SEARCH · USGS Science

Results for “Journal of Interpretation”

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

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 973 records · Page 54Linked to original sources

USGS2019

Activity center selection by northern spotted owls

The federally threatened northern spotted owl ( Strix occidentalis caurina ) has been intensively studied across its range, and habitat needs for the species have influenced forest management in northwestern North America for decades. Dense forest canopies are often reported in the scientific literature and agency management plans as an important habitat attribute for spotted owls, though the means of measuring forest canopy and interpreting species requirements vary across studies and more importantly, among management plans. We used light detection and ranging (lidar) measurements of canopy cover, canopy surface heterogeneity, and upper canopy surface connectivity, and an index of the presence of a competitive invasive species, the barred owl ( S. varia ), in multinomial discrete choice models using a Bayesian framework to evaluate selection of forest cover types by spotted owls in Oregon, USA, 2008–2015. We designated yearly activity centers based on the most biologically significant observation during the nesting season (Mar–Aug), generally centered on the nest tree. Spotted owls selected activity centers with more canopy cover and higher heterogeneity of the canopy surface within 100 m than was available within their territories. The average proportion of canopy cover within 100 m of a spotted owl activity center was 0.79 ± 0.12 (SD; range = 0.34–0.99). The presence of barred owls did not explain variability in selection of spotted owl activity centers, but barred owls might not affect third‐order habitat selection within territories, or our index was too spatially coarse to detect these effects on spotted owl resource selection. We demonstrate that lidar provides researchers and managers with a tool that can accurately measure forest canopies over large areas, and assist in mapping spotted owl habitat.

Oregon↗

USGS2016

Characterization of mean transit time at large springs in the Upper Colorado River Basin, USA: A tool for assessing groundwater discharge vulnerability

Environmental tracers (noble gases, tritium, industrial gases, stable isotopes, and radio-carbon) and hydrogeology were interpreted to determine groundwater transit-time distribution and calculate mean transit time (MTT) with lumped parameter modeling at 19 large springs distributed throughout the Upper Colorado River Basin (UCRB), USA. The predictive value of the MTT to evaluate the pattern and timing of groundwater response to hydraulic stress (i.e., vulnerability) is examined by a statistical analysis of MTT, historical spring discharge records, and the Palmer Hydrological Drought Index. MTTs of the springs range from 10 to 15,000 years and 90 % of the cumulative discharge-weighted travel-time distribution falls within the range of 2−10,000 years. Historical variability in discharge was assessed as the ratio of 10–90 % flow-exceedance ( R 10/90% ) and ranged from 2.8 to 1.1 for select springs with available discharge data. The lag-time (i.e., delay in discharge response to drought conditions) was determined by cross-correlation analysis and ranged from 0.5 to 6 years for the same select springs. Springs with shorter MTTs (<80 years) statistically correlate with larger discharge variations and faster responses to drought, indicating MTT can be used for estimating the relative magnitude and timing of groundwater response. Results indicate that groundwater discharge to streams in the UCRB will likely respond on the order of years to climate variation and increasing groundwater withdrawals.

Upper Colorado River Basin↗

USGS2016

Understanding the past to interpret the future: Comparison of simulated groundwater recharge in the upper Colorado River basin (USA) using observed and general-circulation-model historical climate data

In evaluating potential impacts of climate change on water resources, water managers seek to understand how future conditions may differ from the recent past. Studies of climate impacts on groundwater recharge often compare simulated recharge from future and historical time periods on an average monthly or overall average annual basis, or compare average recharge from future decades to that from a single recent decade. Baseline historical recharge estimates, which are compared with future conditions, are often from simulations using observed historical climate data. Comparison of average monthly results, average annual results, or even averaging over selected historical decades, may mask the true variability in historical results and lead to misinterpretation of future conditions. Comparison of future recharge results simulated using general circulation model (GCM) climate data to recharge results simulated using actual historical climate data may also result in an incomplete understanding of the likelihood of future changes. In this study, groundwater recharge is estimated in the upper Colorado River basin, USA, using a distributed-parameter soil-water balance groundwater recharge model for the period 1951–2010. Recharge simulations are performed using precipitation, maximum temperature, and minimum temperature data from observed climate data and from 97 CMIP5 (Coupled Model Intercomparison Project, phase 5) projections. Results indicate that average monthly and average annual simulated recharge are similar using observed and GCM climate data. However, 10-year moving-average recharge results show substantial differences between observed and simulated climate data, particularly during period 1970–2000, with much greater variability seen for results using observed climate data.

