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USGS2007

Dust deposition on the Mars Exploration Rover Panoramic Camera (Pancam) calibration targets

The Panoramic Camera (Pancam) on the Mars Exploration Rover mission has acquired in excess of 20,000 images of the Pancam calibration targets on the rovers. Analysis of this data set allows estimates of the rate of deposition and removal of aeolian dust on both rovers. During the first 150-170 sols there was gradual dust accumulation on the rovers but no evidence for dust removal. After that time there is ample evidence for both dust removal and dust deposition on both rover decks. We analyze data from early in both rover missions using a diffusive reflectance mixing model. Assuming a dust settling rate proportional to the atmospheric optical depth, we derive spectra of optically thick layers of airfall dust that are consistent with spectra from dusty regions on the Martian surface. Airfall dust reflectance at the Opportunity site appears greater than at the Spirit site, consistent with other observations. We estimate the optical depth of dust deposited on the Spirit calibration target by sol 150 to be 0.44 ?? 0.13. For Opportunity the value was 0.39 ?? 0.12. Assuming 80% pore space, we estimate that the dust layer grew at a rate of one grain diameter per ???100 sols on the Spirit calibration target. On Opportunity the rate was one grain diameter per ???125 sols. These numbers are consistent with dust deposition rates observed by Mars Pathfinder taking into account the lower atmospheric dust optical depth during the Mars Pathfinder mission. Copyright 2007 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2025

The communication of volcano information in New Zealand - A narrative review

Communication of volcano information is critical for effective volcanic risk management. A variety of information is communicated to inform decisions and guide actions for planning, preparedness, and response. Such information needs to be reliable, and fit-for-purpose across different stages of volcanic activity (quiescence, unrest, short or long-term eruptive stages, and the post-eruptive stage). However, an understanding of communication across these different stages of volcanic activity remains limited. We undertook a narrative review of New Zealand literature to explore what information is communicated about volcanoes, across which stages of activity and by whom. Results highlight that NZ literature only documents certain aspects of volcano information and communication, specifically regarding certain locations, stages of volcanic activity (i.e. quiescence or unrest), or hazards. Literature gaps exist regarding volcano communication during unrest and post-eruptive stages, as well as how volcano information evolves between these phases, and how decision-makers use such information. Additional work would be useful to document existing examples of volcano information for different stages of activity. Further research could help in understanding the information needs of decision-makers during each of these stages to improve information and communication.

New Zealand Journal of Geology and Geophysics↗

USGS2012

The transition from hydrostatic to greater than hydrostatic fluid pressure in presently active continental hydrothermal systems in crystalline rock

Fluid flow at hydrostatic pressure (P h ) is relatively common through fractures in silicic and in mafic crystalline rocks where temperatures are less than about 350–370°C. In contrast, pore-fluid pressure (P f ) > P h has been encountered at the bottom of 3 geothermal exploration wells that attained temperatures >370°C (at Larderello, Italy, at Nesjavellir, Iceland, and at The Geysers, California). Chemical sealing by deposition of minerals in veins appears to have allowed the development of the high P f encountered in the above wells. The upper limit for the magnitude of P f that can be attained is controlled by either the onset of shear fracturing (where differential stress is relatively high) that reopens clogged veins, or the hydraulic opening of new or old fractures (at relatively low values of differential stress). The brittle-plastic transition for silicic rocks can occur at temperatures as high as 370–400°C in tectonically active regions. In regions where high-temperature geothermal systems develop and persist, it appears that either strain rates commonly are in the range 10 −12 to 10 −13 , or that silicic rocks in the shallow crust generally behave rheologically more like wet quartz diorite than wet Westerly granite.

