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At least 487 records · Page 27Linked to original sources
USGS2024

Versatile modeling of deformation (VMOD) inversion framework: Application to 20 years of observations at Westdahl Volcano and Fisher Caldera, Alaska, US

We developed an open source, extensible Python-based framework, that we call the Versatile Modeling of Deformation (VMOD), for forward and inverse modeling of crustal deformation sources. VMOD abstracts from specific source model implementations, data types and inversion methods. We implement the most common geodetic source models which can be combined to model and analyze multi-source deformation. VMOD supports Global Navigation Satellite System (GNSS), InSAR, electronic distance measurement, Leveling and tilt data. To infer source characteristics from observations, VMOD implements non-linear least squares and Markov Chain Monte-Carlo Bayesian inversions, including joint inversions using different sources of data. VMOD's structure allows for easy integration of new geodetic models, data types, and inversion strategies. We benchmark the forward models against other published results and the inversion approaches against other implementations. We apply VMOD to analyze deformation at Unimak Island, Alaska, observed with continuous and campaign GNSS, and ascending and descending InSAR time series generated from Sentinel-1 satellite radar acquisitions. These data show an inflation pattern at Westdahl volcano and subsidence at Fisher Caldera. We use VMOD to test a range of source models by jointly inverting the GNSS and InSAR data sets. Our final model simultaneously constrains the parameters of two sources. Our results reveal a depressurizing spheroid under Fisher Caldera ∼4–6 km deep, contracting at a rate of ∼2–3 Mm 3 /yr, and a pressurizing spherical source underneath Westdahl volcano ∼6–8 km deep, inflating at ∼5 Mm 3 /yr. This and past applications of VMOD to volcanic unrest benefit from an extensible framework which supports jointly inversions of data sets for parameters of easily composable multi-source models.

Alaska↗
USGS2011

Investigation of the potential for concealed base-metal mineralization at the Drenchwater Creek Zn-Pb-Ag occurrence, northern Alaska, using geology, reconnaissance geochemistry, and airborne electromagnetic geophysics

In 2005, the U.S. Geological Survey, Bureau of Land Management, and State of Alaska cooperated on an investigation of the mineral potential of a southern part of the National Petroleum Reserve in Alaska, Howard Pass quadrangle, to provide background information for future land-use decisions. The investigation incorporated an airborne electromagnetic (EM) survey covering 1,500 mi 2 (~3,900 km 2 ), including flight lines directly over the Drenchwater Creek sediment-hosted Zn-Pb-Ag occurrence, the largest known base-metal occurrence in the survey area. Samples from the mineralized outcrop and rubblecrop contain metal concentrations that can exceed 11 percent Zn+Pb, with appreciable amounts of Ag. Soil samples with anomalous Pb concentrations are distributed near the sulfide-bearing outcrops and along a >2.5 km zone comprising mudstone, shale, and volcanic rocks of the Kuna Formation. No drilling has taken place at the Drenchwater occurrence, so alternative data sources (for example, geophysics) are especially important in assessing possible indicators of mineralization. Data from the 2005 electromagnetic survey define the geophysical character of the rocks at Drenchwater and, in combination with geological and surface-geochemical data, can aid in assessing the possible shallow (up to about 50 m), subsurface lateral extent of base-metal sulfide accumulations at Drenchwater. A distinct >3-km-long electromagnetic conductive zone (observed in apparent resistivity maps) coincides with, and extends further westward than, mineralized shale outcrops and soils anomalously high in Pb concentrations within the Kuna Formation; this conductive zone may indicate sulfide-rich rock. Models of electrical resistivity with depth, generated from inversion of electromagnetic data, which provide alongflight-line conductivity-depth profiles to between 25 and 50 m below ground surface, show that the shallow subsurface conductive zone occurs in areas of known mineralized outcrops and thins to the east. Broader, more conductive rock along the western ~1 km of the geophysical anomaly does not reach ground surface. These data suggest that the Drenchwater deposit is more extensive than previously thought. The application of inversion modeling also was applied to another smaller geochemical anomaly in the Twistem Creek area. The results are inconclusive, but they suggest that there may be a local conductive zone, possibly due to sulfides.

Professional Paper↗
USGS1987

Solute geochemistry of the Snake River plain regional aquifer system, Idaho and eastern Oregon

