Volcanic Case Studies

When: 25th June 1997, 1pm

Where: Montserrat Island - volcanic arc of islands in Caribbean, British territory

Physical Geography:

• Soufriere Hills Volcano is situated above a destuctive plate boundary
• Oceanic crust from the North American Plate is sinking beneath the Caribbean Plate = Antilles Volcano Arc
• Magma is formed at depths of around 6km at temps of 820-885 degrees
• At the surface a thick voscous dome of lava appeared in the English's crater
• Most of the gas had already escaped - pockets remained = explosive eruptions
• Strata Volcano
• Estimated that 4-5 million metre cubed of material was ejected

Pyroclastic Flows -

• Caused by collapse of other hardened dome to expose hot lava inside
• Horizontal and vertical collapses of ash collapse and flow down volcano
• Incineration of organic material, killed 19, demolished structure e.g. Bramble airport

Lahar -

• Heavy rainfall mixed with loose ash on volcano slopes
• Burial and destruction of Plymouth

Ash and Tephra Fall -

• Day became night, vegetation coated in ash, fires, breathing difficulties, ash plume of 90 miles

Earthquakes -

• Noticeable but not a threat

Volcanic gases

• Captial of Plymouth destroyed - buried in 10m of ash and mud
• Villages and farms evacuated
• Between 1995 and 1999 the island's population decreased from 10,000 to 3000 (by 2006 = 5000)
• Loss of economic potential
• 300 full-time farmers dispossed by eruptions
• Montserrat is no longer self-sufficient
• Enrolment in schools dropped from 2,672 in 1995 to 620 in 1998
• 2 secondary schools collated into one
• Only 4km squared (of islands 100km) considered safe
• People forced to resettle on the North of the island (the safe half)
• Unemplipyment rose to 50%
• Collapse of tourist and rice-processing industries
• 70% rise in rented accomodation
• Agriculture at a standstill
• Skills shortage - people left
• Traffic congestion

• British goernment offered £2,400 to each adult to help with relocation = met by rioting, not enough money
• Funding for redeveloped rose from £10 million to £75 million over 3 years
• Redevelopment will: develop Little Bay Port to replace Plymouth, Conversion of St. John's Hospital to main hospital on the island, provision of water supplies in North, improving air access, housing
• British government introduced scheme to help people return to Montserrat if they have somewhere to stay

When: 2nd May 2008

Where: South-eastern Chile

Physical Geography:

• One of the 112 volcanoes along the western seaboard of South America
• Situated above a subduction zone where the Pacific Plate is being consumed beneath the South American continental crust
• Lava dome was within a caldera about 2.5 km wide and 4km long
• Composed of viscous rhyolitic lavas

• Initial eruption = plume of volcanic ash and steam rose 17km high
• Winds carried the plume east into Argentina and over the Atlantic
• Dominated by pyroclastics
• By late May it had created a new dome of around 540,000m squared and contained 55 million m cubed of new material
• Ash column at its peak reached 20-30km
• Subsequent collapse of column = brought vast amount of ash to the ground
• Eruption triggered thunderstorms and a passing polar storm meant that heavy rainfalls also occured during eruption

• Town of Chaiten blanketed with ash
• 4000 people who lived in Chaiten evacuated by boat and a further 1000 from Futaleufu
• Fall of ash killed animals and blocked roads
• Rainfall from polar storm with ash blocked rivers = flooding
• Ashfalls of up to 15cm blocked rivers and contaminated groundwater supply
• 90% of the town was flooded
• Only one death
• Local hospitals treated people for breathing difficulties
• Between 80-90% of buildings in Chaiten damaged and 20-30% completely destroyed
• 3 encounters of commerical aircraft flying into ash clouds
• Regional airports occassionaly closed - 4 airports in Chile and 3 in Argentina closed for some time
• Several hundred domestic flights cancelled and several dozen international

• By 3rd May the Chilean Navy helped to evacuate 3,900 people and forcible evacuation orders issued to those who refused to leave
• Residents were told not to drink the water as reservoirs were coated with ash
• Chiliean officials distributed fresh water and protective masks
• Chilean government ordered a 50km exclusion zone around the town
• Government issued a montly disaster stipend equivalent to $1,200 or $2,200 per family
• Financial aid to small businesses and there was a 90 day-freese on payment of existing loans to the state bank

Monitoring -

• Managment of this volcano was not a priority before the eruption due to its relatively low pop density
• Key development = Volcano Disaster Assistance Programme (VDAP) to aid monitoring
• Real seismic monitoring began on 17th May

When: most violent eruption to date was in 1790, another in 1924. First explosive eruption since was in 2008 and then 8 more similar events in 2011

Where: Big Island of Hawaii

Physical Geography:

• Explosive eruptions here are thought to be caused by groundwater or surface water comes into contact with hot or molten rock and flashes into steam, rapidly expanding and providing propellant for explosive eruptions
• Theory = when the caldera is deep enough to be at or below the water table, water can seep into the vent and explosive eruptions can take place
• The water table is currently around 50m below the floor of the caldera - if caldera collapses there could be an explosive eruption

• During heavy ash fall breathing is difficult
• Weight of ash fall, when wet especially, can cause roofs to collapse
• In 1924, ash fell 40km from the summit = shut down railway and ash amounting to 4.9-7.4 tonnes accumulated 30km away = contamianted grass for livestock
• Very large eruptions have eruption columns which penetrate into or above the west winds of sub-tropical jet stream = hazard to aircrafts
• Pyroclastic surges, clouds of ash, rock and volcanic gases
• 1790 death estimates range from 80 to over 5000

• Hawaiin Volcano Observatory is siutated at Kilauea and keeps regular records of the eruptions
• Summit recieves 2 million visitors annually = potential hazard if the next explosive eruption is not predicted in advance

When: 19th April 2010

Where: Island of Iceland

Physical Geography:

• Caldera at the top of the volcano = 2.5km wide
• Volcano = 1,666m tall
• Iceland is located on the North American Plate an the Eurasian Plate creating a divergent plate boundary which move 1-5cm apart every year
• Mid-Atlantic Ridge runs through the island
• Fissure eruption

• Lava flow was more dominant on the west side but also on the east
• Ash plume rose 11,000m into the air
• Ash was fine grained with 24% of it being the same size as an aerosol
• Ash was distributed by high velocity jet streams above Iceland
• Melted a 150m thick ice cap

• The melting of the 150m thick ice cap = major flooding and 700 people were evacuated
• Destroyed parts of main Route 1 road
• Other roads were bulldozed to allow the flash flood water to reach the sea
•  Fine ash silted the rivers = blockages one year on
• Government paid to dredge rivers or allow them to flood
• 20 farms destroyed by flooding and ash
• Fine grain ash posed a problems for aircrafts as it can enter engines or turn into glassy substances due to heat of jet engine
• Britain had fine anticyclonic weather when the ash cloud existed = winds dispersed the ash clouds better

• Airspace closed across Europe - at least 17,000 flights a day being cancelled with 6 flightless days
• Overall 95,000 flights were cancelled
• Cost airlines more than $200 million a day with an estimated total lost of $2 billion
• Shares in Air Travel and Tourism Agencies dropped by 4%
• Less fuel required = 1.87 million barrels saved = loss of money for oil industry
• Estimated that London lost £102 million of tourist income