Objectives• To explain why such a wide range of volcanic hazards exist.
The Easy Bit• Definitions• VOLCANO – Main landform comprising of surface accumulations of rock and debris developed from the molten rock (Magma)• ERUPTIONS – The main events associated with rising magma. This leads to the discharge of hot water, outpouring of lavas, explosive gas and debris, torrential rain, flooding, landslides and earthquakes
Threats to Humans• Risk equation.• As we settle in more vulnerable places the more vulnerable we become to hazards.• Our VULNERABILI|TY is often dictated by our ability to COPE with the hazard.• Our exposure to the hazard becomes the RISK we face.
Key Point• It is the combination of human values and vulnerability that converts volcanic phenomena into hazards.
Types of volcanic activity • Primary - Determined by eruptive behaviour • Ejected pyroclastic material • Pyroclastic flows • Lava flows Pyroclastic flows Lava flowsMixture of Ash, rock and Magma that’s lost itsgas volatilesCan travel upto 100km/h for Damages property but70km moves much more slowly300 – 370 C Cools quickly
Geology • Chemical composition can determine lava type: • Iron rich, silica poor are basaltic – have low viscosity so flow quickly and cool slowly • Silica rich, iron poor – Andesitic lavas are Rhyolitic, viscous and cool quickly BASALTIC = flow quickly cool slowlyANDESITIC = viscous, flow slower and cool quicker
Secondary Hazards• Generated by the eruption:• Clouds form of ash, rainfall and thunderstorms develop – flooding and landslides, often high sediment loads in flood water. (Mudflows)• Lahars are like flood water but consists mainly of mud and debris and have the consistency of wet concrete speeds can reach 40m/sec and flow for 300km• Can carry large boulders• Dries like very hard rock
Eruption induced Melting of icecaps• Can result in major flooding• Particularly associated with Iceland• Melting of ice cap on the Nevado del Ruiz volcano, Columbia in 1985 caused mudfloods killing 23,000 people
Tsunami Generation• Discharges of oceanic volcanoes can cause tsunami waves which can engulf coastal areas Krakatau (1883) caused 35m high waves killing 36,000 people on nearby islands
Other Hazards• Gas Discharges – pose little danger except for explosions.• CO2 can be released and can, since heavier than air be released from waters causing it to hug the ground and cause death to nearby inhabitants
Doming• Upward movement of magma used to forecast eruptions.• Pronounced upward movement of land caused over 400,000 people to be evacuated and 100,000 permanently rehoused near Naples Italy during the 1980’s
KEY POINT• The combination of hazards varies between volcanoes as well as within each eruption
What are the Global Significance of Volcanic Hazards• Discuss• Homework• Discuss the degree to which the theory of plate tectonics is supported by the distribution of volcanic and seismic activity across the globe• Marked out of 40• Typed with front sheet• Full bibliography