Geophysical Research Letters↗

USGS2025

Horizontal transport of Picture Gorge Basalt magma through the Monument Dike Swarm determined by magnetic fabric

Flood basalts of the mid-Miocene Columbia River Basalt Group (CRBG) cover 210,000 km 2 of Washington, Oregon, and Idaho. The source of CRBG melt is debated; widely spaced feeder dike swarms can be projected toward hypothetical sources near the Oregon-Idaho border. In this study, we use anisotropy of magnetic susceptibility (AMS) to track magma flow in the Monument dike swarm (MDS), the feeder dikes of the Picture Gorge Basalt (PGB). This small formation of the main-phase CRBG eruptions allows us to explore in detail the localized dynamics of a large igneous province feeder system, with implications for the larger CRBG picture. We measured the magnetic fabric of 205 oriented paleomagnetic specimens subsampled from 97 samples collected from 15 dikes of the MDS. Thermal demagnetization and hysteresis loops show that the magnetic minerals are a mixture of single domain and multidomain sized titanomagnetites. At three dikes, the paleodepth of sampling was determined to be shallow (<350 m). Magma flowing through dikes has been shown—in most cases— to acquire an anisotropic magnetic fabric with an AMS ellipsoid minimum axis perpendicular to the wall and maximum axis aligned in the direction of flow. Of 15 dikes, 12 show horizontal flow directions in the plane of the dike. Only one dike displayed imbricated fabrics, showing westward flow away from the Oregon-Idaho border. We conclude that magma flow in the MDS was sub-horizontal from a distal source.

Oregon↗

USGS1993

Earthquake locations determined by the Southern Alaska seismograph network for October 1971 through May 1989

This report describes the instrumentation and evolution of the U.S. Geological Survey’s regional seismograph network in southern Alaska, provides phase and hypocenter data for seismic events from October 1971 through May 1989, reviews the location methods used, and discusses the completeness of the catalog and the accuracy of the computed hypocenters. Included are arrival time data for explosions detonated under the Trans-Alaska Crustal Transect (TACT) in 1984 and 1985. The U.S. Geological Survey (USGS) operated a regional network of seismographs in southern Alaska from 1971 to the mid 1990s. The principal purpose of this network was to record seismic data to be used to precisely locate earthquakes in the seismic zones of southern Alaska, delineate seismically active faults, assess seismic risks, document potential premonitory earthquake phenomena, investigate current tectonic deformation, and study the structure and physical properties of the crust and upper mantle. A task fundamental to all of these goals was the routine cataloging of parameters for earthquakes located within and adjacent to the seismograph network. The initial network of 10 stations, 7 around Cook Inlet and 3 near Valdez, was installed in 1971. In subsequent summers additions or modifications to the network were made. By the fall of 1973, 26 stations extended from western Cook Inlet to eastern Prince William Sound, and 4 stations were located to the east between Cordova and Yakutat. A year later 20 additional stations were installed. Thirteen of these were placed along the eastern Gulf of Alaska with support from the National Oceanic and Atmospheric Administration (NOAA) under the Outer Continental Shelf Environmental Assessment Program to investigate the seismicity of the outer continental shelf, a region of interest for oil exploration. Since then the region covered by the network remained relatively fixed while efforts were made to make the stations more reliable through improved electronic instrumentation and strengthened antenna systems. The majority of the stations installed since 1980 were operated only temporarily (from one to several years) for special studies in various areas within the network. Due to reduced funding, the network was trimmed substantially in the summer of 1985 with the closure of 15 stations, 13 of which were located in and around the Yakataga seismic gap. To further reduce costs, two telephone circuits were dropped and multiple radio relays were installed in their place. This economy reduced the reliability of these telemetry links. In addition, data collection from the areas around Cordova and Yakutat was compromised by the necessity of relying on triggered event recording using PC-based systems (Rogers, 1993) that were not fully developed and which proved to be less reliable than anticipated. The principal means of recording throughout the time period of this catalog was 20-channel oscillographs on 16-mm film (Teledyne Geotech Develocorder, Model RF400 and 4000D). Initially one Develocorder was operated at the USGS Alaskan headquarters in Anchorage, but in 1972 recording was shifted to the National Oceanic and Atmospheric Administration (NOAA) Palmer Observatory (currently the West Coast and Alaska Tsunami Warning Center). The Develocorders were turned off at the end of May 1989, and after that time recording was done in digital format at the Geophysical Institute of the University of Alaska in Fairbanks (GIUA). Thus, this catalog covers the entire period of film recording.