Upper Colorado River basin↗

USGS2005

Slicing up the San Francisco Bay Area: Block kinematics and fault slip rates from GPS-derived surface velocities

Observations of surface deformation allow us to determine the kinematics of faults in the San Francisco Bay Area. We present the Bay Area velocity unification (BA??VU??, "bay view"), a compilation of over 200 horizontal surface velocities computed from campaign-style and continuous Global Positioning System (GPS) observations from 1993 to 2003. We interpret this interseismic velocity field using a three-dimensional block model to determine the relative contributions of block motion, elastic strain accumulation, and shallow aseismic creep. The total relative motion between the Pacific plate and the rigid Sierra Nevada/Great Valley (SNGV) microplate is 37.9 ?? 0.6 mm yr-1 directed toward N30.4??W ?? 0.8?? at San Francisco (??2??). Fault slip rates from our preferred model are typically within the error bounds of geologic estimates but provide a better fit to geodetic data (notable right-lateral slip rates in mm yr-1: San Gregorio fault, 2.4 ?? 1.0; West Napa fault, 4.0 ?? 3.0; zone of faulting along the eastern margin of the Coast Range, 5.4 ?? 1.0; and Mount Diablo thrust, 3.9 ?? 1.0 of reverse slip and 4.0 ?? 0.2 of right-lateral strike slip). Slip on the northern Calaveras is partitioned between both the West Napa and Concord/ Green Valley fault systems. The total convergence across the Bay Area is negligible. Poles of rotation for Bay Area blocks progress systematically from the North America-Pacific to North America-SNGV poles. The resulting present-day relative motion cannot explain the strike of most Bay Area faults, but fault strike does loosely correlate with inferred plate motions at the time each fault initiated. Copyright 2005 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗

USGS2010

Interpretation and analysis of planetary structures

Structural geology is an integral part of planetary science. Planetary structures provide the framework for determining the character and sequence of crustal deformation while simultaneously establishing the observational basis required to test geodynamic hypotheses for the deformation of planetary and satellite lithospheres. The availability of datasets that record spatial and topographic information with a resolution that matches or, in many cases, exceeds, what is available for Earth-based studies permits the deformation of several planets and satellites to be investigated down to the local or outcrop scales. The geometry and kinematics of common planetary structures such as joints, igneous dikes, deformation bands, faults, and folds can be determined with confidence from their distinctive morphologic and topographic signatures, enabling the structural histories and deformation magnitudes to be determined. Segmentation, displacement profiles, relay ramps, footwall anticlines, displacement-controlled depocenters, and other well-known characteristics of terrestrial normal fault and graben systems reveal the sequence and processes of fault growth in numerous planetary examples. Systems of thrust faults having both blind and surface-breaking components are important elements on several bodies including Mercury, the Moon, and Mars. Strike-slip faults have been identified on bodies including Mars and Europa with oblique extension found on Ganymede. Using field-based studies of Earth-based structures as a guide, planetary structures provide a means to explore and evaluate the causative stresses. Despite the wide range in structural styles across the solar system, plate tectonics is recognized only on the Earth, with the other planets and satellites deforming in the absence of large-scale horizontal motions and attendant plate recycling.

