3:45 PM - 4:00 PM
[SVC27-07] Development of simulator for secondary volcanic lahars, DFSS
Keywords:secondary lahar, debris flow, volcano
A volcanic lahar, which occurs due to a volcanic eruption, causes severe damage. Volcanic lahars can be caused directly by an eruption or by events not directly related to volcanic activity, such as subsequent rainfall. They are called primary lahars and secondary lahars, respectively. According to a literature review of past events of volcanic lahars [1], secondary volcanic lahars occurred more frequently than primary lahars. Disaster prevention and mitigation actions against secondary lahars, such as evacuation activities, can be taken between an eruption and subsequent rainfall, while the implementation of countermeasures against primary lahars, which happen immediately after the eruption, is difficult. Based on this idea, “emergency investigation'' for secondary lahars was stipulated in the Landslide Disaster Prevention Act in 2011.
According to [2], secondary lahars are triggered by small-scale rainfall of about 10 mm/h when the thickness of the volcanic ash layer on the slope is around 10 cm. Therefore, to estimate the flooding area of a secondary lahar, it is desirable to provide the spatial distribution of the ash fall thickness and the precipitation intensity as initial and boundary conditions, respectively. For the distribution of the ash fall thickness, survey results registered in JVDN system can be used as input data, which are surveyed by various organizations after an eruption happens. Furthermore, even immediately after an eruption, the estimated ash fall thickness by simulation tools such as Tephra2 can be used [3]. Regarding precipitation, XRAIN by MLIT and short-term rainfall forecast by JMA can be used as input data. Our research team has developed a program called Debris Flow Simulator for Sabo (DFSS), which inputs these data and executes rainfall-runoff analysis and lahar inundation analysis [4].
In this presentation, we present the DFSS calculation result of the secondary lahar caused by the 1977 eruption of Mt. Usu. The result is compared to the actual records. Through the results, we will discuss applicability of our calculation methods and the difficulties of collecting past volcanic lahar information.
Reference
[1] Sakagami, M. and Kunitomo, M., Historical record of lahar related to phreatic or phreatomagmatic eruption, Joru. Geol. Soc. Japan, Vol.123, No.5, p.283-289, 2017 (in Japanese)
[2] Tamura, K. et al., Civil Engineering Journal, Vol.52, No.3, p.34-39, 2010 (in Japanese)
[3] Shimizu, T., Yamamoto, N., Imamori, N., and Ishida, K., Applicability of Ashfall Simulation to Estimating of Post-eruption Volcanic Debris Flow Occurrence, Programme and Abstracts the Volcanological society Japan, A2-07, 2022 (in Japanese)
[4] Yamazaki, Y., et al., PWRI Technical Note, No.4419, 2022 (in Japanese)
According to [2], secondary lahars are triggered by small-scale rainfall of about 10 mm/h when the thickness of the volcanic ash layer on the slope is around 10 cm. Therefore, to estimate the flooding area of a secondary lahar, it is desirable to provide the spatial distribution of the ash fall thickness and the precipitation intensity as initial and boundary conditions, respectively. For the distribution of the ash fall thickness, survey results registered in JVDN system can be used as input data, which are surveyed by various organizations after an eruption happens. Furthermore, even immediately after an eruption, the estimated ash fall thickness by simulation tools such as Tephra2 can be used [3]. Regarding precipitation, XRAIN by MLIT and short-term rainfall forecast by JMA can be used as input data. Our research team has developed a program called Debris Flow Simulator for Sabo (DFSS), which inputs these data and executes rainfall-runoff analysis and lahar inundation analysis [4].
In this presentation, we present the DFSS calculation result of the secondary lahar caused by the 1977 eruption of Mt. Usu. The result is compared to the actual records. Through the results, we will discuss applicability of our calculation methods and the difficulties of collecting past volcanic lahar information.
Reference
[1] Sakagami, M. and Kunitomo, M., Historical record of lahar related to phreatic or phreatomagmatic eruption, Joru. Geol. Soc. Japan, Vol.123, No.5, p.283-289, 2017 (in Japanese)
[2] Tamura, K. et al., Civil Engineering Journal, Vol.52, No.3, p.34-39, 2010 (in Japanese)
[3] Shimizu, T., Yamamoto, N., Imamori, N., and Ishida, K., Applicability of Ashfall Simulation to Estimating of Post-eruption Volcanic Debris Flow Occurrence, Programme and Abstracts the Volcanological society Japan, A2-07, 2022 (in Japanese)
[4] Yamazaki, Y., et al., PWRI Technical Note, No.4419, 2022 (in Japanese)