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Nishiyama, Nariaki; Kawamura, Makoto; Umeda, Koji*; Niwa, Masakazu
Oyo Chishitsu, 64(3), p.98 - 111, 2023/08
It is important to accumulate research examples on the spatial distribution of dikes under volcanic edifices for risk assessment in volcanic disaster prevention and site selection and safety assessment for the geological disposal of high-level radioactive waste. The topography of volcanoes is considered to represent the location of magma intrusion associated with volcanic activity and its history. In this study, we attempted to determine the predominant orientation of radial dikes and evaluate the central conduit stability based on the distribution, centroid, and area of contour lines comprising the volcanic edifices using GIS-based topographic analysis. As a result of the topographic analysis, the predominant orientation of the dikes was successfully shown for the volcanoes with stable conduits. On the other hand, this analysis was not suitable for determine the predominant orientation of dikes in volcanoes with unstable conduits, thus the applicable range of this analysis is considered to be determined by the conduit stability. In addition, the conduit stability can be evaluated by using the area data of contour polygons, which represents the scope of application to the method for determination of the predominant orientation of dikes. This means that the conduit stability during volcanic activity can be evaluated even for volcanoes of which activity history is not yet known, and that topographic analysis is a useful tool for this purpose. The use of topographic analysis in this study will be expected to provide a new scale for the history of volcanic activity.
Hiura, Yuki; Kawamura, Makoto; Umeda, Koji*; Niwa, Masakazu
no journal, ,
One of the technical issues related to volcanic and igneous activities is the sophistication of technology for grasping the range of influence of magma. To address this issue, it is important to accumulate survey cases, especially when the dike develops over a radius of 15 km from the center of the Quaternary volcano, but it lies beneath the existing volcanic body. It is practically difficult to grasp the distribution of the conduits and the dikes derived from them. Therefore, the purpose of this study was to develop a method for estimating the distribution range of dikes distributed under the Quaternary volcanic body based on topographical data such as digital elevation models. In this study, we used digital maps and GIS software to target six volcanoes, such as stratovolcanoes and calderas. The parameters were measured, and modeling of the three-dimensional distribution range of radial dikes was examined from each parameter for each altitude. As a result, the transition of the center of gravity position for each altitude suggests the transition of the center of activity in the process of forming the volcanic body to some extent, and it is possible to extract not only the activity of the central crater but also the activity of lateral volcanoes. This suggests the possibility of quantitative evaluation of the transition and stability of the conduit even in volcanoes whose activity history is not clear by applying this method.
Nishiyama, Nariaki*; Kawamura, Makoto; Umeda, Koji*; Goto, Akira; Niwa, Masakazu
no journal, ,
The topography of the volcanic mountain body is thought to reflect the actual distribution range of the dike. Based on this idea, we examined the modeling of the dike distribution and the evaluation of the central conduit stability focused on the shape of the contour lines. In this study, we drew the line with the maximum distance (long axis) in the contour distribution of each elevation and aggregated the orientation data, in addition to the data obtained from the analysis of Nishiyama et al. (2021). Moreover, we calculated the topographic parameter of each volcano, using the area data of the area enclosed by the contour lines (contour polygons). As a result, we found that the orientation of the long axis of the contour polygons of volcanic bodies shows the orientation trend in each volcano. The orientation of the line connecting the centroid of many volcanoes is consistent with that of the line connecting the centroid, which is roughly consistent with the direction of sigma 1 around the volcanoes. In general, dikes are characterized by extension in the direction of the maximum compression axis, and our topographic analysis results are consistent with this. As for the topographic parameters of each volcano using the area of contour polygons, the result suggests that it is possible to distinguish between volcanoes classified as central conduit stable and unstable by Takahashi (1994). Therefore, the topographic analysis is expected to be used to evaluate the stability of central conduit even for volcanoes whose activity history is not yet known. In the future, we will develop an evaluation method based on the above topographic features, and establish a method for evaluating the central conduit stability and modeling the distribution of dikes by topographic analysis.
