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At least 1,099 records · Page 61Linked to original sources
USGS2003

Orogenic tectonism on Io

We catalog 143 Ionian mountains (montes) and mountain‐like features (mensae, tholi, plana, and small peaks) in order to investigate orogenic tectonism on Io. From this comprehensive list, we select 96 mountains for which there are sufficient coverage and resolution to discern spatial relationships with surrounding geologic features. Three of the 96 mountains are probably volcanoes, 92 appear to be tectonic massifs, and 1 is ambiguous. Of the 92 tectonic mountains, 38 abut paterae (volcanic or volcano‐tectonic craters with irregular or scalloped margins). This juxtaposition is unlikely to be a coincidence as the probability of it occurring by chance is ∼0.1%. We propose instead that orogenic faults may act as conduits for magma ascent, thus fueling patera formation near mountains. As resurfacing buries a shell of material from Io's surface to the base of the lithosphere, its effective radius is reduced and it heats up. We calculate the lithospheric volume change due to subsidence and thermal expansion as a function of lithospheric thickness. Conservation of volume dictates that this material must be uplifted at Io's surface. By estimating the total volume of the mountains, we are able to place a lower limit of 12 km on Io's lithospheric thickness. We hypothesize that, in some cases, mountain formation may be facilitated by asthenospheric diapirs impinging on the base of the lithosphere. The resulting lithospheric swell could focus the compressive stresses that drive orogenic tectonism. This model is one of several possible mechanisms for uplifting isolated mountains such as are observed on Io.

Journal of Geophysical Research E: Planets↗
USGS2008

Ultrahigh resolution topographic mapping of Mars with MRO HiRISE stereo images: Meter-scale slopes of candidate Phoenix landing sites

The objectives of this paper are twofold: first, to report our estimates of the meter‐to‐decameter‐scale topography and slopes of candidate landing sites for the Phoenix mission, based on analysis of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images with a typical pixel scale of 3 m and Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) images at 0.3 m pixel −1 and, second, to document in detail the geometric calibration, software, and procedures on which the photogrammetric analysis of HiRISE data is based. A combination of optical design modeling, laboratory observations, star images, and Mars images form the basis for software in the U.S. Geological Survey Integrated Software for Imagers and Spectrometers (ISIS) 3 system that corrects the images for a variety of distortions with single‐pixel or subpixel accuracy. Corrected images are analyzed in the commercial photogrammetric software SOCET SET (® BAE Systems), yielding digital topographic models (DTMs) with a grid spacing of 1 m (3–4 pixels) that require minimal interactive editing. Photoclinometry yields DTMs with single‐pixel grid spacing. Slopes from MOC and HiRISE are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully; only the Mars Exploration Rover (MER) B site in Meridiani Planum is smoother. MOC results at multiple locations have root‐mean‐square (RMS) bidirectional slopes of 0.8–4.5° at baselines of 3–10 m. HiRISE stereopairs (one per final candidate site and one in the former site) yield 1.8–2.8° slopes at 1‐m baseline. Slopes at 1 m from photoclinometry are also in the range 2–3° after correction for image blur. Slopes exceeding the 16° Phoenix safety limit are extremely rare.

Journal of Geophysical Research E: Planets↗
USGS2015

Status and trends of land change in the Midwest–South Central United States—1973 to 2000