Three geochemical methods were used to determine chemical reactions that control solute concentrations in the Snake River Plain regional aquifer system: (1) Calculation of a regional solute balance within the aquifer and of mineralogy in the aquifer framework to identify solute reactions, (2) comparison of thermodynamic mineral saturation indices with plausible solute reactions, and (3) comparison of stable-isotope ratios of the ground water with those in the aquifer framework. The geothermal ground-water system underlying the main aquifer system was examined by calculating thermodynamic mineral saturation indices, stable-isotope ratios of geothermal water, geothermometry, and radiocarbon dating. Water budgets, hydrologic arguments, and isotopic analyses for the eastern Snake River Plain aquifer system demonstrate that most, if not all, water is of local meteoric and not juvenile or formation origin. Solute-balance, isotopic, mineralogic, and thermodynamic arguments suggest that about 20 percent of the solutes are derived from reactions with rocks forming the aquifer framework. Solute reactions indicate that calcite and silica are precipitated in the aquifer. Mineralogic evidence and thermodynamic arguments suggest that olivine, pyroxene, pyrite, and anhydrite are being dissolved and plagioclase is being weathered. Large amounts of sodium and chloride, relative to their concentration in the igneous rock, are being removed from the aquifer. Release of fluids from inclusions in the igneous rocks, and initial flushing of grain boundaries and pores of detrital marine sediments in interbeds are believed to be the source of the sodium chloride. Identification and quantification of reactions controlling solute concentrations in ground water in the eastern plain indicate that the aquifer is not a large mixing vessel that simply stores and transmits water and solutes but is undergoing diagenesis and is both a source and sink for solutes. Evaluation of solute concentrations and stable-isotope ratios of hydrogen, oxygen, carbon, and sulfur along ground-water flowpaths that transect irrigated areas suggests that irrigation water may have altered solute concentrations and isotope ratios in the eastern Snake River Plain aquifer system. The changes, however, have been small, owing to similarity of solute concentrations in applied irrigation water and in native ground water and rapid movement and large dispersivity of the aquifer. Reactions controlling solutes in the western Snake River basin are believed to be similar to those in the eastern basin but, because of different hydrologic conditions, a definitive analysis could not be made. The regional geothermal system that underlies the Snake River Plain contains total dissolved solids similar to those in the overlying Snake River Plain aquifer system but contains higher concentrations of sodium, bicarbonate, silica, fluoride, sulfate, chloride, arsenic, boron, and lithium, and lower concentrations of calcium, magnesium, and hydrogen. These solutes are believed to be derived from reactions similar to those in the Snake River Plain aquifer system, except that ion exchange may be a significant mechanism controlling solute concentrations in the geothermal system. Geothermometry calculations of selected ground-water samples from known geothermal areas throughout the basin suggest that the geothermal system is large in areal extent but has relatively low temperatures. Approximately half of the silica-quartz calculated water temperatures are greater than 90 degrees Celsius. Radiocarbon dating of geothermal water in the Salmon Falls and Bruneau-Grand View areas in the south-central part of the Snake River basin suggests that residence time of the geothermal water is about 17,700 years.

Idaho, Oregon↗
USGS2026

Erupted volume during the 2014–2023 Semisopochnoi unrest and eruption constrained by multi-platform InSAR and volcanic gas observations

Volcano deformation data provide important constraints on magma dynamics during volcanic unrest and eruptions. From these observations, we can estimate subsurface pressure changes and relate them to volume change in the reservoir. However, because magma and rock are compressible, this volume change cannot be directly equated with eruptive volume. When we combine geodetic analyses with gas observations, petrologic constraints, volatile solubility modeling, and magma compressibility equations, however, we can estimate realistic lower and upper bounds of eruptive volume. Leveraging multi‐platform InSAR time series and satellite SO 2 data, we apply these methods to the 2014–2023 unrest and eruption of Semisopochnoi, Alaska. We find that this phreatomagmatic eruption sequence was fed by a spherical magma source at 6.5–7.5 km depth bsl, centered beneath the caldera, ∼5 km offset to the east from the vent. Volatile solubility modeling indicates that ∼50% of the initial dissolved CO 2 has exsolved at depths consistent with the geodetic source depth, increasing the magma compressibility. Combining geodetic model constraints with SO 2 observations, petrologic constraints, solubility models, and magma compressibility findings yields 12–32 Mm 3 as the most‐likely juvenile, dense‐rock equivalent eruptive volume, with a best estimate of 20 Mm 3 . Stress change modeling suggests that the local stress field encouraged conduit formation west of the pre‐eruptive inflation center, and that the 2014 M7.9 Rat Island earthquake, ∼65 km to the west of Semisopochnoi, reduced the compressive stress underneath the volcano, supporting prolonged eruptive activity.

Alaska↗
USGS2022

Indicator mineral analyses of stream-sediment samples using automated mineralogy and mineral chemistry: Applicability to exploration in covered terranes in eastern Alaska, USA