Alaska↗

USGS2006

Rayleigh-wave diffractions due to a void in the layered half space

Void detection is challenging due to the complexity of near-surface materials and the limited resolution of geophysical methods. Although multichannel, high-frequency, surface-wave techniques can provide reliable shear (S)-wave velocities in different geological settings, they are not suitable for detecting voids directly based on anomalies of the S-wave velocity because of limitations on the resolution of S-wave velocity profiles inverted from surface-wave phase velocities. Xia et al. (2006a) derived a Rayleigh-wave diffraction traveltime equation due to a void in the homogeneous half space. Encouraging results of directly detecting a void from Rayleigh-wave diffractions were presented (Xia et al., 2006a). In this paper we used four two-dimensional square voids in the layered half space to demonstrate the feasibility of detecting a void with Rayleigh-wave diffractions. Rayleigh-wave diffractions were recognizable for all these models after removing direct surface waves by F-K filtering. We evaluate the feasibility of applying the Rayleigh-wave diffraction traveltime equation to a void in the layered earth model. The phase velocity of diffracted Rayleigh waves is predominately determined by surrounding materials of a void. The modeling results demonstrate that the Rayleigh-wave diffraction traveltime equation due to a void in the homogeneous half space can be applied to the case of a void in the layered half space. In practice, only two diffraction times are necessary to define the depth to the top of a void and the average velocity of diffracted Rayleigh waves. ?? 2005 Society of Exploration Geophysicists.

SEG Technical Program Expanded Abstracts↗

USGS2003

Athena Mars rover science investigation

Each Mars Exploration Rover carries an integrated suite of scientific instruments and tools called the Athena science payload. The primary objective of the Athena science investigation is to explore two sites on the Martian surface where water may once have been present, and to assess past environmental conditions at those sites and their suitability for life. The remote sensing portion of the payload uses a mast called the Pancam Mast Assembly (PMA) that provides pointing for two instruments: the Panoramic Camera (Pancam), and the Miniature Thermal Emission Spectrometer (Mini-TES). Pancam provides high-resolution, color, stereo imaging, while Mini-TES provides spectral cubes at mid-infrared wavelengths. For in-situ study, a five degree-of-freedom arm called the Instrument Deployment Device (IDD) carries four more tools: a Microscopic Imager (MI) for close-up imaging, an Alpha Particle X-Ray Spectrometer (APXS) for elemental chemistry, a Mo??ssbauer Spectrometer (MB) for the mineralogy of Fe-bearing materials, and a Rock Abrasion Tool (RAT) for removing dusty and weathered surfaces and exposing fresh rock underneath. The payload also includes magnets that allow the instruments to study the composition of magnetic Martian materials. All of the Athena instruments have undergone extensive calibration, both individually and using a set of geologic reference materials that are being measured with all the instruments. Using a MER-like rover and payload in a number of field settings, we have devised operations processes that will enable us to use the MER rovers to formulate and test scientific hypotheses concerning past environmental conditions and habitability at the landing sites. Copyright 2003 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2010

Vegetation index methods for estimating evapotranspiration by remote sensing

Evapotranspiration (ET) is the largest term after precipitation in terrestrial water budgets. Accurate estimates of ET are needed for numerous agricultural and natural resource management tasks and to project changes in hydrological cycles due to potential climate change. We explore recent methods that combine vegetation indices (VI) from satellites with ground measurements of actual ET (ETa) and meteorological data to project ETa over a wide range of biome types and scales of measurement, from local to global estimates. The majority of these use time-series imagery from the Moderate Resolution Imaging Spectrometer on the Terra satellite to project ET over seasons and years. The review explores the theoretical basis for the methods, the types of ancillary data needed, and their accuracy and limitations. Coefficients of determination between modeled ETa and measured ETa are in the range of 0.45–0.95, and root mean square errors are in the range of 10–30% of mean ETa values across biomes, similar to methods that use thermal infrared bands to estimate ETa and within the range of accuracy of the ground measurements by which they are calibrated or validated. The advent of frequent-return satellites such as Terra and planed replacement platforms, and the increasing number of moisture and carbon flux tower sites over the globe, have made these methods feasible. Examples of operational algorithms for ET in agricultural and natural ecosystems are presented. The goal of the review is to enable potential end-users from different disciplines to adapt these methods to new applications that require spatially-distributed ET estimates.

