Is that a waterfall up there? Yeah, a big one. And that's a couple
hundred feet high. And the whole canyon
is 600 feet deep. You've been up there? Yeah, that's a cool place. You can see everything
around the volcano. And all of it's just scoured. Steve, it's absolutely
beautiful here. Just the peaceful quiet
and almost overwhelming beauty. And yet it wasn't
always that way. On May 18th 1980, a catastrophic geologic event
occurred that not only shocked the world because of
its explosive power, but it challenged
the way we're thinking about the origin of the earth
at its very foundation. That event is the eruption of this mountain here in
Washington state 35 years ago. So, Steve, tell us about that. What happened on that day? The eruption on May 18th was
really a nine-hour event. If you think about
that nine-hour event, there were seven
different sub-events that were going on during
that big event on May 18th. 17 seconds after 8:32 in the morning there was
a big earthquake, magnitude 5.1. It shook the north slope
of the mountain. The oversteeped and cracked
north slope began to slide. It formed this gigantic
rock fall that became mixed with atmosphere and
gas and dispersed. It became a debris avalanche. This debris avalanche
overtopped this ridge and went 10 miles
from the volcano. And then behind that avalanche, the pressure inside
the volcano released. Super hot liquid water in the neck of the volcano
expanded to steam, and it created
this gigantic steam explosion equivalent to 20,000 tons
of TNT blast energy. That was directed
not up, but northward, over the landscape. And then we had
the debris avalanche going into Spirit Lake. The avalanche displaced
the water of the lake up to 860 feet, creating this enormous
water wave on the lake. And then following
that were mudflows. The heat of the explosion
melted the snow and the ice around the volcano. And we had mudflows
on six major rivers downstream. Then we had pyroclastic flows, especially on the afternoon
of May 18th. The volcano
erupted episodically. These frothy, liquid flows
that came out. And then what followed
over the rest of the day was airfall debris. We call that the pumice
that fell out of the atmosphere, or airfall tephra. So that's kind of the story
of the nine-hour eruption on May 18th. There was a lot
going on that day. Steven, while we
were walking up here, you were telling me
that before 1980, if we looked down there,
we would see a lush forest. But it's a whole lot lower
than what we see. This has all been filled in. What happened? How did all
the material get here? And what do we learn from it? Well, we have a lot
of deposits don't we? There's up to 600 feet
of deposits here in this valley. It was sky before the eruption, and now look
what's going on down there. Okay, that is an amazing thing
to be thinking about. So we’ve got a lot
of the deposition, up to 600 feet of deposits. And then, the way
the erosion occurred in this area allowed
the layers to be exposed so we can see
the sequence of events that formed not just this ridge, but the valley. Some of these events occurred
as much as two or three years after the 1980 eruption. So every event left
a fingerprint of something here on the landscape. So we have earth’s
newest landscape, and we have all the knowledge
from eyewitnesses and photographs to put
together the sequence of events here at the volcano. So we have mudflows. We have pyroclastic flows. We have these explosion pits. We have erosion. And we look out here and see that there’s a lot
of character to this land. But it all occurred rapidly through these
catastrophic events. What does that tell a geologist who now moves their vision
from what happened here at Mount St. Helens, and then begins to look at the geological formations
we have around the world. That's my story! I came here and I'm
looking around elsewhere, and I see the application
of erosion and deposition and those kinds of processes that are here at the volcano to many other features
of the earth’s surface. I have studied strata. Rapid strata formation here indicates rapid
strata formation elsewhere. Rapid erosion features here are
like erosion features that we thought require
millions of years. We thought that layers formed
slowly and gradually, but here at the volcano
they form rapidly. What's the primary difference
between your observations as you see here, and the standard
geological story. And what is that? The standard geologic story is “the present is
the key to the past. ” We look at the present
day process of slow and gradual, and then we think that applies to geologic features
of the earth generally. But it really isn't the story. It's not “the present is
the key to the past,” it's “the catastrophic event is
the key to the past. ” And so Mount St. Helens is
a window to help us understand the catastrophic formations
elsewhere on the earth. So the present is
not the key to the past, the catastrophic event that we're seeing is
the key to the past. Well, Steve, thanks
for making me a hike down here. This is an awesome place. Where are we? We're on the north fork
of the Toutle river, upstream near the crater
