5:15 PM - 6:30 PM
[SVC30-P02] Survey on Fissure Cave and Lava Tube Cave in Kansuyama Lava Flow of Mt.Fuji
Keywords:Mt.Fuji, Lava flow, Lava tube, Lava cave, Fissure vent
[Introduction]
Kansuyama lava flow (Juriki marubi lava flow) is a low-viscosity lava flow of SiO2 50.9 wt% ejected around AD710-800 and covers Kurozuka lava flow1). The length of Kansuyama lava flow is about 5 km, and the existence of Kaminari-ana cave, Jurigi koori ana, Suzumi fuketu, and Jurigi tree mold groups are known in the lava flow2,3,4). Recent investigations have revealed that Kaminari-ana cave is a fissure cave located in the channel-like flow path from Kansu yama pyroclastic cone , and that there are several small lava tube caves in the upstream and downstream on the channel-like flow path surface. We estimate the yield strength and lava temperature from surface lava tube cave. Figures 1 shows the locations of Kaminari-ana cave and surface lava tube caves.
[Kaminari ana cave located in lava channel structure]
Kaminari ana cave shown in Fig. 2 and Table1 is a cave with horizontal hole cavity that communicates with the deep vertical hole openings (Photo 1 and 2). The deep vertical hole opening of Kaminari ana cave is traditionally called the gas ejection hole 2,4), and it is one of the fissure vent because it is on the extension of the fissure vent row according to a survey by Hiroshi Tachihara and Osamu Ohshima in 2010. It is pointed out that the horizontal hole cavity at the bottom has no characteristics as a lava tube cave (roopy lava on the floor, lava shelf on the wall, arched ceiling, etc.), and the fissure wall is covered by lava. It can be clearly regarded as a fissure cave created by draining back of magma. The cavity is sandwiched by parallel walls on both sides, and a scoria layer can be seen behind the collapsed side wall.
[Lava tube cave on the surface of lava channel]
On the surface layer just in the upstream and downstream of Kaminari ana cave, there is a small rectangular lava tube caves (for large one, cavity height: 1 m, width: 4.8 m, length: 5.8 m) shown in Table 1 and Photo 3. Judging from the contour lines, the downstream one has an inclination angle of about α = 8 degrees (sin α = 0.143), and with the tube cavity height H = 1m, g = 9.8m / sec2, ρ = 2500kg / m3, the lava yield strength5) can be obtained as fB = 1168 Pa from fB = (H g ρ sin α) / 3. This yield strength is a reasonable value for basalt. Here, the temperature was calculated as 1068 ° C by using the temperature-dependent equation 7) based on the data created by Ishibashi & Sato6)from Mt. Fuji 1707 eruption basalt.
[Conclusion]
Several surface lava tube caves are formed on the surface of a channel-shaped depression with Kaminari an fissure cave extending from Kansu yama to the south. The yield strength of 1168 Pa obtained from the surface lava tube cave is a reasonable value for basalt. The temperature at which the surface lava tube cave was formed was estimated from this yield value as 1068 ° C.
References:
1) Akira Takada, Takahiro Yamamoto, Yoshihiro Ishizuka, Shun Nakano (2016): Geological Map of Fuji Volcano (2nd Edition) Manual, National Institute of Advanced Industrial Science and Technology
2) Takanori Ogawa (1980): Geological observation of lava caves and lava tree molds on Mt. Fuji, Dojin, Vol. 2, No. 3, Japan Cave Association
3) Hideo Endo (1983): Bizarre and Legendary Cave Exploration of Mt. Fuji, published June 1, 1983, Ryokuseisha
4) Takanori Ogawa (1991): Susono City Cultural Monument Survey Report Vol. 5, Lava Cave at the South Foot of Fuji, Susono City Board of Education
5) Tsutomu Honda (2017): Lava tube formation and application of lava tube cave formation model to the Moon and Mars, Proceedings of the 61st Meeting of the Japan Society for Aeronautical and Space Sciences 1B11
6)H.Ishibashi,H.Sato(2010):Journal of Mineralogical and Petrological Science,volume105,pp334-339
7) Tsutomu Honda (2018): Estimating the yield value of Mt. Fuji and lava flow by lava tube cave and lava tree mold, Japan Geoscience Union Meeting 2018 Proceedings SVC43-02
Kansuyama lava flow (Juriki marubi lava flow) is a low-viscosity lava flow of SiO2 50.9 wt% ejected around AD710-800 and covers Kurozuka lava flow1). The length of Kansuyama lava flow is about 5 km, and the existence of Kaminari-ana cave, Jurigi koori ana, Suzumi fuketu, and Jurigi tree mold groups are known in the lava flow2,3,4). Recent investigations have revealed that Kaminari-ana cave is a fissure cave located in the channel-like flow path from Kansu yama pyroclastic cone , and that there are several small lava tube caves in the upstream and downstream on the channel-like flow path surface. We estimate the yield strength and lava temperature from surface lava tube cave. Figures 1 shows the locations of Kaminari-ana cave and surface lava tube caves.
