5:15 PM - 7:15 PM
[SVC34-P08] Reconstruction of past eruptive activity of Kusatsu-Shirane volcano by historic bird's-eye view maps of Kusatsu Spa
Keywords:historic bird's-eye view map, Kusatsu Spa, Kusatsu-Shirane volcano, phreatic eruption
1. Introduction
Kusatsu-Shirane volcano is one of the most active volcanoes in Japan with frequent phreatic eruptions. This volcano consists of two main pyroclastic cones called Shirane and Motoshirane. Recent eruptive activity has occurred only at the Shirane pyroclastic cone, however, sudden phreatic eruption occurred at the Motoshirane pyroclastic cone on January 23, 2018, resulting in one death and 12 injuries. This eruption is believed to be the first eruption at Mt. Motoshirane during the historical period. Kusatsu-Shirane volcano has been active since the 1882 eruption at the Shirane pyroclastic cone, however, volcanic activity prior to 1882 was not well known because most of past documents were lost in the fire which occurred at the Kusatsu Spa, 6 km from the volcano, in 1869.
In this study we examined historic bird's-eye view maps and old documents depicting Kusatsu Spa. Bird's-eye view maps were frequently updated and used for up-to-date local information and advertising. In these bird's-eye view maps, the mountains and their names are depicted in the distant view of the Kusatsu town. Some of them include depictions of what can be interpreted as volcanic plume. These bird's-eye views were published repeatedly from the mid-Edo period to the early Showa period, and it is expected that the changes in their descriptions reflect the changes in volcanic activities. In this study, we discuss temporal changes in volcanic activity since the late Edo period based mainly on the bird's-eye view maps of Kusatsu Spa.
2. Materials and methods
We examined 69 bird's-eye views map of Kusatsu Spa published between 1810 and 1938. The publication intervals of these bird's-eye views map are mostly within three years. In these bird's-eye views map, we confirmed the mountains with their name in the distant view of the Kusatsu town and confirmed whether volcanic plumes rising from the summits of Mt. Shirane, Motoshirane, and Asama are depicted. In addition, we examined an official map published in 1788 (a village map), a sketch made in 1755 with a document, and three old documents.
3. Results
Mt. Shirane was depicted in 67 bird's-eye views map, probably because Mt. Shirane was considered an important object of worship in this region. Volcanic plumes rising from Mt. Shirane were repeatedly depicted in all 17 bird's-eye view maps published between 1810 and 1848. No volcanic plumes were seen from 1849 to 1883, and again after 1983. This temporal variation is consistent with the oral tradition (Ohashi, 1914).
We found depictions of Mt. Motoshirane on 43 bird's-eye views map. Only one bird's-eye views map, published in the Bunsei period (1818-1830, the correct year of publication is unknown), depicted a rising plume from the top of Mt. Motoshirane. In this map, the topography of the Mt. Motoshirane almost corresponds to the actual pyroclastic cone; the volcanic plum is rising from the Kagami-ike-kita pyroclastic cone, corresponding to the site of the phreatic eruption in 2018.
4. Discussion
Historical records indicate that the plume activity that can be seen from the Kusatsu Spa occurred before and after the 1805 eruption, indicating vigorous thermal activity or frequent phreatic eruptions lasting for decades. Some historical documents describe that volcanic plumes and a hot crater lake at the top of Mt. Shirane in 18th. Throughout the period from 1800 to 1943, there were only about 30 years without volcanic plume activity.
We found a bird's-eye view map depicting a volcanic plume of Mt. Motoshirane, which is the only historical record describing the volcanic activity at Mt. Motoshirane. This suggests the occurrence of vigorous fumarolic activity or phreatic eruptions in the Bunsei period. Although bird's-eye view maps published around this time did not depict Mt. Motoshirane, only this bird's-eye view map depicted Mt. Motoshirane. We believe that the temporary attention given to Mt. Motoshirane was due to its temporary volcanic activity only at this time.
Kusatsu-Shirane volcano is one of the most active volcanoes in Japan with frequent phreatic eruptions. This volcano consists of two main pyroclastic cones called Shirane and Motoshirane. Recent eruptive activity has occurred only at the Shirane pyroclastic cone, however, sudden phreatic eruption occurred at the Motoshirane pyroclastic cone on January 23, 2018, resulting in one death and 12 injuries. This eruption is believed to be the first eruption at Mt. Motoshirane during the historical period. Kusatsu-Shirane volcano has been active since the 1882 eruption at the Shirane pyroclastic cone, however, volcanic activity prior to 1882 was not well known because most of past documents were lost in the fire which occurred at the Kusatsu Spa, 6 km from the volcano, in 1869.
In this study we examined historic bird's-eye view maps and old documents depicting Kusatsu Spa. Bird's-eye view maps were frequently updated and used for up-to-date local information and advertising. In these bird's-eye view maps, the mountains and their names are depicted in the distant view of the Kusatsu town. Some of them include depictions of what can be interpreted as volcanic plume. These bird's-eye views were published repeatedly from the mid-Edo period to the early Showa period, and it is expected that the changes in their descriptions reflect the changes in volcanic activities. In this study, we discuss temporal changes in volcanic activity since the late Edo period based mainly on the bird's-eye view maps of Kusatsu Spa.
2. Materials and methods
We examined 69 bird's-eye views map of Kusatsu Spa published between 1810 and 1938. The publication intervals of these bird's-eye views map are mostly within three years. In these bird's-eye views map, we confirmed the mountains with their name in the distant view of the Kusatsu town and confirmed whether volcanic plumes rising from the summits of Mt. Shirane, Motoshirane, and Asama are depicted. In addition, we examined an official map published in 1788 (a village map), a sketch made in 1755 with a document, and three old documents.
3. Results
Mt. Shirane was depicted in 67 bird's-eye views map, probably because Mt. Shirane was considered an important object of worship in this region. Volcanic plumes rising from Mt. Shirane were repeatedly depicted in all 17 bird's-eye view maps published between 1810 and 1848. No volcanic plumes were seen from 1849 to 1883, and again after 1983. This temporal variation is consistent with the oral tradition (Ohashi, 1914).
We found depictions of Mt. Motoshirane on 43 bird's-eye views map. Only one bird's-eye views map, published in the Bunsei period (1818-1830, the correct year of publication is unknown), depicted a rising plume from the top of Mt. Motoshirane. In this map, the topography of the Mt. Motoshirane almost corresponds to the actual pyroclastic cone; the volcanic plum is rising from the Kagami-ike-kita pyroclastic cone, corresponding to the site of the phreatic eruption in 2018.
4. Discussion
Historical records indicate that the plume activity that can be seen from the Kusatsu Spa occurred before and after the 1805 eruption, indicating vigorous thermal activity or frequent phreatic eruptions lasting for decades. Some historical documents describe that volcanic plumes and a hot crater lake at the top of Mt. Shirane in 18th. Throughout the period from 1800 to 1943, there were only about 30 years without volcanic plume activity.
We found a bird's-eye view map depicting a volcanic plume of Mt. Motoshirane, which is the only historical record describing the volcanic activity at Mt. Motoshirane. This suggests the occurrence of vigorous fumarolic activity or phreatic eruptions in the Bunsei period. Although bird's-eye view maps published around this time did not depict Mt. Motoshirane, only this bird's-eye view map depicted Mt. Motoshirane. We believe that the temporary attention given to Mt. Motoshirane was due to its temporary volcanic activity only at this time.