Journal of Structural Geology↗

USGS1998

Three-dimensional seismic structure and moment tensors of non-double-couple earthquakes at the Hengill-Grensdalur volcanic complex, Iceland

The volcanic and geothermal areas of Iceland are rich sources of non-double-couple (non-DC) earthquakes. A state-of-the-art digital seismometer network deployed at the Hengill–Grensdalur volcanic complex in 1991 recorded 4000 small earthquakes. We used the best recorded of these to determine 3-D V P and V P /V S structure tomographically and accurate earthquake moment tensors. The V P field is dominated by high seismic wave speed bodies interpreted as solidified intrusions. A widespread negative (−4 per cent) V P /V S anomaly in the upper 4km correlates with the geothermal field, but is too strong to be caused solely by the effect of temperature upon liquid water or the presence of vapour, and requires in addition mineralogical or lithological differences between the geothermal reservoir and its surroundings. These may be caused by geothermal alteration. Well-constrained moment tensors were obtained for 70 of the best-recorded events by applying linear programming methods to P - and S -wave polarities and amplitude ratios. About 25 per cent of the mechanisms are, within observational error, consistent with DC mechanisms consistent with shear faulting. The other 75 per cent have significantly non-DC mechanisms. Many have substantial explosive components, one has a substantial implosive component, and the deviatoric component of many is strongly non-DC. Many of the non-DC mechanisms are consistent, within observational error, with simultaneous tensile and shear faulting. However, the mechanisms occupy a continuum in source-type parameter space and probably at least one additional source process is occurring. This may be fluid flow into newly formed cracks, causing partial compensation of the volumetric component. Studying non-shear earthquakes such as these has great potential for improving our understanding of geothermal processes and earthquake source processes in general.

Geophysical Journal International↗

USGS2003

Topographically driven groundwater flow and the San Andreas heat flow paradox revisited

Evidence for a weak San Andreas Fault includes (1) borehole heat flow measurements that show no evidence for a frictionally generated heat flow anomaly and (2) the inferred orientation of ??1 nearly perpendicular to the fault trace. Interpretations of the stress orientation data remain controversial, at least in close proximity to the fault, leading some researchers to hypothesize that the San Andreas Fault is, in fact, strong and that its thermal signature may be removed or redistributed by topographically driven groundwater flow in areas of rugged topography, such as typify the San Andreas Fault system. To evaluate this scenario, we use a steady state, two-dimensional model of coupled heat and fluid flow within cross sections oriented perpendicular to the fault and to the primary regional topography. Our results show that existing heat flow data near Parkfield, California, do not readily discriminate between the expected thermal signature of a strong fault and that of a weak fault. In contrast, for a wide range of groundwater flow scenarios in the Mojave Desert, models that include frictional heat generation along a strong fault are inconsistent with existing heat flow data, suggesting that the San Andreas Fault at this location is indeed weak. In both areas, comparison of modeling results and heat flow data suggest that advective redistribution of heat is minimal. The robust results for the Mojave region demonstrate that topographically driven groundwater flow, at least in two dimensions, is inadequate to obscure the frictionally generated heat flow anomaly from a strong fault. However, our results do not preclude the possibility of transient advective heat transport associated with earthquakes.

Journal of Geophysical Research B: Solid Earth↗

USGS2003

Fracture network of the Ferron Sandstone Member of the Mancos Shale, east-central Utah, USA

The fracture network at the outcrop of the Ferron Sandstone Member of the Mancos Shale was studied to gain an understanding of the tectonic history of the region and to contribute data to studies of gas and water transmissivity related to the occurrence and production of coal-bed methane. About 1900 fracture readings were made at 40 coal outcrops and 62 sandstone outcrops in the area from Willow Springs Wash in the south to Farnham dome in the north of the study area in east-central Utah.Two sets of regional, vertical to nearly vertical, systematic face cleats were identified in Ferron coals. A northwest-striking set trends at a mean azimuth of 321??, and a northeast-striking set has a mean azimuth of 55??. Cleats were observed in all coal outcrops examined and are closely spaced and commonly coated with thin films of iron oxide.Two sets of regional, systematic joint sets in sandstone were also identified and have mean azimuths of 321?? and 34??. The joints of each set are planar, long, and extend vertically to nearly vertically through multiple beds; the northeast-striking set is more prevalent than the northwest-striking set. In some places, joints of the northeast-striking set occur in closely spaced clusters, or joint zones, flanked by unjointed rock. Both sets are mineralized with iron oxide and calcite, and the northwest-striking set is commonly tightly cemented, which allowed the northeast-striking set to propagate across it. All cleats and joints of these sets are interpreted as opening-mode (mode I) fractures. Abutting relations indicate that the northwest-striking cleats and joints formed first and were later overprinted by the northeast-striking cleats and joints. Burial curves constructed for the Ferron indicate rapid initial burial after deposition. The Ferron reached a depth of 3000 ft (1000 m) within 5.2 million years (m.y.), and this is considered a minimum depth and time for development of cleats and joints. The Sevier orogeny produced southeast-directed compressional stress at this time and is thought to be the likely mechanism for the northwest-striking systematic cleats and joints. The onset of the Laramide orogeny occurred at about 75 Ma, within 13.7 m.y. of burial, and is thought to be the probable mechanism for development of the northeast-striking systematic cleats and joints. Uplift of the Ferron in the late Tertiary contributed to development of butt cleats and secondary cross-joints and probably enhanced previously formed fracture sets. Using a study of the younger Blackhawk Formation as an analogy, the fracture pattern of the Ferron in the subsurface is probably similar to that at the surface, at least as far west as the Paradise fault and Joe's Valley graben. Farther to the west, on the Wasatch Plateau, the orientations of Ferron fractures may diverge from those measured at the outcrop. ?? 2003 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗

