Lecture 10: Volcanic eruptions in NW North America: Lessons learned Flashcards
The Caribbean Island of Montserrat is dominated by an active volcano, Soufrière Hills
It was known to be active, but no eruptions occurred since C19th until the late C20th
Eruption began July 1995. Much of the island was evacuated and the main town, Plymouth was buried in a pyroclastic flow.
In 1997, 19 people died in another eruption.
Examples of why people may put themselves in danger
- Local residents gradually build up resistance to precautionary actions (Peter and the Wolf)
- Underprivileged local people (with few options) may defy exclusion zones in order to continue with their livelihoods. There were casualties in the 1997 eruption because of this.
The social and political dynamics around living with a hazard are complex.
• It is easy for those in authority to make mistakes.
• It is easy for the public to blame those in authority.
• Deciding what to do, especially when the event is long-running and unpredictable in both timing and magnitude, can often be extremely difficult.
Mt St Helens, 1980
Mt Redoubt, 2009
Mt. St. Helens 1980
First major eruption in the USA in the era of modern science 57 persons killed
Mt. St. Helens 1980. At the time, the most intensively studied and monitored major eruption ever.
However, it was highly unusual.
A lack of knowledge and experience, plus an underestimated level of public risk, meant nearly 60 people died when the volcano underwent a massive explosive eruption on May 18.
The actions preceding May 18
Earthquakes and tremors occurred for several months preceding the major event and were taken seriously. A meeting in March developed a coordinated plan and was led by the Forest Service.
Many of the resources and communications protocols used for dealing with forest fires were put in place: planes, roadblocks, 24- hour comms, radio and tv briefings, etc
Agencies and scientists influencing decisions and responses:
- US Forest Service
- US Geological Survey
- University of Washington seismology department
- State government
- Local government/county sheriffs
- Federal Aviation Authority
- Utility companies (reservoir, NP station)
Tourists who were interviewed often said they wanted to see the volcano erupt
– it was viewed as entertainment
—poor risk judgement, lack of information
On May 16 (Friday) there would have been hundreds of loggers in the forest.
On May 17 (Saturday) 500 people went up to Spirit Lake (with the authorities’ permission) to check out properties.
In the blast zone, pyroclastic debris currents flattened everything in their path.
The eruption was so deadly because material came out sideways.
One of the longest debris avalanches ever observed flowed away from the mountain…
23 miles down the Toutle River.
It was followed by lahars or mudflows –derived from the volcanic materials and instantly melted ice and snow, which flowed over the debris and even further downstream.
The volcanology:
Shallow intrusion of magma into cone. The bulge suggested
that something odd going on.
Geologists feared a massive landslide…. And there was a landslide; the debris avalanche uncorked the magma, which was cooling but had enough gas in it to expand and blow the magma apart. Hot, full of rock fragments, and with tremendous power a pyroclastic density current – even more devastating than a pyroclastic flow– overtook the avalanche and destroyed everything and everybody in its path.
What were the lessons learned?
Permanent volcano watch needed (Volcano Observatories established)
Designate lead agency for emergencies
Have a clear federal emergency plan (works the same in any state)
You can learn from eruptions and use information to develop contingency plans
Err on the side of caution
Alaska contains…
over 130 volcanoes and volcanic fields, many of which have been active within the last two million years.
Cook Inlet at the north end of the Gulf of Alaska is an oilfield.
In 2009, tankers were uploading at the Drift River Oil Terminal, which is connected by pipelines with the oil rigs, to take the oil to refineries located on the other side of the inlet or elsewhere.
Technological hazard
In 1990…
A lahar reached the oil terminal, depositing about 1 m of mud
The 1990 eruption lahar generated a flood x100 larger than the expected 100- year flood. Dykes and levees were subsequently reinforced