Surveys in Geophysics↗

USGS2023

Impacts of spontaneous waterfall development on bedrock river longitudinal profile morphology

River profiles are shaped by climatic and tectonic history, lithology, and internal feedbacks between flow hydraulics, sediment transport and erosion. In steep channels, waterfalls may self-form without changes in external forcing (i.e., autogenic formation) and erode at rates faster or slower than an equivalent channel without waterfalls. We use a 1-D numerical model to investigate how self-formed waterfalls alter the morphology of bedrock river longitudinal profiles. We modify the standard stream power model to include a slope threshold above which waterfalls spontaneously form and a rate constant allowing waterfalls to erode faster or slower than other fluvial processes. Using this model, we explore how waterfall formation alters both steady state and transient longitudinal profile forms. Our model predicts that fast waterfalls create km-scale reaches in a dynamic equilibrium with channel slope held approximately constant at the threshold slope for waterfall formation, while slow waterfalls can create local channel slope maxima at the location of slow waterfall development. Furthermore, slow waterfall profiles integrate past base level histories, leading to multiple possible profile forms, even at steady-state. Consistency between our model predictions and field observations of waterfall-rich rivers in the Kings and Kaweah drainages in the southern Sierra Nevada, California, supports the hypothesis that waterfall formation can modulate river profiles in nature. Our findings may help identify how bedrock channels are influenced by waterfall erosion and aid in distinguishing between signatures of external and internal perturbations, thereby strengthening our ability to interpret past climate and tectonic changes from river longitudinal profiles.

Journal of Geophysical Research - Earth Surface↗

USGS2008

Mars Exploration Rover Navigation Camera in-flight calibration

The Navigation Camera (Navcam) instruments on the Mars Exploration Rover (MER) spacecraft provide support for both tactical operations as well as scientific observations where color information is not necessary: large-scale morphology, atmospheric monitoring including cloud observations and dust devil movies, and context imaging for both the thermal emission spectrometer and the in situ instruments on the Instrument Deployment Device. The Navcams are a panchromatic stereoscopic imaging system built using identical charge-coupled device (CCD) detectors and nearly identical electronics boards as the other cameras on the MER spacecraft. Previous calibration efforts were primarily focused on providing a detailed geometric calibration in line with the principal function of the Navcams, to provide data for the MER navigation team. This paper provides a detailed description of a new Navcam calibration pipeline developed to provide an absolute radiometric calibration that we estimate to have an absolute accuracy of 10% and a relative precision of 2.5%. Our calibration pipeline includes steps to model and remove the bias offset, the dark current charge that accumulates in both the active and readout regions of the CCD, and the shutter smear. It also corrects pixel-to-pixel responsivity variations using flat-field images, and converts from raw instrument-corrected digital number values per second to units of radiance (W m-2 nm-1 sr-1), or to radiance factor (I/F). We also describe here the initial results of two applications where radiance-calibrated Navcam data provide unique information for surface photometric and atmospheric aerosol studies. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2006

Radiative transfer modeling of dust-coated Pancam calibration target materials: Laboratory visible/near-infrared spectrogoniometry