USGS2006

Rocks of the Columbia Hills

The Mars Exploration Rover Spirit has identified five distinct rock types in the Columbia Hills of Gusev crater. Clovis Class rock is a poorly sorted clastic rock that has undergone substantial aqueous alteration. We interpret it to be aqueously altered ejecta deposits formed by impacts into basaltic materials. Wishstone Class rock is also a poorly sorted clastic rock that has a distinctive chemical composition that is high in Ti and P and low in Cr. Wishstone Class rock may be pyroclastic or impact in origin. Peace Class rock is a sedimentary material composed of ultramafic sand grains cemented by significant quantities of Mg- and Ca-sulfates. Peace Class rock may have formed when water briefly saturated the ultramafic sands and evaporated to allow precipitation of the sulfates. Watchtower Class rocks are similar chemically to Wishstone Class rocks and have undergone widely varying degrees of near-isochemical aqueous alteration. They may also be ejecta deposits, formed by impacts into Wishstone-rich materials and altered by small amounts of water. Backstay Class rocks are basalt/trachybasalt lavas that were emplaced in the Columbia Hills after the other rock classes were, either as impact ejecta or by localized volcanic activity. The geologic record preserved in the rocks of the Columbia Hills reveals a period very early in Martian history in which volcanic materials were widespread, impact was a dominant process, and water was commonly present.

Journal of Geophysical Research E: Planets↗

USGS2003

Tidal-bundle sequences in the Jordan Sandstone (Upper Cambrian), southeastern Minnesota, U.S.A.: Evidence for tides along inboard shorelines of the Sauk Epicontinental Sea

This study documents for the first time tidal bundling in a lower Paleozoic sheet sandstone from the cratonic interior of North America, providing insights into the hydrodynamics of ancient epicontinental seas. The Jordan Sandstone (Upper Cambrian) in the Upper Mississippi Valley contains large-scale planar tabular cross-sets with tidal-bundle sequences, which were analyzed in detail at an exceptional exposure. Tidal-bundle sequences (neap-spring-neap cycles) were delineated by foreset thickening-thinning patterns and composite shale drapes, the latter of which represent accumulations of mud during the neap tides of neap-spring-neap tidal cycles. Fourier analysis of the bundle thickness data from the 26 measurable bundle sequences revealed cycles ranging from 15 to 34 bundles per sequence, which suggests a semidiurnal or mixed tidal system along this part of the Late Cambrian shoreline. We extend the tidal interpretation to widespread occurrences of the same facies in outcrops of lesser quality, where the facies is recognizable but too few bundles are exposed for tidal cycles to be measured. By doing so, this study shows that tidally generated deposits have a significant geographic and temporal extent in Upper Cambrian strata of central mid-continent North America. The deposition and preservation of tidal facies was related to the intermittent development of shoreline embayments during transgressions. The tidally dominated deposits filled ravined topographies that were repeatedly developed on the updip parts of the shoreface. Resulting coastal geomorphologies, accompanied perhaps by larger-scale changes in basinal conditions and/or configuration, led to changes in depositional conditions from wave-dominated to tide-dominated. Outcrops of the Jordan Sandstone tidal facies in the Upper Mississippi Valley represent the farthest inboard recorded transmission of ocean-generated tides in the Laurentian epicontinental seas, demonstrating that tidal currents were significant agents in the transport of sand along the far cratonic interior shorelines of Cambrian North America. The results of this study improve the facies-level understanding of the genesis of sheet sandstones. Furthermore, tidalites documented here occur in a specific position within a sequence stratigraphic architecture for the Jordan Sandstone. This provides a framework to compare these ancient deposits and processes to younger (e.g., Carboniferous) epicontinental systems where stratal and sediment dynamics are better documented.

