SEARCH · Geology Reports

Results for “Journal of Geological Research”

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 1,117 records · Page 62Linked to original sources

USGS2009

Processes that initiate turbidity currents and their influence on turbidites: A marine geology perspective

How the processes that initiate turbidity currents influence turbidite deposition is poorly understood, and many discussions in the literature rely on concepts that are overly simplistic. Marine geological studies provide information on the initiation and flow path of turbidity currents, including their response to gradient. In case studies of late Quaternary turbidites on the eastern Canadian and western U.S. margins, initiation processes are inferred either from real-time data for historical flows or indirectly from the age and contemporary paleogeography, erosional features, and depositional record. Three major types of initiation process are recognized: transformation of failed sediment, hyperpycnal flow from rivers or ice margins, and resuspension of sediment near the shelf edge by oceanographic processes. Many high-concentration flows result from hyperpycnal supply of hyperconcentrated bedload, or liquefaction failure of coarse-grained sediment, and most tend to deposit in slope conduits and on gradients < 0.5° at the base of slope and on the mid fan. Highly turbulent flows, from transformation of retrogressive failures and from ignitive flows that are triggered by oceanographic processes, tend to cannibalize these more proximal sediments and redeposit them on lower gradients on the basin plain. Such conduit flushing provides most of the sediment in large turbidites. Initiation mechanism exerts a strong control on the duration of turbidity flows. In most basins, there is a complex feedback between different types of turbidity-current initiation, the transformation of the flows, and the associated slope morphology. As a result, there is no simple relationship between initiating process and type of deposit.

Journal of Sedimentary Research↗

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↗

USGS2010

Aviation response to a widely dispersed volcanic ash and gas cloud from the August 2008 eruption of Kasatochi, Alaska, USA

The extensive volcanic cloud from Kasatochi's 2008 eruption caused widespread disruptions to aviation operations along Pacific oceanic, Canadian, and U.S. air routes. Based on aviation hazard warnings issued by the National Oceanic and Atmospheric Administration, U.S. Geological Survey, the Federal Aviation Administration, and Meteorological Service of Canada, air carriers largely avoided the volcanic cloud over a 5 day period by route modifications and flight cancellations. Comparison of time coincident GOES thermal infrared (TIR) data for ash detection with Ozone Monitoring Instrument (OMI) ultraviolet data for SO 2 detection shows congruent areas of ash and gas in the volcanic cloud in the 2 days following onset of ash production. After about 2.5 days, the area of SO 2 detected by OMI was more extensive than the area of ash indicated by TIR data, indicating significant ash depletion by fall out had occurred. Pilot reports of visible haze at cruise altitudes over Canada and the northern United States suggested that SO 2 gas had converted to sulfate aerosols. Uncertain about the hazard potential of the aging cloud, airlines coped by flying over, under, or around the observed haze layer. Samples from a nondamaging aircraft encounter with Kasatochi's nearly 3 day old cloud contained volcanic silicate particles, confirming that some fine ash is present in predominantly gas clouds. The aircraft's exposure to ash was insufficient to cause engine damage; however, slightly damaging encounters with volcanic clouds from eruptions of Reventador in 2002 and Hekla in 2000 indicate the possibility of lingering hazards associated with old and/or diffuse volcanic clouds.

Alaska↗

USGS2012

Curie temperature isotherm analysis and tectonic implications of aeromagnetic data from Nevada

Estimates of the depth to the Curie temperature isotherm in Nevada are in accordance with other regional geologic and geophysical information and together can be explained in the context of present-day tectonism. A method to estimate the depth extent of magnetic sources from the statistical properties of magnetic anomalies was applied to a statewide compilation of aeromagnetic data from Nevada. Basal depths of magnetic sources show no apparent correlation with the so-called magnetic quiet zone, which trends northerly through the eastern part of the state, or with basin-and-range topography. However, certain correlations with published heat flow measurements are apparent and suggest that undulations in basal depth of magnetic sources are related in part to undulations in the Curie temperature isotherm. For example, an area of shallow basal depth (<10 km) near Battle Mountain corresponds to an area of exceptionally high conductive heat flow and indicates a shallow depth to the Curie temperature isotherm in this region. A narrow zone of shallow basal depth extends south from the Battle Mountain area along the 118°W meridian to at least latitude 38°N, which also is a zone of historic surface offsets and high-magnitude earthquakes. The correspondence along the 118° meridian of shallow basal depth, high heat flow, high lower crustal seismic velocities, attenuated P and S wave arrivals, historic faulting, and large earthquakes suggests that they each are related to an active north trending spreading zone in this part of the Basin and Range province.

