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USGS2009

Is the track of the Yellowstone hotspot driven by a deep mantle plume? - Review of volcanism, faulting, and uplift in light of new data

Geophysical imaging of a tilted mantle plume extending at least 500 km beneath the Yellowstone caldera provides compelling support for a plume origin of the entire Yellowstone hotspot track back to its inception at 17 Ma with eruptions of flood basalts and rhyolite. The widespread volcanism, combined with a large volume of buoyant asthenosphere, supports a plume head as an initial phase. Estimates of the diameter of the plume head suggest it completely spanned the upper mantle and was fed from sources beneath the transition zone, We consider a mantle–plume depth to at least 1,000 km to best explain the large scale of features associated with the hotspot track. The Columbia River–Steens flood basalts form a northward-migrating succession consistent with the outward spreading of a plume head beneath the lithosphere. The northern part of the inferred plume head spread (pancaked) upward beneath Mesozoic oceanic crust to produce flood basalts, whereas basalt melt from the southern part intercepted and melted Paleozoic and older crust to produce rhyolite from 17 to 14 Ma. The plume head overlapped the craton margin as defined by strontium isotopes; westward motion of the North American plate has likely “scraped off” the head from the plume tail. Flood basalt chemistries are explained by delamination of the lithosphere where the plume head intersected this cratonic margin. Before reaching the lithosphere, the rising plume head apparently intercepted the east-dipping Juan de Fuca slab and was deflected ~ 250 km to the west; the plume head eventually broke through the slab, leaving an abruptly truncated slab. Westward deflection of the plume head can explain the anomalously rapid hotspot movement of 62 km/m.y. from 17 to 10 Ma, compared to the rate of ~ 25 km/m.y. from 10 to 2 Ma. A plume head-to-tail transition occurred in the 14-to-10-Ma interval in the central Snake River Plain and was characterized by frequent (every 200–300 ka for about 2 m.y. from 12.7 to 10.5 Ma) “large volume (> 7000 km 3 )”, and high temperature rhyolitic eruptions (> 1000 °C) along a ~ 200–km-wide east–west band. The broad transition area required a heat source of comparable area. Differing characteristics of the volcanic fields here may in part be due to variations in crustal composition but also may reflect development in differing parts of an evolving plume where the older fields may reflect the eruption from several volcanic centers located above very large and extensive rhyolitic magma chamber(s) over the detached plume head while the younger fields may signal the arrival of the plume tail intercepting and melting the lithosphere and generating a more focused rhyolitic magma chamber. The three youngest volcanic fields of the hotspot track started with large ignimbrite eruptions at 10.21, 6.62, and 2.05 Ma. They indicate hotspot migration N55° E at ~ 25 km/m.y. compatible in direction and velocity with the North American Plate motion. The Yellowstone Crescent of High Terrain (YCHT) flares outward ahead of the volcanic progression in a pattern similar to a bow-wave, and thus favors a sub-lithospheric driver. Estimates of YCHT-uplift rates are between 0.1 and 0.4 mm/yr. Drainage divides have migrated northeastward with the hotspot. The Continental Divide and a radial drainage pattern now centers on the hotspot. The largest geoid anomaly in the conterminous U.S. is also centered on Yellowstone and, consistent with uplift above a mantle plume. Bands of late Cenozoic faulting extend south and west from Yellowstone. These bands are subdivided into belts based both on recency of offset and range-front height. Fault history within these belts suggests the following pattern: Belt I — starting activity but little accumulated offset; Belt II — peak activity with high total offset and activity younger than 14 ka; Belt III — waning activity with large offset and activity younger than 140 ka; and Belt IV — apparently dead on substantial range fronts (south side of the eastern Snake River Plain only). These belts of fault activity have migrated northeast in tandem with the adjacent hotspot volcanism. On the southern arm of the YCHT, fault activity occurs on the inner, western slope consistent with driving by gravitational potential energy, whereas faulting has not started on the eastern, outer, more compressional slope. Range fronts increase in height and steepness northeastward along the southern-fault band. Both the belts of faulting and the YCHT are asymmetrical across the volcanic hotspot track, flaring out 1.6 times more on the south than the north side. This and the southeast tilt of the Yellowstone plume may reflect southeast flow of the upper mantle.