Illinois, Indiana, Iowa, Michigan, Minnesota, Miss↗

USGS2010

Recruitment in a Colorado population of big brown bats: Breeding probabilities, litter size, and first-year survival

We used markrecapture estimation techniques and radiography to test hypotheses about 3 important aspects of recruitment in big brown bats (Eptesicus fuscus) in Fort Collins, Colorado: adult breeding probabilities, litter size, and 1st-year survival of young. We marked 2,968 females with passive integrated transponder (PIT) tags at multiple sites during 2001-2005 and based our assessments on direct recaptures (breeding probabilities) and passive detection with automated PIT tag readers (1st-year survival). We interpreted our data in relation to hypotheses regarding demographic influences of bat age, roost, and effects of years with unusual environmental conditions: extreme drought (2002) and arrival of a West Nile virus epizootic (2003). Conditional breeding probabilities at 6 roosts sampled in 2002-2005 were estimated as 0.64 (95% confidence interval [95% CI] = 0.530.73) in 1-year-old females, but were consistently high (95% CI = 0.940.96) and did not vary by roost, year, or prior year breeding status in older adults. Mean litter size was 1.11 (95% CI = 1.051.17), based on examination of 112 pregnant females by radiography. Litter size was not higher in older or larger females and was similar to results of other studies in western North America despite wide variation in latitude. First-year survival was estimated as 0.67 (95% CI = 0.610.73) for weaned females at 5 maternity roosts over 5 consecutive years, was lower than adult survival (0.79; 95% CI = 0.770.81), and varied by roost. Based on model selection criteria, strong evidence exists for complex roost and year effects on 1st-year survival. First-year survival was lowest in bats born during the drought year. Juvenile females that did not return to roosts as 1-year-olds had lower body condition indices in late summer of their natal year than those known to survive. ?? 2009 American Society of Mammalogists.

Journal of Mammalogy↗

USGS1999

Reference intervals and physiologic alterations in hematologic and biochemical values of free-ranging desert tortoises in the Mojave Desert

Desert tortoise ( Gopherus agassizii ) populations have experienced precipitous declines resulting from the cumulative impact of habitat loss, and human and disease-related mortality. Evaluation of hematologic and biochemical responses of desert tortoises to physiologic and environmental factors can facilitate the assessment of stress and disease in tortoises and contribute to management decisions and population recovery. The goal of this study was to obtain and analyze clinical laboratory data from free-ranging desert tortoises at three sites in the Mojave Desert (California, USA) between October 1990 and October 1995, to establish reference intervals, and to develop guidelines for the interpretation of laboratory data under a variety of environmental and physiologic conditions. Body weight, carapace length, and venous blood samples for a complete blood count and clinical chemistry profile were obtained from 98 clinically healthy adult desert tortoises of both sexes at the Desert Tortoise Research Natural area (western Mojave), Goffs (eastern Mojave) and Ivanpah Valley (northeastern Mojave). Samples were obtained four times per year, in winter (February/March), spring (May/June), summer (July/August), and fall (October). Years of near-, above- and below-average rainfall were represented in the 5 yr period. Minimum, maximum and median values, and central 95 percentiles were used as reference intervals and measures of central tendency for tortoises at each site and/or season. Data were analyzed using repeated measures analysis of variance for significant ( P < 0.01) variation on the basis of sex, site, season, and interactions between these variables. Significant sex differences were observed for packed cell volume, hemoglobin concentration, aspartate transaminase activity, and cholesterol, triglyceride, calcium, and phosphorus concentrations. Marked seasonal variation was observed in most parameters in conjunction with reproductive cycle, hibernation, or seasonal rainfall. Year-to-year differences and long-term alterations primarily reflected winter rainfall amounts. Site differences were minimal, and largely reflected geographic differences in precipitation patterns, such that results from these studies can be applied to other tortoise populations in environments with known rainfall and forage availability patterns.

