Tectonics: Mount St Helens Case Study

Referred to as the event that

spawned the birth of Modern

volcanology as a science, May

the 18th 1980 is a day burned in

the memory of millions of scien-

tists, residents and observers.

This was the first time a volcano-

logical event was so well record-

ed, monitored and predicted, and

then broadcast around the world.

Important to scientists and stu-

dents alike as the only recent

case study iof a major acidic

eruption in an MEDC, the les-

sons learned from this cataclys-

mic eruption were far reaching,

and led to many advanced moni-

toring systems being installed on

other deadly volcanoes around

the world.

In early march, the first signs of

significant activity since 1840

were detected. Starting as a small

swarm of earthquakes around the

volcano. Within 48 hours from

noon on March 25th, over 174

quakes of magnitude 2.6 and

over were recorded. By the week

of the 18th of May, there were 8

magnitude 4 or higher quakes per

day.

For the next two months, the

North side of the mountain

swelled as magma was injected

into the chamber, pushing the

north face upwards and out-

wards. This

started to desta-

bilize the slope,

and numerous

small collapses

and small erup-

tions were ob-

served.

(eruption col-

umns under 3km high)

The United States Geo-

logical Survey (USGS)

had been on site since

the start of the activity.

A series of seismometer

and geodetic stations

(Geodesy is the study of

the shape of the earth)

were positioned around

the volcano.

By April the 3rd, the

governor had declared a state of

emergency and order the evacu-

ation of most of the citizens

within the immediate danger

zone. One infamous resident,

Mr. Harry Truman, was among

those who refused to leave his

property and disbelieved the

geologists warnings.

As the eruption continues in

small bursts and harmonic trem-

ors for the next month, the pub-

lic began to loose interest, and

evacuated residents exerted

pressure on geologists to allow

them back into the exclusion

zone on the 17th of May, a se-

cond trip back to houses for

possessions was planned for 10

O'clock the next morning.

At 8:32 that Sunday morning, a

Magnitude 5.1 tremor loosed

the north face and triggered a

massive landslide. The removal

of just under 3 Km3 of mass

above the magma chamber trig-

gered a massive eruption about

7 seconds after the slide. The

landslide was a significant vol-

ume of material, however, the

initial release of pressure creat-

ed a pyroclastic blast of molten

magma and other ejectiles that

moved at speeds of between

220km/hr at the start to over

650km/hr over 20 miles away

from the vent. The combina-

tion of the slide and flow

caused the lake level to be

raised by 90m, feeding the

new ash deposits with water

creating Lahars, and stripping

bare the 600 square KM of

surrounding pine forests.

This was the first time geolo-

gists had ever realized the a

volcanic blast did not neces-

sarily go straight upwards, but

can come laterally out of the

cone. For USGS Volcanolo-

gist David Johnston, pictured

left, this realization came too

late as he was directly in the

path of the blast.

The eruption continued until

October 1980, killing 57 peo-

ple and the effects were felt as

far away as Wales. Even today

the volcano is still rumbling,

but much has been learned that

aids in current prediction and

management around the

world.

Mt St Helens - What on Earth Happened? Nearly 30 years ago, Americas most beautiful volcano came to life after a 120 year period of dormancy in an explosive demonstration of earths terrifying power. This issue discusses the event, what effects the eruption had, how far on the road to recovery we are, and how much longer it will take. Most importantly this issue will question; can America cope with this disaster again?

The Huish Volcanologist

R I C H A R D H U I S H C O L L E G E 01/06/2009

Timeline:

March—EQ’s signal

awakening from a 123

year sleep

April—State of Emer-

gency and evacuation

of residents and tourists

May 18th—massive

landslide triggers the

first lateral blast ob-

served in history killing

57 people

May 18th 1980 1

The Primary Impacts 2

MSH Lahars 2

Long Term Recovery 3

Potential Hazards 4

Further Reading 4

Inside this issue:

The impacts of any geomorphologi-

cal event are split into primary and

secondary. The most significant pri-

mary impact in this case was the

blast, which at times crossed the

sonic boundary. The debris flow was

superseded by a gas cloud moving

slightly faster, the average tempera-

ture of these clouds is 1000 degrees.

Containing blocks the size of double

Decker buses, molten lava

and parts of the volcano

wall, this cloud instantly

vaporized water it came

into contact with and

carbonized all organic

matter.

The blast itself did not last longer than 30 seconds, but

within that time it had devastated areas as far away as

30km, and the extreme heat caused devastation much

further afield.

What the blast did, was to open up the throat of the

magma chamber, relieving pressure and causing mag-

ma from deeper sources to ruch into and recharge the

chamber. Once started, the volcano formed an eruption column

that reached 19km high within 10 minutes. This column fed other

flows that sped down the flanks, and volcanic bombs to fall fur-

ther from the vent which created pits almost 20m deep and send-

ing as almost 2km up into the air.

