老外有关火山研究的多媒体.ppt

Volcanoes IV Hazards and more! This Lecture Global Hazards Some infamous volcanoes Some unique volcanic phenomena and associated hazards Volcanic Hazards In general, volcanic hazards kill and endanger less people than those of other natural disasters An example Tambora volcanic eruption (Indonesia, 1815) ~92,000 deaths 1970 hurricane, Bangladesh ~500,000 deaths 1976 earthquake, China ~800,000 deaths Volcanic hazards can be anticipated Risk is lessened by preparation Evacuation plans Ash shelters with a fresh air source Emergency food storage Range of Volcanic Hazards Hazards can be classified based on their Spatial effect Local vs. global Temporal effect Short-term vs. Long-term We talked about local hazards last class Local hazards happen quickly, and their effects can last for a few years This class, we will discuss global hazards Effects of global hazards can stretch into the 1000s of years Global Volcanic Environmental Hazards Climate Change Ozone Depletion Volcanic Cooling Volcanogenic Sulphur Dioxide gas Degassing active volcanoes Small amounts add up to ~10 million tonnes/yr (Graf et al. 1996) Explosive activity Amounts up to ~4 million tonnes/yr (Graf et al. 1996) Sulphur Dioxide oxidises to sulphuric acid aerosols in atmosphere Aerosols reflect Sun’s light back to space Cooling is caused mostly by explosive activity Injection of SO2 (and ash) into the upper atmosphere Mt. Pinatubo (1991) Recent example of a single explosive event that caused global cooling Thought to be the largest single injection of volcanic sulphur dioxide since Krakatoa (1883) Released 15 million tonnes of sulphur dioxide Overwhelmed atmospheric sulphur budget Decreased light reaching Earth’s surface by 5% Decreased average northern hemisphere temperature by 0.5 degrees C Lowered global sea level by 0.5 mm Effects persisted for 3 years Toba, Indonesia Toba eruption (~75,000 years ago) Caldera-forming eruption Released 10 BILLION tonnes of sulphur dioxide (1000 times the normal annual