In the 1950s, Rocky Crandall and Don Mullineau of the U.S. Department of the Interior's
Geological Survey began a study of Mount Rainier, the tallest of 12 volcanoes in the Cascade
Range of the Pacific Northwest. The study had unexpected and widespread impact when
it revealed that Mount Rainier and other Cascade volcanoes posed a real threat to the people
of Western Washington. Crandall and Mullineau identified Mount St. Helens, a particularly
explosive volcano, as the most dangerous of all. In 1975, they forecast that Mount St.
Helens might well be the next Cascade volcano to erupt, perhaps even before the year 2000.
Just five years later, in 1980, the north face of the mountain collapsed, unleashing
an explosive eruption and sending a torrent of mud and trees sweeping down the Toutle River.
Today, the expanding population of Western Washington is moving ever closer to the mountains.
As a result, colleagues following in the footsteps of Crandall and Mullineau now warn that Mount
Rainier poses the greatest danger. What are the risks that await us in the shadows of
this mythical giant? Beneath its beauty, what aspects of its volcanic personality lie hidden,
and what have scientists learned about the ways in which Mount Rainier might someday
affect the cities and towns of Western Washington?
Size and scale on Mount Rainier are difficult to grasp. Its 14,000-foot summit towers nearly
two miles above deep canyons. Ice cliffs hundreds of feet high grace its slopes, and the mountain
supports as much ice as all the other Cascade volcanoes combined. Yet for all its size and
grandeur, the mountain is also intimate and comforting. We look to it for inspiration,
challenge and assurance. But the mountain's true nature is far more complex. We easily
forget that Mount Rainier is a live volcano, lying quiet for only 100 years. Over the past
half million years, Mount Rainier has erupted again and again, building up layer after layer
of lava and loose rubble. At the same time, the erosive work of water and ice has shaped
its slopes. Their relentless power has carved steep cliffs, formed massive headwalls and
coated glaciers with rock debris. But most important to us are the sudden landslides
that every now and then tear away vast portions of the cone and send massive mud flows thundering
down its valleys. Many have traveled tens of miles all the way to the Puget Sound lowland.
Development is now crowding into these same valleys, building atop the remains of old
mud flows. What events might affect these towns over the next 50, 100 or even 500 years?
Hameki Crandall began to answer this question quite unexpectedly during a study that began
some 30 miles from the mountain on the edge of the Puget Sound lowland.
I was just out of graduate school in the early 1950s and I was assigned by the Geological
Survey to make a geological map of an area east of Tacoma, Washington.
According from older maps, Crandall expected to find the Hameki remains of glacial deposits
around the towns of Buckley and Enumclaw. When he arrived, he found only a flat plain.
Where he expected to find glacial sediments plastered on the hills, they seemed to occur
only in the valleys. As Crandall attempted to explain how the valley floor had formed,
he found himself moving in a surprising direction and toward a stunning conclusion.
And I came up with the idea that perhaps it had actually flowed into place, like a giant
mud flow. And it was just like a light going on over my head because everything I knew
about the deposit fit this kind of an origin. It had actually flowed into place. It had
not been formed by a glacier at all. But the question in my mind is, if it is a mud flow,
how did it ever get started? Where did it come from? And I had no idea at all. Even
though standing there on the plain that was formed by this mud flow, I could see Mount
Rainier in the distance and I didn't make the connection for a long time.
As Crandall searched vainly for the source of this giant mud flow, known as the Osceola,
its deposits led him up the White River to a point 10,000 feet up the northeast side
of Mount Rainier. We could hardly believe our eyes when we actually
found a remnant of the same deposit there at the tip of Steamboat Prowl.
As he stood on Steamboat Prowl looking toward the summit, Crandall realized that the Osceola
could have come only from the sudden collapse of a major segment of the mountain. This was
a radical idea. Such massive volcanic landslides were virtually unknown.
That is until 1980, when the north flank of Mount St. Helens, weakened by rising magma,
burst in the largest landslide ever witnessed. The landslide released an explosive blast
that laid waste to over 200 square miles of forest.