Fifty-seven people were killed and 200 homes, 27 bridges,

15 miles (24 km) of railways and 185 miles (300 km) of high-

way were destroyed

The eruption ejected more than 1 cubic mile (4 km³) of materi-

al. A quarter of that volume was fresh lava in the form of ash,

pumice, and volcanic bombs while the rest was fragmented,

older rock.

The removal of the north side of the mountain (13% of the

cone's volume) reduced St. Helens' height by about 1,313 feet

(400 m) and left a crater 1 to 2 miles (2 to 3 km) wide and

2,100 feet (640 m) deep with its north end open in a huge

breach. The Ash and subsequent 17 pyroclastic flows deposit-

ed ash in 11 US states. 4 Billion Board feet worth of timber

was destroyed, one of the defining factors in the low mortali-

ty rate was that as it was a Sunday, had it been any other day

of the week, 300 loggers would have been working in the

blast zone.

Environmentally the devastation was total within the baslt

zone, for 30km around the main vent, the thermal blast

seared all life, and covered land and water alike with thick

ash deposits. 1500 elk and 5000 deer were killed, and as

amany as 7000 big game animals such as brown

bear. 12 Million Salmon and Chinook fingerlings

(small fish) died as the lakes acidified and boiled,

and over 40 000 mature salmon were forced to flee

the waters through turbines they normally swam

over.

In terms of issues to populations, poor visibility

closed several airports in Washington state, Inter-

state 90 was closed for two weeks, 1000 commer-

cial flights were cancelled. Sewerage and water sys-

tems were clogged, with many local businesses clos-

ing for the duration.

Melting of the summit glaci-

ers—fed theinitial lahars which

started in the summit zone at

around 90MPH slowing to

3KMPH 30 km away. These

flows moved upstream along

the Cowlitz river by 27 miles, in

a 4m high wall of muddy water

The mountain streams and

brooks—becoming clogged

with ash

In total the lahars were responsible for

some major damage including de-

stroying 27 bridges, 298km of high-

ways, 25km of railways and stranding

31 ships in the Columbia River whose

depth was reduced from 12 to 4m.

One of the most significant hazards

during and after the eruption was the

generation of lahars. These came

from several sources and were used

as an example of what could and in-

deed did happen in the Nevado Del

Ruiz eruption.

Spirit lake– overwhelmed by

the landslide and the lateral

blast, the water boiled killing

all aquatic life and then mobi-

lized the settling ash into a

lahar

Caption describing pic-ture or graphic.

MSH: Lahars

The Primary Impacts

The Huish Volcanologist Special Edition

“The nature of

movement was

eerie.... The

entire mass began

to ripple and

churn up, without

moving laterally.

Then the entire

north side of the

summit began

sliding to the

north”

Keith Stoffel,

Geologist flying

over the eruption

column

Page 2

The eruption phase that started in May

continued actively until October of that

year. There have been numerous phas-

es pf activity since then, but don as

dramatic as the 1980 eruption. The

effects of that day have had reverbera-

tions around the world, and can be split

into distinct groups:

Volcanological:

The eruption ceased by 1982, but there

have been several renewed bursts

since then. There have been 7 domes/

spines since 1980, including the whale-

back, pictured above. These spines

grow and collapse periodically, with the

1987 third dome reaching 900m by

800m. Following the pyroclastic flows

and lahars, ash removal from the state

took 10 weeks and cost $2.2 million.

The flows were still at 300 to 420 De-

grees two weeks after the eruption,

and the interaction of groundwater and

hot deposits caused numerous small

explosions within the flows, continuing

for several months.

Environmental:

Although devastation within the blast

zone was total, all forms of life blown

up, carbonized or buried in ash, recov-

ery speed has taken scientists by sur-

prise. This picture at the bottom of the

page shows the same site in 1988 and

2001, secondary succession has taken

place so rapidly partly due to the na-

ture of the eruption. Unlike basic volca-

noes like Hawaii, the erupted material

was ash and pyroclastics, meaning it

was already broken down into small

fragments, meaning weathering could

take place rapidly. The buried seeds

and bulbs could break through loose

ash and the surrounding intact forests

provided a source of plants that grew

into the damaged area, and birds and

animals transported seeds through drop-

pings into the fertile ash.

Social:

57 people were killed in the eruption, by

the time the blast reached them it

was still 360 degrees Celsius causing

instant asphyxiation. Among those

that died were a National Geograph-

ic Photographer and David John-

ston, a young USGS volcanologist

who was stationed immediately in

front of the bulge. The ridge were

he died has been renamed Johnston

Ridge. Over 200 homes were de-

stroyed completely by the blast, the

loss of homes and land is a signifi-

cant set back to local recovery.

