Tectonics: Mount St Helens Case Study


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An example of the level of detail needed for A2 case studies and a discussion of the Mount St Helens 1980 eruption.

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Tectonics: Mount St Helens Case Study

  1. 1. RICHARD HUISH COLLEGE 01/06/2009The Huish Volcanologist 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? Referred to as the event that umns under 3km high) spawned the birth of Modern The United States Geo-Inside this issue: volcanology as a science, May logical Survey (USGS) the 18th 1980 is a day burned in had been on site sinceMay 18th 1980 1 the memory of millions of scien- the start of the activity. tists, residents and observers. A series of seismometerThe Primary Impacts 2 This was the first time a volcano- and geodetic stations logical event was so well record-MSH Lahars 2 (Geodesy is the study of ed, monitored and predicted, and the shape of the earth) then broadcast around the world.Long Term Recovery 3 were positioned around Important to scientists and stu- the volcano.Potential Hazards 4 dents alike as the only recent case study iof a major acidic By April the 3rd, the eruption in an MEDC, the les- governor had declared a state of magma and other ejectiles thatFurther Reading 4 sons learned from this cataclys- emergency and order the evacu- moved at speeds of between mic eruption were far reaching, ation of most of the citizens 220km/hr at the start to over and led to many advanced moni- within the immediate danger 650km/hr over 20 miles away toring systems being installed on zone. One infamous resident, from the vent. The combina- other deadly volcanoes around Mr. Harry Truman, was among tion of the slide and flow the world. those who refused to leave his caused the lake level to be property and disbelieved the raised by 90m, feeding the In early march, the first signs of new ash deposits with water geologists warnings. significant activity since 1840 creating Lahars, and stripping were detected. Starting as a small As the eruption continues in bare the 600 square KM of swarm of earthquakes around the small bursts and harmonic trem- surrounding pine forests. volcano. Within 48 hours from ors for the next month, the pub- Timeline: noon on March 25th, over 174 lic began to loose interest, and This was the first time geolo- March—EQ’s signal evacuated residents exerted gists had ever realized the a quakes of magnitude 2.6 and awakening from a 123 over were recorded. By the week pressure on geologists to allow volcanic blast did not neces- year sleep of the 18th of May, there were 8 them back into the exclusion sarily go straight upwards, but April—State of Emer- zone on the 17th of May, a se- can come laterally out of the magnitude 4 or higher quakes per gency and evacuation day. cond trip back to houses for cone. For USGS Volcanolo- of residents and tourists possessions was planned for 10 gist David Johnston, pictured May 18th—massive For the next two months, the Oclock the next morning. left, this realization came too landslide triggers the North side of the mountain late as he was directly in the first lateral blast ob- swelled as magma was injected At 8:32 that Sunday morning, a path of the blast. served in history killing into the chamber, pushing the Magnitude 5.1 tremor loosed 57 people the north face and triggered a The eruption continued until north face upwards and out- wards. This massive landslide. The removal October 1980, killing 57 peo- started to desta- of just under 3 Km3 of mass ple and the effects were felt as bilize the slope, above the magma chamber trig- far away as Wales. Even today and numerous gered a massive eruption about the volcano is still rumbling, small collapses 7 seconds after the slide. The but much has been learned that and small erup- landslide was a significant vol- aids in current prediction and tions were ob- ume of material, however, the management around the served. initial release of pressure creat- world. (eruption col- ed a pyroclastic blast of molten