The landslide also spawned a giant mud flow that raged 50 miles all the way to the Columbia
River. When all had settled, Mount St. Helens lay
gutted and bare. The upper Toutle River had become a barren and rocky place where craggy
fragments of the mountain pocked the surface of the landslide.
But scientists working at Mount St. Helens quickly realized that its odd hilly landscape
was not unique. Within a short time, they identified similar landslide deposits here
at Mount Shasta and at some 200 other volcanoes around the world.
Crandall's radical idea was established beyond doubt, and the far-reaching dangers of Mount
Rainier, exemplified by the Osceola mudflow, were brought into clear and chilling perspective.
We now know that the entire summit and northeast face of Mount Rainier fell away suddenly in
an immense landslide accompanied by volcanic explosions.
The landslide became a mudflow that filled the White River Canyon with up to 600 feet
of rock, clay, water, and ice. This cement-like slurry thundered down the valley at speeds
up to 50 miles per hour. As the flow left the mountains, it spread out
to form the Enumclaw Plain that had led to Rocky Crandall's original insight. Finally,
the Osceola disappeared into Puget Sound. It is difficult to grasp the destructive force
of one of these massive mudflows, but try to imagine a towering wall of mud and rock
crashing through a canyon at 50 miles per hour, destroying everything in its path.
These much smaller modern examples, about 5 to 10 feet deep, provide only a hint of
the ferocity of Mount Rainier's major mudflows. Even the giant mudflow produced by the 1980
Mount St. Helens landslide was small compared to the Osceola.
The massive Osceola collapse, which occurred about 5,600 years ago, destroyed the top of
Mount Rainier, lowering it by as much as 1,000 feet.
But this destruction set the stage for new growth. The mountain began to rebuild soon
after the Osceola event. Thick, slow-moving lava oozed out into the crater, building a
new summit cone. The jagged peaks that surround this new cone mark the edge of the old Osceola
crater. Recent studies on and around the mountain confirm Crandall's conclusion that the Osceola
was by far the largest mudflow of the past 10,000 years. And they also support the ominous
news that since the Osceola, at least five other immense landslides have sent massive
mudflows far down the valleys leading from the mountain.
About 500 years ago, one of these landslides broke loose from Sunset Amphitheater, producing
the electron mudflow. As it plunged down to Puget Sound, the electron left behind the
broad plain around the town of Orting. It may be difficult to imagine that the mud and
rock that filled this valley came from Mount Rainier, but it is vitally important to understand
what happened here just 500 years ago. If repeated today, the electron could reach Orting
in less than two hours, arriving as a wall of churning debris some 20 feet high, moving
at about 20 miles per hour, burying the entire valley floor. The flow would destroy every
building and entomb the remains in cement-like sediment. And the electron mudflow may well
have come crashing through this valley with little or no warning from the volcano.
The importance of the electron mudflow to me is that it was not associated with any
form of volcanic activity. This means that we are not going to have any advance warning
that a future flow like the electron is going to occur. This greatly increases the risk
to people living in the valleys downstream from the volcano.
A mudflow caused by a sudden landslide at Mount Rainier might well arrive with no warning,
making this the most dangerous hazard posed by the mountain. But landslides can also be
triggered by large earthquakes or by magma moving into the volcano. Either of these events
could signal a possible mudflow, perhaps only an hour or two ahead for an earthquake, but
days or weeks in advance for moving magma.
Warning or not, large landslides will continue to occur at Mount Rainier, and mudflows will
continue to threaten the Puget Sound lowland. Large landslides occur frequently, about every
500 to 1,000 years. But what is it that makes Mount Rainier so unstable? Why are scientists
so certain that landslides will continue to occur? For answers, we need only look at the
structure of the volcano and at processes that turn solid rock into soft clay.
Many of the ridges low on Mount Rainier are formed of massive lava flows up to 2,000 feet
thick. But high on the mountain, thinner, steeply sloping layers are much less stable. Lava
cliffs 50 to 100 feet high are separated by beds of rubble, fragmented pieces of lava
that are soft and easily eroded. These rocks could break loose at any time, nudged, for
example, by a large regional earthquake or a steam eruption.