Journal of Wildlife Diseases↗

USGS1998

Estimating formation properties from early-time recovery in wells subject to turbulent head losses

A mathematical model is developed to interpret the early-time recovering water level following the termination of pumping in wells subject to turbulent head losses. The model assumes that turbulent head losses dissipate immediately when pumping ends. In wells subject to both borehole storage and turbulent head losses, the early-time recovery exhibits a slope equal to 1/2 on log-log plots of the recovery versus time. This half-slope response should not be confused with the half-slope response associated with a linear flow regime during aquifer tests. The presence of a borehole skin due to formation damage or stimulation around the pumped well alters the early-time recovery in wells subject to turbulent head losses and gives the appearance of borehole storage, where the recovery exhibits a unit slope on log-log plots of recovery versus time. Type curves can be used to estimate the formation storafivity from the early-time recovery data. In wells that are suspected of having formation damage or stimulation, the type curves can be used to estimate the 'effective' radius of the pumped well, if an estimate of the formation storativity is available from observation wells or other information. Type curves for a homogeneous and isotropic dual-porosity aquifer are developed and applied to estimate formation properties and the effect of formation stimulation from a single-well test conducted in the Madison limestone near Rapid City, South Dakota.A mathematical model is developed to interpret the early-time recovering water level following the termination of pumping in wells subject to turbulent head losses. The model assumes that turbulent head losses dissipate immediately when pumping ends. In wells subject to both borehole storage and turbulent head losses, the early-time recovery exhibits a slope equal to 1/2 on log-log plots of the recovery versus time. This half-slope response should not be confused with the half-slope response associated with a linear flow regime during aquifer tests. The presence of a borehole skin due to formation damage or stimulation around the pumped well alters the early-time recovery in wells subject to turbulent head losses and gives the appearance of borehole storage, where the recovery exhibits a unit slope on log-log plots of recovery versus time. Type curves can be used to estimate the formation storativity from the early-time recovery data. In wells that are suspected of having formation damage or stimulation, the type curves can be used to estimate the `effective' radius of the pumped well, if an estimate of the formation storativity is available from observation wells or other information. Type curves for a homogeneous and isotropic dual-porosity aquifer are developed and applied to estimate formation properties and the effect of formation stimulation from a single-well test conducted in the Madison limestone near Rapid City, South Dakota.

Journal of Hydrology↗

USGS2006

Spectrophotometric properties of materials observed by Pancam on the Mars Exploration Rovers: 2. Opportunity

The Panoramic Camera (Pancam) on the Mars Exploration Rover Opportunity acquired visible/near‐infrared multispectral observations of soils and rocks under varying viewing and illumination geometries that were modeled using radiative transfer theory to improve interpretations of the microphysical and surface scattering nature of materials in Meridiani Planum. Nearly 25,000 individual measurements were collected of rock and soil units identified by their color and morphologic properties over a wide range of phase angles (0–150°) at Eagle crater, in the surrounding plains, in Endurance crater, and in the plains between Endurance and Erebus craters through Sol 492. Corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission. Disparity maps created from Pancam stereo images allowed inclusion of local facet orientation estimates. Outcrop rocks overall exhibited the highest single scattering albedos (≤0.9 at 753 nm), and most spherule‐rich soils exhibited the lowest (≤0.6 at 753 nm). Macroscopic roughness among outcrop rocks varied but was typically larger than spherule‐rich soils. Data sets with sufficient phase angle coverage (resulting in well‐constrained Hapke parameters) suggested that models using single‐term and two‐term Henyey‐Greenstein phase functions exhibit a dominantly broad backscattering trend for most undisturbed spherule‐rich soils. Rover tracks and other compressed soils exhibited forward scattering, while outcrop rocks were intermediate in their scattering behaviors. Some phase functions exhibited wavelength‐dependent trends that may result from variations in thin deposits of airfall dust that occurred during the mission.