In the past two decades, significant research efforts have been devoted to porphyry copper indicator mineral (PCIM) identification and mineral chemistry to assist exploration. Such studies are important in the Yukon-Tanana upland region of eastern Alaska because well-established geochemical exploration techniques, such as the geochemistry of stream-sediment samples, are less effective in the search for mineral resources owing to cover materials that subdue geochemical signatures. The unglaciated Yukon-Tanana upland region is well-endowed with mineral resources, including porphyry Cu-Mo-Au deposits at Taurus, Bluff, Dennison, and Oreo. Using automated scanning electron microscope (SEM) techniques, numerous PCIMs have been identified in rocks and stream-sediment samples that would likely not have been observed using visual binocular microscope methods. Sulfide minerals such as chalcopyrite, chalcocite, covellite, bornite, molybdenite, and pyrrhotite were identified in rock samples, and more than half of the stream-sediment samples from drainages containing known porphyry mineral occurrences contain chalcopyrite with or without bornite. Many drainages without known occurrences also contain these minerals, which suggests potential for additional occurrences. Svanbergite, an aluminum phosphate sulfate (APS) mineral [SrAl 3 (PO 4 )(SO 4 )(OH) 6 ], was identified in some of the altered or mineralized rock samples from Taurus, and in stream drainages containing porphyry occurrences and may represent the best indicator mineral for Taurus-like porphyry deposits. Apatite chemistry has great potential as a tool for assessing the presence of porphyry mineralization. Grains from rock and stream-sediment samples that contain high Cl (>∼0.4 wt%), Fe (>0.4 wt%), and Mn (>2000 ppm) clearly distinguish apatite from other sources (metamorphic, unmineralized igneous rocks). This study is one of the first to document new streamlined indicator mineral sample collection and processing methods and to combine automated SEM techniques and chemistry of minerals derived from both bedrock and surficial (stream) sediments as they apply to porphyry exploration.

Alaska↗
USGS1988

Solute geochemistry of the Snake River plain regional aquifer system, Idaho and eastern Oregon

Four geochemical approaches were used to determine chemical reactions controlling solute concentrations in the Snake River Plain regional aquifer system: (1) calculation of a solute balance within the aquifer, (2) identification of weathered products in the aquifer frame- work, (3) comparison of thermodynamic mineral saturation indices with plausible solute reactions, and (4) comparison of stable-isotope ratios of the solutes with those in the aquifer framework. Solutes in the geo- thermal groundwater system underlying the main aquifer were examined by calculating thermodynamic mineral saturation indices, stable-isotope ratios, geothermometry, and radiocarbon dating. Water budgets, hydrologic arguments, and isotopic analyses for the eastern Snake River Plain aquifer system demonstrate that most, if not all, water is of local meteoric and not juvenile or formation origin. Thus, the solutes must also originate within the basin. Solute balance, isotopic, mineralogic, and thermodynamic arguments suggest that about 20 per- cent of the solutes leaving the basin are derived from reactions with rocks forming the aquifer framework. Most of the remaining solutes are introduced from tributary drainage basins. Mass-balance calculations, thermodynamic arguments, and petro- graphic observations indicate that calcite and silica are precipitated in the aquifer. Petrographic evidence and thermodynamic arguments sug- gest that olivine, pyroxene, plagioclase, pyrite, and anhydrite are being weathered from the aquifer framework. Large amounts of sodium, chloride, and sulfate, relative to their concentration in the igneous rock, are being removed from the aquifer. Release of fluids from inclusions in the igneous rocks and initial flushing of grain boundaries and pores of detrital marine sediments in interbeds are believed to be a major source of these solutes. Identification and quantification of reactions controlling solute concentrations in ground water in the eastern plain indicate that the aquifer is not a large mixing vessel that simply stores and transmits water and solutes but is undergoing diagenesis and is both a source and a sink for solutes. Evaluation of solute concentrations and stable-isotope ratios of hydrogen, oxygen, carbon, and sulfur along groundwater flowpaths that transect irrigated areas suggests that irrigation water may have altered solute concentrations and isotope ratios in the eastern Snake River Plain aquifer system. The changes, however, have been small because of the similarity of solute concentrations and ratios in applied irrigation water and in native ground water, and because of rapid movement and large dispersivity of the aquifer. Reactions controlling solutes in the western Snake River basin are believed to be similar to those in the eastern basin but, because of dif- ferent hydrologic conditions, a definitive analysis could not be made. The regional geothermal system that underlies the Snake River Plain contains total dissolved solids similar to those in the overlying Snake River Plain aquifer system but contains higher concentrations of sodium, bicarbonate, silica, fluoride, sulfate, chloride, arsenic, boron, and lithium, and lower concentrations of calcium, magnesium, and hydrogen. These solutes are believed to be derived from reactions similar to those in the Snake River Plain aquifer system, except that ion exchange and hydrol- ysis play a role in controlling solute concentrations in the geothermal system. Geothermometry calculations of selected ground-water samples from known geothermal areas throughout the basin suggest that the geother- mal system is large in areal extent but has relatively low temperatures. Approximately half of the silica-quartz calculated water temperatures are greater than 90 °C. Radiocarbon dating of geothermal water in the Salmon Falls and Bruneau-Grand View areas in the south central part of the Snake River basin suggests that residence time of the geother- mal water is about 17,700 years.