There was a marked increase in depres-

sion and other mental health issues in

the months following the start of recov-

ery

On a more positive side, the information

gained from observing this eruption with

high tech equipment and a range of rele-

vant experts on hand meant that signifi-

cant advances in prediction capability

and monitoring were made. The under-

standing of the lateral blast phenomena

and the lahars produced by the meting of

summit glaciers and snow was used to try

and aid the population of Armero during

the 1985 eruption of Nevado Del Ruiz

(Unfortunately

the advice was

not heeded, and

the Lahars gener-

ated by Glacier

melt killed 23000

people).

The eruption also

led to a significant over hall of most mon-

itoring stations in the Cascades range,

and the CVO (Cascades Volcano Observa-

tory) re-evaluated the status of several

other volcanoes.

Economically:

The most up to date estimate of the costs

of the eruption was $2.74 Billion in 2007

dollars. Congress sent $951 Million to

FEMA the US Army Corps of Engineers

and the Small Business Administration.

Unemployment in the area rose by a fac-

tor of ten a few weeks after the eruption,

and tourism in the region was crippled by

the fact that the Mount Baker camp was

utterly destroyed and access to the area

was restricted . Many conventions and

larger social gatherings were relocated

away from the Washington area.

However, these effects were temporary,

and once the national park was reopened

there was a resurgence of visitors who

had observed the eruption on the news,

attracting an entire new group of volcano

based tourists. This influx still continues

today, in 1987 when the site was reo-

pened to climber, a permit was required

for access to the faces costing $22/day,

and half hour helicopter rides costing

$149 per person give you a guided tour of

the summit.

Mount St. Helens National Volcano Mon-ument, which is run by the U.S. Forest Service and straddles Cowlitz and Skama-nia counties, account for much of Cowlitz County's $90 million annual tourism reve-nue and pump about $15 million a year into Skamania County. About 2,400 jobs in both counties are tourism-dependent.

Educational:

Learning continues apace around the volcano. There were 21 active periods between 1980 and 1990, and a google Scholar search reveals over 20,000 papers written about the eruption.

Long Term Recovery and Impacts

The Huish Volcanologist Special Edition

“half hour

helicopter rides

costing $149 per

person give you a

guided tour of the

summit”

Page 3

Potential for Future Hazards

One of the areas worst affected, that still poses a dangerous risk to the area, is Spirit

Lake. Annihilated by the 1980 eruption, the blast hit the lake, sending water 240m up

the hillside, and blocking the outlet. This led to a 60 m rise in the level of the lake, which

within a month had become devoid of all oxygen and life. Scientists initially despaired

that life would take years to come back, but by 1983, there was more biological activity

than ever before, and fish had returned by 1993.

The risk the lake poses is of overflowing and remobilizing loose ash deposits as cold la-

hars. The outlet was blocked by loose ash and pyroclastic deposits, which being uncon-

solidated, will not hold indefinitely,. To reduce the risk of overflow and lahars, there is

no a drainage tunnel removing water and maintaining a safer lower level.

The other risks relate to periods of renewed activity, there will be lahars following signif-

icant rainfall, and small eruptions related to dome building and collapse. The risk is al-

ways higher over winter and is carefully monitored and managed by hazard mapping and

evacuation routes.

MSH is now one of the most heavily monitored volcanoes in the world. The information

it provides is invaluable for predicting other future eruptions

Geography Department

South Road

Taunton

TA1 3DZ

There is a wealth of information about the vol-

canoes on the web. The best source for infor-

mation is the USGS< who have the dedicated

Cascades Volcano Observatory (CVO):

http://vulcan.wr.usgs.gov/

An interesting comparison can be made by look-

ing at eruptive styles and management on Ha-

waii and in the Cascades, this link takes you to

the Hawaiian Volcanoes Observatory where you

can make detailed comparisons between the

risks posed by acidic composite cones and the

basic effusive activity in the pacific:

http://hvo.wr.usgs.gov/

There is an excellent documentary frequently

on TV called “The eruption of Mt St Helens”

made a camera team dropped in the blast zone

two days after the eruption, who found that

compasses did not work, and the volcano was

still erupting

The other good documentary with excellent

footage is “Seconds from disaster: the eruption

of Mt St Helens”.

Key Questions:

Evaluate the management of this hazard

The eruption of MSH in 1980 had only negative

impacts—to what extent do you agree with this

statement?

Useful Links

Phone: 01823 320800

E-mail: [email protected]

R I C H A R D H U I S H C O L L E G E