Wyoming↗

USGS2010

Porphyry copper deposit model

This report contains a revised descriptive model of porphyry copper deposits (PCDs), the world's largest source (about 60 percent) and resource (about 65 percent) of copper and a major source of molybdenum, gold and silver. Despite relatively low grades (average 0.44 percent copper in 2008), PCDs have significant economic and societal impacts due to their large size (commonly hundreds of millions to billions of metric tons), long mine lives (decades), and high production rates (billions of kilograms of copper per year). The revised model describes the geotectonic setting of PCDs, and provides extensive regional- to deposit-scale descriptions and illustrations of geological, geochemical, geophysical, and geoenvironmental characteristics. Current genetic theories are reviewed and evaluated, knowledge gaps are identified, and a variety of exploration and assessment guides are presented. A summary is included for users seeking overviews of specific topics.

Scientific Investigations Report↗

USGS2015

Sediment-hosted stratabound copper deposit model

This report contains a descriptive model of sediment-hosted stratabound copper (SSC) deposits that supersedes the model of Cox and others (2003). This model is for use in assessments of mineral resource potential. SSC deposits are the second most important sources of copper in the world behind porphyry copper deposits. Around 20 percent of the copper in the world is produced from this class of deposits. They are also the most important sources of cobalt in the world, and they are fourth among classes of ore deposits in production of silver. SSC deposits are the basis of the economies of three countries: Democratic Republic of Congo, Poland, and Zambia. This report provides a description of the key features of SSC deposits; it identifies their tectonic-sedimentary environments; it illustrates geochemical, geophysical, and geoenvironmental characteristics of SSC deposits; it reviews and evaluates hypotheses on how these deposits formed; it presents exploration and assessment guides; and it lists some gaps in our knowledge about the SSC deposits. A summary follows that provides overviews of many subjects concerning SSC deposits.

Scientific Investigations Report↗

USGS2013

Summary of 2012 reconnaissance field studies related to the petroleum geology of the Nenana Basin, interior Alaska

The Alaska Division of Geological & Geophysical Surveys (DGGS) recently initiated a multi-year review of the hydrocarbon potential of frontier sedimentary basins in Alaska (Swenson and others, 2012). In collaboration with the Alaska Division of Oil & Gas and the U.S. Geological Survey we conducted reconnaissance field studies in two basins with recognized natural gas potential—the Susitna basin and the Nenana basin (LePain and others, 2012). This paper summarizes our initial work on the Nenana basin; a brief summary of our work in the Susitna basin can be found in Gillis and others (in press). During early May 2012, we conducted ten days of helicopter-supported fieldwork and reconnaissance sampling along the northern Alaska Range foothills and Yukon–Tanana upland near Fairbanks (fig. 1). The goal of this work was to improve our understanding of the geologic development of the Nenana basin and to collect a suite of samples to better evaluate hydrocarbon potential. Most laboratory analyses have not yet been completed, so this preliminary report serves as a summary of field data and sets the framework for future, more comprehensive analysis to be presented in later publications.

Alaska↗

USGS2011

Book review: Rogue waves in the ocean

Rogue Waves in the Ocean (2009) is a follow-on text to Extreme Ocean Waves (2008) edited by Pelinovsky and Kharif, both published by Springer. Unlike the earlier text, which is a compilation of papers on a variety of extreme waves that was the subject of a scientific conference in 2007, Rogues Waves in the Ocean is written, rather than edited, by Kharif, Pelinovsky, and Slunyaev and is focused on rogue waves in particular. The book consists of six chapters covering 216 pages. As the subject matter of each chapter is distinct, references appear at the end of each chapter rather than at the end of the book. The preface shows how each of the chapters relates to the larger study of rogue waves. The result is a book with a nice mix of eyewitness observations, physical theory, and statistics. Review info: Rogue Waves in the Ocean. Advances in Geophysical and Environmental Mechanics and Mathematics. B y Christian Kharif, Efim Pelinovsky and Alexey Slunyaev, 2009. ISBN: 978-3540884187, xiii, 216 pp.

Pure and Applied Geophysics↗

USGS2023

Geophysical logging For hydrogeology

Geophysical logging is the measurement and analysis of electrical, acoustic, nuclear, and other physical properties in a borehole using wireline or direct push technology. Geophysical logging is one of the primary methods of collecting subsurface information for hydrogeologic investigations. Groundwater scientists and engineers should have a basic understanding of borehole geophysics and how it is applied in the characterization of aquifer systems. In this book, the different types of geophysical logs and equipment used in hydrogeologic investigations are reviewed. Applications and analysis methods are illustrated by specific examples in both unconsolidated deposits and bedrock settings. Key references for further exploration of the methods and applications are provided. Hands-on exercises are included for students to develop and practice log-analysis skills.

