Types of Volcanic Hazard

Types of Hazard

• Gas

• Lahars

• Landslides

• Lava flows

• Pyroclastic flows (Nuee Ardentes)

• Ash (Tephra)

Gas• All volcanic eruptions are caused by gas

escaping from the magma. The viscosity of the magma determines the ease at which it escapes. ~ main gases. H2S, CO2 SO2

• High viscosity ~ Explosive with pyroclastics• Low viscosity ~ Effusive Fumaroles with fire

fountains and lava• Only one example of gas killing people

directly, Lake Nyos • Affects world climates – i.e. Pinatubo

Lake Nyos

Lake Nyos in normal conditions (left) and just after the 1986 gas release (right). The sudden welling up of carbon dioxide from the bottom of the lake brought iron to the surface, which oxidised, creating the brown rust colour.

• August 21, 1986, a limnic eruption occurred at Lake Nyos which triggered the sudden release of about 1.6 million tonnes of CO2; this cloud rose at nearly 100 kilometers per hour

• Carbon dioxide, being about 1.5 times as dense as air, caused the cloud to "hug" suffocating some 1,700 people within 20 km of the lake, mostly rural villagers, as well as 3,500 livestock

• The mass was about 50 metres (164 ft) thick and it travelled downward at a rate of 20-50 km per hour. For roughly 23 metres (75 ft) the cloud remained condensed and dangerous, suffocating many of the people sleeping in the villages

• About 4,000 inhabitants fled the area, and many of these developed respiratory problems, lesions, and paralysis as a result of the gases

Degassing Lakes

• There are now 10 degassing columns inserted into the lake in order to prevent a massive degassing event from occurring again.

• By constantly allowing small amounts of gas to escape the risk is minimised

Lava Flows

• Only Basaltic lavas are runny enough to cause problems. Can travel many miles but slow down when they start to cool

• Basaltic lavas ~ destroy property but rarely kill as the flow is predictable and slow.

• Only example where people have died ~ Nyiragongo in the Congo 1977 and 1999

• Can be managed Iceland and Etna – the only people who have died recently in Sicily have been volcanologists and climbers

Nyiragongo

• 2002 eruption: • 1 Rivers of lava pour down the

volcano's flanks into a valley to the south, destroying 14 villages

• 2 Stream of lava flows across the runway at Goma airport, igniting aviation fuel stores

• 3 Lava reaches Goma, cutting the town in half and causing widespread devastation

• 4 About 300,000 people flee into neighbouring Rwanda

• 5 Lava reaches Lake Kivu, raising fears it would disturb methane on the lake bed

• Previous major eruptions:• 1994-96, 1982, 1977 • 1977:Lava lake at the summit of Nyiragongo

suddenly drains from fissures at speeds of up to 40 miles per hour (60 km/h). About 70 people were killed.

• 1994: A smaller lake reforms in the crater approximately 130 feet (40 m) in diameter.

Lake Kivu

• This is a volcanic crater lake identified after the eruption of Nyos, and is 2000 times bigger than Nyos was identified along with Lake Monoun

• The 2002 eruption sent lava into the lake but luckily no limnic eruption occurred

• Any landslides, eruptions, earthquakes or intense storms could trigger an eruption – termed “Overturn”

• This would be a catastrophic disaster

City on Lake Kivu:

Population

DRC  Goma 77,908Bukavu 167,950Rwanda  Cyangugu 514, 656

Kibuye 469, 016Gisenyi 864,377Total 2,093,907

Pyroclastic flows

• Mixture of rock, gas and magma blasted out of Composite volcanoes. Viscous lavas like Rhyolite and Andesite (destructive margins)

• Travel at over 300mph with inner temps of over 500C.

• Deadly killers as can affect up to 40km from the vent

• Examples ~ St Helens, Pinatubo and Unzen

Lahars

Volcanic Mudflows

2 main types

1. Set off by the eruption by the melting of a summit glacier ~ ex ~ Nevado del Ruiz and Iceland (jokulhlaup)

2. Caused by rain mixing with ash and causing massive and continuous flooding. Ex ~ Pinatubo

Landslides

• Landslides set off by eruptions can cause destruction

• Mt St Helens was caused by a landslide http://uk.youtube.com/watch?v=bgRnVhbfIKQ

• Landslides also cause tsunamis on islands and coastal volcanoes ie Stromboli and Krakatoa

Ash.

• Ash causes total destruction for 100s of sq km.

• Building collapse is a common cause of death

• Destroys land and kills animals. Contaminates water supply and sets like concrete with rain

• Causes global cooling, Pinatubo cooled world temps by 1degree C for 5 years

Management of Volcanic Hazards

• Prediction – now very advanced and volcanoes generally give plenty of warning

• Hazard maps of past eruptions• Monitoring• Evacuation plans and procedures• Education• Diversion of lava flows – Etna• Channelling of Lahars – Japan• Post disaster relief operations

Classification of Volcanic Impacts

• Direct(primary) and/or Indirect(secondary)

• Localised and/or National/international

• Short Term and/or long Term

• Economic, Social/Cultural and Environmental

Impacts

Key points• The variation of impacts due to the types

of volcanic eruption.• Variations determined by degree of

development and perception.Remember people should not really die

directly from volcanic eruptions due to the ability to predict them. It is the secondary impacts that cause the most problem

Case Studies

Management case studies • Lava flows of basaltic eruptions ~ Etna

and Iceland• Prediction success ~ Pinatubo, Unzen

Montserrat • Prediction failure ~ Nevado del Ruiz , St

Helens• Large Secondary impacts ~ Pinatubo,

Montserrat, Krakatoa