U.S. Geological Survey (USGS) Professional Paper 1794–C is the third in a four-volume series on the status and trends of the Nation’s land use and land cover, providing an assessment of the rates and causes of land-use and land-cover change in the Midwest–South Central United States between 1973 and 2000. Volumes A, B, and D provide similar analyses for the Western United States, the Great Plains of the United States, and the Eastern United States, respectively. The assessments of land-use and land-cover trends are conducted on an ecoregion-by-ecoregion basis, and each ecoregion assessment is guided by a nationally consistent study design that includes mapping, statistical methods, field studies, and analysis. Individual assessments provide a picture of the characteristics of land change occurring in a given ecoregion; in combination, they provide a framework for understanding the complex national mosaic of change and also the causes and consequences of change. Thus, each volume in this series provides a regional assessment of how (and how fast) land use and land cover are changing, and why. The four volumes together form the first comprehensive picture of land change across the Nation. Geographic understanding of land-use and land-cover change is directly relevant to a wide variety of stakeholders, including land and resource managers, policymakers, and scientists. The chapters in this volume present brief summaries of the patterns and rates of land change observed in each ecoregion in the Midwest–South Central United States, together with field photographs, statistics, and comparisons with other assessments. In addition, a synthesis chapter summarizes the scope of land change observed across the entire Midwest–South Central United States. The studies provide a way of integrating information across the landscape, and they form a critical component in the efforts to understand how land use and land cover affect important issues such as the provision of ecological goods and services and also the determination of risks to, and vulnerabilities of, human communities. Results from this project also are published in peer-reviewed journals, and they are further used to produce maps of change and other tools for land management, as well as to provide inputs for carbon-cycle modeling and other climate change research.

Professional Paper↗
USGS2015

Status and trends of land change in the Great Plains of the United States--1973 to 2000

Preface U.S. Geological Survey (USGS) Professional Paper 1794–B is the second in a four-volume series on the status and trends of the Nation’s land use and land cover, providing an assessment of the rates and causes of land-use and land-cover change in the Great Plains of the United States between 1973 and 2000. Volumes A, C, and D provide similar analyses for the Western United States, the Midwest–South Central United States, and the Eastern United States, respectively. The assessments of land-use and land-cover trends are conducted on an ecoregion-by-ecoregion basis, and each ecoregion assessment is guided by a nationally consistent study design that includes mapping, statistical methods, field studies, and analysis. Individual assessments provide a picture of the characteristics of land change occurring in a given ecoregion; in combination, they provide a framework for understanding the complex national mosaic of change and also the causes and consequences of change. Thus, each volume in this series provides a regional assessment of how (and how fast) land use and land cover are changing, and why. The four volumes together form the first comprehensive picture of land change across the Nation. Geographic understanding of land-use and land-cover change is directly relevant to a wide variety of stakeholders, including land and resource managers, policymakers, and scientists. The chapters in this volume present brief summaries of the patterns and rates of land change observed in each ecoregion in the Great Plains of the United States, together with field photographs, statistics, and comparisons with other assessments. In addition, a synthesis chapter summarizes the scope of land change observed across the entire Great Plains of the United States. The studies provide a way of integrating information across the landscape, and they form a critical component in the efforts to understand how land use and land cover affect important issues such as the provision of ecological goods and services and also the determination of risks to, and vulnerabilities of, human communities. Results from this project also are published in peer-reviewed journals, and they are further used to produce maps of change and other tools for land management, as well as to provide inputs for carbon-cycle modeling and other climate change research. This report is only one of the products produced by USGS on land-use and land-cover change in the United States. Other reports and land-cover statistics are available online at http://landcovertrends.usgs.gov .

Great Plains↗
USGS2017

Identification of alginite and bituminite in rocks other than coal. 2006, 2009, and 2011 round robin exercises of the ICCP Identification of Dispersed Organic Matter Working Group

