The Tephras of Yotei Volcano

Kashiwabara, Makoto; Hirose, Yasushi; Kagawa, Masahito; Kan, Keiichi; Kasugai, Akira; Yamagishi, Kazuo

doi:10.4116/jaqua.15.75

Cited by 3 publications

(1 citation statement)

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“…The database generated by Suto et al (2007) Takarada et al, 2016) should also be included. (ii) Secondly, some records in the database (e.g., Yotei tephras, SW Hokkaido; Kashiwabara et al, 1976) should be refined to integrate recent revisions (e.g., Uesawa et al, 2016;Tsuji et al, 2018;Albert et al, 2019). (iii) There are numerous problems associated with the interpolation methods.…”

Section: Future Workmentioning

confidence: 99%

Creating a digital database of tephra fallout distribution and frequency in Japan

et al. 2022

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Tephra fallout is a potential hazard to livelihoods, critical infrastructure, and health, even in areas that are far from volcanoes. Therefore, it is important to quantitatively evaluate tephra fall hazards for both residents and infrastructure around hazardous volcanoes. Modern probabilistic volcanic hazard assessments of tephra fallout strongly rely on computer modeling; however, assessments based on isopach maps can also be also helpful in assisting decision-makers. To assess the tephra fall hazards in Japan, we created a digital database “Isopach map-Based Tephra fall Hazard Analysis (IB-THA)” and a tool to draw the cumulative number of tephra fallout events exceeding a specific thickness at a particular location. The database was re-digitized using an existing catalog of 551 tephra fall deposit distribution maps. The re-digitized datasets were utilized here to estimate the cumulative number of tephra fallout events exceeding a specific thickness at 47 prefectural offices for the last 150 kyr. This allowed the characterization of regional tephra fall hazards in Japan for the first time. High cumulative numbers (20) of tephra fall deposits > 0 mm were identified in the NE-E region (e.g., Maebashi), whereas low numbers (2) were recognized in the SW and W regions of Japan (e.g., Naha). The thickest tephra fall deposit (2850 mm) was observed at Kagoshima. We used IB-THA to create a hazard curve for Tokyo. This hazard curve provides the minimum frequency needed to exceed the tephra fall thickness at any location. To refine the digital database presented here, further studies are required to incorporate recent (i.e., 2003 or younger) tephra distributions, review questionable isopach maps, and improve the interpolation method for digitizing tephra fall distributions.

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Section: Future Workmentioning

confidence: 99%

Creating a digital database of tephra fallout distribution and frequency in Japan

et al. 2022

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Restored Image of Volcanic Sector Collapse at Old Yotei Volcano, Southwestern Hokkaido, Japan, from a Geomorphological Interpretation of the Distribution of Hummocks

Yoshida

2015

Journal of Geography(Chigaku Zasshi)

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Hummocks are conically shaped mounds, which occur following catastrophic sector collapses, and are mainly observed around volcanoes. Empirical relationships of hummocks proposed by Yoshida et al. (2012) are basically applicable if hummocks now distributed on a debris avalanche depositional area do not have remarkable disturbances due to topographical barriers or modifications after deposition. Using these empirical relationships, the Old Yotei volcano, whose megacollapse in the Late Pleistocene has not been clarified yet, is examined. The results show that the size-distance relationship of hummocks (N ＝ 297) , distributed west of the volcano can be expressed by an exponential function as, A ＝ exp (-D) , where A is the average area of a hummock within a certain span and D is the average distance from the source. For the Old Yotei volcano, the values of coefficients and of the fitted curve are 170286.4 and 0.000429, respectively. Based on a geomorphological interpretation of both and values, it can be concluded that the collapse volume of the Old Yotei volcano is ca.1.3 km 3 , and the equivalent coefficient of friction of the debris avalanche is 0.129. The latter also reveals a high probability that the pre-collapse summit of the Old Yotei volcano reached 1700 m a.s.l. Thus, the image of the flank collapse of the Old Yotei volcano has been restored more decisively by the distribution of hummocks.

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