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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 847 records · Page 47Linked to original sources
USGS2010

Genetic diversity of lake whitefish in lakes Michigan and Huron: sampling, standardization, and research priorities

We combined data from two laboratories to increase the spatial extent of a genetic data set for lake whitefish Coregonus clupeaformis from lakes Huron and Michigan and saw that genetic diversity was greatest between lakes, but that there was also structuring within lakes. Low diversity among stocks may be a reflection of relatively recent colonization of the Great Lakes, but other factors such as recent population fluctuation and localized stresses such as lamprey predation or heavy exploitation may also have a homogenizing effect. Our data suggested that there is asymmetrical movement of lake whitefish between Lake Huron and Lake Michigan; more genotypes associated with Lake Michigan were observed in Lake Huron. Adding additional collections to the calibrated set will allow further examination of diversity in other Great Lakes, answer questions regarding movement among lakes, and estimate contributions of stocks to commercial yields. As the picture of genetic diversity and population structure of lake whitefish in the Great Lakes region emerges, we need to develop methods to combine data types to help identify important areas for biodiversity and thus conservation. Adding genetic data to existing models will increase the precision of predictions of the impacts of new stresses and changes in existing pressures on an ecologically and commercially important species.

Journal of Great Lakes Research↗
USGS2003

Summary of recent research in Long Valley Caldera, California

Since 1978, volcanic unrest in the form of earthquakes and ground deformation has persisted in the Long Valley caldera and adjacent parts of the Sierra Nevada. The papers in this special volume focus on periods of accelerated seismicity and deformation in 1980, 1983, 1989-1990, and 1997-1998 to delineate relations between geologic, tectonic, and hydrologic processes. The results distinguish between earthquake sequences that result from relaxation of existing stress accumulation through brittle failure and those in which brittle failure is driven by active intrusion. They also indicate that in addition to a relatively shallow (7-10-km) source beneath the resurgent dome, there exists a deeper (???15-km) source beneath the south moat. Analysis of microgravimety and deformation data indicates that the composition of the shallower source may involve a combination of silicic magma and hydrothermal fluid. Pressure and temperature fluctuations in wells have accompanied periods of crustal unrest, and additional pressure and temperature changes accompanying ongoing geothermal power production have resulted in land subsidence. The completion in 1998 of a 3000-m-deep drill hole on the resurgent dome has provided useful information on present and past periods of circulation of water at temperatures of 100-200??C within the crystalline basement rocks that underlie the post-caldera volcanics. The well is now being converted to a permanent geophysical monitoring station. ?? 2003 Elsevier B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗
USGS2019

Hillslope hydrology in global change research and earth system modeling

Earth System Models (ESMs) are essential tools for understanding and predicting global change, but they cannot explicitly resolve hillslope‐scale terrain structures that fundamentally organize water, energy, and biogeochemical stores and fluxes at subgrid scales. Here we bring together hydrologists, Critical Zone scientists, and ESM developers, to explore how hillslope structures may modulate ESM grid‐level water, energy, and biogeochemical fluxes. In contrast to the one‐dimensional (1‐D), 2‐ to 3‐m deep, and free‐draining soil hydrology in most ESM land models, we hypothesize that 3‐D, lateral ridge‐to‐valley flow through shallow and deep paths and insolation contrasts between sunny and shady slopes are the top two globally quantifiable organizers of water and energy (and vegetation) within an ESM grid cell. We hypothesize that these two processes are likely to impact ESM predictions where (and when) water and/or energy are limiting. We further hypothesize that, if implemented in ESM land models, these processes will increase simulated continental water storage and residence time, buffering terrestrial ecosystems against seasonal and interannual droughts. We explore efficient ways to capture these mechanisms in ESMs and identify critical knowledge gaps preventing us from scaling up hillslope to global processes. One such gap is our extremely limited knowledge of the subsurface, where water is stored (supporting vegetation) and released to stream baseflow (supporting aquatic ecosystems). We conclude with a set of organizing hypotheses and a call for global syntheses activities and model experiments to assess the impact of hillslope hydrology on global change predictions.

Water Resources Research↗
USGS2012

A deep research drill hole at the summit of an active volcano, Kilauea, Hawaii

Drilling and geophysical logging data for a 1,262 m‐deep bore hole in the area inferred to overlie the magma reservoir of Kilauea Volcano, Hawaii, support earlier interpretations based on surface geophysical surveys that a zone of brackish or saline water lies above the reservoir. Temperatures encountered within the hole are not sufficiently high to warrant commercial interest; the maximum temperature, 137°C, is at the hole bottom. However, the temperature gradient toward the bottom of the hole (approximately 160 m below sea level) increases sharply to about 370°C/km, perhaps partly reflecting the effect of decreased water circulation as suggested by the geophysical logging data. If this gradient persists or increases with depth, magmatic temperatures would be attained within 3 km from the hole bottom (i.e., approximately 4 km from ground surface)—a depth in accord with data from ground‐deformation and seismic studies.

Hawaii↗
USGS2021

Short‐period surface‐wave tomography in the continental United States— A resource for research

The variation of phase and group velocity dispersion of Love and Rayleigh waves was determined for the continental United States and adjacent Canada. By processing ambient noise from the broadband channels of the Transportable Array (TA) of USArray and several Program for the Array Seismic Studies of the Continental Lithosphere experiments and using some earthquake recordings, the effort was focused on determining dispersion down to periods as short as 2 s. The relatively short distances between TA stations permitted the use of a 25    km × 25    km "> 25 km × 25 km grid for the four independent tomographic inversions (Love and Rayleigh and phase and group velocity). One reason for trying to obtain short‐period dispersion was to have a data set capable of constraining upper crust velocity models for use in determining regional moment tensors. The benefit of focusing on short‐period dispersion is apparent in the tomography maps—shallow geologic structures such as the Mid‐Continent Rift, and the Michigan, Illinois, Anadarko, Arkoma, and Appalachian basins are imaged. In our processing, we noted that the phase velocities were more robustly determined than the group velocities. We also noted that the inability to obtain dispersion at short periods shows distinct regional patterns that may be related to the local upper crust structure.

Seismological Research Letters↗
USGS1993

Digital imaging of sediment cores for archives and research

A system is described for digitally imaging split sediment cores that is relatively inexpensive, simple, and provides an image of the core that can be used for quantitative measurements as well as for archiving. The system is composed of a Macintosh computer equipped for 24-bit color, a large-volume storage medium, a Hi-8 video camera, and a digital framegrabber.

Journal of Sedimentary Research↗