Idaho;Oregon↗
USGS2007

Integrated geoscience studies in the Greater Yellowstone Area - Volcanic, tectonic, and hydrothermal processes in the Yellowstone geoecosystem

Yellowstone National Park, rimmed by a crescent of older mountainous terrain, has at its core the Quaternary Yellowstone Plateau, an undulating landscape shaped by forces of volcanism, tectonism, and later glaciation. Its spectacular hydrothermal systems cap this landscape. From 1997 through 2003, the United States Geological Survey Mineral Resources Program conducted a multidisciplinary project of Yellowstone National Park entitled Integrated Geoscience Studies of the Greater Yellowstone Area, building on a 130-year foundation of extensive field studies (including the Hayden survey of 1871, the Hague surveys of the 1880s through 1896, the studies of Iddings, Allen, and Day during the 1920s, and NASA-supported studies starting in the 1970s—now summarized in USGS Professional Paper 729 A through G) in this geologically dynamic terrain. The project applied a broad range of scientific disciplines and state-of-the-art technologies targeted to improve stewardship of the unique natural resources of Yellowstone and enable the National Park Service to effectively manage resources, protect park visitors from geologic hazards, and better educate the public on geologic processes and resources. This project combined a variety of data sets in characterizing the surficial and subsurface chemistry, mineralogy, geology, geophysics, and hydrothermal systems in various parts of the park. The sixteen chapters presented herein in USGS Professional Paper 1717, Integrated Geoscience Studies in the Greater Yellowstone Area—Volcanic, Tectonic, and Hydrothermal Processes in the Yellowstone Geoecosystem , can be divided into four major topical areas: (1) geologic studies, (2) Yellowstone Lake studies, (3) geochemical studies, and (4) geophysical studies. The geologic studies include a paper by Ken Pierce and others on the influence of the Yellowstone hotspot on landscape formation, the ecological effects of the hotspot, and the human experience and human geography of the greater Yellowstone ecosystem as influenced by the Yellowstone hotspot. Another paper by Paul Carrara describes the recent movement of a large landslide block dated by tree-ring analyses in the Tower Falls area. The section under Yellowstone Lake studies begins with a classic paper by J. David Love and others on ancestral Lake Yellowstone. Other papers in this section include results and interpretation of the high-resolution bathymetric, seismic reflection, and submersible studies by Lisa Morgan and others. Ken Pierce and others describe results from their studies of shorelines along Yellowstone Lake and their interpretation of inflation-deflation cycles, tilting, and faulting in the Yellowstone caldera. The influence of sublacustrine hydrothermal vent fluids on the geochemistry of Yellowstone Lake is described by Laurie Balistrieri and others. In Pat Shanks and others’ chapter, hydrothermal reactions, stable-isotope systematics, sinter deposition, and spire formation are related to the geochemistry of sublacustrine hydrothermal deposits in Yellowstone Lake. The geochemical studies section considers park-wide geochemical systems in Yellowstone National Park. In Bob Rye and Alfred Truesdell’s paper, the question of recharge to the deep thermal reservoir underlying the geysers and hot springs of Yellowstone National Park is discussed. Irving Friedman and Dan Norton report on the chloride flux emissions from Yellowstone in their paper questioning whether Yellowstone is losing its steam. Wildlife issues as addressed by examining trace-element and stable-isotope geochemistry are discussed in a chapter by Maurice Chaffee and others. In another chapter by Chaffee and others, natural and anthropogenic anomalies and their potential impact on the environment using geochemistry is reported. Pam Gemery-Hill and others present geochemical data for selected rivers, lake waters, hydrothermal vents, and subaerial geysers for the time interval of 1996–2004. The life cycle of gold deposits near the northeast corner of the park is discussed by Brad Van Gosen. Under the geophysical studies segment, Ray Kokaly and others use AVIRIS (Airborne Visible and Infrared Spectroscopy) data to map vegetation cover and microbial communities in Yellowstone National Park. Eric Livo and others report their results using AVIRIS data on hydrothermally altered rock and hot-spring deposits. In his final paper following a half century of scientific research, Irving Friedman presents data on monitoring changes in geothermal activity at Norris Geyser Basin using satellite telemetry. These papers summarize a near-decade-long effort by the USGS from the late 1990s to mid-2000s. In 2001, the USGS in cooperation with the National Park Service (Yellowstone National Park) and the University of Utah established the Yellowstone Volcano Observatory, the 5th volcano observatory in the United States.

Idaho, Montana, Wyoming↗
USGS2016

Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California

Plate-boundary rifting between transform faults is opening the Imperial Valley of southern California and the rift is rapidly filling with sediment from the Colorado River. Three 65–90 km long seismic refraction profiles across and along the valley, acquired as part of the 2011 Salton Seismic Imaging Project, were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock. Both first arrival travel-time tomography and frequency-domain full-waveform inversion were applied to provide P-wave velocity models down to ∼7 km depth. The valley margins are fault-bounded, beyond which thinner sediment has been deposited on preexisting crystalline rocks. Within the central basin, seismic velocity increases continuously from ∼1.8 km/s sediment at the surface to >6 km/s crystalline rock with no sharp discontinuity. Borehole data show young sediment is progressively metamorphosed into crystalline rock. The seismic velocity gradient with depth decreases approximately at the 4 km/s contour, which coincides with changes in the porosity and density gradient in borehole core samples. This change occurs at ∼3 km depth in most of the valley, but at only ∼1.5 km depth in the Salton Sea geothermal field. We interpret progressive metamorphism caused by high heat flow to be creating new crystalline crust throughout the valley at a rate comparable to the ≥2 km/Myr sedimentation rate. The newly formed crystalline crust extends to at least 7–8 km depth, and it is shallower and faster where heat flow is higher. Most of the active seismicity occurs within this new crust.

