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[SVC46-07] Estimation of surface tension of lava from lava stalactite and lava stalagmite appeared in lava tube cave and tree mold
Keywords:lava tube, volcanic cave, surface tension, lava tree mold
[Introduction] Inside the lava cave and lava tree mold void formed by the basalt lava flow, lava stalactite and lava stalagmite are often observed. It is a phenomenon which the droplet of lava falls from a ceiling and deposits on the floor. The estimation of surface tension of lava from the pitch of lava stalactite and size of lava stalagmite appeared in lava tube cave and tree mold void are performed and compared with various lavas.
[Estimate of surface tension from lava stalactite] Lava stalactites are positioned periodically on the surface of the ceiling wall or side wall. From the periodical pitch of the stalactites, we can obtain the surface tension of the lava. The pitch will be critical wave length of the occurrence of instability of thin liquid film attached on the surface of the ceiling of the lava tube cave or lava tree mold void. The pitch P is shown as P=2π(γ/gρL)1/2, whereγis surface tension of liquid ρL is density of liquid, g is gravity acceleration. From the pitch of lava stalactites on the roof surface (P=3 to 4cm), the surface tension of lava γ=P2 gρL /4π2 was determined as 560~990 dyne/cm.
[Estimate of surface tension from lava stalagmite] After the droplet's falling either from the liquid layer of a ceiling or from a straw formed from a ceiling, the droplets of lava may be acumulated one after another on the floor. The cylindrical configuration of the lava droplet has a certain radius and length in such a way that the configuration of the droplets has almost the same size. It is thought that the surface tension of the droplet is playing an important role in this phenomenon. When it becomes impossible for surface tension to bear the weight of the droplet, the droplet will fall down. After that, again the liquid lava will be supplied, then, the droplet will repeat to fall down. Consequently many lava droplets will be deposited on a floor area. This phenomenon is very similar to the "weight of falling drops technique" which is the general method of measuring the surface tension of a liquid. Based on this idea, the study model for determining the surface tension γof lava is made. When mass of the droplet is set to m, the force which pulls the droplet downward is f1=mg (g is acceleration due to gravity), and the force of pulling up this upwards is f2=2πrγ, where r is the radius of the lava droplet. The surface tension γis calculable for f1=f2 if the weight of the lava droplet is known. As f1=mg=πr2lρLg, where l is length of the lava droplet, ρL is the density of the lava, the surface tension γ=rlρLg/2 can be obtained from r and l of the lava droplets accumulated on the floor. If we introduce ρL=2.5g/cm3 and g= 980 cm/s2, and by the fields observation of r and l, for example, the surface tension γ=490 dyne/cm can be obtained for r=0.2 cm, and l=2cm, and γ=980 dyne/cm can be obtained for r=0.25 cm, and l=4cm.
[Conclusions] The value of such surface tension obtained from the lava stalagmite is in good agreement with the surface tension acquired from the pitch of the waving of the liquid layer by the simple hydrodynamic instability model of gravity/surface tension acting on the melting liquid layer attached on the inner surface of the lava cave. This value also agrees well with the extrapolated value obtained by I. Yokoyama and S.Iizuka1) in the melting lava surface tension measurement experiments in Laboratory. As a conclusion, we could say that the surface tension plays a preponderant role for the lava stalactite and stalagmite formation in the lava cave and lava tree void. It seems that there is no significant difference between surface tensions of different basaltic lavas though further study for various lavas will be continued .
[References]
1) I.Yokoyama,S.Iizuka(1970):Technical Report,Hokkaido Univ. p57
[Estimate of surface tension from lava stalactite] Lava stalactites are positioned periodically on the surface of the ceiling wall or side wall. From the periodical pitch of the stalactites, we can obtain the surface tension of the lava. The pitch will be critical wave length of the occurrence of instability of thin liquid film attached on the surface of the ceiling of the lava tube cave or lava tree mold void. The pitch P is shown as P=2π(γ/gρL)1/2, whereγis surface tension of liquid ρL is density of liquid, g is gravity acceleration. From the pitch of lava stalactites on the roof surface (P=3 to 4cm), the surface tension of lava γ=P2 gρL /4π2 was determined as 560~990 dyne/cm.
[Estimate of surface tension from lava stalagmite] After the droplet's falling either from the liquid layer of a ceiling or from a straw formed from a ceiling, the droplets of lava may be acumulated one after another on the floor. The cylindrical configuration of the lava droplet has a certain radius and length in such a way that the configuration of the droplets has almost the same size. It is thought that the surface tension of the droplet is playing an important role in this phenomenon. When it becomes impossible for surface tension to bear the weight of the droplet, the droplet will fall down. After that, again the liquid lava will be supplied, then, the droplet will repeat to fall down. Consequently many lava droplets will be deposited on a floor area. This phenomenon is very similar to the "weight of falling drops technique" which is the general method of measuring the surface tension of a liquid. Based on this idea, the study model for determining the surface tension γof lava is made. When mass of the droplet is set to m, the force which pulls the droplet downward is f1=mg (g is acceleration due to gravity), and the force of pulling up this upwards is f2=2πrγ, where r is the radius of the lava droplet. The surface tension γis calculable for f1=f2 if the weight of the lava droplet is known. As f1=mg=πr2lρLg, where l is length of the lava droplet, ρL is the density of the lava, the surface tension γ=rlρLg/2 can be obtained from r and l of the lava droplets accumulated on the floor. If we introduce ρL=2.5g/cm3 and g= 980 cm/s2, and by the fields observation of r and l, for example, the surface tension γ=490 dyne/cm can be obtained for r=0.2 cm, and l=2cm, and γ=980 dyne/cm can be obtained for r=0.25 cm, and l=4cm.
[Conclusions] The value of such surface tension obtained from the lava stalagmite is in good agreement with the surface tension acquired from the pitch of the waving of the liquid layer by the simple hydrodynamic instability model of gravity/surface tension acting on the melting liquid layer attached on the inner surface of the lava cave. This value also agrees well with the extrapolated value obtained by I. Yokoyama and S.Iizuka1) in the melting lava surface tension measurement experiments in Laboratory. As a conclusion, we could say that the surface tension plays a preponderant role for the lava stalactite and stalagmite formation in the lava cave and lava tree void. It seems that there is no significant difference between surface tensions of different basaltic lavas though further study for various lavas will be continued .
[References]
1) I.Yokoyama,S.Iizuka(1970):Technical Report,Hokkaido Univ. p57