mt. st. helens 1980 eruption before, during and after
TRANSCRIPT
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Mt. St. Helens1980 Eruption
Before, During and After
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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
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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
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First Evidence of Activity Initial ice
fractures on March 27, 1980
3/28- First phreatic (steam) eruption
The vent: 250 ft in diameter
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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
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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
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Steam Explosion -4/10/80
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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!
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Another View of the Bulge April 27,1980
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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
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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
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For more than nine hours, the eruption continued. People that escaped had to drive
80+mph on old logging roads to escape
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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
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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
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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!
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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
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Eleven States Had Ash Fallout
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View from the NE on June 19, 1980
This area was completely forested prior to the May 18, 1980 eruption
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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
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The initial blast flattened over four billion board feet - Enough
to build over 150,000 homes.
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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
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The remains of Spirit Lake, once surrounded by lush forest
Mt. Rainier, 14,410ft in the distance
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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
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Reid Blackburn, a National Geographic Photographer’s car
Ried Blackburn along with Volcanologist David A. Johnston were never found
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The “U” shaped basin formed by the landslide and 5/18/80 eruption
June 4th 1980 - Mudflows are visible in the picture
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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
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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
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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
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Mt. St. Helens soon after the 5/18/80 eruption from Johnston’s Ridge
Taken September 10, 1980
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USGS Scientist Explore Pumice Blocks from a Pyroclastc flow
October 17, 1980
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Geologists install a seismic station near the dome.
An increase in seismicity is often the first precursor to an approaching eruption
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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
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Harry's Ridge Was Named After Harry Truman of Spirit Lake
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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
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USGS scientists survey the dome 5/26-84
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April 18, 1988 USGS Deformation Monitoring on the
Dome
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Mt. St. Helens, Sept. 1994
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Aerial View of Mt. St. Helens 2002
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Mt.St Helens night shot of Dome 10-22-86
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Mt.St Helens Spirit Lake before The May1980 Eruption
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Mt.St. Helens Lake Reflection- After the Eruption
Picture taken May 19, 1982
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2005 Saw An Increase In Activity
Picture Taken May 7, 2005