Volcanic Explosivity( 화산폭발지수 ) 화산폭발의 폭발성과 크기를 정량화하여 표기 VEI :0-8 기준 the volume of material (lava and particles) erupted the height of the eruption column how long the eruption lasts The larger the VEI value, the larger the eruption. Two main factors determine the size and explosivity of a volcano’s eruption: 1. The amount of time that has passed since the last eruption. 2. The viscosity (thickness) and gas content of the magma.

화산 폭발의 폭발성과 크기의 결정요소 the amount of time that has passed since the last eruption the viscosity and gas content of the magma Viscosity ( 점성도 ) -The more viscous (silica-rich) the magma, the more violent the eruption. The gas content - The higher the gas content, the more violent the eruption. 판구조론과 화산 발산경계 (mid-ocean ridges) 와 hot spots - 상부맨틀, 염기성 마그마 ( Mafic magma) : 상대적으로 적은 양의 SiO 2 와 gas 함량. 염기성 마그마 - 일반적으로 조용한 분출 (the eruptions have low VEI). 수렴경계는 해양판의 섭입에 의해 마그마 생성 - 산성 마그마 (FELSIC MAGMA,) 상태적으로 많은 양의 SiO 2 와 gas 함량. 산성마그마 - 일반적으로 폭발성 분출 (the eruptions have high VEI). 세계적으로 위험한 화산은 대부분 수렴경계에서 발생한다 !

화산의 분출형태와 화산지형 - shield volcanoes - stratovolcanoes - calderas - lava domes - cinder cones

Shield volcanoes are very large, with gently sloping sides and a convex shape. They form from relatively quiet eruptions of mafic magma. You will find shield volcanoes at oceanic hot spots (like the Hawaiian Islands and Galapagos Islands) and places where mid-ocean ridges stick up above sea level (the country of Iceland). The photo shows a shield volcano in the Galapagos Islands. Stratovolcanoes are high and steep-sided. Unlike shield volcanoes, they form from violent eruptions of felsic magma. You will find stratovolcanoes at almost all convergent plate boundaries, where subduction makes viscous (silica-rich) and gas-rich magma. The photo shows Mount Rainier in Washington state. Due to its location near the heavily populated Seattle area, this stratovolcano is considered by many geologists to be the most dangerous volcano in the U.S.! Some eruptions of stratovolcanoes are so violent that after the eruption ends the volcano collapses into the empty magma chamber beneath, leaving a large crater behind called a caldera. Lava domes form when viscous lava piles up in and around a volcanic vent. Some domes appear to form in the last stages of an eruption, when the final masses of felsic magma squeeze out of a vent and plug it up. Cinder cones are smaller volcanic cones that occur worldwide. They appear to be largely “one-shot” events where a source of magma erupts once and then becomes inactive. Cinder cones form as erupted rock particles pile up around a vent, building up a cone-shaped hill. The photo shows the eruption of Paricutin Volcano, Mexico, a classic example of a cinder cone.

- 1~4 번의 연구 결과를 종합하여 마그마의 모델링 - 구체적인 지질조사 및 과거 분출역사의 이해 가. 분화구 칼데라 호수, 분기공, 근처 우물의 온도 변화 나. 분출되는 가스의 조성변화 - (SO 2 +HCl)/ 증기 의 비가 증가 다. 화산 분출의 sequence - 미소지진의 기록 - 최근 단기적 예보에 어느 정도의 성과를 거둠 → 그러나 화산활동 즉 분출의 시기를 정확하게 예측하는 것은 매우 어 려운 일이다. → 1980 년 세인트 헬렌스 화산 분출 이후, 예측에 필요한 정보 확보 There is little that can be done to mitigate against most volcanic hazards once they have begun, but fortunately many volcanic eruptions can be predicted quite accurately. However present methods allow us only to predict approximately when an eruption may occur; not how large that eruption may be. To predict an eruption, geologists depend on various precursors: events that occur prior to an eruption. The main precursors that signal an impending volcanic eruption are: 1. Increased seismic activity below the volcano. Many small earthquakes -- called earthquake swarms -- often precede a major eruption. Earthquakes swarms are thought to be caused by fresh magma rising below the volcano. 2. Tilting and swelling of the volcano ’ s sides. As magma rises below a volcano, it forces the earth ’ s surface upward and outward, somewhat like a balloon being inflated. 3. Increased gas emissions, probably caused by rising magma emitting gas as it approaches the surface.