Journal of Geophysical Research Solid Earth↗

USGS2006

One-way coupling of an atmospheric and a hydrologic model in Colorado

This paper examines the accuracy of high-resolution nested mesoscale model simulations of surface climate. The nesting capabilities of the atmospheric fifth-generation Pennsylvania State University (PSU)-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) were used to create high-resolution, 5-yr climate simulations (from 1 October 1994 through 30 September 1999), starting with a coarse nest of 20 km for the western United States. During this 5-yr period, two finer-resolution nests (5 and 1.7 km) were run over the Yampa River basin in northwestern Colorado. Raw and bias-corrected daily precipitation and maximum and minimum temperature time series from the three MM5 nests were used as input to the U.S. Geological Survey's distributed hydrologic model [the Precipitation Runoff Modeling System (PRMS)] and were compared with PRMS results using measured climate station data. The distributed capabilities of PRMS were provided by partitioning the Yampa River basin into hydrologic response units (HRUs). In addition to the classic polygon method of HRU definition, HRUs for PRMS were defined based on the three MM5 nests. This resulted in 16 datasets being tested using PRMS. The input datasets were derived using measured station data and raw and bias-corrected MM5 20-, 5-, and 1.7-km output distributed to 1) polygon HRUs and 2) 20-, 5-, and 1.7-km-gridded HRUs, respectively. Each dataset was calibrated independently, using a multiobjective, stepwise automated procedure. Final results showed a general increase in the accuracy of simulated runoff with an increase in HRU resolution. In all steps of the calibration procedure, the station-based simulations of runoff showed higher accuracy than the MM5-based simulations, although the accuracy of MM5 simulations was close to station data for the high-resolution nests. Further work is warranted in identifying the causes of the biases in MM5 local climate simulations and developing methods to remove them. ?? 2006 American Meteorological Society.

Journal of Hydrometeorology↗

USGS2000

Distribution of surficial sediment in Long Island Sound and adjacent waters: Texture and total organic carbon

The surficial sediment distribution within Long Island Sound has been mapped and described using bottom samples, photography, and sidescan sonar, combined with information from the geologic literature. The distributions of sediment type and total organic carbon (TOC) reveal several broad trends that are largely related to the sea-floor geology, the bathymetry, and the effects of modern tidal- and wind-driven currents. Sediment types are most heterogeneous in bathymetrically complex and shallow nearshore areas; the heterogeneity diminishes and the texture fines with decreasing bottom-current energy. Lag deposits of gravel and gravelly sand dominate the surficial sediment texture in areas where bottom currents are the strongest (such as where tidal flow is constricted) and where glacial till crops out at the sea floor. Sand is the dominant sediment type in areas characterized by active sediment transport and in shallow areas affected by fine-grained winnowing. Silty sand and sand-silt-clay mark transitions within the basin from higher- to lower-energy environments, suggesting a diminished hydraulic ability to sort and transport sediment. Clayey silt and silty clay are the dominant sediment types accumulating in the central and western basins and in other areas characterized by long-term depositional environments. The amount of TOC in the sediments of Long Island Sound varies inversely with sediment grain size. Concentrations average more than 1.9% (dry weight) in clayey silt, but are less than 0.4% in sand. Generally, values for TOC increase both toward the west in the Sound and from the shallow margins to the deeper parts of the basin floor. Our data also suggest that TOC concentrations can vary seasonally.