California↗
USGS2020

Using conceptual models to relate multiparameter satellite data to subsurface volcanic processes in Latin America

Satellite data have been extensively used to identify volcanic behavior. However, the physical subsurface processes causing any individual manifestation of activity can be ambiguous. We propose a classification scheme for the cause of unrest that simultaneously considers three multiparameter satellite observations. The scheme is based on characteristics of the volcanic system (open, closed, and eruptive) and unrest mechanisms (intrusion, evolution, and withdrawal) occurring at shallow depths in the volcanic system. We applied these models to satellite observations acquired at 47 of the most active volcanoes in Latin America. Of the volcanoes studied, 44 had a robust enough dataset for classification and were clustered into 4 groups and 10 subgroups with common behavioral characteristics. By identifying that these volcanoes can be clustered into a number of groupings significantly less than the number of volcanoes, we have demonstrated that commonalities in behavior patterns exist among diverse volcanic systems. Identifying volcanoes with similar characteristics underpins the use of past observations at one volcano to forecast activity at another and diverges from typical volcanic groupings, which are focused on geologic parameters (i.e., composition, volcano type, and tectonic setting). Based on satellite data alone, we have identified preeruptive intrusion prior to 15 eruptions at 12 different volcanoes, magma evolution prior to 18 eruptions at 13 volcanoes, and magma withdrawal at 3 eruptions and 3 volcanoes. Improvements to the spatial and temporal resolution are needed to make these relations robust. This classification scheme provides a framework for future automated clustering of volcanoes.

Geochemistry, Geophysics, Geosystems↗
USGS2022

Low-density geochemical mapping and the robustness of geochemical patterns

Geochemical mapping of entire continents and, ultimately, the world is still a challenge for applied geochemists. At sample densities traditionally used for geochemical exploration (1 site per 1-25 km2), geochemical mapping of whole continents is logistically extremely demanding and tremendously expensive. The first low-density geochemical surveys (1 site per 200 km2) were carried out during the late 1960s in Africa. Later surveys conducted in various parts of the world had sample densities ranging from 1 site per 300 km2 to 1 site per 18 000 km2. Although these surveys were deemed successful by the investigators in defining variations in background element content on a regional scale, the scientific community was sceptical that low-density geochemical mapping was possible and would provide useful information. The main area of criticism centred around the concern that at such low sample densities the resulting maps would not be robust, i.e. if the same area were resampled and remapped, different geochemical patterns would emerge. Different examples from the USA, Europe, China and Africa demonstrate that low-density geochemical mapping will result in stable and robust geochemical patterns at the continental scale. Such maps are urgently needed for a wide variety of applications. ?? 2008 AAG/ Geological Society of London.

Geochemistry: Exploration, Environment, Analysis↗
USGS2008

Assessing the contribution of wetlands and subsided islands to dissolved organic matter and disinfection byproduct precursors in the Sacramento-San Joaquin River Delta: A geochemical approach

This study assesses how rivers, wetlands, island drains and open water habitats within the Sacramento-San Joaquin River Delta affect dissolved organic matter (DOM) content and composition, and disinfection byproduct (DBP) formation. Eleven sites representative of these habitats were sampled on six dates to encompass seasonal variability. Using a suite of qualitative analyses, including specific DBP formation potential, absorbance, fluorescence, lignin content and composition, C and N stable isotopic compositions, and structural groupings determined using CPMAS (cross polarization, magic angle spinning) 13C NMR, we applied a geochemical fingerprinting approach to characterize the DOM from different Delta habitats, and infer DOM and DBP precursor sources and estimate the relative contribution from different sources. Although river input was the predominant source of dissolved organic carbon (DOC), we observed that 13-49% of the DOC exported from the Delta originated from sources within the Delta, depending on season. Interaction with shallow wetlands and subsided islands significantly increased DOC and DBP precursor concentrations and affected DOM composition, while deep open water habitats had little discernable effect. Shallow wetlands contributed the greatest amounts of DOM and DBP precursors in the spring and summer, in contrast to island drains which appeared to be an important source during winter months. The DOM derived from wetlands and island drains had greater haloacetic acid precursor content relative to incoming river water, while two wetlands contributed DOM with greater propensity to form trihalomethanes. These results are pertinent to restoration of the Delta. Large scale introduction of shallow wetlands, a proposed restoration strategy, could alter existing DOC and DBP precursor concentrations, depending on their hydrologic connection to Delta channels. ?? 2008 Elsevier Ltd.