The paper presents results of round robin exercises on photomicrograph-based identification of dispersed organic matter in source rocks that represent a range of marine and lacustrine deposits from worldwide localities and cover a range of thermal maturities. The round robin exercises were conducted by the Identification of Dispersed Organic Matter Working Group (IDOM WG) of the International Committee for Coal and Organic Petrology (ICCP). The round robin exercises aimed to (1) assess the applicability of the established ICCP definitions of bituminite, (2) identify deficiencies and improve the existing nomenclatures, and (3) provide a basis for the revision of the bituminite and alginite definitions in the ICCP Handbook (Taylor et al., 1998). Three round robin exercises performed in 2006, 2009 and 2011 involved 18 participants from research laboratories at universities and within government and industry. Participants were asked to identify macerals on the basis of existing definitions in 129 photomicrographs taken in incident white light and fluorescent mode and also in fluorescence light mode at prolonged (15 min) blue light irradiation. The results indicate that the definition of telalginite permits its positive and satisfactory agreement among the participants. In contrast, the descriptive characteristics of lamalginite referring to film-like appearance (filamentous) and lack of inner or outer structure are insufficient and inadequate to enable an unequivocal discrimination between it and telalginite. Furthermore, based on the amorphous nature of bituminite and lack of adherence to its established description and character (Taylor et al., 1998), the highest discrepancies were observed in its identification. Differentiation of bituminite from a fluorescent groundmass and in some cases from lamalginite proved to be particularly challenging. The findings of these round robin exercises are useful for improving the identification of sedimentary organic matter in source rocks and may be an important foundation for the modification of the ICCP definitions of alginite and bituminite.

International Journal of Coal Geology↗
USGS1999

NEOCHIM: An electrochemical method for environmental application

Ion migration and electroosmosis are the principal processes underlying electrokinetic remediation of hazardous wastes from soils. These processes are a response of charged species to an applied electrical current and they are accompanied by electrolysis of water at the electrodes through which the current is applied. Electrolysis results in the formation of OH- at the cathode and H+ at the anode. The current drives the OH- and H+ thus formed from the electrodes, through the soil and to the electrode of opposite charge. Introduction of OH- and H+ into the soil being treated modifies soil chemistry and can interfere with either the collection or immobilization of hazardous waste ions. The introduction of either OH- or H+ to the soil can be problematic to electrokinetic remediation but the problem caused by OH- has been the focus of most researchers. The problem has been addressed by flushing the OH- from the soil near the cathode or treating the soil with buffers. These treatments would apply as well to soils affected by H+. With the NEOCHIM technology, developed by the U.S. Geological Survey (USGS) for use as a sampling technique in exploration for buried ore deposits, OH- and H+ are retained in the inner compartment of two-compartment electrodes and are thus prevented from reaching the soil. This enables the extraction of cations and anions, including anionic forms of toxic metals such as HAsO42-. One of the principal attributes of NEOCHIM is the large volume of soil from which ions can be extracted. It is mathematically demonstrable that NEOCHIM extraction volumes can be orders of magnitude greater than volumes typically sampled in more conventional geochemical exploration methods or for environmental sampling. The technology may also be used to introduce selected ions into the soil that affect the solubility of ceratin ions present in the soil. Although field tests for mineral exploration have shown NEOCHIM extraction efficiencies of about 25-35%, laboratory experiments suggest that significantly higher efficiencies are possible. The attributes of NEOCHIM combined with relatively low cost of electrical power, indicate that the technology may be useful for remediation and monitoring of hazardous waste sites. Of particular importance is that NEOCHIM extractions affect only dissolved and electrically charged species, hence those prone to move in groundwater.The U.S. Geological Survey (USGS) has developed a technology called NEOCHIM for use as a sampling technique in exploration for buried deposits. With this technology, OH- and H+ are retained in the inner compartment of two-compartment electrodes and are thus prevented from reaching the soil. This enables the extraction of cations and anions. Laboratory experiments suggest extraction efficiencies higher than 25-35%.

