A research group led by Postdoctoral Researcher Nariaki Nishiyama of the Tono Geoscience Center at the Japan Atomic Energy Agency (JAEA), and Leader Masakazu Niwa of the Neotectonics Research Group at the Tono Geoscience Center at JAEA announced that they had developed a computer-based method to estimate the traces (pathways) of past magma movements in volcanoes from topographic data for stable volcanoes. Whether a volcano is stable or unstable can be estimated by differences in the area of the contour lines surrounding areas other than the mountain peak of the volcano. For stable volcanoes, the direction of the extension of the contour lines reflects the distribution of radial veins (magma pathways).
Verification was conducted on a volcano with a known history of past activity, confirming that the method can be applied to stable volcanoes. The results were published in the academic journal, Applied Geology, Vol. 64, No. 3, published by the Japan Society of Applied Geology (JSEG). A manual that can be used by non-specialists was released by JSEG on October 3 (JAEA-Testing 2022-003).
Volcanic disasters, such as lava flows, phreatomagmatic explosions, pyroclastic flows, and volcanic ashfall, are generated and spread from craters as a result of magma pathways reaching the ground surface. Therefore, in disaster prevention and mitigation measures for volcanoes and safety assessments regarding the geological disposal of high-level radioactive waste, estimating where craters are likely to form on volcanoes is necessary. Research conducted in the 1990s suggested that radial veins spread around vertical magma pathways leading to the main crater and magma pathways occurred along these veins as side vents. Furthermore, the shape of the mountain body varied depending on the magma supply route. However, because of the lack of technology for quantitatively analyzing topography, no further studies were conducted.
In this study, the research group verified whether the distribution of volcanic channels and radial veins and the stability of volcanic channels could be estimated from a computer-based topographic analysis (e.g., a geographic information system, GIS) of volcanoes with activity histories.
First, a topographic analysis was conducted of 22 volcanoes for which data on the distribution history of craters over the past 10,000 years were available. Specifically, using volcanic contour lines, information related to the direction of the contour line extension, characteristics of the distribution of contour lines surrounding areas other than mountain peaks, and the area of the region enclosed by the contour lines was collected and analyzed using GIS software. The total area of contour lines surrounding areas other than mountain peaks of volcanoes with unstable volcanic channels, such as Mt. Kirishima, where the supply of magma is unstable and many volcanic channels are formed, were found to be significantly larger than that of stable volcanoes, such as Mt. Fuji. However, the study findings indicated that the method may not apply to volcanoes with calderas.
In general, stable volcanoes tend to erupt repeatedly in the same crater, and the shape of a volcano becomes an ellipse extending from the crater to the radial veins over time. This indicates that the direction of the development of radial veins (i.e., the direction in which new craters are likely to form) can be estimated from the direction of extension of the contour lines. Therefore, when the researchers estimated the direction in which new craters are likely to be formed for stable volcanoes with known activity history based on the contour line data, they found that the direction of extension of radial veins matched the actual distribution trend of craters, confirming the validity of the estimate. This means that the method can be applied to volcanoes with side vents.
Nishiyama commented, "Since this method can obtain estimation results only from topographic data, we expect that it can be combined with other exploration results and discussed. Also, since it is topographical data, we believe that it is advantageous to be able to determine the area that needs to be surveyed before the on-site survey. The method has already been documented in a manual, and we expect it to be used for a wide range of purposes outside of research."
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