[SVC47-P14] Identification of lava flow temperature by lava tube cave structure of Mt.Etna
Keywords:lava tube, Etna volcano, lava temperature, yield strength
[Introduction]
Like Mt.Fuji, there are many lava tube caves formed in the past on Mt.Etna. An attempt was made to identify the lava flow temperature during the formation of a lava tube by using the yield strength obtained from the height of the lava tube cave at Mt.Etna. The viscosity coefficient of the lava flow was also estimated from the identified temperature.
[Lava yield strength obtained from lava tube cave]
Table 1 shows a list of major lava tube caves at Mt.Etna1) along with their length, cavity height, and slope angle. Considering the tube cave as the drain of lava from the inside of the tube, the yield strength can be obtained from the flow limit condition 2) in the inclined tube:
fB = H (ρgsinα) / 4 ····· (eq-1)
where fB is the yield value, H is the cavity height, ρ is the lava density, g is the gravitational acceleration, and α is the slope angle. The yield strength of the cave obtained from (eq-1) is shown in the rightmost column of Table 1. The yield strength is in the range of 1.6x104~1.1x105 dyne/cm2(1.6x103~1.1x104Pa).
[Temperature change of yield value and viscosity of Etna volcano]
Mt.Etna is the only example where temperature-dependent curves of yield strength and viscous coefficient have been obtained by actual measurement of lava flow3,4,5). The fitting equation from that data can be obtained as follows,
log10fB = 35.1836-0.0289θ, ······· (eq-2)
θ is the temperature in degrees Celsius and the yield strength fB is dyne / cm2
log10ηB = 24.0469-0.0175θ, ······· (eq-3)
θ is the temperature in degrees Celsius and the viscosity coefficient ηB is poise
The lava tube cave formation temperature is in the range of 1044℃~1073℃ judging from the yield strength-temperature curve (eq-2) according to the yield strength 1.6x104~1.1x105 dyne/cm2(1.6x103~1.1x104Pa)obtained from the cave. According to the viscosity coefficient -temperature curve (eq-3), the lava viscosity coefficient with respect to the temperature is in the range of 1.9x105~6.2x105 poise(1.9x104~6.2x104 Pa.s). It should be noted that the temperature of 1056~1067℃ obtained from the yield strength of 2.4x103~4.8x103Pa and the viscosity coefficient of 2.6x104~4.0x104Pa.s obtained for the Cutrona cave formed in the 1991-1993 lava flow, are close to the measured temperature 1020 ~ 1080 ℃ and the viscosity coefficient 0.8x104~1.9x104Pa.s, which were measured in the lava flow at an altitude of 2000m at Serra Pirciata by Calvari et al 6)
[Conclusion]
It is possible to identify the lava temperature at the time of lava tube cave formation by obtaining the yield strength from the cave by obtaining the temperature change dependence curve of the lava yield value in advance. Moreover, the viscosity coefficient can be obtained from the temperature dependence curve of the lava viscosity coefficient by the temperature. Therefore, it is considered that this method can be used to identify the temperature and viscosity coefficient of lava flow during the formation of a lava tube cave whose temperature has not been measured in the past.
References:
1) S.Calvari, M.Luizzo (1999): ”Excursion Guide, Lava tubes and lava caverns Etna volcano, 1999”, 9th International Symposium on Vulcanospeleology,
Catania, Italy, 11-19 September, 1999.
2) T.Honda(2001): B-10 Mt.Fuji lava cave formation mechanism and findings, 2001 Autumn Meeting of the Volcano Society of Japan.
3) T.Mizuyama, A.Kurihara, K.Kawamura, I.Kitahara (1989): Lava flow simulation and countermeasures, Shinsabo Vol.42 No.4 (165) Nov.1989
4) H.Pinkerton,and R.S.J.Sparks(1978): Field measurements of the rheology of lava., Nature (London), Vol. 2, 76, No. 5686, pp.383-385, 1978.
5) M.Dragoni, M.Bonafede,E.Boschi(1986): Downslope flow models of a Bingham liquid: Implications for lava flows. Jour. Volcanol. Geotherm Res., 30, pp. 305-325, 1986.
