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23_hazards3_09_post - 23: Natural Hazards 3 Volcanic...

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Unformatted text preview: 23: Natural Hazards 3 Volcanic Eruptions Direct hazards Pyroclastic flows (nuee ardente): mass of volcanic ash, gases, and other volcanic fragments that flows downslope at great speed (100-300 km/hr). --30% of all fatalities related to volcanoes (greatest lethal hazard) Fig. 9.5 Hazards 3: 1 Hazards 3: 2 Direct hazards: Pyroclastic flows Direct hazards: Pyroclastic flows Pyroclastic flows: mass of volcanic ash, gases, and other volcanic fragments that flows downslope at great speed (100-300 km/hr) Mt. Pelee, Martinique (Caribbean), 1902, 28,000 fatalities Fig. 9.22e Mount Unzen, Japan, June 1991. Photo: AP Hazards 3: 3 Hazards 3: 4 Direct hazards: Tsunamis 20% of all fatalities related to volcanoes Krakatau, Indonesia, 1883, almost 36,000 fatalities 1883: Tsunamis generated by massive explosion and water rushing into caldera Fig. 10.36 Anak Krakatau, 2007 Fig. 9.15 2/3 of volcano blown away Other direct hazards: 10% Direct volcanic hazards Lahars: volcanic mudflows; travel at speeds of >50 km/hr. ~15% of all fatalities Ash mixes with melting snow / ice Volcanic gases--may poison people and livestock Lake Nyos, Cameroon, 1986; 1742 fatalities CO2: denser than air; hugged ground; caused suffocation Fig. 9.23 Photo: J. Marso Hazards 3: 7 Amount of material blown out of volcano (including parts of volcano itself) in cubic km Direct hazards: Tsunamis Hazards 3: 8 Other direct hazards Other direct hazards: 10% Volcanic ash may bury crops and collapse roofs (ash mixed with water is like cement). Volcanic ash--hazard to aviation; clogs jet engines Mt. Pinatubo, Philippines, 1991, 200-800 fatalities Fig. 9.22d Hazards 3: 10 Other direct hazards Other direct hazards Lava flows may bury roads, burn houses, cover farm fields; very few fatalities Lava flows may bury roads, burn houses, cover farm fields; extensive property damage Fig. 9.22a Photo: USGS Hazards 3: 12 Indirect volcanic hazards: ~25% Disruption of transportation and destruction of crops cause illness and starvation Volcanic Hazards: Summary 1. Pyroclastic flows: ~30% of fatalities 2. Famine: ~25% 3. Tsunamis: ~20% 6. 4. Lahars: ~15% 5. (a) Volcanic gasses, (b) ashfalls (e.g., roof collapse): ~10% 6. Lava flows: ~0% 4. 3. 1. Laki, Iceland (1783-84); 50% of livestock and 21% of population died 5a. Photo: Y. Arthus-Bertrand Hazards 3: 13 Hazards 3: 14 Volcanic hazards Most dangerous volcanoes Which are the most dangerous volcanoes? All are stratovolcanoes (composite volcanoes). Hazards 3: 15 5b. Hazards 3: 16 Volcanic hazards Volcanic hazards Where are the most dangerous volcanoes? Convergent plate boundaries El Chichon Santa Maria Soufriere Where are the most dangerous volcanoes? Convergent plate boundaries --> wet-partial melting of mantle --> andesitic magma --> high silica & viscosity --> high explosiveness Awu Nevado del Ruiz Cotopaxi Taal Mayon Lamington Tambora Galunggung Merapi Kelud Agung Volcanoes in red font or underlined in red are listed in table in slide 15. Fig. 6.19 Hazards 3: 17 Volcanoes & Climate • CO2 is a greenhouse gas: Earth heats up • Ash particles and acid droplets: reflect sunlight; Earth cools down lowers melting point Hazards 3: 18 Review Questions 23-1. A fast moving flow consisting of a mixture of water and volcaniclastic debris is termed a ____________. A. lahar B. pyroclastic flow C. flood basalt D. ash fall 23-2. A mass of volcanic ash, gases, and other volcanic fragments that flows downslope at great speed is termed a ___. A. lahar B. pyroclastic flow C. flood basalt D. ash fall 23-3. The most lethal hazard associated with volcanic eruptions is ___. A. ash falls B. lava flows C. poisonous gas D. pyroclastic flows 23-4. The least lethal hazard associated with volcanic eruptions is ___. A. ash falls B. lava flows C. poisonous gas D. pyroclastic flows 23-5. Which of the following is not a hazard associated with volcanic ash? A. burial/destruction of crops B. collapsed roofs C. clogged