We developed a radiographic technique to image a subsurface conduit shape using cosmic‐ray muons. The test measurement was performed in Showa‐Shinzan lava dome located in Hokkaido, Japan as an example. A muon detector with an area of 6000 cm2 was set up at the foot of the lava dome. Muon tracks recorded in nuclear emulsion films in the detector were analyzed to determine the level of energy absorption along different ray paths through subsurface beneath the lava dome. A typical angular resolution of the muon detector of 10 mrad corresponds to a spatial resolution of 10 m at a distance of 1 km, which is difficult to be addressed with seismological technique. We mapped differentially absorbed cosmic‐ray muons, which depend upon the varying thickness and density beneath the dome. We successfully imaged the conduit shape and determined a conduit diameter of 102 ± 15 m, assuming the observed high absorption region beneath the dome is localized in the vent area.

Calderas are ubiquitous topographic features of volcanos, yet caldera formation itself has not been recorded intensively by modern measurement techniques. Here we report the spatiotemporal gravity changes before and after caldera collapse at the Miyakejima volcano, Japan in 2000. A gravity decrease of as much as 145 μGal (1 μGal = 10−8 m/s2) at the summit area since June 1998 was detected 2 days prior to the collapse, interpreted as reflecting the formation of a large void beneath the volcano. Gravity changes detected after the initiation of collapse can mostly be corrected by the effect of collapsed topography, from which a rapid rate of collapse of more than 1.6 × 107 m3/d can be inferred. Correcting for the effect of topography change, we identified a temporal decrease in gravity from the middle of July to late August despite ground subsidence. The gravity decrease is interpreted as a reduction of the density in a cylindrical conduit, attributed to water inflow from an ambient aquifer that also promoted intensive magma‐water interaction and subsequent explosive eruptions. From September to at least November 2000, gravity values at all sites increased significantly by a degree that cannot be explained by ground displacement alone. We interpret this temporal evolution as primarily due to magma ascent and refilling of the conduit.

Equilibrium conditions of propane hydrates in aqueous solutions of methanol, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, and glycerol were measured at temperatures of (267.5 to 278.1) K and pressures of up to 0.527 MPa by the use of both isochoric and isothermal methods. The inhibiting effect on the propane hydrate equilibria on a mass fraction basis decreased in the following order: methanol, ethanol, ethylene glycol, glycerol, diethylene glycol, and triethylene glycol.

We have developed an integrated processing method for muon radiography and gravity anomaly data for determining the 3-D density structures of volcanoes with a higher spatial resolution than is possible by conventional gravity inversion. In the present paper, we demonstrate the performance of the proposed method by performing numerical tests using synthesized data, and we present the results obtained by applying the proposed method to a volcano, Showa-Shinzan lava dome, Hokkaido, Japan. We obtained the detailed shape of a vent beneath the dome and detected the presence of solidified dense lava near the top of the dome. The results demonstrate the advantage of a hybrid measurement based on both gravity and muon radiography for imaging small structures with sizes of a few hundreds of meters near the surface of a volcano.

The equilibrium conditions were experimentally determined for gas hydrate of methane and ethane mixtures in pure water and 3.0 wt% NaCl solution. The present results indicate that the addition of ethane stabilizes gas hydrate and shifts the equilibrium conditions to higher temperature and lower pressure. As ethane concentration increases from 0 vol% to 10 vol%, the equilibrium pressure of gas hydrate decreases non-proportionally with gas composition, which implies a change in the hydrate structure over this range of gas composition. The equilibrium temperature of gas hydrates of methane and ethane mixtures in 3.0 wt% NaCl solution is approximately 1.0 K lower than that in pure water at a constant pressure.

Equilibrium conditions for carbon dioxide hydrates in the presence of aqueous solutions of methanol, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, and glycerol were experimentally measured at temperatures ranging from (264.1 to 283.1) K and pressures up to 4.54 MPa using an isochoric method. On a mass fraction basis, the inhibiting effect on the carbon dioxide hydrate equilibria decreased in the following order: methanol > ethanol > ethylene glycol > glycerol > diethylene glycol > triethylene glycol. The order is the same as predicted by the Hammerschmidt equation.

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