Organic Geochemistry↗
USGS2025

Applying geological unit distribution and chemical weathering indices to evaluate potential lithological sources of Al, As and Pb to the San Juan River, Four Corners region, USA

In arid to semi-arid landscapes, sporadic monsoonal events, varying widely in scale and distribution, can generate overland flow resulting in streamflow in ephemeral channels. These channels may contain metal-laden sediments that are a by-product of the weathering and erosion of local geological units. To evaluate the potential for local geology to contribute aluminium (Al), arsenic (As) and lead (Pb) to the San Juan River, northwestern New Mexico, USA, the distributions of geological units were delineated for 12 hydrological basins within the greater San Juan River watershed. Concentrations of Al, As and Pb in the predominant geological units were compiled from data in the National Geochemical Database. Chemical indices of weathering (CIW) were calculated for geological units with greater than 5% coverage in the entire San Juan River watershed. Based on CIWs of the major geological units, the Mesaverde Group (CIW = 95.2), Chinle and Dolores Formations ( combined ) (CIW = 93.3), and Mancos Shale ( combined ) (CIW = 82.6) are the most likely units to weather, erode and contribute sediments with elevated concentrations of Al, As and Pb to the San Juan River. The results of this study show the importance of understanding geological sources of sediments because they could be substantial contributors of constituents of concern to water, especially in arid environments where surface water may be the only source of water in the region.

Arizona, Colorado, New Mexico, Utah↗
USGS2014

From headwaters to coast: Influence of human activities on water quality of the Potomac River Estuary

The natural aging process of Chesapeake Bay and its tributary estuaries has been accelerated by human activities around the shoreline and within the watershed, increasing sediment and nutrient loads delivered to the bay. Riverine nutrients cause algal growth in the bay leading to reductions in light penetration with consequent declines in sea grass growth, smothering of bottom-dwelling organisms, and decreases in bottom-water dissolved oxygen as algal blooms decay. Historically, bay waters were filtered by oysters, but declines in oyster populations from overfishing and disease have led to higher concentrations of fine-sediment particles and phytoplankton in the water column. Assessments of water and biological resource quality in Chesapeake Bay and tributaries, such as the Potomac River, show a continual degraded state. In this paper, we pay tribute to Owen Bricker’s comprehensive, holistic scientific perspective using an approach that examines the connection between watershed and estuary. We evaluated nitrogen inputs from Potomac River headwaters, nutrient-related conditions within the estuary, and considered the use of shellfish aquaculture as an in-the-water nutrient management measure. Data from headwaters, nontidal, and estuarine portions of the Potomac River watershed and estuary were analyzed to examine the contribution from different parts of the watershed to total nitrogen loads to the estuary. An eutrophication model was applied to these data to evaluate eutrophication status and changes since the early 1990s and for comparison to regional and national conditions. A farm-scale aquaculture model was applied and results scaled to the estuary to determine the potential for shellfish (oyster) aquaculture to mediate eutrophication impacts. Results showed that (1) the contribution to nitrogen loads from headwater streams is small (about 2 %) of total inputs to the Potomac River Estuary; (2) eutrophic conditions in the Potomac River Estuary have improved in the upper estuary since the early 1990s, but have worsened in the lower estuary. The overall system-wide eutrophication impact is high, despite a decrease in nitrogen loads from the upper basin and declining surface water nitrate nitrogen concentrations over that period; (3) eutrophic conditions in the Potomac River Estuary are representative of Chesapeake Bay region and other US estuaries; moderate to high levels of nutrient-related degradation occur in about 65 % of US estuaries, particularly river-dominated low-flow systems such as the Potomac River Estuary; and (4) shellfish (oyster) aquaculture could remove eutrophication impacts directly from the estuary through harvest but should be considered a complement—not a substitute—for land-based measures. The total nitrogen load could be removed if 40 % of the Potomac River Estuary bottom was in shellfish cultivation; a combination of aquaculture and restoration of oyster reefs may provide larger benefits.

Maryland, Pennsylvania, Virginia, West Virginia↗
USGS2022

Chemical geodynamics insights from a machine learning approach

The radiogenic isotope heterogeneity of oceanic basalts is often assessed using 2D isotope ratio diagrams. But because the underlying data are at least six dimensional ( 87 Sr/ 86 Sr, 143 Nd/ 144 Nd, 176 Hf/ 177 Hf, and 208,207,206 Pb/ 204 Pb), it is important to examine isotopic affinities in multi-dimensional data space. Here, we apply t-distributed stochastic neighbor embedding (t-SNE), a multi-variate statistical data analysis technique, to a recent compilation of radiogenic isotope data of mid ocean ridge (MORB) and ocean island basalts (OIB). The t-SNE results show that the apparent overlap of MORB-OIB data trends in 2-3D isotope ratios diagrams does not exist in multi-dimensional isotope data space, revealing that there is no discrete “component” that is common to most MORB-OIB mantle sources on a global scale. Rather, MORB-OIB sample stochastically distributed small-scale isotopic heterogeneities. Yet, oceanic basalts with the same isotopic affinity, as identified by t-SNE, delineate several globally distributed regional domains. In the regional geodynamic context, the isotopic affinity of MORB and OIB is caused by capturing of actively upwelling mantle by adjacent ridges, and thus melting of mantle with similar origin in on, near, and off-ridge settings. Moreover, within a given isotopic domain, subsidiary upwellings rising from a common deep mantle root often feed OIB volcanism over large surface areas. Overall, the t-SNE results define a fundamentally new basis for relating isotopic variations in oceanic basalts to mantle geodynamics, and may launch a 21st century era of “chemical geodynamics.”