Long Island Sound↗

USGS2000

The use of mathematical models to predict beach behavior for U.S. coastal engineering: A critical review

A number of assumed empirical relationships (e.g., the Bruun Rule, the equilibrium shoreface profile, longshore transport rate equation, beach length: durability relationship, and the renourishment factor) and deterministic numerical models (e.g., GENESIS, SBEACH) have become important tools for investigating coastal processes and for coastal engineering design in the U.S. They are also used as the basis for making public policy decisions, such as the feasibility of nourishing recreational beaches. A review of the foundations of these relationships and models, however, suggests that they are inadequate for the tasks for which they are used. Many of the assumptions used in analytical and numerical models are not valid in the context of modern oceanographic and geologic principles. We believe the models are oversimplifications of complex systems that are poorly understood. There are several reasons for this, including: (1) poor assumptions and important omissions in model formulation; (2) the use of relationships of questionable validity to predict the morphologic response to physical forcing; (3) the lack of hindsighting and objective evaluation of beach behavior predictions for engineering projects; (4) the incorrect use of model calibration and verification as assertions of model veracity; and (5) the fundamental inability to predict coastal evolution quantitatively at the engineering and planning time and space scales our society assumes and demands. It is essential that coastal geologists, beach designers and coastal modelers understand these model limitations. Each important model assumption must be examined in isolation; incorporating them into a model does not improve their validity. It is our belief that the models reviewed here should not be relied on as a design tool until they have been substantially modified and proven in real-world situations. The 'solution,' however, is not to increase the complexity of a model by increasing the number of variables. What is needed is a thoughtful review of what beach behavior questions should or could be answered by modeling. Viable alternatives to the use of models do exist to predict the behavior of beaches. Three such alternatives to models are discussed for nourished beach design.

Journal of Coastal Research↗

USGS2000

Record of late holocene debris avalanches and lahars at Iliamna Volcano, Alaska

Iliamna Volcano is a 3053-meter high, glaciated stratovolcano in the southern Cook Inlet region of Alaska and is one of seven volcanoes in this region that have erupted multiple times during the past 10,000 yr. Prior to our studies of Iliamna Volcano, little was known about the frequency, magnitude, and character of Holocene volcanic activity. Here we present geologic evidence of the most recent eruptive activity of the volcano and provide the first outline of Late Holocene debris-avalanche and lahar formation. Iliamna has had no documented historical eruptions but our recent field investigations indicate that the volcano has erupted at least twice in the last 300 yr. Clay-rich lahar deposits dated by radiocarbon to ???1300 and ???90 yr BP are present in two major valleys that head on the volcano. These deposits indicate that at least two large, possibly deep-seated, flank failures of the volcanic edifice have occurred in the last 1300 yr. Noncohesive lahar deposits likely associated with explosive pyroclastic eruptions date to 2400-1300,>1500,???300, and <305 yr BP. Debris-avalanche deposits from recent and historical small-volume slope failures of the hydrothermally altered volcanic edifice cover most of the major glaciers on the volcano. Although these deposits consist almost entirely of hydrothermally altered rock debris and snow and ice, none of the recently generated debris avalanches evolved to lahars. A clay-rich lahar deposit that formed <90??60 radiocarbon yr BP and entered the Johnson River Valley southeast of the volcano cannot be confidently related to an eruption of Iliamna Volcano, which has had no known historical eruptions. This deposit may record an unheralded debris avalanche and lahar. ?? 2000 Elsevier Science B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗

USGS2017

Predicted pH at the domestic and public supply drinking water depths, Central Valley, California