[Kaminari ana cave located in lava channel structure]
Kaminari ana cave shown in Fig. 2 and Table1 is a cave with horizontal hole cavity that communicates with the deep vertical hole openings (Photo 1 and 2). The deep vertical hole opening of Kaminari ana cave is traditionally called the gas ejection hole 2,4), and it is one of the fissure vent because it is on the extension of the fissure vent row according to a survey by Hiroshi Tachihara and Osamu Ohshima in 2010. It is pointed out that the horizontal hole cavity at the bottom has no characteristics as a lava tube cave (roopy lava on the floor, lava shelf on the wall, arched ceiling, etc.), and the fissure wall is covered by lava. It can be clearly regarded as a fissure cave created by draining back of magma. The cavity is sandwiched by parallel walls on both sides, and a scoria layer can be seen behind the collapsed side wall.
[Lava tube cave on the surface of lava channel]
On the surface layer just in the upstream and downstream of Kaminari ana cave, there is a small rectangular lava tube caves (for large one, cavity height: 1 m, width: 4.8 m, length: 5.8 m) shown in Table 1 and Photo 3. Judging from the contour lines, the downstream one has an inclination angle of about α = 8 degrees (sin α = 0.143), and with the tube cavity height H = 1m, g = 9.8m / sec2, ρ = 2500kg / m3, the lava yield strength5) can be obtained as fB = 1168 Pa from fB = (H g ρ sin α) / 3. This yield strength is a reasonable value for basalt. Here, the temperature was calculated as 1068 ° C by using the temperature-dependent equation 7) based on the data created by Ishibashi & Sato6)from Mt. Fuji 1707 eruption basalt.
[Conclusion]
Several surface lava tube caves are formed on the surface of a channel-shaped depression with Kaminari an fissure cave extending from Kansu yama to the south. The yield strength of 1168 Pa obtained from the surface lava tube cave is a reasonable value for basalt. The temperature at which the surface lava tube cave was formed was estimated from this yield value as 1068 ° C.
References:
1) Akira Takada, Takahiro Yamamoto, Yoshihiro Ishizuka, Shun Nakano (2016): Geological Map of Fuji Volcano (2nd Edition) Manual, National Institute of Advanced Industrial Science and Technology
2) Takanori Ogawa (1980): Geological observation of lava caves and lava tree molds on Mt. Fuji, Dojin, Vol. 2, No. 3, Japan Cave Association
3) Hideo Endo (1983): Bizarre and Legendary Cave Exploration of Mt. Fuji, published June 1, 1983, Ryokuseisha
4) Takanori Ogawa (1991): Susono City Cultural Monument Survey Report Vol. 5, Lava Cave at the South Foot of Fuji, Susono City Board of Education
5) Tsutomu Honda (2017): Lava tube formation and application of lava tube cave formation model to the Moon and Mars, Proceedings of the 61st Meeting of the Japan Society for Aeronautical and Space Sciences 1B11
6)H.Ishibashi,H.Sato(2010):Journal of Mineralogical and Petrological Science,volume105,pp334-339
7) Tsutomu Honda (2018): Estimating the yield value of Mt. Fuji and lava flow by lava tube cave and lava tree mold, Japan Geoscience Union Meeting 2018 Proceedings SVC43-02