Flow

ABSTRACT Borehole USDP-4 was drilled into the Unzen volcanic conduit 9 years after its last eruption. The sub-surface mechanism of eruption at Unzen Volcano was investigated by taking cores and by geophysical logging. The drilling operations were carried out in 2003–04, as a joint research program sponsored by the Japanese Government and the International Continental Scientific Drilling Program (ICDP). Borehole USDP-4 was a directional 6-1/4 in. (158.8 mm) borehole drilled from a site located on the northern slope of the volcano at 840 m above sea level, and was designed to penetrate into the conduit at sea level with a final deviation angle of over 70° from vertical and a borehole depth of 1800 m.An igneous dyke with a high likelihood of being the Unzen conduit was encountered at 1996 m depth and core samples were taken from that location. Chemical analysis of drill cores confirmed the identification of the conduit. Geophysical logging, including recording of gamma ray, resistivity, self-potential, density, neutron porosity, sonic velocity, and temperature suggested an alternation of dykes and flows in rock penetrated during the drilling, and in-hole pictures confirmed the lithologic identifications. Although borehole collapse and high temperature had been expected in the conduit, the actual drilling and logging into the conduit experienced no gas or fluid kick, and the measured temperatures within the dyke were below 200 °C.

ABSTRACT We conducted microlite textural analyses for the 1991–1995 eruptions at Unzen, Japan, in order to clarify the relationship between the discharge rate (exit velocity) and the kinetics of the microlite crystallization processes. The temporal variations in the plagioclase microlite crystallinity and the average size are negatively correlated with the variation in the magma discharge rate. On the other hand, the variation in the microlite number density (MND) exhibits a positive correlation with the discharge rate without a significant time lag. Groundmass microlites contain calcic plagioclase microlite (An45–65) and pargasite, suggesting that the microlite crystallization occurred at a depth (70–160 MPa) in the region of stability of the pargasite and plagioclase. The MND is determined at a depth (nucleation depth) with a certain effective undercooling rate (dT/dt) that is proportional to the exsolution rate of H2O from magma (dCH2O/dt). According to the MND water-exsolution rate meter, dCH2O/dt is calculated as 3.5 to 34.6 × 10− 6 wt.%/s at the final stage of the nucleation depth (zn: 70–100 MPa). By assuming that H2O exsolution occurs in equilibrium, the temporal variation in the decompression rate can be associated with the ascent velocity, provided the conduit flow is steady. The calculated ascent velocity of magma at zn (70–100 MPa; 0.8–7.6 cm/s) is higher than the exit velocity of magma (0.1 MPa; 0.2–3.9 mm/s). Using reasonable bulk densities, the difference in the velocities at the nucleation depth and surface results in the cross-section of the conduit (ellipse elongated dykes 2:5) at the nucleation depth (from 3 to 21 m) to be smaller than that at the surface (20 × 50–100 m) according to the mass conservation law along the conduit. The estimated temporal variation in the ascent velocity at zn (70–100 MPa) is positively correlated with the observed discharge rate of magma, except at the final stage of eruptive activity. Furthermore, the variation in the conduit dimension at zn is correlated with the variation in the exit velocity, thereby implying that the observed discharge rate of magma is controlled by the ascent velocity at zn (70–100 MPa) and the conduit dimension. With regard to the final stage of eruptive activity, a decrease in the conduit dimension from 19 to 3 m indicates that the conduit is finally closed due to the termination of the magma supply.

Permeability measurement was made on five rock samples from USDP-4 cores. Rock samples were collected from the conduit zone and its country rock. One sample (C14-1-1) is considered as a part of the feeder dyke for the 1991–1995 eruption. The transient pulse method was employed under confining pressure up to 50 MPa. Compressional wave velocity was measured along with permeability. The measured permeability ranges from 10−19 to 10−17 m2 at the atmospheric pressure, and is as low as that reported for tight rocks such as granite. The permeability decreases with increasing confining pressure, while the compressional wave velocity increases. Assuming that pores are parallel elliptical tubes, the pressure dependence of permeability requires aspect ratio of 10−4–10−2 at the atmospheric pressure. The pore aperture is estimated to be less than 1 μm. The estimated aspect ratio and pore aperture suggest that connectivity of pores is maintained by narrow cracks. The existence of cracks is supported by the pressure dependence of compressional wave velocity. Narrow cracks (<1 μm) are observed in dyke samples, and they must have been created after solidification. Dyke samples do not provide us information of pore structures during degassing, since exsolved gas has mostly escaped and pores governing the gas permeable flow should have been lost. Both dyke and country rock samples provide us information of materials around ascending magma. Although the measured small-scale permeability cannot be directly applied to geological-scale processes, it gives constrains on studies of large-scale permeability.

Page 1. Article Title Page Exp-function Method for solitary and periodic solutions of Fitzhugh-Nagumo Equation Author Details Syed Tauseef Mohyud-Din HITEC University, Taxila Cantt, Pakistan Yasir Khan Modern Textile Institute, Donghua University, Shanghai, China ...

This study presents the design, fabrication, analysis and testing of a novel crescent micropump fabricated using surface micromachining technology. The pump utilizes a ring gear driven through teeth on its outer surface to drive the pumping mechanism through teeth on its inner surface. An analytical solution for the volumetric flow rate for the micropump agrees with the obtained experimental results.

Yousef Haik1,2, Jason Hendrix1, Paul Galambos3, Mohammad Kilani4,5 1 Center for Research Excellence in Nanobiosciences, University of North Carolina at Greensboro 2 Department of Mechanical Engineering, United Arab Emirates University, Al Ain, UAE 3Intelligent ...

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