[1] Numerous faults crosscut the poorly lithified, basin-fill sands found in New Mexico's Rio Grande rift and in other extensional regimes. The deformational processes that created these faults sharply reduced both fault porosity and fault saturated hydraulic conductivity by altering grains and pores, particularly in structures referred to as deformation bands. The resulting pore distribution changes, which create barriers to saturated flow, should enhance fault unsaturated flow relative to parent sand under the relatively dry conditions of the semiarid southwest. We report the first measurements of unsaturated hydraulic properties for undisturbed fault materials, using samples from a small-displacement normal fault and parent sands in the Bosque del Apache Wildlife Refuge, central New Mexico. Fault samples were taken from a narrow zone of deformation bands. The unsaturated flow apparatus (UFA) centrifuge system was used to measure both relative permeability and moisture retention curves. We compared these relations and fitted hydraulic conductivity-matric potential models to test whether the fault has significantly different unsaturated hydraulic properties than its parent sand. Saturated conductivity is 3 orders of magnitude less in the fault than the undeformed sand. As matric potential decreases from 0 to À200 cm, unsaturated conductivity decreases roughly 1 order of magnitude in the fault but 5-6 orders of magnitude in undeformed sands. Fault conductivity is greater by 2-6 orders of magnitude at matric potentials between À200 and À1000 cm, which are typical potentials for semiarid and arid vadose zones. Fault deformation bands have much higher air-entry matric potential values than parent sands and remain close to saturation well after the parent sands have begun to approach residual moisture content. Under steady state, one-dimensional, gravity-driven flow conditions, moisture transport and solute advection is 10 2 -10 6 times larger in the fault material than parent sands. Faults are sufficiently conductive to hasten the downward movement of water and solutes through vadose-zone sands under semiarid and arid conditions like those in the Rio Grande rift, thereby potentially enhancing recharge, contaminant migration, and diagenesis.
Abstract. Between 1969 and 1981 open pit methods were used to recover the molybdenum ore producing some 317.5 million metric tons of mined rock from the Questa molybdenum mine, which went into nine rock piles. The mine is located in the Sangre de Cristo Mountains of Taos County in northern New Mexico. As part of a multi-disciplinary study to determine the effects of weathering on the long-term stability of the rock piles, we are searching for areas where weathering is occurring within the rock piles. Pyrite oxidation is a weathering process that typically generates large amounts of heat, making it a good candidate for detection by infrared thermography. We conducted surveys of surface temperatures on two rock piles during February and May 2004 using the FLIR SC 3000 infrared thermal camera.Thermal imaging of the rock piles revealed at one rock pile, a "heat vent" of roughly 40 m by 30 m that had the same maximum temperature of 18°C during February and May 2004. The maximum temperature of this heat vent was much larger than the ambient temperature in February (0-2°C) and May (4-6°C). During the February survey, the heat vent had little or no snow cover and appeared to be very wet, whereas the area surrounding the heat vent was snowcovered and frozen at the same time. The heat vent is likely the result of pyrite oxidation within the rock pile. Thermal imaging results from a second rock pile indicate that it is less likely to have a heat vent because the differences between the ambient and maximum surface temperature were much less significant. The small temperature difference could be explained by spatial variations in emissivity from local variations in rock thermal properties or moisture content or by a relatively small heat flux out of the rock pile.
[1] Centrifugal methods are gaining increased attention for use in hydrologic experiments within partially saturated media. Through use of a Modified Invasion Percolation (MIP) model, we examine the influence of a stabilizing centrifugal (buoyancy) force on the invasion of a light nonwetting fluid (e.g., air) into a heterogeneous porous media initially saturated with a denser, wetting fluid (e.g., water). Results show that while capillary heterogeneity controls phase structure outside of a centrifugal field, the influence of capillary heterogeneity varies with angular velocity in a centrifugal field. As the angular velocity is increased, the invasion processes and phase structure become increasingly insensitive to heterogeneity, regardless of its style or orientation. Because phase structure critically influences flow processes and petrophysical properties (pressuresaturation, relative permeability, electrical resistivity, etc.), the design of centrifugal experiments must carefully consider this interplay between capillary heterogeneity and centrifugal force.
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