7/8/2023 0 Comments Pyroclastic flowThe results were released to newspaper and television reporters by the Ministry of Education, Culture, Sports, Science and Technology (Former Science and Technology Agency). The results were useful for projecting the expansion of the damage areas that accompanied subsequent volcanic activity, and as a database for disaster prevention measures against the occurrence of debris flows.Ĥ. Pyroclastic flow damage area map: created by interpreting aerial photograph exposures following the occurrence of pyroclastic flowsīy combining high spatial resolution satellite images with detailed pyroclastic flow damage information from aerial photographs taken immediately after the eruption plus topographic information, we were able to achieve a far more detailed understanding of the downstream pyroclastic flow areas and damage areas according to the layout of topographic features than is possible using two-dimensional information. Digital elevation model: 60m mesh, 1m elevation points (newly created)ģ. This aims to understand the topographical extent, scale, point of origin and other characteristics of the pyroclastic flow and contribute to the creation of disaster relief measures and recovery plans, by superimposing and describing detailed pyroclastic flow starting points and resulting damage zones interpreted from aerial photographs and investigations with satellite data obtained prior to the eruption and creating a bird's-eye view by combining this with digital topographic data.Ģ. Unzen pyroclastic flow" from SPOT data.Ģ. Unzen, in Nagasaki Prefecture in June 1991 (pyroclastic flow montage)Ĭreate a "montage image of the Mt. Slope disasters/Volcanoes (Pyroclastic flow, etc.)Įruption of Fugendake, Mt. This means that the development of pyroclastic flows is controlled not only by the volume of lava and gravitational force, but also by the explosivity related to the pore gases in the lava.Terrestrial phenomena disasters/Volcanoes/Pyroclastic flows. The infrasonic energy is almost the same order as the seismic energy but the ratio of infrasonic to seismic energies increases for larger and more mobile pyroclastic flows. The excitation of infrasonic and seismic signals is affected by the topography of the mountain slope. The speed of pyroclastic flows is estimated as 10-30 m/s from the infrasonic records. This suggests that the fragmentation of pyroclastics occurs mainly near the front of pyroclastic flows. The migrating source of infrasonic signals and probably seismic signals is inferred to be located near the front of pyroclastic flows by comparison with video images. The location of dome collapse and the path of pyroclastic flows can be identified and traced by a network of low-frequency microphones. Some of the infrasonic signals show an obvious Doppler effect, indicating that the pyroclastic flows emit infrasonic signals during their propagation. This suggests that the seismic waves are generated by the collision of pyroclastics on the mountain slope and that the infrasonic waves are excited by small fractures of the dome and the fragmentation of pyroclastics. When the lava blocks fall onto the mountain slope and are fragmented, larger waves are excited. Small infrasonic and seismic waves are excited when the lava dome starts to collapse. Characteristic infrasonic and seismic signals were recorded corresponding to the collapse of lava blocks from the dome, the drop of blocks on the slope and the migration of pyroclastic flow on the mountain slope. The process of the collapse of the dacitic lava dome and the development of pyroclastic flows at Unzen volcano, Japan, were studied using infrasonic, seismic and video records.
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