Journal of Geochemical Exploration↗
USGS2013

Photometric properties of Mars soils analogs

We have measured the bidirectional reflectance of analogs of dry, wet, and frozen Martian soils over a wide range of phase angles in the visible spectral range. All samples were produced from two geologic samples: the standard JSC Mars-1 soil simulant and Hawaiian basaltic sand. In a first step, experiments were conducted with the dry samples to investigate the effects of surface texture. Comparisons with results independently obtained by different teams with similar samples showed a satisfying reproducibility of the photometric measurements as well as a noticeable influence of surface textures resulting from different sample preparation procedures. In a second step, water was introduced to produce wet and frozen samples and their photometry investigated. Optical microscope images of the samples provided information about their microtexture. Liquid water, even in relatively low amount, resulted in the disappearance of the backscattering peak and the appearance of a forward-scattering peak whose intensity increases with the amount of water. Specular reflections only appeared when water was present in an amount large enough to allow water to form a film at the surface of the sample. Icy samples showed a wide variability of photometric properties depending on the physical properties of the water ice. We discuss the implications of these measurements in terms of the expected photometric behavior of the Martian surface, from equatorial to circum-polar regions. In particular, we propose some simple photometric criteria to improve the identification of wet and/or icy soils from multiple observations under different geometries.

Journal of Geophysical Research E: Planets↗
USGS2012

Structural evidence for northeastward movement on the Chocolate Mountains Thrust, southeasternmost California

The Late Cretaceous Chocolate Mountains thrust of southeastern California and southwestern Arizona places a block of Proterozoic and Mesozoic continental crust over the late Mesozoic continental margin oceanic sedimentary and volcanic rocks of the regionally distinctive Orocopia Schist. The Chocolate Mountains thrust is interpreted as a thrust (burial, subduction) fault rather than a low-angle normal (exhumation, unroofing, uplift) fault. An important parameter required to understand the tectonic significance of the Chocolate Mountains and related thrusts is their sense of movement. The Chocolate Mountains thrust zone contains sparse to locally abundant mesoscopic asymmetric folds. Fabric relations, supported by regional geologic evidence, indicate that these folds are an integral part of and coeval with the thrust zone. On a lower hemisphere equal-area plot representing the orientation and sense of asymmetry of 80 thrust zone folds from 36 localities, spread over an area 60 by 10 km, Z folds plot northwest of and S folds plot southeast of a northeast-southwest striking vertical plane of overall monoclinic symmetry. The only sense of movement consistent with the collective asymmetry of the thrust zone folds is top to the northeast. Asymmetric microstructures studied at several localities also indicate top to the northeast movement. Paleomagnetic data suggest that the original sense of thrusting, prior to Neogene vertical axis tectonic rotation related to the San Andreas fault system, was northward. The essential point is that movement of the upper plate of the Chocolate Mountains thrust evidently was continentward. Continentward thrusting suggests a tectonic scenario in which an insular or peninsular microcontinental fragment collided with mainland southern California. The suture predicted by this model is elusive; but the Chocolate Mountains thrust and underlying Orocopia Schist themselves may represent the suture, at the present level of exposure. Alternative tectonic models involving subduction of the Orocopia Schist eastward beneath continental southern California circumvent the suture problem but are presently not supported by any direct structural evidence.

Journal of Geophysical Research↗
USGS2024

Pockmarks offshore Big Sur, California provide evidence for recurrent, regional, and unconfined sediment gravity flows

Recent surface ship multibeam surveys of the Sur Pockmark Field, offshore Central California, reveal >5,000 pockmarks in an area that is slated to host a wind farm, between 500- and 1,500-m water depth. Extensive fieldwork was conducted to characterize the seafloor environment and its recent geologic history, including visual observations with remotely operated vehicles, sediment core sampling, and high-resolution, near-bottom Chirp and multibeam surveys collected with autonomous underwater vehicles to capture the morphology and stratigraphy of the pockmarks. No evidence of high methane concentrations in sediments, chemosynthetic biological communities, or methane-derived diagenetic byproducts was found. Chirp data and sediment cores showed alternating layers of slowly accumulating hemipelagic drapes interrupted by more reflective turbidite horizons that extend throughout the pockmark field and beyond. Chirp data showed multiple episodes of lateral migration over time in some of the pockmarks in association with erosion and infilling events. Laterally continuous turbidite horizons that overlay erosional surfaces indicated that pockmark migration occurred synchronously in multiple pockmarks separated by tens of kilometers. These shifts are presumed to be the result of asymmetrical erosion of the pockmark flanks caused by passing sediment gravity flows. While some pockmarks occur in chains, most are not clustered or randomly spaced but are regularly dispersed within the pockmark field. We hypothesize that intermittent, unconfined sediment gravity flows occurring over at least the last 280,000 years are the source of the regionally continuous turbidite deposits and the mechanism that maintained the regularly dispersed pockmarks.