Laboratory visible/near-infrared multispectral observations of Mars Exploration Rover Pancam calibration target materials coated with different thicknesses of Mars spectral analog dust were acquired under variable illumination geometries using the Bloomsburg University Goniometer. The data were fit with a two-layer radiative transfer model that combines a Hapke formulation for the dust with measured values of the substrate interpolated using a He-Torrance approach. We first determined the single-scattering albedo, phase function, opposition effect width, and amplitude for the dust using the entire data set (six coating thicknesses, three substrates, four wavelengths, and phase angles 3??-117??). The dust exhibited single-scattering albedo values similar to other Mars analog soils and to Mars Pathfinder dust and a dominantly forward scattering behavior whose scattering lobe became narrower at longer wavelengths. Opacity values for each dust thickness corresponded well to those predicted from the particles sizes of the Mars analog dust. We then restricted the number of substrates, dust thicknesses, and incidence angles input to the model. The results suggest that the dust properties are best characterized when using substrates whose reflectances are brighter and darker than those of the deposited dust and data that span a wide range of dust thicknesses. The model also determined the dust photometric properties relatively well despite limitations placed on the range of incidence angles. The model presented here will help determine the photometric properties of dust deposited on the MER rovers and to track the multiple episodes of dust deposition and erosion that have occurred at both landing sites. Copyright 2006 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2008

Surface albedo observations at Gusev Crater and Meridiani Planum, Mars

During the Mars Exploration Rover mission, the Pancam instrument has periodically acquired large-scale panoramic images with its broadband (739??338 nm) filter in order to estimate the Lambert bolometric albedo of the surface along each rover's traverse. In this work we present the full suite of such estimated albedo values measured to date by the Spirit and Opportunity rovers along their traverses in Gusev Crater and Meridiani Planum, respectively. We include estimated bolometric albedo values of individual surface features (e.g., outcrops, dusty plains, aeolian bed forms, wheel tracks, light-toned soils, and crater walls) as well as overall surface averages of the 43 total panoramic albedo data sets acquired to date. We also present comparisons to estimated Lambert albedo values taken from the Mars Global Surveyor Mars Orbiter Camera (MOC) along the rovers' traverses, and to the large-scale bolometric albedos of the sites from the Viking Orbiter Infrared Thermal Mapper (IRTM) and Mars Global Surveyor/Thermal Emission Spectrometer (TES). The ranges of Pancam-derived albedos at Gusev Crater (0.14 to 0.25) and in Meridiani Planum. (0.10 to 0.18) are in good agreement with IRTM, TES, and MOC orbital measurements. These data sets will be a useful tool and benchmark for future investigations of albodo variations with time, including measurements from orbital instruments like the Context Camera and High Resolution Imaging Science Experiment on Mars Reconnaissance Orbiter. Long-term, accurate albedo measurements could also be important for future efforts in climate modeling as well as for studies of active surface processes. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2008

Short-term response of methane fluxes and methanogen activity to water table and soil warming manipulations in an Alaskan peatland

Growing season CH 4 fluxes were monitored over a two year period following the start of ecosystem-scale manipulations of water table position and surface soil temperatures in a moderate rich fen in interior Alaska. The largest CH 4 fluxes occurred in plots that received both flooding (raised water table position) and soil warming, while the lowest fluxes occurred in unwarmed plots in the lowered water table treatment. A combination of treatment and soil hydroclimate variables explained more than 70% of the variation in ln-transformed CH 4 fluxes, with mean daily water table position representing the strongest predictor. We used quantitative PCR of the α -subunit of mcr operon to explore the influence of soil climate manipulations on methanogen abundances. Methanogen abundances were greatest in warmed plots, and showed a positive relationship with mean daily CH 4 fluxes. Our results show that water table manipulations that led to soil inundation (flooding) had a stronger effect on CH 4 fluxes than water table drawdown. Seasonal CH 4 fluxes increased by 80–300% under the combined wetter and warmer soil climate treatments. Thus, while warming is expected to increase CH 4 emissions from Alaskan wetlands, higher water table positions caused by increases in precipitation or disturbances such as permafrost thaw that lead to thermokarst and flooding in wetlands will stimulate CH 4 emissions beyond the effects of soil warming alone. Consequently, we argue that modeling the effects of climate change on Alaskan wetland CH 4 emissions needs to consider the interactive effects of soil warming and water table position on CH 4 production and transport.

