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[SVC29-P05] Volcanic caves(Fissure vent cave,Lava tube cave,Fracture cave) of Nishiyama in Hachijojima island
Keywords:fissure vent cave, lava tube cave, fracture cave, Hachijojima-island, Nishiyama-volcano
[Introduction]
It is known that there is Hachijo fuketsu cave No. 1 (total length: 1404m), which is the second longest lava tube cave in Japan, located in the southeastern part of the hillside of Nishiyama, Hachijojima [1]. The deepest (65m) fissure vent cave in Japan (Fissure vent cave) [2] is located in the north, and the Hachijo Fuji fuketsu cave, which is a fissure vent cave with a cavity height of 10m and a length of 103m, also exists at the summit [3]. In addition, the lava dome inside the summit crater has a Kanbotsu ana (Sink hole) with a diameter of 150 m and a depth of 60 m due to the depression of a part of the dome called a small hole, and the central surface of the dome has a depth of 100 m. A cracked crater cave [4, 5], which seems to have been formed by shrinkage of 78 m in width and several meters during cooling, can be seen [4,5], therefore, Nishiyama is called "a department store of volcanic caves" [6]. This report introduced these caves and also mentions the possibility of similarities to the cavities under the vertical holes of the extraterrestrial Martian Arsia-mons volcano.
[Volcanic caves of Nishiyama in Hachijojima (Hachijo Fuji) and its distribution: Fissure vent cave, lava tube cave, crack cave, sink hole]
In the list of volcanic caves shown in Table 1, the names of lava flows belonging to the location of the caves are listed based on the lava flow distribution map [7] of AIST, classified according to the origin of the cave formation. This list was revised based on the data list of Ogawa [8] by a subsequent investigations. Figure 1 shows the distribution of volcanic caves and lava flows in Nishiyama.
Fig. 2 is a survey map of the Hachijo wind cave no.1, which is a long lava tube cave, Fig. 3 is a survey map of the fissure vent cave at the foot of the mountain (Eigo Lift Cave No. 3) [3], and Fig. 4 is a survey map of the hillside fissure vent cave (Hachijo Fuji Wind cave) [3,5] is shown. The lava tube cave (Hachijo wind cave no.1) [9] is on a gentle slope (inclination angle 4 to 14 degrees), and the Hachijo Fuji wind cave (inclination angle 27 degrees) [3,5] and the fissure vent cave group (inclination angle 27 degrees) of the fissure vent. The surface inclination angle (20 degrees) exists along the fissure vent row of the steep slope. The crack cave inside the lava dome at the top of the mountain is thought to be formed during the cooling contraction of the lava dome [5].
[Possible Analogies to Mars' Arsia mons volcano]
Several vertical holes have been found on the steep hillsides and skirts of Arsia mons volcano [10, 11]. If the slope is steep(inclination angle 1.0 ° to 3.5 °), the lava flow is not thick enough to form a large lava tube. There is a high possibility of a fissure vent cave. On the other hand, It is highly likely that the existence of a lava tube cave shows a value almost equivalent to the estimated tube height in the vertical hole on the gentle slope of the foot (inclination angle 0.12 ° to 0.54 °).
[Conclusion]
By analogy with the survey results of Hachijojima Nishiyama, there is a possibility that there is a crater cave at the top of the mountain, a fissure vent cave at the hillside, and a lava tube cave at the skirt of Mars Arsia mons volcano, although the size of the mountain is different. It has been reported that there is a vertical hole between the large hole (crater) of Hachijojima Nishiyama volcano and the dome, and there is a large cavity under it, which requires further investigation. A flat lava cave found during land preparation work in the Mitsune Katase area (near the entrance of the Fuji mountain trail) (length 20 to 30 meters, width 5 to 6 meters, height is some places where humans can stand, Lava stalactite on the ceiling surface and ribbed lava wall (sometimes 50-60 cm) are preserved [12,13]. It is possible that such an internal structure exists inside the cavity of Arsia mons volcano.
