Volcano Case Studies

Question 1

1980 Mount St. Helens, USA: MAIN FACTS

Answer 1

• Eruption in 1980
• Stratovolcano
• It formed because of the subduction of the Juan de Fuca plate beneath the North American plate
• It produced the biggest volcanic landslide of all time

Question 2

1980 Mount St. Helens, USA; HAZARDS

Answer 2

• On May 18 the North Flank broke open along with the summit of the Volcano and fell downhill as a massive rock landslide 2.3km cubed in volume. It left a new horseshoe crater
• Majority of the rock was deposited in the North Fork Toutle Valley
• Immediately after the landslide, a gigantic cloud of gas, rock, ash and ice blasted laterally upwards. Hot pyroclastic flows drained swiftly down the volcano’s slides, spreading over and beyond the landslide to cover 550km squared.

Question 3

1980 Mount St. Helens, USA: IMPACTS

Answer 3

• So much debris reached the Columbia River that ocean-going ships could not sail on it because the previously 200m deep channel was reduced to less than 70m wide and 3m deep
• More than 100 people were rescued by helicopters
• Only 57 died
• Ash had to be cleared from roads
• People suffered from post-traumatic stress disorder for years afterwards

Question 4

1980 Mount St. Helens, USA: PREDICTION

Answer 4

• US Geological Survey keeps volcanoes in the country under close observation. They draw up hazard maps and monitor gas emissions
• In March 1980, there were shallow earthquakes on the North Side of the volcano which were different from the thousands that occur every year
• The harmonic tremor of continuous rhythmic earthquakes often precedes volcanic eruptions, so plans were made to evacuate
• Ash eruptions followed for a few weeks and the North Flank of the volcano started to bulge. People were not allowed within 13km of the summit. Most property owners moved away and emergency evacuation plans were made for communities further down the valleys.
• Ground deformation was monitored using lasers, but is done by GPS now
• By the end of April, the bulge had grown into a sizeable dome

Question 5

1991 Mount Pinatubo, Philippines: MAIN FACTS

Answer 5

• 2nd largest volcanic cataclysm in 20th century
• Stratovolcano
• Philippines plate (oceanic) subducting underneath the Eurasian plate (continental)
• Island of Luzon
• At least 20,000 lives were saved
• only around 700 died

Question 6

1991 Mount Pinatubo, Philippines: ERUPTION AND PREDICTIONS

Answer 6

• March 1991 - Earthquakes were felt by villagers on the north western side of the volcano of increasing intensity for the next 2 weeks
• April 1991 - Phreatic eruptions along a 3km fissure on the summit. Small eruptions of volcanic ash over the next few weeks. Seismometers were set up and recorded between 30 and 180 small earthquakes a day
• May 1991 - airborne measurements of sulphur dioxide took place and showed increasing emissions from 500 metric tons a day to more than 5000 tons per day
• June 1991 - volcano continued rumbling and ash was ejected into the atmosphere. Lava dome appeared on the peak, which was a sign that hot magma was pushing up against the surface - tilt metres leaned outwards
• June 12 1991 - eruption - the volcano sent a column of ash and steam 20km into the air

Question 7

1991 Mount Pinatubo, Philippines: MITIGATION

Answer 7

• At the start of June, the evacuation radius extended to 20km
• About 200,000 people were relocated
• Red Cross, Action Aid and Oxfam provided food and blankets in evacuation camps
• 23 USGS personnel helped advise the community and government officials for 8 weeks

Question 8

1991 Mount Pinatubo, Philippines IMPACTS

Answer 8

ENVIRONMENTAL
- Ash cloud covered 125000km2 bringing darkness to central Luzon.
- Volcanic ash smothered 80000 hectares of land. 150km2 of reforestation projects destroyed.
- Lahars caused severe erosion to rivers.
- Global cooling caused by the ash.
- Lahars continued to affect the area for 6 years.
ECONOMIC
- 800km2 agricultural land destroyed and 800,000 livestock and poultry killed costing 1.5 billion pesos.
- Full economic recovery cost £10 billion
SOCIAL
- 847 people killed by collapsing roofs
- Ash and pumice destroyed 42000 homes
- 1.2 million people lost their homes
- 100 people killed by lahars
- 500 people died from diseases such as measles in refugee camps

