Transcript Mt St. Helens

Mt. St. Helens
1980 Eruption
Before, During and After
Where is Mt. St. Helens
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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
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Initial ice
fractures on
March 27, 1980
3/28- First
phreatic (steam)
eruption
The vent: 250 ft
in diameter
March 29, 1980 Second Crater
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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
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Ash came from
rock pulverized by
the explosivelyexpanding, hightemperature steam
and other gases- No
new rock produced
Mt. Rainier in the
background
Steam Explosion -4/10/80
Bulge Forms on N-NE Flank
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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
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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
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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
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The initial earthquake
and eruption triggered
one of the largest
landslides in recorded
history.
The slide traveled 110155mph
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
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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 1215 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
This area was completely forested prior
to the May 18, 1980 eruption
View from the NE on June 19, 1980
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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
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
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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
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
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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
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 ReflectionAfter the Eruption
Picture taken May 19, 1982
2005 Saw An Increase In Activity
Picture Taken May 7, 2005