Alaska↗

USGS2006

Crater gradation in Gusev crater and Meridiani Planum, Mars

The Mars Exploration Rovers investigated numerous craters in Gusev crater and Meridiani Planum during the first ???400 sols of their missions. Craters vary in size and preservation state but are mostly due to secondary impacts at Gusev and primary impacts at Meridiani. Craters at both locations are modified primarily by eolian erosion and infilling and lack evidence for modification by aqueous processes. Effects of gradation on crater form are dependent on size, local lithology, slopes, and availability of mobile sediments. At Gusev, impacts into basaltic rubble create shallow craters and ejecta composed of resistant rocks. Ejecta initially experience eolian stripping, which becomes weathering-limited as lags develop on ejecta surfaces and sediments are trapped within craters. Subsequent eolian gradation depends on the slow production of fines by weathering and impacts and is accompanied by minor mass wasting. At Meridiani the sulfate-rich bedrock is more susceptible to eolian erosion, and exposed crater rims, walls, and ejecta are eroded, while lower interiors and low-relief surfaces are increasingly infilled and buried by mostly basaltic sediments. Eolian processes outpace early mass wasting, often produce meters of erosion, and mantle some surfaces. Some small craters were likely completely eroded/buried. Craters >100 m in diameter on the Hesperian-aged floor of Gusev are generally more pristine than on the Amazonian-aged Meridiani plains. This conclusion contradicts interpretations from orbital views, which do not readily distinguish crater gradation state at Meridiani and reveal apparently subdued crater forms at Gusev that may suggest more gradation than has occurred. Copyright 2006 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2012

Modeling thermal dynamics of active layer soils and near-surface permafrost using a fully coupled water and heat transport model

Thawing and freezing processes are key components in permafrost dynamics, and these processes play an important role in regulating the hydrological and carbon cycles in the northern high latitudes. In the present study, we apply a well-developed soil thermal model that fully couples heat and water transport, to simulate the thawing and freezing processes at daily time steps across multiple sites that vary with vegetation cover, disturbance history, and climate. The model performance was evaluated by comparing modeled and measured soil temperatures at different depths. We use the model to explore the influence of climate, fire disturbance, and topography (north- and south-facing slopes) on soil thermal dynamics. Modeled soil temperatures agree well with measured values for both boreal forest and tundra ecosystems at the site level. Combustion of organic-soil horizons during wildfire alters the surface energy balance and increases the downward heat flux through the soil profile, resulting in the warming and thawing of near-surface permafrost. A projection of 21st century permafrost dynamics indicates that as the climate warms, active layer thickness will likely increase to more than 3 meters in the boreal forest site and deeper than one meter in the tundra site. Results from this coupled heat-water modeling approach represent faster thaw rates than previously simulated in other studies. We conclude that the discussed soil thermal model is able to well simulate the permafrost dynamics and could be used as a tool to analyze the influence of climate change and wildfire disturbance on permafrost thawing.

Journal of Geophysical Research D: Atmospheres↗

USGS2015

Coevolution of bed surface patchiness and channel morphology: 2. Numerical experiments

In gravel bed rivers, bed topography and the bed surface grain size distribution evolve simultaneously, but it is not clear how feedbacks between topography and grain sorting affect channel morphology. In this, the second of a pair of papers examining interactions between bed topography and bed surface sorting in gravel bed rivers, we use a two-dimensional morphodynamic model to perform numerical experiments designed to explore the coevolution of both free and forced bars and bed surface patches. Model runs were carried out on a computational grid simulating a 200 m long, 2.75 m wide, straight, rectangular channel, with an initially flat bed at a slope of 0.0137. Over five numerical experiments, we varied (a) whether an obstruction was present, (b) whether the sediment was a gravel mixture or a single size, and (c) whether the bed surface grain size feeds back on the hydraulic roughness field. Experiments with channel obstructions developed a train of alternate bars that became stationary and were connected to the obstruction. Freely migrating alternate bars formed in the experiments without channel obstructions. Simulations incorporating roughness feedbacks between the bed surface and flow field produced flatter, broader, and longer bars than simulations using constant roughness or uniform sediment. Our findings suggest that patches are not simply a by-product of bed topography, but they interact with the evolving bed and influence morphologic evolution.