Question 9

1991 Mount Pinatubo, Philippines: MANAGEMENT

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Answer 9

Before

• Installed monitoring equipment after first signs were seen
• Compared data to previous eruptions
• Radio carbon dating of charcoal found old major explosive volcanic deposits
• Surrounding plains were made of pyroclastic material

During

• Evacuation zones were defined
• Five stages of volcanic alert were defined to warn the public
• Daily alerts were issued on all forms of media about the alert level

After

• Airlift evacuation
• Government resettlement areas were put into place for destroyed villages
• Tourist attraction, sit of Pinatubo, more jobs for locals

Question 10

Sustainable Management

Answer 10

a way for people to enable a risky environment to be lived in safely and productively, over a long period of time

Question 11

Sustainable Management of Soufriere Hills, Montserrat: MAIN FACTS

Answer 11

• a volcanic island in the Caribbean
• It is above a destructive plate boundary (Atlantic plate subducting underneath the Carribean)
• The Volcano Soufriere Hills, was dormant for hundreds of years, until 1995 when it erupted
• classed as a ‘British Overseas Territory’, originally occupied by Irish settlers in 1632. It has its own government but the official head of state is The Queen and it retains strong links to the UK.
• Relatively poor LIC with average household income of around £2,800 a year.
• many problems when sustainably managing a hazardous environment

Question 12

Sustainable Management of Soufriere Hills, Montserrat: Timeline of events (1995 - 1997)

Answer 12

• 1992-1994: Swarms of microquakes are detected under Mount Soufriere.
• Jul 1995: Eruptions of ash and steam. People are
  encouraged to evacuate the south of the island
• Dec 1995: A bulging lava dome appears in the crater at the top of the mountain. The capital, Plymouth is evacuated.
• Jan 1996: The volcano enters a quiet phase and residents are allowed to return to their homes
• Mar-Sep 1996: A return to volcanic activity, including the first of many pyroclastic flows. All people ordered out of the south of the island.
• Jun 1997: A devastating eruption occurs, killing 19 people who had returned to their homes in the danger zone. Plymouth is completely destroyed.
• July 1997: The compulsory exclusion zone is expanded and camps are set up in the north of the island. The government grants powers to forcibly remove people. 5,000 now settled in temporary camps.
• Sep-Dec 1997 Eruptions of volcanic gases (mainly sulphur dioxide), ash and pyroclastic flows continue on a regular basis.
• 1998 onwards: Ongoing monitoring of the volcano from the monitoring station. Eruptions of ash and gases continue, plus lahars following heavy rains.

Question 13

Sustainable Management of Soufriere Hills, Montserrat: Problems of managing the 1995-97 eruption

Answer 13

• Montserrat is a LIC (farming nation) – lack of capital for facilities and no scientific advice and expertise.
• Lack of preparedness – Before 1995, the inhabitants weren’t adequately prepared for evacuation.
• Complacency – volcano had been dormant for centuries. Low risk perceived.

During eruption

• Evacuation – approx 6,000 moved to north of island. Temporary shelters inadequate. But lives were saved, so overall successful.
• Exclusion zone set up in south of island but not strictly adhered to.
• Re-settlement – on other islands and UK. Population loss.
• Setting up of volcanic observatory

Question 14

Sustainable Management of Soufriere Hills, Montserrat: Montserrat Today

Answer 14

• 2011 census recorded a population of 5,100 – less than half what it was before the eruption but 3 times what it had fallen to by 2001.
• Aim is to restore the population eventually to 10,000.
• Some emigrants have returned to slowly rebuild their lives and the island economy.
• Tourism has recovered well (‘volcano tourism’). Income from tourism more than £12m last year.
• Severe skills shortage (‘brain drain’) and fears of over-reliance on handouts from UK.
• Ongoing monitoring of the potential for more eruptions.
• The southern part of the country is now an exclusion zone where no entry is allowed except for scientific monitoring
• The central zone is the residential area, with all residents on heightened state of alert
• The Northern Zone is safe, with significantly lower risk, suitable for residential and commerical occupation