Volcanic Hazards and Management

Cards to assist in your learning of geological hazards, please don not rely on it but do some revision of your own as well1



Description: A volcanic mudflow created when water interacts with ash either during or after an eruption. Can be generated by two methods 1. rainfall on ash laden slopes (Pinatubo) 2. eruptions underneath an icecap (Galeras - Columbia). Lahars can be either hot or cold, depending on the temperature of the ash when the lahar starts. 

Examples: Galeras (Nevado Del Ruiz (NDR)) - 1985, Mt St Helens - 1980, Pinatubo (1991 - 2010), Herculaneum - AD79. 

Volcano Type: Intermediate to acidic as a large amount of ash is needed

Management: Can be managed through channeling, and filtering the larger blocks (Japan). Prediction and monitoring are essential, done through speed cameras in Japan, though their path is normally easy to predict as it follows river valleys. Land-use planning is useful as some areas are more at risk, and mapping  previous events

Further Notes: Can be very deadly, over 23,000 died in NDR.

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Ash Fall

Description: Fine Grained material (<2mm) falling as a result of an ash plume, generated in three ways 1. Release of pressurised gas fracturing rock 2. Thermal contraction from chilling on water/ice 3. Particles entrained in steam driven eruptions. 

Examples: Iceland 2010, Vesuvius AD79, Pinatubo 1991, Mt St Helens 1980, Laki 1783. 

Volcano Type: Acidic/Intermediate/Basaltic under ice

Management: Not much can be done, but roofs need to be cleared to prevent collapse. Airlines and routes are monitored regularly, and paths diverted in air exceeds 0.002g/sec

Further Notes: Breaks down into highly fertile soil, hence ash prone regions are often densely populated. When it sets can form a very solid rock called tuff. The glass particles can melt in a jet engine and clog the air outtake, hence the 2010 disruption.  

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Description: Molten rock that has been erupted through the vent of a volcano, erupted normally between 700 and 1200 degrees. Rarely kills as it moves relatively slowly, but has been recorded flowing at over 100km/hr at Nyiragongo. Flows are named, either Pa *** *** (Ropey) or Aa Aa (blocky) after the noise you make when walking over it. 

Examples: Hawaii (ongoing), Heimay - 1973, Etna 1983 and ongoing, Nyiragongo (1977 and 2002), Paricutin (Mexico) - 1943-52

Volcano Type: Basaltic volcanoes produce the least viscous lava, and can run the furthest, acidic volcanoes tend to produce domes or spines of solid hot magma, such as MSH. 

Management: Two successful diversions, Etna '83 and Heimay '77, diverted through walls and explosives, and at Heimay the advancing front was cooled with sea water to relocate the path of flow

Further Notes: The only recent example of lava flows directly causing fatalities is Nyiragongo when 70, and 47 people were killed in 77 and 2002 respectively

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Pyroclastic Flows

Description: Hot clouds of Ash, Gas and debris travelling at up to 450mph and at temperatures of up to 1000 degrees. There are several causes, collapse of an eruption column, lateral blasts and collapse of a dome can all generate flows. Blocks can be the size of large cars, the flow tends to destroy everything in its path

Examples: Montserrat (1995), MSH - Lateral Blast 1980, Mt Unzen 1991 (Killed the Krafft's), Pelee (1902) killed 30,000 people

Volcano Type: Acidic

Management: Only land use planning and hazard mapping, monitoring systems, evacuation plans and emergency kit such as air masks are essential.

Further Notes: These are some of the most powerful forces that can be generated, they are too fast and too hot to be designed against. Mitigation is the only form of effective management. Your board sometimes refer to lateral blasts/PC flows as "Blast eruptions"

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Description: Landslides are common on steep sided volcanoes, the inherent weakness of steeply dipping layers of different materials, they are regularly shaken by small earthquakes that destabilise the slope. Landslides often occur in the same location as mass movement can further over-steepen and destabilise slopes.

Examples: MSH 1980 (landslide caused by the over-steepened slope with a shallow magma chamber), Stromboli - regular landslides down the NE side.

Volcano Type: All, common on volcanic islands where the slopes are undercut 

Management: Some stabilisation, mitigation through setting off smaller landslides, tsunami warning systems and constant monitoring with tiltmeters, satellites etc

Further Notes: Landslides generate Tsunamis if collapsing into the sea (8 on Stromboli since 1920) roughly 10m high. 

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Description: Small frequent tremors, either formed through magma moving through the shallow crust, or tectonic stresses create frequent quakes. These can be quite significant and can can start other hazards such as landslides. They often occur as swarms which can indicate magma is rising. The slow steady rise of magma produces Harmonic tremors.

Examples: Katla 2010, Galeras 1993, MSH 1980. 

Volcano Type: All

Management: None, there are normally a wide range of monitoring techniques around volcanoes, particularly in the run up to an eruption. 

Further Notes: These rarely pose a hazard, they are most frequent just before an eruption adn normally only felt close to the summit of the eruption. 

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Description: Gas can be emitted as an eruptive product in its own right, and as a by-product in other eruptions. There are three volcanic gas lakes in the Rift Valley, with vast stores of CO2, CO and SO2 in them (Kivu, Monoun and Nyos). The most common volcanic gas is sulphur, with CO2, CO, Hydrogen Bromide, Hydrogen Flouride and Hydrogen Sulphide, all of which are very fatal.

Examples: Lake Nyos (1986) 2000 dead, Hawaii, gas clouds common, gas produces the blast behind pyroclastic flows

Volcano Type: All, more gas is emitted from basic eruptions as the lava is less viscous

Management: Nyos is now degassed, used for early warning of eruptions

Further Notes: Can affect global climates, SO2 can cause global cooling (PInatubo 1991, half a degree colder for five years, MSH v similar). CO2 can cause global warming such as the Siberian and Deccan traps which have caused mass extinctions

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