This scientific investigations map is a product of the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) project modeling and mapping team. The prediction grids depicted in this map are of continuous pH and are intended to provide an understanding of groundwater-quality conditions at the domestic and public supply drinking water zones in the groundwater of the Central Valley of California. The chemical quality of groundwater and the fate of many contaminants is often influenced by pH in all aquifers. These grids are of interest to water-resource managers, water-quality researchers, and groundwater modelers concerned with the occurrence of natural and anthropogenic contaminants related to pH. In this work, the median well depth categorized as domestic supply was 30 meters below land surface, and the median well depth categorized as public supply is 100 meters below land surface. Prediction grids were created using prediction modeling methods, specifically boosted regression trees (BRT) with a Gaussian error distribution within a statistical learning framework within the computing framework of R ( http://www.r-project.org/ ). The statistical learning framework seeks to maximize the predictive performance of machine learning methods through model tuning by cross validation. The response variable was measured pH from 1,337 wells and was compiled from two sources: USGS National Water Information System (NWIS) database (all data are publicly available from the USGS: http://waterdata.usgs.gov/ca/nwis/nwis ) and the California State Water Resources Control Board Division of Drinking Water (SWRCB-DDW) database (water quality data are publicly available from the SWRCB: http://www.waterboards.ca.gov/gama/geotracker_gama.shtml ). Only wells with measured pH and well depth data were selected, and for wells with multiple records, only the most recent sample in the period 1993–2014 was used. A total of 1,003 wells (training dataset) were used to train the BRT model, and 334 wells (hold-out dataset) were used to validate the prediction model. The training r-squared was 0.70, and the root-mean-square error (RMSE) in standard pH units was 0.26. The hold-out r-squared was 0.43, and RMSE in standard pH units was 0.37. Predictor variables consisting of more than 60 variables from 7 sources were assembled to develop a model that incorporates regional-scale soil properties, soil chemistry, land use, aquifer textures, and aquifer hydrology. Previously developed Central Valley model outputs of textures (Central Valley Textural Model, CVTM; Faunt and others, 2010) and MODFLOW-simulated vertical water fluxes and predicted depth to water table (Central Valley Hydrologic Model, CVHM; Faunt, 2009) were used to represent aquifer textures and groundwater hydraulics, respectively. In this work, wells were attributed to predictor variable values in ArcGIS using a 500-meter buffer. Faunt, C.C., ed., 2009, Groundwater availability in the Central Valley aquifer, California: U.S. Geological Survey Professional Paper 1776, 225 p., accessed at https://pubs.usgs.gov/pp/1766/ . Faunt, C.C., Belitz, K., and Hanson, R.T., 2010, Development of a three-dimensional model of sedimentary texture in valley-fill deposits of Central Valley, California, USA: Hydrogeology Journal, v. 18, no. 3, p. 625–649, https://doi.org/10.1007/s10040-009-0539-7 .

California↗

USGS2018

A new generation of the United States National Land Cover Database: Requirements, research priorities, design, and implementation strategies

The U.S. Geological Survey (USGS), in partnership with several federal agencies, has developed and released four National Land Cover Database (NLCD) products over the past two decades: NLCD 1992, 2001, 2006, and 2011. These products provide spatially explicit and reliable information on the Nation’s land cover and land cover change. To continue the legacy of NLCD and further establish a long-term monitoring capability for the Nation’s land resources, the USGS has designed a new generation of NLCD products named NLCD 2016. The NLCD 2016 design aims to provide innovative, consistent, and robust methodologies for production of a multi-temporal land cover and land cover change database from 2001 to 2016 at 2–3-year intervals. Comprehensive research was conducted and resulted in developed strategies for NLCD 2016: a streamlined process for assembling and preprocessing Landsat imagery and geospatial ancillary datasets; a multi-source integrated training data development and decision-tree based land cover classifications; a temporally, spectrally, and spatially integrated land cover change analysis strategy; a hierarchical theme-based post-classification and integration protocol for generating land cover and change products; a continuous fields biophysical parameters modeling method; and an automated scripted operational system for the NLCD 2016 production. The performance of the developed strategies and methods were tested in twenty World Reference System-2 path/row throughout the conterminous U.S. An overall agreement ranging from 71% to 97% between land cover classification and reference data was achieved for all tested area and all years. Results from this study confirm the robustness of this comprehensive and highly automated procedure for NLCD 2016 operational mapping.