Mount Rainier is weakened even further by hydrothermal alteration, a process that turns
solid rock into soft and slippery clay. Atop the end of the Tahoma Glacier, in a landscape
of altered rock, the smell of sulfur taints the air. Boulders fall apart. Iron minerals
crust the rock like rust. Slippery clay minerals coat the volcanic debris.
In the early 1900s, this material fell suddenly onto the Tahoma Glacier from Sunset Amphitheater.
Here this 600-foot cliff has been transformed from hard lava into a crumbling mass of weak
rock by hot acid water moving through the volcano.
This chemical transformation requires water and heat, which travels from the magmatic
heart of the volcano. Water is present everywhere on Mount Rainier, released by sun and rain.
And heat is present as well. On the frozen summit, volcanic steam keeps snow and ice
from the crater rims and melts a maze of caves that extend more than 400 feet below the surface.
For decades, climbers have used these caves for shelter. Some of the water here and elsewhere
on the mountain seeps into rubbly layers and mixes with volcanic gases, creating an acidic
brew. Alteration occurs mainly where this acid water travels along heated pathways associated
with rock bodies called dikes. These narrow bodies form when magma rising toward the surface
follows zones of weakness in the surrounding rock. As the acidic brew moves along these
dike pathways, it filters out along permeable layers.
The hydrothermal alteration is most intense near the dike swarms, and the largest dike
swarm lies on the west flank of the volcano in a line from roughly the summit through
Sunset Amphitheater and down Puyallup Cleaver. And the hot fluids have moved along the dike
surfaces and have pervaded out into the rubbly zones, so those tend to be the most intensely
altered material.
Extensive alteration at Mount Rainier causes landslides such as the Osceola to transform
almost completely to mudflows. Most of the landslide debris is carried far downstream,
making Mount Rainier especially dangerous. While the landslide at Mount St. Helens was
almost as large as the Osceola, less than 1% of its volume continued downstream as a
mudflow.
Mudflows from major landslides are the most far-reaching hazard at Mount Rainier, but
eruptions on high-glaciated volcanoes can also produce mudflows, less extensive but
still dangerous. Lava flowing over snow and ice seldom melts enough water to produce a
mudflow, but large, slow-moving lava flows like those that have formed Mount Rainier
sometimes collapse and break apart, producing avalanches of hot volcanic rocks, gas and
ash called pyroclastic flows. These flows can plummet down a volcano at speeds up to
100 miles per hour, destroying everything in their path. Imagine the collapse of such
a flow on Mount Rainier. Hot boulders tumbling down the face of the mountain would tear up
snow and ice, melting them almost instantly. Surging water would pluck up loose sediment
and transform rapidly to a mudflow.
Mudflow deposits are loose and easily eroded. Only a few are preserved on the mountain,
but ash that billows up from pyroclastic flows can settle over a large area, leaving behind
a thin layer that records its passage. Jim Velance has been studying the history revealed
by ash deposits in Mount Rainier's Alpine Meadows. Beneath the meadow's surface, more
than 25 thin, dark layers of ash and lava fragments record pyroclastic flows that have
occurred since the Osceola collapse. Some of these flows could have melted enough snow
and ice to form major mudflows.
Pyroclastic flows have actually occurred throughout Mount Rainier's history. Early
investigators thought that many of the rubbly layers on the mountain were the remains of
ancient mudflows, but Tom Sisson has found that many of them record pyroclastic flows.
These large buttresses behind us made up of resistant rock are lava flows. Each one of
those cliffs is an individual lava flow. And then underneath them we see this rubbly appearing
material that looks like blocks sitting in cliffs of dirt. Those are pyroclastic flow
deposits. Very probably we had lava flows coming down in one area and then pyroclastic
flows rushing down the mountain to either side of them.
Mount Rainier can also generate smaller, more frequent mudflows that begin as floods from
glaciers. Hidden channels inside glaciers can become overloaded with water from heavy
rain or rapid melting. When this water is released suddenly in a glacial outburst flood,
it can rapidly pluck up sediment and form a mudflow.