Journal of Geophysical Research F: Earth Surface↗

USGS2015

The emergence of volcanic oceanic islands on a slow-moving plate: The example of Madeira Island, NE Atlantic

The transition from seamount to oceanic island typically involves surtseyan volcanism. However, the geological record at many islands in the NE Atlantic—all located within the slow-moving Nubian plate—does not exhibit evidence for an emergent surtseyan phase but rather an erosive unconformity between the submarine basement and the overlying subaerial shield sequences. This suggests that the transition between seamount and island may frequently occur by a relative fall of sea level through uplift, eustatic changes, or a combination of both, and may not involve summit volcanism. In this study, we explore the consequences for island evolutionary models using Madeira Island (Portugal) as a case study. We have examined the geologic record at Madeira using a combination of detailed fieldwork, biostratigraphy, and 40 Ar/ 39 Ar geochronology in order to document the mode, timing, and duration of edifice emergence above sea level. Our study confirms that Madeira's subaerial shield volcano was built upon the eroded remains of an uplifted seamount, with shallow marine sediments found between the two eruptive sequences and presently located at 320–430 m above sea level. This study reveals that Madeira emerged around 7.0–5.6 Ma essentially through an uplift process and before volcanic activity resumed to form the subaerial shield volcano. Basal intrusions are a likely uplift mechanism, and their emplacement is possibly enhanced by the slow motion of the Nubian plate relative to the source of partial melting. Alternating uplift and subsidence episodes suggest that island edifice growth may be governed by competing dominantly volcanic and dominantly intrusive processes.

Geochemistry, Geophysics, Geosystems↗

USGS2013

Correlation of geothermal springs with sub-surface fault terminations revealed by high-resolution, UAV-acquired magnetic data

There is widespread agreement that geothermal springs in extensional geothermal systems are concentrated at fault tips and in fault interaction zones where porosity and permeability are dynamically maintained (Curewitz and Karson, 1997; Faulds et al., 2010). Making these spatial correlations typically involves geological and geophysical studies in order to map structures and their relationship to springs at the surface. Geophysical studies include gravity and magnetic surveys, which are useful for identifying buried, intra-basin structures, especially in areas where highly magnetic, dense mafic volcanic rocks are interbedded with, and faulted against less magnetic, less dense sedimentary rock. High-resolution magnetic data can also be collected from the air in order to provide continuous coverage. Unmanned aerial systems (UAS) are well-suited for conducting these surveys as they can provide uniform, low-altitude, high-resolution coverage of an area without endangering crew. In addition, they are more easily adaptable to changes in flight plans as data are collected, and improve efficiency. We have developed and tested a new system to collect magnetic data using small-platform UAS. We deployed this new system in Surprise Valley, CA, in September, 2012, on NASA's SIERRA UAS to perform a reconnaissance survey of the entire valley as well as detailed surveys in key transition zones. This survey has enabled us to trace magnetic anomalies seen in ground-based profiles along their length. Most prominent of these is an intra-basin magnetic high that we interpret as a buried, faulted mafic dike that runs a significant length of the valley. Though this feature lacks surface expression, it appears to control the location of geothermal springs. All of the major hot springs on the east side of the valley lie along the edge of the high, and more specifically, at structural transitions where the high undergoes steps, bends, or breaks. The close relationship between the springs and structure terminations revealed by this study is unprecedented. Collecting magnetic data via UAS represents a new capability in geothermal exploration of remote and dangerous areas that significantly enhances our ability to map the subsurface.

California↗