Download Volcanic hazards (Chap. 5)

Volcanic hazards
•
•
•
•
•
•
•
•
Lava flows
Ash Falls
Pyroclastic flows
Lahars (mud flows)
Volcanic tsunamis
Weather/climate change
Gases (CO2; SO2)
Ash in Jet engines
Lava flows
•
•
•
•
•
•
Lower viscosity flows farther
Higher temperature flows farther
2 types:
Pahoehoe: ropy surface (Fig 5.21a)
Aa lava: Blocky surface (Fig 5. 21b)
Slow or divert flows: earth dams; water
Ash Falls
•
•
•
•
Large particles fall nearby
Ash and dust travel downwind
Plinian column:
Vertical pyroclastic explosion (named after Pliny the elder, killed in 79 AD, Mt.
Vesivius.
•
•
•
Famous Plinian eruptions
Vesuvius, Italy, 79 AD- buried Pompeii
St. Helens, Washington 1980 – 600 km2 destroyed
Pinatubo, Philipines, 1992- cold summer
•
•
•
•
•
Pyroclastic flows
Hot gases + ash: Nuee ardente (glowing cloud; fig. 5.23.
Move very fast downhill: 60-90 mph
Destroy all in path
Examples: Mt St Helens; 600 km2 destroyed
Mt. Pelee, Martinique, West Indies (1902)
•
•
•
Lahars
Melt water + pyroclastic debris: mudflow
Magma melts ice cap
Fig. 5.27- Mt. Rainier, Washington
•
Volcanic Tsunamis
Rare (earthquake related more common)
•
Krakatoa (Java/sumatra): island arc: 1883
•
Large tsunamis killed 36,000
Volcanic gases
• Most dangerous : CO2, SO2
•
Carbon dioxide heavier than air – displaces oxygen.
•
SO2 creates sulfuric acid= acid rain (e.g. Hawaii)
Cameroon, 1986
•
Lake Nyos – lake in Caldera
•
CO2 trapped beneath lake
•
Pressure built up and CO2 cloud escaped silently; no volcanic activity
•
CO2 settled in valleys- suffocation
Eruption forecasting
•
•
•
•
•
•
Need equipment monitoring
Tiltmeter- changes in slope
Seismometers- earthquakes
Global positioning system (satellites)
Gravimeters- changes in gravity
Magnetometers – change in magnetic field
•
Weather and climate
Large eruptions put dust into atmosphere and sometimes stratosphere
•
Dust reflects sunlight and causes cold weather- e.g. crop failure.
•
No long term climate change
end