Journal of Geophysical Research E: Planets↗

USGS2013

Temporal and spatial distribution of alteration, mineralization and fluid inclusions in the transitional high-sulfidation epithermal-porphyry copper system at Red Mountain, Arizona

Red Mountain, Arizona, is a Laramide porphyry Cu system (PCD) that has experienced only a modest level of erosion compared to most other similar deposits in the southwestern United States. As a result, the upper portion of the magmatic–hydrothermal system, which represents the transition from shallower high-sulfidation epithermal mineralization to deeper porphyry Cu mineralization, is well preserved. Within the Red Mountain system, alteration, mineralization and fluid inclusion assemblages show a systematic distribution in both time and space. Early-potassic alteration (characterized by the minerals biotite and magnetite) is paragenetically earlier than late-potassic alteration (K-feldspar–anhydrite) and both are followed by later phyllic (sericite–pyrite) alteration. Advanced argillic alteration (pyrophyllite–alunite–other clay minerals) is thought to be coeval with or postdate phyllic alteration. Minerals characteristic of advanced argillic alteration are present in the near surface. Phyllic alteration extends to greater depths compared to advanced argillic alteration. Early-potassic and late-potassic alteration are only observed in the deepest part of the system. Considerable overlap of phyllic alteration with both early-potassic and late-potassic alteration zones is observed. The hypogene mineralization contains 0.4–1.2% Cu and is spatially and temporally related to the late-potassic alteration event. Molybdenum concentration is typically < 300 ppm but positive anomalies (between 600 and 1200 ppm) occur, and typically correlate with the zones of higher Cu grades. Silver and Au range up to 50 ppm and 1 ppm, respectively, and mostly occur in the deeper parts of the system. Individual assays of up to 18 ppm Au and 274 ppm Ag in the shallower part of the system are interpreted to be associated with areas of highly focused fluid flow (i.e., breccias and thick veins). A near-surface, discontinuous chalcocite blanket is represented by scattered Cu anomalies within the mixed oxide/sulfide zone and its discontinuous nature may reflect differential permeability along fractures and faults. In the deepest part of the system, an early generation of low-to-moderate density and salinity liquid + vapor inclusions with opaque daughter minerals is followed in time by halite-bearing inclusions that also contain opaque daughter minerals indicating that an early intermediate-density magmatic fluid evolved to a high-density, high-salinity mineralizing fluid. The increase in density and salinity of fluids with time observed in the deeper parts of the system may be the result of immiscibility (“boiling”) of the earlier magmatic fluids or may reflect the compositional evolution of fluids that exsolved from the magma. Trails of inclusions consisting of only vapor-rich inclusions are common in the shallow parts of the system, and are associated with advanced argillic alteration, suggesting that intense boiling (“flashing”) occurred at (or below) this level. Fluid inclusion assemblages consisting of coexisting vapor-rich and halite-bearing inclusions are observed in samples extending from the surface to the upper part of the late-potassic zone, indicating that fluid immiscibility occurred within this depth interval.

Arizona↗

USGS2010

Development of a global land cover characteristics database and IGBP DISCover from 1 km AVHRR data

Researchers from the U.S. Geological Survey, University of Nebraska-Lincoln and the European Commission's Joint Research Centre, Ispra, Italy produced a 1 km resolution global land cover characteristics database for use in a wide range of continental-to global-scale environmental studies. This database provides a unique view of the broad patterns of the biogeographical and ecoclimatic diversity of the global land surface, and presents a detailed interpretation of the extent of human development. The project was carried out as an International Geosphere-Biosphere Programme, Data and Information Systems (IGBP-DIS) initiative. The IGBP DISCover global land cover product is an integral component of the global land cover database. DISCover includes 17 general land cover classes defined to meet the needs of IGBP core science projects. A formal accuracy assessment of the DISCover data layer will be completed in 1998. The 1 km global land cover database was developed through a continent-by-continent unsupervised classification of 1 km monthly Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) composites covering 1992-1993. Extensive post-classification stratification was necessary to resolve spectral/temporal confusion between disparate land cover types. The complete global database consists of 961 seasonal land cover regions that capture patterns of land cover, seasonality and relative primary productivity. The seasonal land cover regions were aggregated to produce seven separate land cover data sets used for global environmental modelling and assessment. The data sets include IGBP DISCover, U.S. Geological Survey Anderson System, Simple Biosphere Model, Simple Biosphere Model 2, Biosphere-Atmosphere Transfer Scheme, Olson Ecosystems and Running Global Remote Sensing Land Cover. The database also includes all digital sources that were used in the classification. The complete database can be sourced from the website: http://edcwww.cr.usgs.gov/landdaac/glcc/glcc.html.

