Elucidation of contributing factors affecting the ζ-potential of volcanic rocks

用流动电位法测量了几个不同火山岩样的ζ电势。在计算ζ势时也考虑了表面电导率的影响。这一过程是必要的，因为与通过孔的电流相比，样品池上的表面电流是不可忽略的。压力计已经在仪器系统中应用了第二年。总的来说，岩石样品的ζ-电势与循环流体的pH有很强的相关性。在无pH控制的自然条件下，7个样品中有4个样品的ζ-电位为正。哈斯等人已经报道了这种具有正ζ电势的岩石样品。(2004年)测量了阿索火山样品的ζ-电势。目前的研究表明，这种“异常”岩石并不罕见。作者研究了岩石样品中主要元素与ζ-电位的关系，以阐明影响ζ-电位极性的成因。然而，每种元素与ζ电位之间的相关性似乎并不是很清楚。认为除了岩样本身的成分外，还应存在一定的隐蔽因素。本研究的另一个贡献是对北海道塔鲁美火山的电阻率进行了现场测量。我们的大地电磁测量显示，在火山顶端火山口的正下方有一个非常导电的物体。这一结果支持了从火山自然电位异常推断的热液环流模型。

ζ-potential of several rock samples from various volcanoes was measured by using streaming potential method. Effects of surface conductivity was also taken into accounted for calculating ζ-potential. This procedure is necessary because surface current on the sample cell is not negligible when compared to the current through pore. Pressure gauge has been implemented to the instrumentation system in the second year.In general, ζ-potential of rock samples show strong dependency on pH of the circulating fluid. Four of the seven samples showed positive ζ-potential under the natural condition without pH control. Such rock samples with positive ζ-potential have already been reported by Hase et al. (2004) which measured the ζ-potential of samples from Aso Volcano. The present study has revealed that such 'anomalous' rocks are not very rare.The author investigated the relationship between major elements and ζ-potential of the rock samples in order to elucidate the contributing factors affecting the polarity of the ζ-potential. However, the correlation between each element and ζ-potential does not seem to be very clear. It was suggested that there should be some hidden factor other than the composition of rock sample itself. Further investigation including mineral composition and dissolved component in the fluid is necessary.Another contribution of the present research is the field measurement of electrical resistivity of Tarumae Volcano, Hokkaido. Our magnetotelluric measurement has revealed that there is a very conductive body just beneath the summit crater of the volcano. This result supports the hydrothermal circulation model that is inferred from self-potential anomaly on the volcano.