jet engines D. mixed with melting snow / ice or rain to produce lahars E. causes heat to be trapped in the lower atmosphere, causing global warming. Hazards 3: 19 Hazards 3: 20 Review Questions Mt. St. Helens eruption 23-6. Which type of volcano is associated with the most deadly volcanic eruptions? A. cinder cone B. composite volcano C. fissure eruption D. shield volcano Before 1980 eruption After 1980 eruption 23-7. Which of the following is associated with the most deadly volcanic eruptions? A. conservative plate boundary B. convergent plate boundary C. divergent plate boundary D. hot spots 23-8. A. True / B. False: Explosive volcanic eruptions are associated with higherviscosity andesitic magmas that form when water released from subducting plates lowers the melting point of mantle rocks. 23-9. A. True / B. False: Higher-viscosity magmas prevent the release of volcanic gases; this builds up pressure and eventually leads to explosions. Photo: E. Muench Photo: D. Weintraub 23-10. A. True / B. False: CO2 emitted from volcanoes may produce global cooling. Hazards 3: 21 Hazards 3: 22 Mt. St. Helens eruption Mt. St. Helens eruption Effects of lateral blast Earthquake--> landslides --> lateral blasts (sideways rather than upward directed explosions). Example: Mt. St. Helens, 1980, 61 fatalities Fig. 9.16 Hazards 3: 23 Fig. 9.16e Hazards 3: 24 Photo: US Dept. of Agriculture Mt. St. Helens eruption Mt. St. Helens Q1. What is the name of the subducting plate responsible for Mt. St. Helens? A. Cocos B. Juan de Fuca C. North American D. Pacific Fig. 9.15c 21 km Mt. St. Helens Hazards 3: 25 Predicting eruptions: earthquakes • Movement of magma: causes surrounding rocks to crack • Earthquake activity increases prior to eruption • Earthquakes located 1-7 km beneath a volcano Hazards 3: 26 Predicting eruptions: higher heat flow • Reflects magma near surface • Secondary effects: may melt snow & ice, triggering lahars & flash floods Predicting eruptions • Increases in gas emissions and steam Mitigating eruptions • Danger assessment map: shows areas that lie in the path of potential lava flows, lahars, and pyroclastic flows. • Maps are useful for designating areas to be evacuated during volcanic eruptions • Lahars can travel 10’s of km from volcano: avoid stream valleys Fig. 9.24 Tacoma No data No data Q2. Which of the following precede eruptions at Kilauea volcano? A. decreasing tilt and decreasing number of long-period quakes B. decreasing tilt and increasing number of short-period quakes C. increasing tilt and increasing number of short-period quakes D. increasing tilt and increasing number of long-period quakes No data No data No data • Movement of magma into magma chamber causes volcano to bulge • Detected using laser sighting, tiltmeters, and GPS Predicting eruptions No data Predicting eruptions: change in shape Controlling eruptions Review Questions • Diverting flows using explosives, building dams, and spraying cold water on hot lava, which produced a lava dam that blocked the flow of other lava 23-11. A. True / B. False: The main eruption of Mt. St. Helens was caused when an earthquake triggered a landslide that "uncorked" the volcano. Fig. 9.25 23-12. A. True / B. False: One of the reasons volcanic eruptions are so deadly is that there is no way to predict where an eruption will occur in the near future. 23-13. Which of the following is not an indicator that a volcanic eruption will soon happen? A. increase in heat flow B. increase in short-period earthquake activity C. increase in gas and steam emissions D. increase in surface tilt of the volcano E. all are indicators than an eruption will soon happen 23-14. A. True / B. False: Icelanders have managed to prevent some property damage by spraying cold water into the crater of a volcano, which stopped the eruption. 1973, Eldfell volcano, Heimaey, Iceland Hazards 3: 34 ...
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This note was uploaded on 09/25/2011 for the course GEOLOGY 100 taught by Professor Lepre during the Fall '11 term at Rutgers.

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