International Journal of Remote Sensing↗

USGS2015

Magma extrusion during the Ubinas 2013–2014 eruptive crisis based on satellite thermal imaging (MIROVA) and ground-based monitoring

After 3 years of mild gases emissions, the Ubinas volcano entered in a new eruptive phase on September 2nd, 2013. The MIROVA system (a space-based volcanic hot-spot detection system), allowed us to detect in near real time the thermal emissions associated with the eruption and provided early evidence of magma extrusion within the deep summit crater. By combining IR data with plume height, sulfur emissions, hot spring temperatures and seismic activity, we interpret the thermal output detected over Ubinas in terms of extrusion rates associated to the eruption. We suggest that the 2013–2014 eruptive crisis can be subdivided into three main phases: ( i ) shallow magma intrusion inside the edifice, (ii) extrusion and growing of a lava plug at the bottom of the summit crater coupled with increasing explosive activity and finally, (iii) disruption of the lava plug and gradual decline of the explosive activity. The occurrence of the 8.2 Mw Iquique (Chile) earthquake (365 km away from Ubinas) on April 1st, 2014, may have perturbed most of the analyzed parameters, suggesting a prompt interaction with the ongoing volcanic activity. In particular, the analysis of thermal and seismic datasets shows that the earthquake may have promoted the most intense thermal and explosive phase that culminated in a major explosion on April 19th, 2014. These results reveal the efficiency of space-based thermal observations in detecting the extrusion of hot magma within deep volcanic craters and in tracking its evolution. We emphasize that, in combination with other geophysical and geochemical datasets, MIROVA is an essential tool for monitoring remote volcanoes with rather difficult accessibility, like those of the Andes that reach remarkably high altitudes.

Journal of Volcanology and Geothermal Research↗

USGS2016

Reevaluating the age of the Walden Creek Group and the kinematic evolution of the western Blue Ridge, southern Appalachians

An integrated synthesis of existing datasets (detailed geologic mapping, geochronologic, paleontologic, geophysical) with new paleontologic and geochemical investigations of rocks previously interpreted as part of the Neoproterozoic Walden Creek Group in southeastern Tennessee suggest a necessary reevaluation of the kinematics and structural architecture of the Blue Ridge Foothills. The western Blue Ridge of Tennessee, North Carolina, and Georgia is composed of numerous northwest-directed early and late Paleozoic thrust sheets, which record pronounced variation in stratigraphic/structural architecture and timing of metamorphism. The detailed spatial, temporal, and kinematic relationships of these rocks have remained controversial. Two fault blocks that are structurally isolated between the Great Smoky and Miller Cove-Greenbrier thrust sheets, here designated the Maggies Mill and Citico thrust sheets, contain Late Ordovician-Devonian conodonts and stable isotope chemostratigraphic signatures consistent with a mid-Paleozoic age. Geochemical and paleontological analyses of Walden Creek Group rocks northwest and southeast of these two thrust sheets, however, are more consistent with a Late Neoproterozoic (550–545 Ma) depositional age. Consequently, the structural juxtaposition of mid-Paleozoic rocks within a demonstrably Neoproterozoic-Cambrian succession between the Great Smoky and Miller Cove-Greenbrier thrust sheets suggests that a simple foreland-propagating thrust sequence model is not applicable in the Blue Ridge Foothills. We propose that these younger rocks were deposited landward of the Ocoee Supergroup, and were subsequently plucked from the Great Smoky fault footwall as a horse, and breached through the Great Smoky thrust sheet during Alleghanian emplacement of that structure.

North Carolina, Tennessee↗