References:
[1]Nankai Times:1980.01.27,[2]Nankai Times:1991.11.03,[3]T.Ohsako(1992):Report on Hachijojima volcanic caves,Volcano-Speleological Society of Japan,vol.29,No.1,p12-33,[4]Nankai Times:1993.05.30,[5]T.Ohsako(1994)Relation between the volcanic activity of Mt.Hachijo-Fuji and volcanic caves on Hachijojima island,the seven izu islands,Japan,7th International Symposium on Vulcanospeleology,[6]Nankai Times:2000.07.28,[7]O.Ishizuka,N.Geshi(2018):Geological Map of Hachijojima volcano,Geological Survey of Japan,AIST,[8] T.Ogawa(1988):Dojin,Vol.7,No.3,p 79,[9]T.Honda(2003):PB24, Fall meeting of 2003 of the Volcanological Society of Japan,[10]T.Honda(2017):P117, Fall meeting of 2017 of the Volcanological Society of Japan,[11]T.Honda(2021):MIS12-P02,2021JPGU,[12]Nankai Times:2009.05.29,[13]Nankai Times:2014.09.12
It is known that there is Hachijo fuketsu cave No. 1 (total length: 1404m), which is the second longest lava tube cave in Japan, located in the southeastern part of the hillside of Nishiyama, Hachijojima [1]. The deepest (65m) fissure vent cave in Japan (Fissure vent cave) [2] is located in the north, and the Hachijo Fuji fuketsu cave, which is a fissure vent cave with a cavity height of 10m and a length of 103m, also exists at the summit [3]. In addition, the lava dome inside the summit crater has a Kanbotsu ana (Sink hole) with a diameter of 150 m and a depth of 60 m due to the depression of a part of the dome called a small hole, and the central surface of the dome has a depth of 100 m. A cracked crater cave [4, 5], which seems to have been formed by shrinkage of 78 m in width and several meters during cooling, can be seen [4,5], therefore, Nishiyama is called "a department store of volcanic caves" [6]. This report introduced these caves and also mentions the possibility of similarities to the cavities under the vertical holes of the extraterrestrial Martian Arsia-mons volcano.
[Volcanic caves of Nishiyama in Hachijojima (Hachijo Fuji) and its distribution: Fissure vent cave, lava tube cave, crack cave, sink hole]
In the list of volcanic caves shown in Table 1, the names of lava flows belonging to the location of the caves are listed based on the lava flow distribution map [7] of AIST, classified according to the origin of the cave formation. This list was revised based on the data list of Ogawa [8] by a subsequent investigations. Figure 1 shows the distribution of volcanic caves and lava flows in Nishiyama.
Fig. 2 is a survey map of the Hachijo wind cave no.1, which is a long lava tube cave, Fig. 3 is a survey map of the fissure vent cave at the foot of the mountain (Eigo Lift Cave No. 3) [3], and Fig. 4 is a survey map of the hillside fissure vent cave (Hachijo Fuji Wind cave) [3,5] is shown. The lava tube cave (Hachijo wind cave no.1) [9] is on a gentle slope (inclination angle 4 to 14 degrees), and the Hachijo Fuji wind cave (inclination angle 27 degrees) [3,5] and the fissure vent cave group (inclination angle 27 degrees) of the fissure vent. The surface inclination angle (20 degrees) exists along the fissure vent row of the steep slope. The crack cave inside the lava dome at the top of the mountain is thought to be formed during the cooling contraction of the lava dome [5].
[Possible Analogies to Mars' Arsia mons volcano]
Several vertical holes have been found on the steep hillsides and skirts of Arsia mons volcano [10, 11]. If the slope is steep(inclination angle 1.0 ° to 3.5 °), the lava flow is not thick enough to form a large lava tube. There is a high possibility of a fissure vent cave. On the other hand, It is highly likely that the existence of a lava tube cave shows a value almost equivalent to the estimated tube height in the vertical hole on the gentle slope of the foot (inclination angle 0.12 ° to 0.54 °).
[Conclusion]
By analogy with the survey results of Hachijojima Nishiyama, there is a possibility that there is a crater cave at the top of the mountain, a fissure vent cave at the hillside, and a lava tube cave at the skirt of Mars Arsia mons volcano, although the size of the mountain is different. It has been reported that there is a vertical hole between the large hole (crater) of Hachijojima Nishiyama volcano and the dome, and there is a large cavity under it, which requires further investigation. A flat lava cave found during land preparation work in the Mitsune Katase area (near the entrance of the Fuji mountain trail) (length 20 to 30 meters, width 5 to 6 meters, height is some places where humans can stand, Lava stalactite on the ceiling surface and ribbed lava wall (sometimes 50-60 cm) are preserved [12,13]. It is possible that such an internal structure exists inside the cavity of Arsia mons volcano.
References:
[1]Nankai Times:1980.01.27,[2]Nankai Times:1991.11.03,[3]T.Ohsako(1992):Report on Hachijojima volcanic caves,Volcano-Speleological Society of Japan,vol.29,No.1,p12-33,[4]Nankai Times:1993.05.30,[5]T.Ohsako(1994)Relation between the volcanic activity of Mt.Hachijo-Fuji and volcanic caves on Hachijojima island,the seven izu islands,Japan,7th International Symposium on Vulcanospeleology,[6]Nankai Times:2000.07.28,[7]O.Ishizuka,N.Geshi(2018):Geological Map of Hachijojima volcano,Geological Survey of Japan,AIST,[8] T.Ogawa(1988):Dojin,Vol.7,No.3,p 79,[9]T.Honda(2003):PB24, Fall meeting of 2003 of the Volcanological Society of Japan,[10]T.Honda(2017):P117, Fall meeting of 2017 of the Volcanological Society of Japan,[11]T.Honda(2021):MIS12-P02,2021JPGU,[12]Nankai Times:2009.05.29,[13]Nankai Times:2014.09.12