Geology topics

S. Rojstaczer

Publications and source records attributed to S. Rojstaczer.

4 recordsLinked to original sources

USGS2012

The influence of formation material properties on the response of water levels in wells to Earth tides and atmospheric loading

The water level in an open well can change in response to deformation of the surrounding material, either because of applied strains (tidal or tectonic) or surface loading by atmospheric pressure changes. Under conditions of no vertical fluid flow and negligible well bore storage (static-confined conditions), the sensitivities to these effects depend on the elastic properties and porosity which characterize the surrounding medium. For a poroelastic medium, high sensitivity to applied areal strains occurs for low porosity, while high sensitivity to atmospheric loading occurs for high porosity; both increase with decreasing compressibility of the solid matrix. These material properties also influence vertical fluid flow induced by areally extensive deformation and can be used to define two types of hydraulic diffusivity which govern pressure diffusion, one for applied strain and one for surface loading. The hydraulic diffusivity which governs pressure diffusion in response to surface loading is slightly smaller than that which governs fluid flow in response to applied strain. Given the static-confined response of a water well to atmospheric loading and Earth tides, the in situ drained matrix compressibility and porosity (and hence the one-dimensional specific storage) can be estimated. Analysis of the static-confined response of five wells to atmospheric loading and Earth tides gives generally reasonable estimates for material properties.

Journal of Geophysical Research Solid Earth↗

USGS2003

Variability in geyser eruptive timing and its causes: Yellowstone National Park

Field data from Upper Geyser Basin, Yellowstone, indicate that geyser frequency is less sensitive to elastic deformation than might be surmised from a review of the literature. Earth-tide influences are not identifiable in any of the geysers we monitored. Though atmospheric-pressure influences are observed, only long-period variations on the order of 5 mBars or greater seem to influence geyser frequency. Long-distance interconnections between geysers are common and add to the difficulty of identifying strain influences. Additional variations in geyser periodicity may be governed by the internal dynamics of the geysers rather than external influences.

Geophysical Research Letters↗

USGS1987

The local effects of groundwater pumpage within a fault-influenced groundwater basin, Ash Meadows, Nye County, Nevada, U.S.A.

Large-scale groundwater pumpage and water-level decline data are used in a preliminary attempt to identify the hydraulic connection between several wells and Devils Hole, a small pond in Nye County, Nevada, U.S.A. Results indicate that despite the discontinuous nature of the local aquifers, many wells have good hydraulic connection with Devils Hole. Hydraulic connection between the wells and Devils Hole exhibits a complex spatial variability typical of carbonate terrane. Zones or directions of minimal hydraulic connection may result from fault-controlled structural discontinuities. Zones or directions of enhanced hydraulic connection point to the presence of large-scale groundwater flow through fractures or conduits. The orientation of waterbearing fractures or conduits inferred from this study is qualitatively consistent with the major orientation of local and regional structural features.

Nevada↗

USGS1985

Hydrologic and geochemical monitoring in Long Valley caldera, Mono County, California, 1982-1984

The Long Valley caldera is a potentially active volcanic area on the eastern side of the Sierra Nevada in east-central California. Hydrologic and geochemical monitoring of surface and subsurface features began in July 1982 to determine if changes were occurring in response to processes causing earthquakes and crustal deformation. Differences since 1982 in fluid chemistry of springs has been minor except at Casa Diablo, where rapid fluctuations in chemistry result from near surface boiling and mixing. Ratios of 3 He/ 4 He and 13 C/ 12 C in hot springs and fumaroles are consistent with a magnetic source for some of the carbon and helium discharged in thermal areas, and observed changes in 3 He/ 4 He between 1978 and 1984 suggest changes in the magmatic component. Significant fluctuations in hot spring discharge recorded at several sites since 1982 closely followed earthquake activity. Water levels in wells have been used as strain meters to detect rock deformation associated with magmatic and tectonic activity and to construct a water table contour map. Coseismic water level fluctuations of as much as 0.6 ft have been observed but no clear evidence of deformation caused by magmatic intrusions can be seen in the well records through 1984. Temperature profiles in wells, which can be used to delineate regionally continuous zones of lateral flow of hot water across parts of the caldera, have remained constant at all but two sites.

California↗