Conterminous United States↗

USGS2025

Assessing decadal-scale coastal change likelihood to define the accuracy and application of scientific information

Defining the accuracy and uncertainties of scientific data products is critical to the usability and trustworthiness of scientific information for environmental management and conservation purposes, such as coastal resource prioritization, design, adaptation, and mitigation. The U.S. Geological Survey has a new decadal-scale coastal change assessment product that synthesizes nearly two dozen coastal datasets. A supervised machine-learning framework is used to combine existing datasets that describe the landscape and the hazards that affect it to determine the coastal change likelihood (CCL) in the coming decade at a resolution of 10 m per pixel for the NE United States from Maine to Virginia. Here, results from a series of statistical tests conducted on source data, the supervised classification, and the CCL outcomes as compared with historical land-cover change are presented. The overall accuracy of the aggregated land-cover dataset that serves as the foundation to which other source datasets are appended is 94%. The supervised learning classification that determines the final CCL output has an overall accuracy of 92%. The CCL predictions of high expected coastal change were consistent with 95% of the coastal and low-elevation landscape change in the last 20 years, as recorded by the Coastal Change Analysis Program land-cover change atlas. Results suggest that CCL provides accurate estimates of coastal landscape change in the next decade that are consistent with recent observed change. Additionally, best practices for applying CCL for planning purposes are outlined, and citing limitations, knowledge gaps, and opportunities for improved accuracy and further investigation are considered.

Journal of Coastal Research↗

USGS2025

Insights from growing Globorotalia truncatulinoides and Globorotalia menardii in the laboratory

The vast majority of planktic foraminiferal culture studies have been carried out on spinose species of foraminifera, with relatively few studies on non-spinose species. We conducted a pilot study to test whether live specimens of the non-spinose planktic foraminifera, Globorotalia truncatulinoides and Globorotalia menardii , could be successfully harvested from offshore plankton tow samples in the Gulf of America (Gulf of Mexico) and kept alive in a laboratory at the US Geological Survey St. Petersburg Coastal and Marine Science Center. We collected several G. truncatulinoides specimens (n = 39) from the surface mixed-layer (0–80 meters) via vertical plankton tow in February 2020 during a sediment trap mooring recovery cruise. We collected G. menardii (n = 27) from the upper 200 meters of the water column on follow-up cruises in December 2021 and November 2022. The G. truncatulinoides specimens stayed alive in the laboratory for 8–76 days, and G. menardii for 7–29 days. All non-spinose foraminifera in this study showed a strong preference for eating marine snow aggregates from the plankton tow over Artemia nauplii. Using a combination of morphometric observations and geochemical analysis of the foraminiferal tests, we demonstrate that some specimens of both species grew new chambers while in culture, whereas other individuals added a calcite crust to the final whorl. The G. menardii were cultured in 87 Sr-labeled seawater, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to verify the presence of laboratory-grown calcite. Our results shed light on the feeding behavior and growth patterns in these two upper-ocean species of non-spinose foraminifera. This study demonstrates the feasibility of conducting laboratory culture experiments with G. truncatulinoides and G. menardii collected via plankton tow in the open ocean.

Journal of Foraminiferal Research↗

USGS2023

Spatial and temporal analysis of geologic slip rates, Cucamonga Fault, California, USA: Implications for along-strike applications and multi-fault rupture

To constrain fault processes and hazard, fault slip rates may be extrapolated over different fault lengths or time intervals. Here, we investigate slip rates for the Cucamonga Fault (CF). The CF is located at the junction of the Transverse Range fault system with the San Andreas and San Jacinto Faults, and it is hypothesized to connect with these faults, promoting the propagation of large, multi-fault earthquakes. Previous work has shown that CF displacements on late Quaternary alluvial fan surfaces are highly variable along strike. We present two new 10 Be surface exposure ages from depth profiles on the alluvial fans. Slip rates are consistent with a rate of 1.4 ± 0.3 m/kyr over time intervals of ∼20, ∼30, and ∼40 kyr. If the CF participates in multi-fault ruptures, then these earthquakes occur either rarely or with sufficient regularity to maintain apparently steady rates over multiple intervals. We also explore along-strike fault displacement variability using a calibrated morphological model. The model successfully reproduces scarp profiles and indicates that fault displacement variability can be explained in part by scarp age but not uplift rate. We infer that both erosion by ephemeral gullying and distributed deformation contribute to fault displacement variability, although both are difficult to detect confidently without excavations across the scarp. These investigations show that better characterization of cumulative-slip variability along strike may improve accuracy and precision of slip rates. Slip rates that do not consider epistemic uncertainties may not be suitable for extrapolation over longer fault sections.