6)S.Calvari,M.Coltelli,M.Neri,M.Pompilio,V.Scribano(1994):The 1991-1993 Etna eruption chronology and lava flow field evolution,Acta Vulcanonologica Vol.4 1994 pp1-14
Like Mt.Fuji, there are many lava tube caves formed in the past on Mt.Etna. An attempt was made to identify the lava flow temperature during the formation of a lava tube by using the yield strength obtained from the height of the lava tube cave at Mt.Etna. The viscosity coefficient of the lava flow was also estimated from the identified temperature.
[Lava yield strength obtained from lava tube cave]
Table 1 shows a list of major lava tube caves at Mt.Etna1) along with their length, cavity height, and slope angle. Considering the tube cave as the drain of lava from the inside of the tube, the yield strength can be obtained from the flow limit condition 2) in the inclined tube:
fB = H (ρgsinα) / 4 ····· (eq-1)
where fB is the yield value, H is the cavity height, ρ is the lava density, g is the gravitational acceleration, and α is the slope angle. The yield strength of the cave obtained from (eq-1) is shown in the rightmost column of Table 1. The yield strength is in the range of 1.6x104~1.1x105 dyne/cm2(1.6x103~1.1x104Pa).
[Temperature change of yield value and viscosity of Etna volcano]
Mt.Etna is the only example where temperature-dependent curves of yield strength and viscous coefficient have been obtained by actual measurement of lava flow3,4,5). The fitting equation from that data can be obtained as follows,
log10fB = 35.1836-0.0289θ, ······· (eq-2)
θ is the temperature in degrees Celsius and the yield strength fB is dyne / cm2
log10ηB = 24.0469-0.0175θ, ······· (eq-3)
θ is the temperature in degrees Celsius and the viscosity coefficient ηB is poise
The lava tube cave formation temperature is in the range of 1044℃~1073℃ judging from the yield strength-temperature curve (eq-2) according to the yield strength 1.6x104~1.1x105 dyne/cm2(1.6x103~1.1x104Pa)obtained from the cave. According to the viscosity coefficient -temperature curve (eq-3), the lava viscosity coefficient with respect to the temperature is in the range of 1.9x105~6.2x105 poise(1.9x104~6.2x104 Pa.s). It should be noted that the temperature of 1056~1067℃ obtained from the yield strength of 2.4x103~4.8x103Pa and the viscosity coefficient of 2.6x104~4.0x104Pa.s obtained for the Cutrona cave formed in the 1991-1993 lava flow, are close to the measured temperature 1020 ~ 1080 ℃ and the viscosity coefficient 0.8x104~1.9x104Pa.s, which were measured in the lava flow at an altitude of 2000m at Serra Pirciata by Calvari et al 6)
[Conclusion]
It is possible to identify the lava temperature at the time of lava tube cave formation by obtaining the yield strength from the cave by obtaining the temperature change dependence curve of the lava yield value in advance. Moreover, the viscosity coefficient can be obtained from the temperature dependence curve of the lava viscosity coefficient by the temperature. Therefore, it is considered that this method can be used to identify the temperature and viscosity coefficient of lava flow during the formation of a lava tube cave whose temperature has not been measured in the past.
References:
1) S.Calvari, M.Luizzo (1999): ”Excursion Guide, Lava tubes and lava caverns Etna volcano, 1999”, 9th International Symposium on Vulcanospeleology,
Catania, Italy, 11-19 September, 1999.
2) T.Honda(2001): B-10 Mt.Fuji lava cave formation mechanism and findings, 2001 Autumn Meeting of the Volcano Society of Japan.
3) T.Mizuyama, A.Kurihara, K.Kawamura, I.Kitahara (1989): Lava flow simulation and countermeasures, Shinsabo Vol.42 No.4 (165) Nov.1989
4) H.Pinkerton,and R.S.J.Sparks(1978): Field measurements of the rheology of lava., Nature (London), Vol. 2, 76, No. 5686, pp.383-385, 1978.
5) M.Dragoni, M.Bonafede,E.Boschi(1986): Downslope flow models of a Bingham liquid: Implications for lava flows. Jour. Volcanol. Geotherm Res., 30, pp. 305-325, 1986.
6)S.Calvari,M.Coltelli,M.Neri,M.Pompilio,V.Scribano(1994):The 1991-1993 Etna eruption chronology and lava flow field evolution,Acta Vulcanonologica Vol.4 1994 pp1-14