California↗
USGS1999

Observations of Phobos, Deimos, and bright stars with the Imager for Mars Pathfinder

The Imager for Mars Pathfinder (IMP) was used to observe several objects during the Martian night. The satellites, Phobos and Deimos, were observed on two occasions each, through the IMP geological filters covering the wavelength range 440 nm to 1 μm. The observations were converted to geometric albedo using triaxial ellipsoid models of the satellites and phase functions derived from Viking Orbiter images. The spectral slopes over the full wavelength range were 7.9(±0.5)% (100 nm) −1 and 9.6(±0.6)% (100 nm) −1 , respectively, referenced to 600 nm. In the Deimos spectra, some evidence for decreased reddening toward the trailing hemisphere was found. The geometric albedoes of Phobos and Deimos were found to be 0.065 (±0.010) and 0.068 (±0.009), respectively, averaged over 440 and 600 nm, in good agreement with previous measurements. The nighttime optical depth was investigated using observations of stars. A mean value of 0.56 (±0.09) was determined from measurements at different airmass. A possible maximum in the optical depth near 0200 local time was found, which may result from condensation during the night. A measurement of the egress of Phobos from eclipse was made. Modeling of the light curve gave a scale height for the scatterers of 10–15 km. The exact time of the eclipse reappearance over the limb could be reconstructed from the measurements and was in reasonable accord with predictions, although a small modification to the predicted position of Phobos of 6.8 (±6.0) km would have produced better agreement.

Journal of Geophysical Research E: Planets↗
USGS2010

Using Landsat satellite data to support pesticide exposure assessment in California

Background The recent U.S. Geological Survey policy offering Landsat satellite data at no cost provides researchers new opportunities to explore relationships between environment and health. The purpose of this study was to examine the potential for using Landsat satellite data to support pesticide exposure assessment in California. Methods and Results We collected a dense time series of 24 Landsat 5 and 7 images spanning the year 2000 for an agricultural region in Fresno County. We intersected the Landsat time series with the California Department of Water Resources (CDWR) land use map and selected field samples to define the phenological characteristics of 17 major crop types or crop groups. We found the frequent overpass of Landsat enabled detection of crop field conditions (e.g., bare soil, vegetated) over most of the year. However, images were limited during the winter months due to cloud cover. Many samples designated as single-cropped in the CDWR map had phenological patterns that represented multi-cropped or non-cropped fields, indicating they may have been misclassified. Conclusions We found the combination of Landsat 5 and 7 image data would clearly benefit pesticide exposure assessment in this region by 1) providing information on crop field conditions at or near the time when pesticides are applied, and 2) providing information for validating the CDWR map. The Landsat image time-series was useful for identifying idle, single-, and multi-cropped fields. Landsat data will be limited during the winter months due to cloud cover, and for years prior to the Landsat 7 launch (1999) when only one satellite was operational at any given time. We suggest additional research to determine the feasibility of integrating CDWR land use maps and Landsat data to derive crop maps in locations and time periods where maps are not available, which will allow for substantial improvements to chemical exposure estimation.