California↗

USGS2021

Summer runoff generation in foothill catchments of the Colorado Front Range

Climatic shifts, disturbances, and land-use change can alter hydrologic flowpaths, water quality, and water supply to downstream communities. Prior research investigating streamflow generation processes in mountainous areas has largely focused on high-elevation alpine and subalpine catchments; less is known about these processes in lower-elevation foothills and montane catchments. In these lower-elevation ecoregions, precipitation shifts seasonally from snow to rain, which can result in differing seasonal flowpaths. We analyzed stream water for electrical conductivity, SiO 2 , Ca, Mg, Na, Cl, SO 4 , K, and dissolved organic carbon on both a weekly and storm event basis from April to August 2018 in three small (<10 km 2 ) foothill catchments, and one larger (63.2 km 2 ) catchment extending from the foothills to the subalpine ecoregions, in the Colorado Front Range. Using two end-member hydrograph separations and concentration-runoff relationships, we inferred the dominant catchment-scale flowpaths of precipitation to the streams. We selected catchments with varying land use to investigate the relationship between these characteristics and hydrologic flowpaths. We observed that concentrations of lithogenic constituents generally increased and dissolved organic carbon decreased as seasonal runoff decreased in the three foothill catchments, reflecting a transition from shallow subsurface flowpaths to deeper subsurface flowpaths. Elevated SO 4 and Cl concentrations during low-flow periods in two of our catchments suggest that historical or current anthropogenic activities, such as mining, application of road salt, and/or near-stream septic systems, affect local stream and groundwater chemistry. In a foothill catchment with anthropogenic and geologic impervious surfaces, streamflow during storm responses was sourced from faster, surficial flowpaths compared to a less disturbed neighboring catchment, highlighting the influence of anthropogenic land-use on runoff generation. This study provides insight into the fundamental hydrology of foothill catchments and how they may function in the future with human development, precipitation shifts and disturbances.

Colorado↗

USGS2016

Magnetotelluric investigation of the Vestfold Hills and Rauer Group, East Antarctica

The Vestfold Hills and Rauer Group in East Antarctica have contrasting Archean to Neoproterozoic geological histories and are believed to be juxtaposed along a suture zone that now lies beneath the Sørsdal Glacier. Exact location and age of this suture zone are unknown, as is its relationship to regional deformation associated with the amalgamation of East Gondwana. To image the suture zone, magnetotelluric (MT) data were collected in Prydz Bay, East Antarctica, mainly along a profile crossing the Sørsdal Glacier and regions inland of the Vestfold Hills and Rauer Group islands. Time-frequency analysis of the MT time series yielded three important observations: (1) Wind speeds in excess of &sim;8 m/s reduce coherence between electric and magnetic fields due to charged wind-blown particles of ice and snow. (2) Estimation of the MT transfer function is best between 1000 and 1400 UT when ionospheric Hall currents enhance the magnetic source field. (3) Nonplanar source field effects were minimal but detectable and removed from estimation of the MT transfer function. Inversions of MT data in 2-D and 3-D produce similar resistivity models, where structures in the preferred 3-D resistivity model correlate strongly with regional magnetic data. The electrically conductive Rauer Group is separated from the less conductive Vestfold Hills by a resistive zone under the Sørsdal Glacier, which is interpreted to be caused by oxidation during suturing. Though a suture zone has been imaged, no time constrains on suturing can be made from the MT data.