In 1947, a glacial outburst flood and mudflow on Couts Creek buried the main park road under
28 feet of mud and debris. And since 1967, more than 20 such mudflows along Tahoma Creek
have diverted the stream. Water now rushes through a tangle of trees and blocks the west
side access road. The old roadbed is now a deep, rubbly water course. Mudflows such as
these pose a danger along all of Mount Rainier's streams, but they seldom travel far beyond
the boundaries of Mount Rainier National Park.
Mount Rainier will continue to produce mudflows from landslides, eruptions and glacial floods,
though no one can predict exactly when or where these events will occur. But scientists
have established the extent of past mudflows, and have also produced a series of new maps
that identify areas that are likely to be inundated in the future.
Great mudflows triggered by landslides, such as the electron, are likely to affect the
areas shown here in blue. Anyone living in these areas runs a one in ten chance of being
affected by such a mudflow during their lifetime.
Scientists cannot yet provide warning of these sudden mudflows that arise from landslides.
But before an eruption, magma forces its way upward, shaking the earth and deforming the
surface of the volcano. By tracking these warning signs, scientists can anticipate the
onset of an eruption, commonly days or even weeks before the event.
Since 1970, geophysicist Steve Malone and his colleagues at the University of Washington
have recorded thousands of small earthquakes beneath Mount Rainier. They occur mainly in
two zones, one related to the volcano, the other probably associated with an ancient
buried fault system. With any change in the normal pattern of earthquakes, the U.S. Geological
Survey's Volcano Hazards Team will gear up and increase its monitoring activity.
Scientists will re-survey the mountain, measuring small changes in shape and the growth of cracks,
features that allow them to track the movement of magma within the volcano. Such changes
often signal an imminent eruption, and the chemistry of volcanic gases sampled from the
air can also signal that magma is rising.
When the volcano becomes restless, we'll probably need to set up a temporary volcano
observatory close to Mount Rainier in order to bring all of the monitoring information
into that observatory in real time, and to have a team of scientists there who can assess
hazards, determine what kinds of things are likely to happen if an eruption actually occurs,
and which areas will be affected, and a group of scientists who can communicate this information
24 hours a day if necessary to public officials.
Through years of experience monitoring volcanoes around the world, the U.S. Geological Survey
now has the ability to anticipate eruptions and provide warning to surrounding populations.
Even so, when people are unprepared, the results can be disastrous.
In the case of Nevada del Rolís, the volcano in Colombia, a small eruption in 1985 produced
hot products that melted large volumes of snow and produced water that coursed down
the valleys leading away from the volcano. The water became mudflows and the mudflows
devastated communities, causing the loss of about 25,000 lives.
Most loss of life at Nevada del Rolís occurred in the city of Armero. Similar mudflows had
buried Armero only 140 years earlier, in 1845. Then, one Jose Acosta had written,
It is astonishing that none of the inhabitants of these villages, built on the solidified
mud of old mass movements, has even suspected the origin of this vast terrain, although
ancient traditions testify to the frequent mudflows in this region.
Towns in the river valleys that drain Mount Rainier are also built on the solidified mud
of old mass movements. Will they someday suffer the same fate as the city of Armero?
They need not. Scientists, public officials, land use planners and emergency response agencies
are working together to prepare for future destructive events from Mount Rainier.
But any useful plan ultimately depends on many people understanding the hazards and
making decisions that lower their risks. Decisions involving use of land in hazard-prone areas
and community response to volcano emergencies.
We've seen that major landslides and volcanic eruptions on Mount Rainier have sent mudflows
into areas far from the mountain that are now densely populated. Even so, Mount Rainier's
inspirational power might easily tempt us to ignore this evidence. Yet the volcano's
darker face is ever there, waiting for some certain yet unknown moment to remind us of
its instability and power.
Actions taken now to prepare for that event can make the difference for us or perhaps
for our children's children. When Mount Rainier next threatens, will we be surprised or prepared?
Here's what happened.
Thank you.