California↗
USGS2016

Creating a Coastal National Elevation Database (CoNED) for science and conservation applications

The U.S. Geological Survey is creating the Coastal National Elevation Database, an expanding set of topobathymetric elevation models that extend seamlessly across coastal regions of high societal or ecological significance in the United States that are undergoing rapid change or are threatened by inundation hazards. Topobathymetric elevation models are raster datasets useful for inundation prediction and other earth science applications, such as the development of sediment-transport and storm surge models. These topobathymetric elevation models are being constructed by the broad regional assimilation of numerous topographic and bathymetric datasets, and are intended to fulfill the pressing needs of decision makers establishing policies for hazard mitigation and emergency preparedness, coastal managers tasked with coastal planning compatible with predictions of inundation due to sea-level rise, and scientists investigating processes of coastal geomorphic change. A key priority of this coastal elevation mapping effort is to foster collaborative lidar acquisitions that meet the standards of the USGS National Geospatial Program's 3D Elevation Program, a nationwide initiative to systematically collect high-quality elevation data. The focus regions are located in highly dynamic environments, for example in areas subject to shoreline change, rapid wetland loss, hurricane impacts such as overwash and wave scouring, and/or human-induced changes to coastal topography.

Journal of Coastal Research↗
USGS1995

Wind shear stress measurements in a coastal marsh during Hurricane Andrew

Hurricane Andrew produced changes to the Louisiana wetlands not normally observed after lesser, more common storms. For example, the <25 m/s wind speeds generated by cold fronts and winter storms, and any accompanying storm surge, do not cause substantial, wide-spread alteration of marsh vegetation. During Hurricane Andrew, however, the wind, the wind-driven storm surge, or both produced severe, wide-spread wetland alteration, especially in areas that primarily consisted of densely vegetated floating mats. In a few hours, vegetated brackish marsh was severely torn and large areas were converted to open water, a process that takes decades when driven by geologic subsidence, human intervention, and lesser storms. During the passage of Hurricane Andrew, wind measurements were taken inside an impoundment within a brackish part of Louisiana's coastal wetlands system. At its closest point, the site lay 50 km to the right of the north-trending storm track, placing it in or near the zone of maximum wind (the eye wall). As the hurricane approached, the wind blew from the north; after it passed, the wind direction swung around to the southeast. Several hours after the eye passed, the southeasterly wind drove a 1.5-m storm surge through the area, causing the collapse of the meteorology tower. Wind shear stress calculations, based on data from two vertically stacked sensors, showed a direct correlation between wind shear stress and wind speed. The greatest increase in wind shear stress occurred when wind speed exceeded 20 m/s. Overall, wind shear stress increased more than three orders of magnitude — from approximately 0.01 N/m² at a wind speed of 6 m/s through 1 N/m² at 20 m/s to 18 N/m² at the maximum sustained speed of 43 m/s. Drag-coefficient calculations show that the open-ocean CD formulations, such as the popular WAMDI model, cannot be employed for wetland use because it overestimates CD for velocities less than approximately 20 m/s and underestimates it for higher velocities.

Louisiana↗
USGS2011

Value of a dual-polarized gap-filling radar in support of southern California post-fire debris-flow warnings

A portable truck-mounted C-band Doppler weather radar was deployed to observe rainfall over the Station Fire burn area near Los Angeles, California, during the winter of 2009/10 to assist with debris-flow warning decisions. The deployments were a component of a joint NOAA–U.S. Geological Survey (USGS) research effort to improve definition of the rainfall conditions that trigger debris flows from steep topography within recent wildfire burn areas. A procedure was implemented to blend various dual-polarized estimators of precipitation (for radar observations taken below the freezing level) using threshold values for differential reflectivity and specific differential phase shift that improves the accuracy of the rainfall estimates over a specific burn area sited with terrestrial tipping-bucket rain gauges. The portable radar outperformed local Weather Surveillance Radar-1988 Doppler (WSR-88D) National Weather Service network radars in detecting rainfall capable of initiating post-fire runoff-generated debris flows. The network radars underestimated hourly precipitation totals by about 50%. Consistent with intensity–duration threshold curves determined from past debris-flow events in burned areas in Southern California, the portable radar-derived rainfall rates exceeded the empirical thresholds over a wider range of storm durations with a higher spatial resolution than local National Weather Service operational radars. Moreover, the truck-mounted C-band radar dual-polarimetric-derived estimates of rainfall intensity provided a better guide to the expected severity of debris-flow events, based on criteria derived from previous events using rain gauge data, than traditional radar-derived rainfall approaches using reflectivity–rainfall relationships for either the portable or operational network WSR-88D radars. Part of the reason for the improvement was due to siting the radar closer to the burn zone than the WSR-88Ds, but use of the dual-polarimetric variables improved the rainfall estimation by ~12% over the use of traditional Z – R relationships.