  2. 2. Page 2 The Huish Volcanologist Special Edition (400 m) and left a crater 1 to 2 miles (2 to 3 km) wide and The Primary Impacts 2,100 feet (640 m) deep with its north end open in a huge breach. The Ash and subsequent 17 pyroclastic flows deposit- The impacts of any geomorphologi- ed ash in 11 US states. 4 Billion Board feet worth of timber cal event are split into primary and was destroyed, one of the defining factors in the low mortali- secondary. The most significant pri- mary impact in this case was the ty rate was that as it was a Sunday, had it been any other day blast, which at times crossed the of the week, 300 loggers would have been working in the sonic boundary. The debris flow was blast zone. superseded by a gas cloud moving Environmentally the devastation was total within the baslt slightly faster, the average tempera- zone, for 30km around the main vent, the thermal blast ture of these clouds is 1000 degrees. seared all life, and covered land and water alike with thick Containing blocks the size of double ash deposits. 1500 elk and 5000 deer were killed, and as Decker buses, molten lava amany as 7000 big game animals such as brown and parts of the volcano bear. 12 Million Salmon and Chinook fingerlings wall, this cloud instantly “The nature ofCaption describing pic- movement was (small fish) died as the lakes acidified and boiled, vaporized water it came eerie.... Theture or graphic. entire mass began and over 40 000 mature salmon were forced to flee into contact with and to ripple and the waters through turbines they normally swam carbonized all organic churn up, without moving laterally. over. matter. Then the entire north side of the In terms of issues to populations, poor visibilityThe blast itself did not last longer than 30 seconds, but summit beganwithin that time it had devastated areas as far away as sliding to the closed several airports in Washington state, Inter- north” state 90 was closed for two weeks, 1000 commer-30km, and the extreme heat caused devastation muchfurther afield. cial flights were cancelled. Sewerage and water sys- Keith Stoffel, Geologist flying tems were clogged, with many local businesses clos-What the blast did, was to open up the throat of the over the eruption column ing for the duration.magma chamber, relieving pressure and causing mag-ma from deeper sources to ruch into and recharge thechamber. Once started, the volcano formed an eruption columnthat reached 19km high within 10 minutes. This column fed otherflows 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 destroyedThe 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 Melting of the summit glaci-cones volume) reduced St. Helens height by about 1,313 feet ers—fed theinitial lahars which started in the summit zone at MSH: Lahars around 90MPH slowing to 3KMPH 30 km away. These One of the most significant hazards flows moved upstream along during and after the eruption was the the Cowlitz river by 27 miles, in generation of lahars. These came a 4m high wall of muddy water from several sources and were used as an example of what could and in- The mountain streams and deed did happen in the Nevado Del brooks—becoming clogged Ruiz eruption. with ash Spirit lake– overwhelmed by In total the lahars were responsible for the landslide and the lateral some major damage including de- blast, the water boiled killing stroying 27 bridges, 298km of high- all aquatic life and then mobi- ways, 25km of railways and stranding lized the settling ash into a 31 ships in the Columbia River whose lahar depth was reduced from 12 to 4m.
  3. 3. The Huish Volcanologist Special Edition Page 3Long Term Recovery and ImpactsThe eruption phase that started in May ash and the surrounding intact forests (Unfortunately “half hourcontinued actively until October of that provided a source of plants that grew the advice was helicopter ridesyear. There have been numerous phas- into the damaged area, and birds and not heeded, and costing $149 peres pf activity since then, but don as animals transported seeds through drop- the Lahars gener- person give you adramatic as the 1980 eruption. The pings into the fertile ash. ated by Glaciereffects of that day have had reverbera- melt killed 23000 guided tour of the Social:tions around the world, and can be split people). summit”into distinct groups: 57 people were killed in the eruption, by The eruption also the time the blast reached them it led to a significant over hall of most mon- was still 360 degrees Celsius causing itoring stations in the Cascades range, instant asphyxiation. Among those and the CVO (Cascades Volcano Observa- that died were a National Geograph- tory) re-evaluated the status of several ic Photographer and David John- other volcanoes. ston, a young USGS volcanologist who was stationed immediately in Economically: front of the bulge. The ridge were The most up to date estimate of the costs he died has been renamed Johnston of the eruption was $2.74 Billion in 2007 Ridge. Over 200 homes were de- dollars. Congress sent $951 Million to stroyed completely