Geochemistry, Geophysics, Geosystems↗
USGS2009

Rupture imaging of the M w 7.9 12 May 2008 Wenchuan earthquake from back projection of teleseismic P waves

[1] The M w 7.9 Wenchuan earthquake of 12 May 2008 was the most destructive Chinese earthquake since the 1976 Tangshan event. Tens of thousands of people were killed, hundreds of thousands were injured, and millions were left homeless. Here we infer the detailed rupture process of the Wenchuan earthquake by back-projecting teleseismic P energy from several arrays of seismometers. This technique has only recently become feasible and is potentially faster than traditional finite-fault inversion of teleseismic body waves; therefore, it may reduce the notification time to emergency response agencies. Using the IRIS DMC, we collected 255 vertical component broadband P waves at 30-95?? from the epicenter. We found that at periods of 5 s and greater, nearly all of these P waves were coherent enough to be used in a global array. We applied a simple down-sampling heuristic to define a global subarray of 70 stations that reduced the asymmetry and sidelobes of the array response function (ARF). We also considered three regional subarrays of seismometers in Alaska, Australia, and Europe that had apertures less than 30?? and P waves that were coherent to periods as short as 1 s. Individual ARFs for these subarrays were skewed toward the subarrays; however, the linear sum of the regional subarray beams at 1 s produced a symmetric ARF, similar to that of the groomed global subarray at 5 s. For both configurations we obtained the same rupture direction, rupture length, and rupture time. We found that the Wenchuan earthquake had three distinct pulses of high beam power at 0, 23, and 57 s after the origin time, with the pulse at 23 s being highest, and that it ruptured unilaterally to the northeast for about 300 km and 110 s, with an average speed of 2.8 km/s. It is possible that similar results can be determined for future large dip-slip earthquakes within 20-30 min of the origin time using relatively sparse global networks of seismometers such as those the USGS uses to locate earthquakes in near-real time. Copyright 2009 by the American Geophysical Union.

Geochemistry, Geophysics, Geosystems↗
USGS1991

Part A: Geochemistry of Soil Samples from 50 Solution-Collapse Features on the Coconino Plateau, Northern Arizona

Soil sampling surveys were conducted during 1984-1986 across 50 solution-collapse features exposed on the Coconino Plateau of northern Arizona in order to determine whether soil geochemistry can be used to distinguish mineralized breccia pipes from unmineralized collapse features. The 50 sampled features represent the variety of collapse features that crop out on plateau surfaces in northwestern Arizonaoodeeplyorooted solution-collapse breccia pipes, near-surface gypsum collapses, and sinkholes. Of the 50 features that were sampled in this study, 3 are confirmed breccia pipes that contain significant uranium and base-metal minerals, I is believed to be a sinkhole with no economic potential, and 4 are stratabound copper deposits whose possible relationship to breccia pipes is yet to be determined. The remaining collapse features are suspected to overlie breccia pipes, although some of these may represent near surface gypsum collapse features. However, no exploratory drilling results or breccia exposures exist to indicate their underlying structure. The low cost and ease of soil sampling suggested that this technique be evaluated for breccia pipe exploration. This report provides the locations and geochemical results for the soil sampling surveys and brief descriptions of the 50 collapse features. The analytical results of almost 2,000 soil samples are provided in tabular hardcopy and dBase III Plus diskcopy format. The analytical data is provided in digital format to allow the reader to choose their own methods for evaluating the effectiveness of soil sampling over known and suspected breccia pipes. A pilot survey conducted over 17 collapse features in 1984 suggested that soil sampling might be useful in distinguishing mineralized breccia pipes from other circular features. Followup detailed surveys in 1985 and 1986 used a radial sampling pattern at each of 50 sites; at least one third of the samples were collected from areas outside of the collapse feature to provide background data. Samples were consistently collected from 3-4 inches depth after the pilot survey showed that metal concentrations were similar in samples from 3-4 inches and 7-8 inches depth. The geochemical analyses of the <80 mesh fractions of the soil samples were performed by the U.S. Geological Survey Analytical Laboratories and Geochemical Services, Inc. The analytical methods applied to these samples by the U.S. Geological Survey laboratories included inductively coupled plasma-atomic emission spectroscopy, X-ray fluorescence spectrometry, neutron activation, atomic absorption, delayed neutron activation, and classical wet chemistry for carbon, fluorine, and sulfur. Geochemical Services, Inc. analyzed the soil samples by inductively coupled plasma emission spectroscopy.