of Mount St. Helens. We're in this area that's been profoundly
impacted by the deposition and erosion associated with
the volcanic eruption of 1980. So are you saying that the ground we are standing
on was not here 40 years ago? Yeah. This was the sky
before the eruption in 1980. So up to 600 feet
of deposits have formed here. We just see the upper
hundred feet of layers. But it's now
been carved out for us so that we can look
at it, you know? We can see some of those layers. What do we see? What are we looking at? Well, we're looking
at mostly the bottom of the cliff over here. We're looking at the airfall
deposit from May 18th. Is that the lower level
that we see? Yeah, the lower level. It’s kind of a massive
and fragmental deposit. That's what was falling
out of the atmosphere from the volcano late
in the afternoon of May 18. Right around 4 o'clock
in the afternoon is when the eruption subsided, and so the top of that layer
there about halfway up the cliff is the last airfall debris
from May 18 1980. And then this area
was impacted by buried ice. Underneath us was
large glacial ice buried in the debris avalanche. Then what happens is
steam is reaming a hole to the surface, and we're seeing
a steam explosion occur in the coarse debris right
about halfway up the cliff. How long did that happen
after May 18th? In the first week or so,
there was a big pit here. It was a hundred feet deep,
reamed out by steam. It was 2,000 feet long
and a thousand feet wide. And then into that pit
came the next deposits. On June 12, 1980,
about 9 p.m. to midnight, there was a big eruption
of Mount St. Helens. Another big eruption. And during that
three-hour period, there were enormous
pyroclastic flows. These were slurries
of high-density, very hot slurries of volcanic ash
that came out of the crater. This lahar in the pit collected
those volcanic ash layers. So we see behind us, about halfway to three-quarters
of the way up the cliff, a 25-foot thickness of
layered volcanic ash. That’s the pyroclastic
flow deposit from June 12, 1980. And it formed just
in the three hours there, late in the evening. Then this pit sat here
with the landslide debris and other kinds of debris
and volcanic ash all around it. And on March 19th of 1982, that came down here
at 90 miles an hour! It filled in this low area,
the pit, with mud. You’re seeing the residue
of the mud of about 25 feet in thickness there
at the top of the cliff. As the mud came into this pit, it actually filled the pit with
a hundred-foot thickness of mud. The pit was filled. Then what happened was mud
overtopped the debris dam that was downstream of here and then it cut a spillway
over the top of that dam, which cut back through here
and gouged out the bottom of this pit and released
the mud downstream. And so the canyon formed
in a day, on March 19th, 1982, by the drainage of the mud in this big pit
through the debris avalanche. So you sit here, and you look at the complexity
of the geological formations. If we blindfolded someone,
it would be easy to bring them down here, take their blindfold off and have them look
around and think, as a lot of people do, “Man,
this is really, really old! Look at all
these different layers, and all of the stuff
that's going on. ” And yet, all each of these layers is laid
down rapidly within a day, and breached within a day. That’s amazing! So although it’s spread out
over a two-year period, each of those individual events happens in just
minutes or hours. So we end up having a very
complex geological formation here that was all done rapidly. Yeah. You know when I see thin layers, I think of slow
and gradual sedimentation. One sand grain at a time. That was my normal
way of thinking. But here at the volcano, I learned that grains
can segregate rapidly in layers by hurricanes, essentially. Those pyroclastic flows make
thin layers in just seconds. Mudflows can move very fast,
90 miles an hour, and bring big boulders
and lots of debris. And of course,
they're very erosive. So we see the power
of these agents, and the speed of these agents. Fortunately, because of
Mount St. Helens, I can understand
those processes, and I can go elsewhere and see
if I see the same thing. So you go around the world, and you see those complex
geological formations. It's easy to see how rapidly they
could have formed as well. Is that right? Rapid stratification. Rapid erosion. That's the story
at Mount St. Helens, and it's the story
around the world. I think there's plenty
of application here to other geologic
features of the earth. It’s a wonderful laboratory for
studying catastrophic processes. Steve, this is kind of
an interesting place. What do we see here? And where did it come from? We're on the north fork
of the Toutle River. We're looking upstream
toward Mount St. Helens, and we see this major alluvial, or mudflow, deposit
in this valley. This mudflow deposit
ripped loose logs and all kinds of material
that was in the valley, cut it down, and then filled it
back up with mud. So where did it
come from originally? The mud is up from
the blast zone, essentially, There's 150 square miles of blown-down trees
