5:15 PM - 7:15 PM
[SVC31-P05] Mapping risk induced by pyroclastic density currents in Nasudake region (3)
Keywords:Nasudake, pyroclastic density current, risk map
Most hazard maps created for volcanoes nationwide show the maximum expected range of the hazard, and it is impossible to read the level of danger from them. Therefore, we are currently working on a prototype risk map that includes probability information. Kohno and Takarada (2024, JpGU) attempted to create a pyroclastic density current risk map that takes into account the uncertainty of the crater location and the initial volume of the pyroclastic density current. In addition, the Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (GSJ, AIST), is developing a crater location map for volcanoes constantly monitored nationwide (Oikawa et al., 2022). In this presentation, we report the results of a pyroclastic density current risk map created using information from the newly created Nasudake crater location map.
In this presentation, risk values were calculated according to the risk definition by Founier d'Albe (1979): [Risk] = [Hazard] × [Exposure] × [Vulnerability]. Note that vulnerability was assumed to be "1". This means that an object will be damaged by pyroclastic density current. In the hazard assessment, we first performed a crater opening assessment and an eruption scale assessment at Nasudake volcano. In the crater opening assessment, the method of Alberico et al. (2008) was applied to the fumarolic points and the crater location map of Oikawa et al. (2022). The crater locations, according to the Nasu Volcano Geological Map (Yamamoto and Ban, 1997), were distributed on the west side of the summit of Nasudake volcano, while the crater structures in the crater location map by Oikawa et al. (2022) were also distributed on the east side of the summit, and the area where an opening could occur was wider than that of Kohno and Takarada (2024). For the eruption scale assessment, the methods of Sandri et al. (2016) and Shimizu and Tanabe (2022) were applied to Nasudake volcano, and probability values were calculated in increments of 0.5 for eruption magnitudes of 2-4 (Hayakawa, 1993). The results of these crater opening assessments and eruption scale assessments were used as input values for pyroclastic flow simulations. Simulations were performed using Titan2D ver.4 (Pitman et al., 2003; Patra et al., 2005). The basal friction angle was determined based on the relationship between the initial volume and the basal friction angle in Ogburn and Calder (2017). The initial volume was determined based on the eruption magnitude. The initial flow velocity was fixed at 40 m/s. The final hazard information was obtained by weighting a linear combination of all the simulation results using the weights obtained from the crater opening assessment.
Information on social infrastructure facilities in the Nasudake volcano region (four types: building distribution, population, roads and railways, and land use classification) was used for the exposure evaluation. These were downloaded from the National Land Numerical Information of the Ministry of Land, Infrastructure, Transport and Tourism. The distribution of various exposures was converted to a 0-1 relative importance distribution using the method of Del Negro et al. (2020) and integrated by weighted linear combination to obtain the exposure information.
The risk value was obtained by multiplying the hazard information and the exposure information. Recent updates to crater location information have resulted in an increase in sources to the north and east of the summit, resulting in an expansion of the area with risk values in the northern and southeastern parts of the eastern foot of Nasudake volcano. In addition, the risk values have been raised overall, with the average value now being five times higher than in the previous results. On the other hand, the risk value for the area within 3km east of the summit is now significantly higher in comparison. This suggests once again that crater location information is extremely important when creating hazard and risk maps.
In this presentation, risk values were calculated according to the risk definition by Founier d'Albe (1979): [Risk] = [Hazard] × [Exposure] × [Vulnerability]. Note that vulnerability was assumed to be "1". This means that an object will be damaged by pyroclastic density current. In the hazard assessment, we first performed a crater opening assessment and an eruption scale assessment at Nasudake volcano. In the crater opening assessment, the method of Alberico et al. (2008) was applied to the fumarolic points and the crater location map of Oikawa et al. (2022). The crater locations, according to the Nasu Volcano Geological Map (Yamamoto and Ban, 1997), were distributed on the west side of the summit of Nasudake volcano, while the crater structures in the crater location map by Oikawa et al. (2022) were also distributed on the east side of the summit, and the area where an opening could occur was wider than that of Kohno and Takarada (2024). For the eruption scale assessment, the methods of Sandri et al. (2016) and Shimizu and Tanabe (2022) were applied to Nasudake volcano, and probability values were calculated in increments of 0.5 for eruption magnitudes of 2-4 (Hayakawa, 1993). The results of these crater opening assessments and eruption scale assessments were used as input values for pyroclastic flow simulations. Simulations were performed using Titan2D ver.4 (Pitman et al., 2003; Patra et al., 2005). The basal friction angle was determined based on the relationship between the initial volume and the basal friction angle in Ogburn and Calder (2017). The initial volume was determined based on the eruption magnitude. The initial flow velocity was fixed at 40 m/s. The final hazard information was obtained by weighting a linear combination of all the simulation results using the weights obtained from the crater opening assessment.
Information on social infrastructure facilities in the Nasudake volcano region (four types: building distribution, population, roads and railways, and land use classification) was used for the exposure evaluation. These were downloaded from the National Land Numerical Information of the Ministry of Land, Infrastructure, Transport and Tourism. The distribution of various exposures was converted to a 0-1 relative importance distribution using the method of Del Negro et al. (2020) and integrated by weighted linear combination to obtain the exposure information.
The risk value was obtained by multiplying the hazard information and the exposure information. Recent updates to crater location information have resulted in an increase in sources to the north and east of the summit, resulting in an expansion of the area with risk values in the northern and southeastern parts of the eastern foot of Nasudake volcano. In addition, the risk values have been raised overall, with the average value now being five times higher than in the previous results. On the other hand, the risk value for the area within 3km east of the summit is now significantly higher in comparison. This suggests once again that crater location information is extremely important when creating hazard and risk maps.