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[SVC30-P01] Yield strength obtained from lava flow and lava tube cave of Undara volcano
Keywords:Lava tube, Yield strength, Lava flow, Undara volcano
[Introduction]
The Undara Cave is a huge lava tube system with a maximum height of 20 m and a maximum width of 32 m, formed on a gentle slope with an average inclination angle of 0.3 °,in a lava flow length of 160 km(Fig.1) which was erupted by Undara volcano 190,000 years ago[1,2]. The lava eruption temperature of Undara volcano is said to be 1170-1220 ℃, and the silicic acid weight fraction is 48.9wt% [1,2]. By using the published data of Atkinson et al.[1,2,3], the lava yield strength is estimated by two methods [4]: the lava flow stop condition and the lava tube formation limit condition.
[Yield strength obtained from the thickness of the Undara volcanic lava flow]
Table 1 shows the lava flow thickness, slope angle and yield strength obtained for each lava flow section. The column ① to ③ in Table1 are based on reference [1]. ④ is yield strength obtained from the values of column ② and ③. The yield strength was obtained from the lava flow stop condition [4]: fB = H (ρgsinα). The high apparent yield strength fB = 4.3 to 6.4x103 Pa may be due to lava inflation and/or lava superposition. The true lava yield strength is considered to be the lower yield strength fB = 1.5 ~ 2.1x103 Pa.
[Yield strength obtained from the height of the cavity in Undara Cave]
Table 2 shows the cavity height, width, and slope angle of representative parts of the Undara cave system [3]. The columns ① to ⑤ in Table2 are based on the reference [3]. The column ⑥ is yield strength obtained from the values of ③ and ⑤. The longest among these caves, Bayliss cave and Barkers cave, clearly show the tube like structure[1]. Others are fragmentary caves that occupy a small part of the lava cave system due to the burial of the floor. As shown in ⑥ of Table 2, the yield strength by using the limit condition for lava tube cave formation [4]:fB = H (ρgsinα) / 4 is obtained from this cavity height and slope angle. Tayler cave, Bayliss cave, and Barkers cave show high yield strength, on the other hand, other small caves show low yield strength due to low cavity height with buried floor. It is considered that several layers of lava flow have accumulated and the cavity height has decreased, showing a low apparent yield value fB = 272 to 834 Pa. High lava yield strength obtained from Tayler cave, Bayliss cave, and Barkers cave:fB = 1.4 ~ 3.4x103 Pa is considered to be close to the true yield strength. This yield strength is also consistent with the lava yield strength fB = 1.5 ~ 2.1x103 Pa obtained from the lava flow stop condition.
[Conclusion]
The lava yield strength fB = 1.4 ~ 3.4x103 Pa obtained from Tayler cave, Bayliss cave, and Barkers cave is a reasonable value for basalt with a silicic acid weight fraction of 48.9 wt%. For other small fragmentary caves with low apparent yield values, the floor is buried and the cavity height is decreased. It is necessary to judge whether the estimated yield strength is a reasonable value or not by observing the structure inside the cave in detail.
References:
[1] Anne Atkinson (2010): Undara Volcano, North Queensland, Australia and its Lava Field – Lava Caves, Depressions and The Wall – a Possible Lunar Analogue, Proceedings 14th International Symposium on Vulcanospeleology, 2010. www.vulcanospeleology.org/sym14 /papers/Atkinson.pdf
[2] Anne and Vernon Atkinson (1995): Undara Volcano and its Lava tubes, A geological Wonder of Australia in Undara Volcanic National Park, North Queensland
[3] Graeme P. Melville (1994): Lava tubes and channels of the Earth, Venus, Moon and Mars, Master of Science (Hons.) Thesis, Department of Physics, University of Wollongong, 1994.
