Presenter: Aprilia Nurmawati
Date: 2017/06/08
Abstract
This study investigates the hazard produced by Volcanic Ballistic Projectiles (VBP) at Tatun Volcano Group (TVG), northern Taiwan. VBP is a material with a diameter more than 0.1 m ejected from a vent during an explosive eruption and following nearly parabolic trajectories. Two eruption models are considered hydrothermal and vulcanian. Hydrothermal explosion model is built based on the parameters known from previous studies which describe the sudden fluid pressure drop in order to obtain the initial velocity of VBP. These velocities are then used to obtain the ballistic trajectory model for each eruption scenario. The model for a vulcanian eruption considers the energy during rapid decompression when a caprock is blasted. The remaining pressure after fragmentation of caprock is then considered as able to produce energy to eject the VBPs. The ballistic equation is used to investigate the distance of VBP which also takes into account the reduced drag zone, wind speed, and VBP diameter of 0.2, 1.0, and 2.0 meters. Hazard maps are generated by mapping the points of impacts according to each scenario considering also the topography at TVG. VBP impact on hydrothermal explosions with 50 m/s initial velocity shows that it reaches no more than 310 m from Hsiaoyoukeng fumarole at NW of Mt. Chishin. This study also determines the VBPs produced by the highest initial velocity on hydrothermal explosion ever recorded, which is 200 m/s. Due to the narrow extent of hydrothermal explosion hazard zones, the only place that is inside the danger zone is a public garden which is within the landing area of VBPs with diameter of 2.0 m. However, since Hsiaoyoukeng fumarole is located in a national park, it should be noted that the VBPs may be a serious threat to the tourists visiting the fumarole. During a vulcanian eruption with 370 m/s initial velocity, the maximum extent of VBPs reached a much larger area, with radius of 5,158 m, around the peak of Mt. Chishin. The hazard maps for vulcanian eruption show that the danger zone covers schools, offices, and Central Weather Bureau stations for all eruption scenarios. The VBP may also cause threat to the aircraft as its maximum height, 2,450 m, may reach the flightpath of an airplane. Moreover, during the investigation of landing kinetic energy, the VBPs with diameter 0.2 m may not be able to penetrate building made of RC slabs, while the bigger ones are able to penetrate all building materials investigated in this study.
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