up there and ash in the sediment debris
that was ripped loose. There was a major
source of sediment, not just volcanic ash, but also the landscape itself is
very erosive, and erodible. Here we are tens of miles away
from the base of the volcano. Some people thought they were safe in the valley
this far away from the volcano, but their home
was buried in mud. So there's a lot of destruction from this mudflow
down even this far. Yeah. On six major rivers downstream on the north fork
of the Toutle River, here, and five other major
rivers there was significant mudflow damage. Logging camps were overcome. Homes were buried. There were bridges washed away. There was more dollar damage from the mudflows than
from the steam blast itself. And so you can imagine
the threat of mud and how it's able to radically
alter a landscape. Well, other than giving
us a healthy fear of mud, what has a geologist learned? What have you learned from this? And especially, what does that then tell you
about the rest of the world? Yeah, we've learned
how effective, and how mobile, and how easily transported mud
is by studying the mudflows in Mount St. Helens
and other things. We did not appreciate the way
that mud is able to move things. And it's like ketchup. It has a shear
thinning rheology. That mud, once it gets moving,
is very low friction. It has in itself the ability
to overcome barriers and by its momentum
just erode things. So this energy that has come back to our discussions of mud
has proven very beneficial for the understanding
of limestone layers. I can see the
effect in limestone, how fossils are buried, sandstones with graded beds
and these coarse clastic layers called conglomerates, with large pebbles
floating in mud matrix. All of this has
tremendous implications from the mudflow angle
of looking at it. So when I drive around and I see a lot
of these sedimentary layers, I ought to be thinking more about how it used to be mud then
the way I used to think of it. Yeah. Now, geologists used to think
about dilute flow, you know. The bottom of a creek
is a dilute flow that might be 5% sediment
during a big flood going by. That type of flow, the sweeping action of
the bottom of a creek, is not the major mode of
sediment movement in the past, at least, judging
from the frequency of mudflows. Now mudflows are 50% sediment
and 50% water. It's not a dilute mass. So it has huge energy
in just its momentum. So we have a mudflow with a lot
of sediment material in it. How do we get from that
to the layers? Mud can simply freeze
by friction, and dewater. You know, it's only 50% water
and 50% sentiment. It's easy, or somewhat easy, for a mudflow to lose
its momentum and become a sediment layer very rapidly. That shows up in the fossil record as some
of these massive beds. But mud can also go
through a process where it deposits sediment, and then becomes
a dilute fluid flow. What's observed here
at Mount St. Helens is the mudflow goes along and loses sediment
at a low place like here, and then the water
increases, changing the sediment-to-water ratio. Now we have dilute fluid flows
that are very erosive. That creates the familiar
sandy layering that we know about in creek beds
and other places. Through a process
called flow transformation, a mudflow can resurrect
itself into a tractive, or sweeping action, current. When that happens, boy, you can make all kinds
of sedimentary strata. So the understanding of that
has really revolutionized a geologist's understanding
of how strata form. When a mudflow itself is still saturated with a lot
of that material, can it be erosive itself? It's very erosive, and that's what
was observed here. The mudflows came by
and they picked up bridges, logs and everything that floats. Even an automobile
floats on a mudflow. Mudflows float things along. We chuckle at thinking
about how mud moves things, and I'm sure the people involved
in the disaster don't like what they're seeing, but it is obvious that we need to think
this way about the process. Can a mud flow also cut down, rather than just go
through and collect bridges and so forth? Can it also cut down in below? Yes. Now, mud is seen to do that on the slopes
of Mount St. Helens. The two canyons
on the north slope of the volcano are very deep. Step Canyon is
over 600 feet deep and eroded through solid rock
made by moving mud after the summer of 1980. And there's another canyon
called Lewitt Canyon where it's over a hundred
feet deep and eroded through solid rock by
a 500-year old lava flow. It didn’t take tens of thousands
of years to do that. It was basically mud moving
down that channel very rapidly, plucking away and
grabbing solid rock and excavating a canyon. There are people that say
that today on the ocean floor, the main way that sediment
moves is by mudflows. They’re concealed down there. They think that mudflows
can go a thousand kilometers under the flat floor
of the ocean. So it may be that,
even today, mudflows on a more regular basis
than we think of at Mount. St. Helens are making significant
sedimentary deposits. Our world is more
mudflow than ever. That's really interesting.