Journal of Hydrometeorology↗
USGS2006

The changing shapes of active volcanoes: History, evolution, and future challenges for volcano geodesy

At the very heart of volcanology lies the search for the 'plumbing systems' that form the inner workings of Earth’s active volcanoes. By their very nature, however, the magmatic reservoirs and conduits that underlie these active volcanic systems are elusive; mostly they are observable only through circumstantial evidence, using indirect, and often ambiguous, surficial measurements. Of course, we can infer much about these systems from geologic investigation of materials brought to the surface by eruptions and of the exposed roots of ancient volcanoes. But how can we study the magmatic processes that are occurring beneath Earth’s active volcanoes? What are the geometry, scale, physical, and chemical characteristics of magma reservoirs? Can we infer the dynamics of magma transport? Can we use this information to better forecast the future behavior of volcanoes? These questions comprise some of the most fundamental, recurring themes of modern research in volcanology. The field of volcano geodesy is uniquely situated to provide critical observational constraints on these problems. For the past decade, armed with a new array of technological innovations, equipped with powerful computers, and prepared with new analytical tools, volcano geodesists have been poised to make significant advances in our fundamental understanding of the behavior of active volcanic systems. The purpose of this volume is to highlight some of these recent advances, particularly in the collection and interpretation of geodetic data from actively deforming volcanoes. The 18 papers that follow report on new geodetic data that offer valuable insights into eruptive activity and magma transport; they present new models and modeling strategies that have the potential to greatly increase understanding of magmatic, hydrothermal, and volcano-tectonic processes; and they describe innovative techniques for collecting geodetic measurements from remote, poorly accessible, or hazardous volcanoes. To provide a proper context for these studies, we offer a short review of the evolution of volcano geodesy, as well as a case study that highlights recent advances in the field by comparing the geodetic response to recent eruptive episodes at Mount St. Helens. Finally, we point out a few areas that continue to challenge the volcano geodesy community, some of which are addressed by the papers that follow and which undoubtedly will be the focus of future research for years to come.

Journal of Volcanology and Geothermal Research↗
USGS2003

The mechanics of unrest at Long Valley caldera, California. 2. Constraining the nature of the source using geodetic and micro-gravity data

We model the source of inflation of Long Valley caldera by combining geodetic and micro-gravity data. Uplift from GPS and leveling, two-color EDM measurements, and residual gravity change determinations are used to estimate the intrusion geometry, assuming a vertical prolate ellipsoidal source. The U.S. Geological Survey occupied the Long Valley gravity network six times from 1980 to 1985. We reoccupied this network twice, in the summer of 1998 (33 stations), and the summer of 1999 (37 stations). Before gravity data can be used to estimate the density of the intrusion, they must be corrected for the effect of vertical deformation (the free-air effect) and changes in the water table. We use geostatistical techniques to interpolate uplift and water table changes at the gravity stations. The inflation source (a vertical prolate ellipsoid) is located 5.9 km beneath the resurgent dome with an aspect ratio equal to 0.475, a volume change from 1982 to 1999 of 0.136 km3 and a density of around 1700 kg/m3. A bootstrap method was employed to estimate 95% confidence bounds for the parameters of the inflation model. We obtained a range of 0.105-0.187 km3 for the volume change, and 1180-2330 kg/m3 for the density. Our results do not support hydrothermal fluid intrusion as the primary cause of unrest, and confirm the intrusion of silicic magma beneath Long Valley caldera. Failure to account for the ellipsoidal nature of the source biases the estimated source depth by 2.9 km (a 33% increase), the volume change by 0.019 km3 (a 14% increase) and the density by about 1200 kg/m3 (a 40% increase). ?? 2003 Elsevier B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗
USGS2022

