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Mt. St. Helens - Facts
· When:18th May 1980
· Where: Washington State, USA
· Catastrophic eruption, the biggest eruption ever to hit the USA
· From March onwards in 1980, there had been minor earthquakes which
were recorded - the increased in size and frequency, indicated that the
volcano was preparing to erupt
· Small ash and steam eruptions during the 2 months prior to the eruption
· A bulge on the north side of the volcano indicated that magma was moving
up into the magma chamber.
· Tiltmeters were used to monitor the changing size and shape of the
· Identified danger zone and residents were evacuated from these areas,
however some refused to leave and scientists stayed to study the volcano.
· Emergency Helicopters and aeroplanes were on hand in case of an
· The experts did not predict that the eruption blast would occur on the north
side of the volcano. The exclusion zones set up were in the wrong place
· 90% of the people that died were outside the exclusion zone in what were
thought to be `safe areas'…read more

Slide 2

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Mt. St. Helens - Effects
· 400 metres was blown off the top of the mountain and a one mile horse
shoe-shaped crater was left that was 500m deep
· Every plant and animal within 25km north of the volcano was killed
· Approximately 7000 animals died
· Every tree within 30km of the volcano was flattened
· The water produced from melting ice and snow, created mudflows, which
choked rivers and killed all fish and water life
· 12 million salmon died.
Social & Economic
· The eruption also destroyed 250 homes, 47 bridges, 15 miles of railways
and 185 miles of highway
· 57 people died - most of whom were outside of the evacuated zones
· 15cm of ash fell causing traffic chaos and airline flights to be cancelled
· The timber industry in the area was destroyed by the flattening of trees
· Telephone lines and electricity supplies were knocked out
· Tourists no long visited the area causing a reduction in the local economy…read more

Slide 3

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Mt. St. Helens - Responses
· Rescuing stranded people
· Providing shelter for those who has lost their homes
· Giving medical supplies to those who were injured
· The authorities were able to mobilise many people and much equipment
quickly to help in these operations
· A million tonnes of ash were removed from roads, buildings and airports -
cost over $1million in the town of Yakima and it took 10 weeks
· Millions of trees were replanted because there was a huge loss of timber
which cost $300million
· Compensation was given to farmers because what they produced on
their farms was destroyed by being covered by ash. This would cost about
· New tourist facilities were built
· A channel was dredged to remove logs and levees were rebuilt to reduce
future floods
· A new highway was built and major repairs were undertaken because
250km of roads and 25km of railways were damaged, costing $7million
· Money was given to rebuild houses…read more

Slide 4

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Nevado del Ruiz - Facts
· When: November 13th 1985
· Where: Nevado del Ruiz, Colombia
· Took place during night
· Although Armero was 74 km from the crater of Nevado del Ruiz, it took
the lahar only two and a half hours to reach the village
· A warning did not reach the people in time…read more

Slide 5

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Nevado del Ruiz - Effects
· Bridges destroyed and roads buried by lahars. This greatly
delayed rescuers getting there quickly
· Colombia has a very limited number of helicopters. People
stranded in the mud couldn't be reached because of the depth
· Risk of spreading disease
· By the end of last week, soldiers had set fire to piles of bodies
and shot stray dogs and pigs to prevent the spread of disease
· Thousands of prime farming land was destroyed
· About 23,000 people and 15,000 animals were killed
· Another 4500 people were injured and about 8000 people
were made homeless
· The estimated cost of the disaster is $7.7 billion, about 20% of
Colombia's GNP…read more

Slide 6

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Nevado del Ruiz - Responses
· 3 days after the disaster the government still had no plan of action
· A lack of preparation contributed to the high death toll
· Armero had been built directly on old mudflows and authorities ignored a hazard-
zone map which showed the potential damage to the town if lahars were to occur
· Habitants were also told to stay inside and avoid the falling ash, thinking the
mudflows wouldn't bury them
· In April 2008, the Nevado del Huila volcano erupted, and thousands were
evacuated. Volcanologists were worried that this could be another "Nevado del
· Survivors who fled to other towns in the area were gradually housed in new
government schemes
· Armero was not rebuilt because the old lahar traces were discovered, and
Colombian government declared the site "holy ground"
· A new system can detect lahars, giving people more warning to evacuate before
they happen. The system involves the use of Acoustic Flow Monitors (AFM)
which analyse ground shaking that could result in a lahar
· These AFMs are placed in the volcano and warn officials if there is a high
amount of shaking
· These devices were tested on Mount Rainier in the United States…read more

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