Journal of Geophysical Research B: Solid Earth↗

USGS2014

A synoptic examination of causes of land loss in southern Louisiana as related to the exploitation of subsurface geologic resources

During the last 80 years, Louisiana has been losing wetlands at an average rate of 62 km 2 /y (24 mi 2 /y) for an accumulated loss of approximately 4900 km 2 (1900 mi 2 ). The loss seems to be the combined result of natural and anthropogenic causes that are behind primarily land subsidence averaging about 10 mm/y (0.4 in/y) coinciding with a sea level rise now at 3 mm/y (0.1 in/y), both contributing to coastal inundation. Upon completing extensive review of often controversial and conflicting views only synoptically reported here, conclusions reached by applying Monte Carlo simulation include: (1) geodetic measurements are consistent with independently postulated causes of regional subsidence; (2) ranking of subsidence factors shows that the main contributor to the regional subsidence is adjustment to sediment load in the form of lithosphere flexure followed by normal faulting dipping basinward, which combined, account on average for 70% of the subsidence, with compaction accounting for another 23%; and (3) production of oil and gas plays a tertiary role. The literature supports the historical view that before experiencing engineering modifications across the catchment area, sedimentation from the Mississippi River system was able to build a prograding coastline by overcoming subsidence rates of similar magnitude with more generous sediment loads of coarser particle size. Sea level rise will become an increasingly dominant factor in land loss only if the acceleration predicted by simulation model scenarios materializes. Wetland losses most likely will continue for as long as there is no compensation to counterbalance the negative effects of land subsidence and sea level rise, with the latter determining the pace of future losses.

Louisiana↗

USGS2012

The hydrothermal system at Newberry Volcano, Oregon

Results of recent geological and geophysical studies at Newberry Volcano have been incorporated into conceptual and numerical models of a magma-based hydrothermal system. Numerical simulations begin with emplacement of a small magma body, the presumed source of silicic eruptions at Newberry that began about 10,000 B.P., into a thermal regime representing 100,000 years of cooling of a large underlying intrusion. Simulated flow patterns and thermal histories for three sets of hypothetical permeability values are compatible with data from four geothermal drill holes on the volcano. Meteoric recharge cools the caldera-fill deposits, but thermal water moving up a central conduit representing a permeable volcanic vent produces temperatures close to those observed in drill holes within the caldera. Meteoric recharge from the caldera moves down the flanks and creates a near-isothermal zone that extends several hundred meters below the water table, producing temperature profiles similar to those observed in drill holes on the flanks. The temperatures observed in drill holes on the flanks are not influenced by the postulated Holocene magma body. The elevated temperature gradients measured in the lower portions of these holes may be related to the cumulative effect of older intrusions. The models also indicate that meteoric recharge to the deep hydrothermal system probably originates within or near the caldera. Relatively low fluid velocities at depth suggest that at least a significant fraction of the thermal fluid may be very old.

Journal of Geophysical Research Solid Earth↗

USGS2017

Geologic overview of the Mars Science Laboratory rover mission at the Kimberley, Gale crater, Mars

The Mars Science Laboratory (MSL) Curiosity rover completed a detailed investigation at the Kimberley waypoint within Gale crater from sols 571-634 using its full science instrument payload. From orbital images examined early in the Curiosity mission, the Kimberley region had been identified as a high-priority science target based on its clear stratigraphic relationships in a layered sedimentary sequence that had been exposed by differential erosion. Observations of the stratigraphic sequence at the Kimberley made by Curiosity are consistent with deposition in a prograding, fluvio-deltaic system during the late Noachian to early Hesperian, prior to the existence of most of Mt. Sharp. Geochemical and mineralogic analyses suggest that sediment deposition likely took place under cold conditions with relatively low water-to-rock ratios. Based on elevated K2O abundances throughout the Kimberley formation, an alkali feldspar protolith is likely one of several igneous sources from which the sediments were derived. After deposition, the rocks underwent multiple episodes of diagenetic alteration with different aqueous chemistries and redox conditions, as evidenced by the presence of Ca-sulfate veins, Mn-oxide fracture-fills, and erosion-resistant nodules. More recently, the Kimberley has been subject to significant aeolian abrasion and removal of sediments to create modern topography that slopes away from Mt. Sharp, a process that has continued to the present day.

Journal of Geophysical Research E: Planets↗