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Mount St Helens

Location and general.

  • One of the five volcanoes in the Cascade Range in Washington State, USA.
  • Caused by the oceanic crust (Juan de Fuca) plate subducting under the continental crust (North American plate). The oceanic  crust was destroyed and formed magma which rose to the surface. 
  • Like the others, had been dormant for many years. 
  • In March 1980 there were signs of an impending eruption, as first earthquakes occurred and then steam filled with ash exploded onto the white glacial summit of the mountain.
  • Residents had been told to leave and visitors were not allowed inside a 8km exclusion zone around the crater.
  • The eruption happened at 8:32am on 18th May.

​The Effects

  • An earthquake measuring 5.1 on the Richter Scale caused a landscape on the north-east side of the mountain - the biggest landslide ever recorded and the sideways blast of pulverised rock, glacier ice and ash wiped out all living things 27km north of the crater,
  • In the outer 'blow-down' zone, the trees (some 500 year old cedars) were uprooted and tossed about like matchsticks.
  • 57 people died including the vulcanologist David Johnston.  

Immediate Responses

  • Those in the immediate vicinity could not have survived, but tourists caught in mudflows or by the lateral blast could be rescued.
  • Many people were stranded as the roads were blocked by ash, so the roads were cleared in three days so that traffic could flow. 
  • The ash also posed a health risk, so President Carter promised to send two million more face masks. 

Long-Term Responses

  • The ash improved soil fertility, allowing vegetation to return, so letting animals such as insects, birds and animals to survive there also. 
  • Trees had been knocked over and killed by wind and heat, especially those near the volcano, so many were replanted.
  • Also, buildings and bridges had to be rebuilt, as many were damaged by falling trees and heat. 

Environmental hazards Case study: Mt. St Helens 1980

Understanding why natural hazards occur can help countries to manage or prevent their consequences. Case studies illustrate the impact of natural hazards in the short and long term.

Case study: Mt. St Helens 1980

Mt. st. helens 1980.

A very common case study for volcanoes is the eruption of Mount St Helens in the USA in 1980. Other case studies include the eruption of Mount Etna in Sicily in 1974 and Heimaey eruption in Iceland in 1973.

The underlying causes

Mount St. Helens, Washington State, began its most recent series of eruptions in 1980 when a massive landslide close landslide When the rocks on the side of a steep slope give way. and powerful explosive eruption created a large crater close crater The hole at the top of a volcano where lava and ash escape. , and ended six years later after more than a dozen eruptions of lava built a dome in the crater.

The first sign of activity began in the spring of 1980 with a series of small earthquakes began. After thousands of additional earthquakes and steam explosions, a cataclysmic eruption occurred on 18 May 1980.

Mount St Helens lies close to a destructive plate boundary close destructive plate boundary This happens where crustal plates move together and one is forced beneath the other. where the smaller Juan de Fuca plate is being forced into the mantle by the larger North American plate.

Friction and heat cause the plate to melt and, as it melts, molten rocks are formed. The molten rock builds up until it has the chance to reach the surface through cracks in the Earth’s crust.

Impact on landscape and population

  • The mountain was reduced from a height of 2950m to 2560m as the eruption created the largest landslide ever recorded.
  • All plant and animal life within a 25km radius of the volcano was killed, including fully grown trees.
  • Mudflows close mudflows A mixture of water and soil combined to form a liquid that travels downhill quickly. poured down the valleys choking rivers with rock debris, killing fish and ripping trees from their roots.
  • Sixty one people died due to mudflows, being crushed to death and poisonous gases close poisonous gases Small harmful particles released from a volcano. , while 198 had to be rescued.
  • Mudflows destroyed bridges, houses and logging camps.
  • The explosion flattened buildings and trees and knocked out power supplies and telephones.
  • Ash clouds close ash cloud Fine fragments of rock, minerals and volcanic glass created during eruptions and thrown into the atmosphere. resulted in airline flights being cancelled.
  • Ash caused £100 million of damage to farm machinery and crops.

Methods of prediction and planning

Volcanoes are difficult to predict but, although they were unable to give a precise date scientists tried to predict the eruption of Mount St Helens by measuring the frequency of earthquakes on the mountain.

The greater the frequency, the nearer the eruption and measuring the size of the volcanic cone close volcanic cone The shape of a volcano. shows the build-up of magma in the vent. Scientists can also check for gas emissions close gas emissions Small particles released from a volcano. (sulphur dioxide) and increased thermal activity close thermal activity Increased heat in a volcanic area. at the crater. However, even before the eruption of Mount St Helens, scientists thought that the it might still be a few weeks away.

The authorities were able to evacuate people from the areas surrounding Mount St Helens, after the areas affected by the previous eruption and they set up an exclusion zone close exclusion zone An area where people are not permitted to be. around the volcano. Emergency services were also on hand to rescue close rescue When people are removed from danger. those people needing help.

