Narrator The eruption of Mt.
St. Helens on May 18, 1980 was one of the most
dramatic geologic moments in American History.
It was a Sunday morning.
8:32 AM
"Vancouver, Vancouver.
This is it" was the excited call on the radio from David A. Johnston to his colleagues.
Within minutes the colossal eruption had caused 100�s of millions of
dollars in damage and 57 lives were lost...including Dave Johnston.
For two months prior to that eruption geologists with the
U.S. Geological Survey and the University of Washington�s
Pacific Northwest Seismic Network had been closely monitoring
the volcano.
Don Swanson all the deformation on the mountain was local
to the mountain and even more local than that was on the north
side of the mountain only.
C. Dan Miller In the nearly two month period before May
18 what was essentially happening at Mt.
St. Helens was that magma or molten material
was moving up from some deep reservoir beneath the mountain up
into the volcano itself...and it began to grow and form what
we call a dome or cryptodome inside the volcano and that
inflating body of magma or molten material actually broke the
north side of the volcano and began to cause the north side of
the volcano to expand out toward the north.
Norm Banks We were measuring the rate of northward movement
of the bulge at about six feet a day.
And we knew that wasn�t so good.
C. Dan Miller On the morning of May 18 I was driving up
Interstate five heading up to the north side of Mt.
St. Helens with some parts and some
batteries for out timelapse cameras.
And as I glanced over at Mt.
St. Helens it was a beautiful blue sky day and the mountain
was sitting out there and suddenly I saw this mushroom cloud go
up above the volcano and climb rapidly into the stratosphere.
Don Swanson I was down in the room where the seismographs
were at 8:32 in the morning and I heard a sound and I just
looked over my
shoulder, probably just a split second after the big earthquake
had started and saw that this was something very large larger
than we�d seen before, watched it for a few seconds just to
confirm that and then I ran upstairs to the next floor up to
the radio desk of the forest service and called Dave.
And what I wanted to do was to ask him if anything was happening
at the mountain.
And we couldn�t get through there was no answer.
C. Dan Miller So, I guess I had the realization right away
that this was some kind of tragedy.
And on the one hand it was this huge and
interesting magmatic eruption and on the other hand I was
pretty certain that something terrible had happened to Dave so
it was a strange day for me.
Don Swanson And uh we were off the ground probably at 9 oh five or something
like that.
It was really really rapid.
And got up to the point where we could really see the mountain well I suppose
between 9:20 and 9:25
Something like that.
Don Swanson There was terrific, very vigorous vertical eruption
column that was the stem of the mushroom or the toadstool it then
blossomed out at greater height.
Don Swanson And, for most of the morning we saw this...tremendous
ash cloud roiling out toward the northwest and I can
only assume that
that was coming off of the big pyroclastic flows that were going
off in that direction that later built the pumice plane.
It was a very eventful morning but it was sobering because I
remember thinking up in the airplane that Dave just couldn�t
have survived this.
Especially when we got around to the west side and saw all the ash heading in his direction.
C. Dan Miller On the morning of May 18th what actually happened...the
landslide basically uncorked this pressurized body of
magma and allowed it
to explode or expand out towards the north very rapidly,
this is what we call the lateral blast...it was a horizontally
directed explosion of incredible magnitude it caused this
expanding cloud of ash rocks and gases to move out across
the countryside to the north at speeds of several hundreds of
miles an hour.
The directed blast was really the most
destructive event that occurred on the morning of may 18.
It completely destroyed an area of 230 square miles in a
matter of somewhere between five and nine minutes.
It essentially killed every living thing within an area of
230 square miles.
And it destroyed hundreds of acres of virgin forest and was an incredibly spectacular
event.
Don Swanson We put out new stations and we quickly started
to re-monitor the volcano again because we had no idea what
was going to happen.
C. Dan Miller Before the dust had literally settled in the
summer of 1980 there were usgs scientists swarming all over
the area outin the
blast zone studying the pyroclastic flows studying the debris a
valanche deposit studying the directed blast.
Don Swanson We thought it was likely that there would
be more eruptions during the summer and indeed that
took place.
C. Dan Miller suddenly this immense black eruption cloud came
pouring out of the white layer, the cloud tops and I couldnt
believe my eyes I thought this is the most incredible thing
I've ever seen in my life.
Norm Banks We learned a lot about how you interact with
the civil defense with the public with the press, and that was
transferred by
the press to the world and as a result volcanology took a
quantum leap in science as well as applicability to societies needs.
C. Dan Miller The subsequent eruptions were actually most
of them were forecast fairly accurately by the USGS team
of scientists so
when it looked like another explosion was about to take place
our helicopter crews would pick us up and we'd move to the
outskirts of the blast zone we'd watch and photograph the new
eruption as soon as the eruption stopped we'd race out there
and study the deposits while they were still hot just after
they'd settled onto the ground.
So, it turned out that the
six years that Mt.
St. Helens was erupting in the 1980's was an opportunity, an unprecedented opportunity
for USGS scientists
to study hot fresh young and exciting deposits from explosive
vulcanism.
And we learned incredibly new and important bits
of information about how volcanoes like Mt St Helens work,
what kinds of deposits are produced during these explosive
eruptions and how to anticipate and mitigate the
consequences of explosive eruptions.