http://ro.uow.edu.au/theses/2859
[4]Tsutomu Honda, Takayoshi Katsumata, Yutaka Ito, Masaru Hatanaka(2017): B3-06 Examination of Mt. Fuji and Suyama womb lava flow by lava tube cave and lava tree type, 2017 Proceedings of the Autumn Meeting of the Volcanic Society of Japan
https://www.jstage.jst.go.jp/article/vsj/2017/0/2017_96/_pdf/-char/ja
The Undara Cave is a huge lava tube system with a maximum height of 20 m and a maximum width of 32 m, formed on a gentle slope with an average inclination angle of 0.3 °,in a lava flow length of 160 km(Fig.1) which was erupted by Undara volcano 190,000 years ago[1,2]. The lava eruption temperature of Undara volcano is said to be 1170-1220 ℃, and the silicic acid weight fraction is 48.9wt% [1,2]. By using the published data of Atkinson et al.[1,2,3], the lava yield strength is estimated by two methods [4]: the lava flow stop condition and the lava tube formation limit condition.
[Yield strength obtained from the thickness of the Undara volcanic lava flow]
Table 1 shows the lava flow thickness, slope angle and yield strength obtained for each lava flow section. The column ① to ③ in Table1 are based on reference [1]. ④ is yield strength obtained from the values of column ② and ③. The yield strength was obtained from the lava flow stop condition [4]: fB = H (ρgsinα). The high apparent yield strength fB = 4.3 to 6.4x103 Pa may be due to lava inflation and/or lava superposition. The true lava yield strength is considered to be the lower yield strength fB = 1.5 ~ 2.1x103 Pa.
[Yield strength obtained from the height of the cavity in Undara Cave]
Table 2 shows the cavity height, width, and slope angle of representative parts of the Undara cave system [3]. The columns ① to ⑤ in Table2 are based on the reference [3]. The column ⑥ is yield strength obtained from the values of ③ and ⑤. The longest among these caves, Bayliss cave and Barkers cave, clearly show the tube like structure[1]. Others are fragmentary caves that occupy a small part of the lava cave system due to the burial of the floor. As shown in ⑥ of Table 2, the yield strength by using the limit condition for lava tube cave formation [4]:fB = H (ρgsinα) / 4 is obtained from this cavity height and slope angle. Tayler cave, Bayliss cave, and Barkers cave show high yield strength, on the other hand, other small caves show low yield strength due to low cavity height with buried floor. It is considered that several layers of lava flow have accumulated and the cavity height has decreased, showing a low apparent yield value fB = 272 to 834 Pa. High lava yield strength obtained from Tayler cave, Bayliss cave, and Barkers cave:fB = 1.4 ~ 3.4x103 Pa is considered to be close to the true yield strength. This yield strength is also consistent with the lava yield strength fB = 1.5 ~ 2.1x103 Pa obtained from the lava flow stop condition.
[Conclusion]
The lava yield strength fB = 1.4 ~ 3.4x103 Pa obtained from Tayler cave, Bayliss cave, and Barkers cave is a reasonable value for basalt with a silicic acid weight fraction of 48.9 wt%. For other small fragmentary caves with low apparent yield values, the floor is buried and the cavity height is decreased. It is necessary to judge whether the estimated yield strength is a reasonable value or not by observing the structure inside the cave in detail.
References:
[1] Anne Atkinson (2010): Undara Volcano, North Queensland, Australia and its Lava Field – Lava Caves, Depressions and The Wall – a Possible Lunar Analogue, Proceedings 14th International Symposium on Vulcanospeleology, 2010. www.vulcanospeleology.org/sym14 /papers/Atkinson.pdf
[2] Anne and Vernon Atkinson (1995): Undara Volcano and its Lava tubes, A geological Wonder of Australia in Undara Volcanic National Park, North Queensland
[3] Graeme P. Melville (1994): Lava tubes and channels of the Earth, Venus, Moon and Mars, Master of Science (Hons.) Thesis, Department of Physics, University of Wollongong, 1994.
http://ro.uow.edu.au/theses/2859
[4]Tsutomu Honda, Takayoshi Katsumata, Yutaka Ito, Masaru Hatanaka(2017): B3-06 Examination of Mt. Fuji and Suyama womb lava flow by lava tube cave and lava tree type, 2017 Proceedings of the Autumn Meeting of the Volcanic Society of Japan
https://www.jstage.jst.go.jp/article/vsj/2017/0/2017_96/_pdf/-char/ja