by the blast, the FEMA the US Army Corps of Engineers loss of homes and land is a signifi- and the Small Business Administration. cant set back to local recovery. Unemployment in the area rose by a fac-Volcanological: There was a marked increase in depres- tor of ten a few weeks after the eruption, sion and other mental health issues inThe eruption ceased by 1982, but there and tourism in the region was crippled by the months following the start of recov-have been several renewed bursts the fact that the Mount Baker camp was erysince then. There have been 7 domes/ utterly destroyed and access to the areaspines since 1980, including the whale- On a more positive side, the information was restricted . Many conventions andback, pictured above. These spines gained from observing this eruption with larger social gatherings were relocatedgrow and collapse periodically, with the high tech equipment and a range of rele- away from the Washington area.1987 third dome reaching 900m by vant experts on hand meant that signifi- However, these effects were temporary,800m. Following the pyroclastic flows cant advances in prediction capability and once the national park was reopenedand lahars, ash removal from the state and monitoring were made. The under- there was a resurgence of visitors whotook 10 weeks and cost $2.2 million. standing of the lateral blast phenomena had observed the eruption on the news,The flows were still at 300 to 420 De- and the lahars produced by the meting of attracting an entire new group of volcanogrees two weeks after the eruption, summit glaciers and snow was used to try based tourists. This influx still continuesand the interaction of groundwater and and aid the population of Armero during today, in 1987 when the site was reo-hot deposits caused numerous small the 1985 eruption of Nevado Del Ruiz pened to climber, a permit was requiredexplosions within the flows, continuing for access to the faces costing $22/day,for several months. and half hour helicopter rides costingEnvironmental: $149 per person give you a guided tour of the summit.Although devastation within the blastzone was total, all forms of life blown Mount St. Helens National Volcano Mon-up, carbonized or buried in ash, recov- ument, which is run by the U.S. Forest Service and straddles Cowlitz and Skama-ery speed has taken scientists by sur- nia counties, account for much of Cowlitzprise. This picture at the bottom of the Countys $90 million annual tourism reve-page shows the same site in 1988 and nue and pump about $15 million a year2001, secondary succession has taken into Skamania County. About 2,400 jobsplace so rapidly partly due to the na- in both counties are tourism-dependent.ture of the eruption. Unlike basic volca- Educational:noes like Hawaii, the erupted materialwas ash and pyroclastics, meaning it Learning continues apace around the volcano. There were 21 active periodswas already broken down into small between 1980 and 1990, and a googlefragments, meaning weathering could Scholar search reveals over 20,000 paperstake place rapidly. The buried seeds written about the eruption.and bulbs could break through loose
  4. 4. RICHARD HUISH COLLEGE Potential for Future Hazards Geography Department One of the areas worst affected, that still poses a dangerous risk to the area, is Spirit South Road Lake. Annihilated by the 1980 eruption, the blast hit the lake, sending water 240m up Taunton TA1 3DZ 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 Phone: 01823 320800 that life would take years to come back, but by 1983, there was more biological activity E-mail: milliew@richuish.ac.uk 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 eruptionsUseful LinksThere is a wealth of information about the vol-canoes on the web. The best source for infor-mation is the USGS< who have the dedicatedCascades 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 tothe Hawaiian Volcanoes Observatory where youcan make detailed comparisons between therisks posed by acidic composite cones and thebasic effusive activity in the pacific:http://hvo.wr.usgs.gov/There is an excellent documentary frequentlyon TV called “The eruption of Mt St Helens”made a camera team dropped in the blast zonetwo days after the eruption, who found thatcompasses did not work, and the volcano wasstill eruptingThe other good documentary with excellentfootage is “Seconds from disaster: the eruptionof Mt St Helens”.Key Questions:Evaluate the management of this hazardThe eruption of MSH in 1980 had only negativeimpacts—to what extent do you agree with thisstatement?