Bedrock geochemistry and alteration history of the clay-bearing Glen Torridon region of Gale crater, Mars

Glen Torridon is a topographic trough located on the slope of Aeolis Mons, Gale crater, Mars. It corresponds to what was previously referred to as the “clay-bearing unit”, due to the relatively strong spectral signatures of clay minerals (mainly ferric smectites) detected from orbit. Starting in January 2019, the Curiosity rover explored Glen Torridon for more than 700 sols (Martian days). The objectives of this campaign included acquiring a detailed understanding of the geologic context in which the clay minerals were formed and determining the intensity of aqueous alteration experienced by the sediments. Here, we present the major-element geochemistry of the bedrock as analyzed by the ChemCam instrument. Our results reveal that the two main types of bedrock exposures identified in the lower part of Glen Torridon are associated with distinct chemical compositions (K-rich and Mg-rich), for which we are able to propose mineralogical interpretations. Moreover, the topmost stratigraphic member exposed in the region displays a stronger diagenetic overprint, especially at two locations close to the unconformable contact with the overlying Stimson formation, where the bedrock composition significantly deviates from the rest of Glen Torridon. Overall, the values of the Chemical Index of Alteration determined with ChemCam are elevated by Martian standards, suggesting the formation of clay minerals through open system weathering. However, there is no indication that the alteration was stronger than in some terrains previously visited by Curiosity , which in turn implies that the enhanced orbital signatures are mostly controlled by non-compositional factors.

Journal of Geophysical Research E: Planets↗
USGS2016

Topobathymetric elevation model development using a new methodology: Coastal National Elevation Database

During the coming decades, coastlines will respond to widely predicted sea-level rise, storm surge, and coastalinundation flooding from disastrous events. Because physical processes in coastal environments are controlled by the geomorphology of over-the-land topography and underwater bathymetry, many applications of geospatial data in coastal environments require detailed knowledge of the near-shore topography and bathymetry. In this paper, an updated methodology used by the U.S. Geological Survey Coastal National Elevation Database (CoNED) Applications Project is presented for developing coastal topobathymetric elevation models (TBDEMs) from multiple topographic data sources with adjacent intertidal topobathymetric and offshore bathymetric sources to generate seamlessly integrated TBDEMs. This repeatable, updatable, and logically consistent methodology assimilates topographic data (land elevation) and bathymetry (water depth) into a seamless coastal elevation model. Within the overarching framework, vertical datum transformations are standardized in a workflow that interweaves spatially consistent interpolation (gridding) techniques with a land/water boundary mask delineation approach. Output gridded raster TBDEMs are stacked into a file storage system of mosaic datasets within an Esri ArcGIS geodatabase for efficient updating while maintaining current and updated spatially referenced metadata. Topobathymetric data provide a required seamless elevation product for several science application studies, such as shoreline delineation, coastal inundation mapping, sediment-transport, sea-level rise, storm surge models, and tsunami impact assessment. These detailed coastal elevation data are critical to depict regions prone to climate change impacts and are essential to planners and managers responsible for mitigating the associated risks and costs to both human communities and ecosystems. The CoNED methodology approach has been used to construct integrated TBDEM models in Mobile Bay, the northern Gulf of Mexico, San Francisco Bay, the Hurricane Sandy region, and southern California.

Journal of Coastal Research↗