5:15 PM - 7:15 PM
[HGM04-P11] Geomorphometric Analysis for Estimating the Yield Stress of Lava Flows on Mt. Fuji
Keywords:Geomorphometric Analysis, Lava Flows, Yield Stress, Mt. Fuji, Slope Angle, Digital Elevation Model
Volcanic landforms preserve the history of past eruptions, with their structure reflecting the interplay of factors such as magma composition, eruption style, and environmental conditions at the time of eruption. These landforms contain vast geomorphological information that can be deciphered through geomorphometric analysis to infer the underlying dynamic processes governing their formation.
Efforts have been made to estimate the physical properties of lava flows by analyzing the morphological characteristics formed during eruptions. It is widely recognized that lavas behave as Bingham fluids, which are characterized by a yield stress and a plastic viscosity. The yield stress, an important physical property of lava flows, can be estimated through geomorphometric analysis[1]. Lava flow models suggest that the flow stops when its thickness drops below a threshold determined by the yield stress and the underlying ground slope. Most lava flow simulations in Japan incorporate observations from Minakami during the 1951 Izu-Oshima eruption[2] into equations proposed by Ishihara et al. (1990) [3], though the estimated values differ by an order of magnitude. Furthermore, the initial lava temperature at Mt. Fuji is assumed to be 1200℃, which differs from the 1038–1125℃ range at Izu-Oshima. This discrepancy raises concerns about the direct application of data from other volcanoes to Mt. Fuji, highlighting the need for reliable, site-specific estimates based on Mt. Fuji’s geomorphometric data.
However, standardized methods for lava flow morphometric data analysis are still lacking, and several issues remain in interpreting lava flow morphology. To estimate the thickness and volume of a lava flow, knowledge of the pre-eruption morphology is required. Since current topography reflects post-emplacement modifications, reconstructing pre-eruption surfaces from modern data is challenging. In this study, we conducted morphometric analyses of lava flows using several methodological approaches and compared the results to assess their validity.
First, we applied the method proposed by Ishimine (2024) to calculate yield stress values. The sample number of lava flows analyzed was expanded compared to previous studies to verify the robustness and reproducibility of the results. The estimation procedure from morphology was as follows: high-resolution DEM data from Yamanashi Prefecture were utilized, assuming that the shape of the lava flow and its surrounding landform remained unchanged since the time of the eruption. The lava flow, which showed minimal anthropogenic geomorphic modification, was selected, and the flow direction was estimated. Elevation values were then obtained at both the lava flow front and a reference point 100 meters upstream, allowing for the calculation of the ground slope. Subsequently, the thickness of the lava flow was estimated by assuming that its base corresponded to the pre-eruption ground surface, and the yield stress was calculated using Ishihara et al.'s (1990) equation.
As a result, yield stresses consistent with previous findings were obtained for the Hinokimarubi 2 and Nakanochaya-Marubi lava flows, with estimated values ranging from 6500 to 7400 N/m². For other lava flows, yield stresses ranged from 5400 to 25000 N/m². To investigate the reasons behind these order-of-magnitude differences, we analyzed the correlation between yield stress, ground slope, and elevation at the lava flow’s stopping point. A positive correlation trend was observed, though it was not clearly defined. Further comparisons with other measurement methods and detailed interpretations will be presented in the conference presentation.
[1] Ishimine, Y. (2024) MFRI Research Report, 57, R-05-2024. (in Japanese).
[2] Minakami, T. (1951) Bull Earthq Res Inst, 29, 487-498.
[3] Ishihara, K., Iguchi, M., and Kamo, K. (1990) In Lava Flows and Domes, Springer, 174-207.
Efforts have been made to estimate the physical properties of lava flows by analyzing the morphological characteristics formed during eruptions. It is widely recognized that lavas behave as Bingham fluids, which are characterized by a yield stress and a plastic viscosity. The yield stress, an important physical property of lava flows, can be estimated through geomorphometric analysis[1]. Lava flow models suggest that the flow stops when its thickness drops below a threshold determined by the yield stress and the underlying ground slope. Most lava flow simulations in Japan incorporate observations from Minakami during the 1951 Izu-Oshima eruption[2] into equations proposed by Ishihara et al. (1990) [3], though the estimated values differ by an order of magnitude. Furthermore, the initial lava temperature at Mt. Fuji is assumed to be 1200℃, which differs from the 1038–1125℃ range at Izu-Oshima. This discrepancy raises concerns about the direct application of data from other volcanoes to Mt. Fuji, highlighting the need for reliable, site-specific estimates based on Mt. Fuji’s geomorphometric data.
However, standardized methods for lava flow morphometric data analysis are still lacking, and several issues remain in interpreting lava flow morphology. To estimate the thickness and volume of a lava flow, knowledge of the pre-eruption morphology is required. Since current topography reflects post-emplacement modifications, reconstructing pre-eruption surfaces from modern data is challenging. In this study, we conducted morphometric analyses of lava flows using several methodological approaches and compared the results to assess their validity.
First, we applied the method proposed by Ishimine (2024) to calculate yield stress values. The sample number of lava flows analyzed was expanded compared to previous studies to verify the robustness and reproducibility of the results. The estimation procedure from morphology was as follows: high-resolution DEM data from Yamanashi Prefecture were utilized, assuming that the shape of the lava flow and its surrounding landform remained unchanged since the time of the eruption. The lava flow, which showed minimal anthropogenic geomorphic modification, was selected, and the flow direction was estimated. Elevation values were then obtained at both the lava flow front and a reference point 100 meters upstream, allowing for the calculation of the ground slope. Subsequently, the thickness of the lava flow was estimated by assuming that its base corresponded to the pre-eruption ground surface, and the yield stress was calculated using Ishihara et al.'s (1990) equation.
As a result, yield stresses consistent with previous findings were obtained for the Hinokimarubi 2 and Nakanochaya-Marubi lava flows, with estimated values ranging from 6500 to 7400 N/m². For other lava flows, yield stresses ranged from 5400 to 25000 N/m². To investigate the reasons behind these order-of-magnitude differences, we analyzed the correlation between yield stress, ground slope, and elevation at the lava flow’s stopping point. A positive correlation trend was observed, though it was not clearly defined. Further comparisons with other measurement methods and detailed interpretations will be presented in the conference presentation.
[1] Ishimine, Y. (2024) MFRI Research Report, 57, R-05-2024. (in Japanese).
[2] Minakami, T. (1951) Bull Earthq Res Inst, 29, 487-498.
[3] Ishihara, K., Iguchi, M., and Kamo, K. (1990) In Lava Flows and Domes, Springer, 174-207.