

Mt. St. Helens, Sept. 1994

Aerial View of Mt. St. Helens 2002

Mt.St Helens night shot of Dome 10-22-86

Mt.St Helens Spirit Lake before The May1980 Eruption

Mt.St. Helens Lake Reflection- After the Eruption

Picture taken May 19, 1982

2005 Saw An Increase In Activity

Picture Taken May 7, 2005