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Mount St Helens Case Study

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Impacts 2 month warning build up and very closely monitored Knowledge on the past historical eruption pattern Social Impacts 57 killed 200 homes lost Little shock/stress as population were fully aware it would happen Economic Impacts $3 billion damage Ash made roads slippery Lahars blocked roads Crops destroyed in ash cover -economic decline for agriculture 47 bridges were destroyed 300km of roads blocked visibility poor for 2 weeks -aiports had to shut ash caused power cuts and blackouts Envirnomental Impacts Fish killed in hot choked rivers Wildlife wiped out eg 5000 deer Thousands of trees blasted over 600km2 540m tonnes of ash fell on 60 000 km2 -thick cover

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... Chapter 3: Near-Real-Time Information Products for Mount St. Helens—Tracking the Ongoing Eruption, by Anthony I. Qamar, Stephen D. Malone, Seth C. Moran, William P. Steele, and Weston A. Thelen (10-page PDF; 7.2 MB). ...

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Executive summary All explosive volcanic eruptions generate volcanic ash, fragments of rock that are produced when magma or vent material is explosively disintegrated. Volcanic ash is then convected upwards within the eruption column and carried downwind, falling out of suspension and potentially affecting communities across hundreds, or even thousands, of square kilometres. Ash is the most frequent, and often widespread, volcanic hazard and is produced by all explosive volcanic eruptions. Although ash falls rarely endanger human life directly, threats to public health and disruption to critical infrastructure services, aviation and primary production can lead to potentially substantial societal impacts and costs, even at thicknesses of only a few millimetres. Communities exposed to any magnitude of ash fall commonly report anxiety about the health impacts of inhaling or ingesting ash (as well as impacts to animals and property damage), which may lead to temporary socioeconomic disruption (e.g. evacuation, school and business closures, cancellations). The impacts of any ash fall can therefore be experienced across large areas and can also be long-lived, both because eruptions can last weeks, months or even years and because ash may be remobilised and re-deposited by wind, traffic or human activities. Given the potentially large geographic dispersal of volcanic ash, and the substantial impacts that even thin (a few mm in thickness) deposits can have for society, this chapter elaborates upon the ash component of the overviews provided in Chapters 1 and 2. We focus on the hazard and associated impacts of ash falls; however, the areas affected by volcanic ash are potentially much larger than those affected by ash falling to the ground, as fine particles can remain aloft for extended periods of time. For example, large portions of European airspace were closed for up to five weeks during the eruption of Eyjafjallajökull, Iceland, in 2010 because of airborne ash (with negligible associated ash falls outside of Iceland). The distance and area over which volcanic ash is dispersed is strongly controlled by wind conditions with distance and altitude from the vent, but also by the size, shape and density of the ash particles, and the style and magnitude of the eruption. These factors mean that ash falls are typically deposited in the direction of prevailing winds during the eruption and thin with distance. Forecasting ash dispersion and the deposition 'footprint' is typically achieved through numerical simulation. https://www.cambridge.org/core/terms. https://doi.


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Mount St. Helens’ 1980 Eruption

Changed the future of volcanology.

If scientists armed with today's monitoring tools and knowledge could step back in time to the two months before May 18, 1980, they would have been able to better forecast the forthcoming devastating eruption.

Plinian column from May 18, 1980 eruption of Mount St. Helens. Aeri...

Forty years ago, after two months of earthquakes and small explosions, Mount St. Helens cataclysmically erupted. A high-speed blast leveled millions of trees and ripped soil from bedrock. The eruption fed a towering plume of ash for more than nine hours, and winds carried the ash hundreds of miles away. Lahars (volcanic mudflows) carried large boulders and logs, which destroyed forests, bridges, roads and buildings. These catastrophic events led to 57 deaths, including that of David Johnston , a dedicated USGS scientist, and caused the worst volcanic disaster in the recorded history of the conterminous United States. 

Had we known then what we know today about volcanoes, could the loss of life and economic damage caused by the Mount St. Helens eruption have been prevented or mitigated?

For the answer, let’s travel forward to the present. Over the past 40 years, technology and the scientific study of volcanoes have made significant advances.  Better cooperation, monitoring and forecasting possibly could have allowed for earlier evacuations, hazard mitigation and reduced risk. But the truth is the eruption of Mount St. Helens sparked the advances in cutting-edge volcano science and monitoring that exist today. 

Mount St. Helens turned out to be the ideal laboratory to study volcanic activity. The 1980 eruption was the first large explosive eruption studied by scientists and observers using modern volcanology. The volcano was also easily viewed and accessible. As a result, the eruption and its effects were heavily photographed from numerous vantage points. The debris avalanche opened the cone, and scientists were able to inspect its interior in a new and novel way. The eruption jump-started interest in the study of explosive eruptions and monitoring efforts to improve warning systems that help mitigate hazards. The eruption underscored the importance of using as many monitoring tools as possible to track unrest and eruption activity.

