[1] We investigate spatio-temporal relationships between soil CO 2 flux (F CO2 ), meteorological variables, and topography over a ten-day period (09/12/2006 to 09/21/ 2006) at the Horseshoe Lake tree kill, Mammoth Mountain, CA. Total CO 2 discharge varied from 16 to 52 t d À1 , suggesting a decline in CO 2 emissions over decadal timescales. We observed systematic changes in F CO2 in space and time in association with a weather front with relatively high wind speeds from the west and low atmospheric pressures. The largest F CO2 changes were observed in relatively high elevation areas. The variations in F CO2 may be due to dynamic coupling of wind-driven airflow through the subsurface and flow of source CO 2 at depth. Our results highlight the influence of weather fronts on volcanic gas flow in the near-surface environment and how this influence can vary spatially within a study area.
Abstract. The Taupo Volcanic Zone (TVZ) of New
Attslract. We have made a paleomagnetic study of Tertiary rocks from the Oga Peninsula, northers Honshu Island. Vokanic and sedimentary rocks were sampled from 26 sites in the peninsula. The ages of the rocks range from 62 Ma to the present. The resuRs indicate a couaterclockwise rotation of Northeast Japan with respect to eastern Asia around a pole at 58øN, 149øE, between about 22 Ma and 15 Ms. The amount of the rotation is about 20 ø. Before the rotation, Northeast Japan was situated along the east coast of the Asian continent. INTRODUCTION More than two decades ago, Kawai et aJ. [1961] demonstrated the bending of Honshu Island on the basis of the comparison of the paleomagnetic field directions from Northeast and Southwest Japan. Recent paleomagnetic studies in Japan have aimed at determining the mode and the timing of the bending and at relating the bending to the opening of the Sea of Japan. For Southwest Japan, Otofuji and Matsuds [1983] performed paleomagnetic investigations on the acidic rocks exposed on the Sea of Japan side of Southwest Japan and concluded that the clockwise rotation of that region took place from 28 to 12 Ms. The timing of the rotation was narrowed to around 15 Ma by Otofaji and Matsuds [1984]. For Northeast Japan, Tosha [1983] and Otofuji et aL [1985] recently made paleomagnetic studies. Otofuji et aL [1985] collected samples from a wide area of Northeast Japan, and their results indicate that the region north of the Tanakura Tectonic Line (see Figure la) behaved as one block, at least during the Tertiary period. However, the timing of the rotation of Northeast Japan is not clear from their data, since the relative ages of the rocks are usknown, partly because of the wide spread of the sampling sites. On the other hand, Tosha [1983] collected samples from the Oga Peninsula, where the sequence of Tertiary rocks is well preserved. Therefore his data are suitable for determining the chronologic progression of the movement of Northeast Japan. Recently, Celaya and McCabe [1987] and Morean et aL [1987] used Tosha's [1983] data and interpreted the tectonic evolution of Japan. These workers discussed the opening of the Sea of Japan by using the temporal declination changes in Japan, and later workers argued the remagnetization of pre-Tertiary rocks. Since the thesis by Tosha [1983] is not widely known and the above authors' iaterpretation of his data is quite different from his own interpretation, we here present the original data and results of recent studies, and discuss the tectonic implications. Some geological and geophysical studies suggest the tectonic continuity between the northeastern part of Honshu Island and the western part of Hokkaido Island in Cretaceous time [Takahashi, 1983; Takigaml; 1983; Segawa and Furuta, 19T8]. In the present study we assume the area north of the Tanakura Tectonic Line and the western part of Hokkaido to be one tectonic block since the Early Cretaceous, and we call the block Northeast Japan. GEOLOGICAL SETTING, AND SAMPLINGIn Northeast Japan, Tertiary an...
, annual self-potential (SP) surveys were carried out on Izu-Oshima, a small volcanic island. A terrain-related SP distribution of about -1 mV per meter of elevation was observed outside the caldera in all five surveys. Inside the caldera, SP increases from about -350 mV to near 0 mV (relative to the coastline) as the summit crater is approached, although negative anomalies of small spatial extent are manifest. Selfpotential inside the caldera decreased by about 100 mV between the March 1989 and the March 1990 surveys, which appears to be correlated with a significant decline in the degassing rate from the summit crater. After 1990, the SP distribution is quite steady along the entire survey line which extends from the west coast through the southern part of the caldera, and ends east of Ura-sabaku. Recently a postprocessor has been developed to calculate space/time distributions of electrokinetic potentials resulting from histories of underground conditions (pressure, temperature, salt concentration, fiowrate etc.) computed by multiphase multi-component unsteady geothermal reservoir simulations (Ishido and Pritchett, 1996). We applied this postprocessor to a simple two-dimensional model of hydrothermal activity in a volcanic island. The low potentials in areas of high elevation are reproduced in the model, and are caused by downflow of meteoric waters. The high potential centered at the summit crater is found to be produced by upflows of volcanic gas and vapor which diminish meteoric water downflow near the volcanic conduit.
[1] Streaming potential was measured in an intact granite sample, saturated with aqueous KCl solutions at three different concentrations, at temperatures between 25°and 200°C. The magnitudes of the streaming potential coefficient and of the surface conductance (which dominates the sample conductivity) both increase with increasing temperature. Using a capillary model, we found that the magnitude of the zeta potential also increases with increasing temperature.INDEX TERMS: 5109 Physical Properties of Rocks: Magnetic and electrical properties; 5114 Permeability and porosity; 3947 Mineral Physics: Surfaces and interfaces; 8424 Volcanology: Hydrothermal systems (8135). Citation: Tosha, T., N. Matsushima, and T. Ishido, Zeta potential measured for an intact granite sample at temperatures
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