Open-File Report↗
USGS1991

Geochemistry of Soil Samples from 50 Solution-Collapse Features on the Coconino Plateau, Northern Arizona

Soil sampling surveys were conducted during 1984-1986 across 50 solution-collapse features exposed on the Coconino Plateau of northern Arizona in order to determine whether soil geochemistry can be used to distinguish mineralized breccia pipes from unmineralized collapse features. The 50 sampled features represent the variety of collapse features that crop out on plateau surfaces in northwestern Arizonaoodeeplyorooted solution-collapse breccia pipes, near-surface gypsum collapses, and sinkholes. Of the 50 features that were sampled in this study, 3 are confirmed breccia pipes that contain significant uranium and base-metal minerals, I is believed to be a sinkhole with no economic potential, and 4 are stratabound copper deposits whose possible relationship to breccia pipes is yet to be determined. The remaining collapse features are suspected to overlie breccia pipes, although some of these may represent near surface gypsum collapse features. However, no exploratory drilling results or breccia exposures exist to indicate their underlying structure. The low cost and ease of soil sampling suggested that this technique be evaluated for breccia pipe exploration. This report provides the locations and geochemical results for the soil sampling surveys and brief descriptions of the 50 collapse features. The analytical results of almost 2,000 soil samples are provided in tabular hardcopy and dBase III Plus diskcopy format. The analytical data is provided in digital format to allow the reader to choose their own methods for evaluating the effectiveness of soil sampling over known and suspected breccia pipes. A pilot survey conducted over 17 collapse features in 1984 suggested that soil sampling might be useful in distinguishing mineralized breccia pipes from other circular features. Followup detailed surveys in 1985 and 1986 used a radial sampling pattern at each of 50 sites; at least one third of the samples were collected from areas outside of the collapse feature to provide background data. Samples were consistently collected from 3-4 inches depth after the pilot survey showed that metal concentrations were similar in samples from 3-4 inches and 7-8 inches depth. The geochemical analyses of the <80 mesh fractions of the soil samples were performed by the U.S. Geological Survey Analytical Laboratories and Geochemical Services, Inc. The analytical methods applied to these samples by the U.S. Geological Survey laboratories included inductively coupled plasma-atomic emission spectroscopy, X-ray fluorescence spectrometry, neutron activation, atomic absorption, delayed neutron activation, and classical wet chemistry for carbon, fluorine, and sulfur. Geochemical Services, Inc. analyzed the soil samples by inductively coupled plasma emission spectroscopy.

Open-File Report↗
USGS1991

Part B: Geochemistry of Soil Samples from 50 Solution-Collapse Features on the Coconino Plateau, Northern Arizona

Soil sampling surveys were conducted during 1984-1986 across 50 solution-collapse features exposed on the Coconino Plateau of northern Arizona in order to determine whether soil geochemistry can be used to distinguish mineralized breccia pipes from unmineralized collapse features. The 50 sampled features represent the variety of collapse features that crop out on plateau surfaces in northwestern Arizonaoodeeplyorooted solution-collapse breccia pipes, near-surface gypsum collapses, and sinkholes. Of the 50 features that were sampled in this study, 3 are confirmed breccia pipes that contain significant uranium and base-metal minerals, I is believed to be a sinkhole with no economic potential, and 4 are stratabound copper deposits whose possible relationship to breccia pipes is yet to be determined. The remaining collapse features are suspected to overlie breccia pipes, although some of these may represent near surface gypsum collapse features. However, no exploratory drilling results or breccia exposures exist to indicate their underlying structure. The low cost and ease of soil sampling suggested that this technique be evaluated for breccia pipe exploration. This report provides the locations and geochemical results for the soil sampling surveys and brief descriptions of the 50 collapse features. The analytical results of almost 2,000 soil samples are provided in tabular hardcopy and dBase III Plus diskcopy format. The analytical data is provided in digital format to allow the reader to choose their own methods for evaluating the effectiveness of soil sampling over known and suspected breccia pipes. A pilot survey conducted over 17 collapse features in 1984 suggested that soil sampling might be useful in distinguishing mineralized breccia pipes from other circular features. Followup detailed surveys in 1985 and 1986 used a radial sampling pattern at each of 50 sites; at least one third of the samples were collected from areas outside of the collapse feature to provide background data. Samples were consistently collected from 3-4 inches depth after the pilot survey showed that metal concentrations were similar in samples from 3-4 inches and 7-8 inches depth. The geochemical analyses of the <80 mesh fractions of the soil samples were performed by the U.S. Geological Survey Analytical Laboratories and Geochemical Services, Inc. The analytical methods applied to these samples by the U.S. Geological Survey laboratories included inductively coupled plasma-atomic emission spectroscopy, X-ray fluorescence spectrometry, neutron activation, atomic absorption, delayed neutron activation, and classical wet chemistry for carbon, fluorine, and sulfur. Geochemical Services, Inc. analyzed the soil samples by inductively coupled plasma emission spectroscopy.

Open-File Report↗