The north flank collapse and eruption at Mount St. Helens also informed volcano scientists on how to interpret the hummocky terrain near other Cascades volcanoes, such as California’s Mt. Shasta. We now know that type of terrain is evidence of a past flank collapse at that volcano about between 300,000 and 380,000 years ago that occurred without an eruption.

Before 1980, scientists saw sharp divisions among volcano hazard studies, volcano monitoring and basic volcanology research. The 1980 eruption, however, required scientists to work together in a more integrated manner. Mount St. Helens changed the way that scientists do business by linking specialists from many disciplines. Now, 40 years later, it is routine for geologists, seismologists, geophysicists, hydrologists, geochemists and biologists to cooperate in studies of natural science processes resulting in well-integrated research, monitoring and communication. 

The eruption also led to a new era of volcanic monitoring. During studies at Mount St. Helens, scientists refined their interpretations of monitoring data in order to better forecast future eruptions. Earthquakes, ground deformation and gas measurements took on new meaning as the volcano demonstrated that patterns of change could help scientists forecast lava-dome building eruptions. Scientists now use similar patterns of change to forecast future activity at volcanoes around the world. 

Mount St. Helens and North Fork Toutle River Channel....

Since the eruption of Mount St. Helens, volcano monitoring has evolved from placing a few scientific instruments on a volcano’s flanks to a broader integrated network of monitoring devices that measure earthquakes, deformation and volcanic gases, and can detect eruptions or changes on the Earth’s surface from space. The evolution of tools like photogrammetry, Geographic Information Systems (GIS), and Light Detection and Ranging (lidar) enable scientists to make precise measurements and illustrations of changes to Earth’s surface, including inflation and deflation at volcanoes. Technological revolutions in telemetry, broad-band seismometer technology, and low-power instrumentation are fueling a new era of volcano monitoring equipment capable of collecting and transmitting real-time data remotely with increased precision, efficiency, portability and value, and with reduced risk to scientists. 

The explosive eruption of May 18, 1980, illustrates the importance of developing new tools for measuring ground deformation at explosive volcanoes. Tiltmeters and surveying instruments were the only instruments available for monitoring the large .9- to 1.2-mile bulge (1.5 by 2 km) in the north face of Mount St. Helens in 1980. Today, scientists can remotely use high-precision Global Positioning System receivers, sophisticated borehole tiltmeters and strainmeters, and other sensors to measure and report even small amounts of deformation at the centimeter scale continuously and in real time. In addition, using a remote sensing technique called InSAR (interferometric synthetic aperture radar), they combine satellite radar images to map ground deformation in remarkable detail over large areas. With the experience gained at Mount St. Helens, new deformation monitoring tools have enabled scientists to reduce risks to lives and property globally.

The Mount St. Helens eruption also gave credibility to U.S. volcanologists who were subsequently invited to participate in the response to volcanic crises in other countries. Scientists at the U.S. Geological Survey (USGS) Cascades Volcano Observatory , for example, developed a mobile observatory to help respond to quickly developing volcanic situations. This rapid-deployment capability led to the formation of the Volcano Disaster Assistance Program, which is co-funded by the U.S. Agency for International Development (USAID) and the USGS. VDAP scientists have traveled to volcanoes world-wide to share their experience at Mount St. Helens and to learn from other volcanic events. Since 1986, VDAP has responded to more than two dozen major volcanic crises in a dozen countries.

Now, let’s step into to the future. The eruption of Mount St. Helens has influenced volcanology in many ways, and the next step in this evolution is the National Volcano Early Warning System, or NVEWS . In March 2019, USGS was authorized by Congress to develop and implement NVEWS to more fully monitor volcanoes and to warn and protect citizens of the United States from danger caused by volcanic activity. When NVEWS is fully implemented, all hazardous U.S. volcanoes will be monitored at levels consistent with the threat they pose to communities, infrastructure and aviation. Pro-active early warning of a potential eruption is key to minimizing loss of life and economic disruption by increasing the time that emergency managers can initiate mitigation measures, improve evacuation alerts and better position resources for recovery.  Earliest detection of eruption precursors with multiple instrument types allows for more accurate forecasts of hazardous eruptive activity needed by land managers and the aviation sector.

USGS scientist observing Mount St. Helens' crater and dome from the...

As we reflect on the influences of the Mount St. Helens eruption over the last 40 years, we should remember that many volcanoes are basically unstable mountains. They grow by piling up lava and ash into cones with steep-sided slopes that are prone to collapse causing massive landslides known as debris avalanches. The debris avalanche caused by the 1980 eruption was the third large debris avalanche known to have happened there in the last 20,000 years. By understanding its history, scientists know that over time Mount St. Helens will be rebuilt again, a process already evident in the volcano’s 2004 eruptive events. 

To learn more about how the eruption influenced Volcanology please read, “ Ten Ways Mount St. Helens Changed Our World—The Enduring Legacy of the 1980 Eruption .”

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