Book↗

USGS2008

Inventory and review of existing PRISM hydrogeologic data for the Islamic Republic of Mauritania, Africa

The USGS entered into an agreement with the Mauritania Ministry of Mines and Industry to inventory and review the quality of information collected as part of the Project for Strengthening of the Institutions in the Mining Sector (PRISM). Whereas the PRISM program collected geophysical, geochemical, geological, satellite, and hydrogeologic information, this report focuses on an inventory and review of available hydrogeologic data provided to the USGS in multiple folders, files, and formats. Most of the information pertained to the hydrogeologic setting and the water budget of evaporation, evapotranspiration, and precipitation in the Choum-Zouerate area in northwestern Mauritania, and the country of Mauritania itself. Other information about the quantity and quality of groundwater was found in the relational Access database. In its present form, the limited hydrogeologic information was not amenable to conducting water balance, geostatistical, and localized numerical modeling studies in support of mineral exploration and development. Suggestions are provided to remedy many of the data's shortcomings, such as performing quality assurance on all SIPPE2 data tables and sending questionnaires to appropriate agencies, mining and other companies to populate the database with additional meteorology, hydrology, and groundwater data.

Open-File Report↗

USGS1968

Feasibility study for an airborne geophysical survey of the Republic of Liberia

A feasibility study for an airborne geophysical survey of the Republic of Liberia indicates that airborne magnetometer and airborne scintillation detector surveys would be useful 1) in providing support for the current geologic mapping program, 2) as a guide in locating concentrations of economic minerals, and 3) delimiting the extent of known mineral deposits. Preliminary study of earlier airborne magnetometer surveys covering several iron ore localities shows that future geophysical surveys should be flown at a slightly closer flight-line spacing, and that the iron ore localities are characterized by anomalies interpreted as being produced by rocks having a strong anomalous remanent magnetization. In areas of the United States and Canada underlain by crystalline rock types similar to those found in Liberia, airborne geophysical surveys have been successful in locating additional buried economic mineral deposits, in extending known economic mineral deposits, and in contributing useful information to geologic mapping programs, especially in areas overlain by thick glacial deposits or by weathered rock. Some problems regarding the availability of accurate base maps for Liberia, combined with the inherent complex relationships that exist between a rock's geological properties and its magnetization, are briefly reviewed. The importance of obtaining a meaningful geologic interpretation of the geophysical data and coordinating the geophysical survey with the geological mapping program is stressed. Specifications and tolerances for the proposed airborne magnetometer and scintillometer survey of the Republic of Liberia are outlined.

Open-File Report↗

USGS2014

Dynamics of the Yellowstone hydrothermal system

The Yellowstone Plateau Volcanic Field is characterized by extensive seismicity, episodes of uplift and subsidence, and a hydrothermal system that comprises more than 10,000 thermal features, including geysers, fumaroles, mud pots, thermal springs, and hydrothermal explosion craters. The diverse chemical and isotopic compositions of waters and gases derive from mantle, crustal, and meteoric sources and extensive water-gas-rock interaction at variable pressures and temperatures. The thermal features are host to all domains of life that utilize diverse inorganic sources of energy for metabolism. The unique and exceptional features of the hydrothermal system have attracted numerous researchers to Yellowstone beginning with the Washburn and Hayden expeditions in the 1870s. Since a seminal review published a quarter of a century ago, research in many fields has greatly advanced our understanding of the many coupled processes operating in and on the hydrothermal system. Specific advances include more refined geophysical images of the magmatic system, better constraints on the time scale of magmatic processes, characterization of fluid sources and water-rock interactions, quantitative estimates of heat and magmatic volatile fluxes, discovering and quantifying the role of thermophile microorganisms in the geochemical cycle, defining the chronology of hydrothermal explosions and their relation to glacial cycles, defining possible links between hydrothermal activity, deformation, and seismicity; quantifying geyser dynamics; and the discovery of extensive hydrothermal activity in Yellowstone Lake. Discussion of these many advances forms the basis of this review.

Idaho, Montana, Wyoming↗

USGS2011

Magma at depth: A retrospective analysis of the 1975 unrest at Mount Baker, Washington, USA

Mount Baker volcano displayed a short interval of seismically-quiescent thermal unrest in 1975, with high emissions of magmatic gas that slowly waned during the following three decades. The area of snow-free ground in the active crater has not returned to pre-unrest levels, and fumarole gas geochemistry shows a decreasing magmatic signature over that same interval. A relative microgravity survey revealed a substantial gravity increase in the ~30 years since the unrest, while deformation measurements suggest slight deflation of the edifice between 1981-83 and 2006-07. The volcano remains seismically quiet with regard to impulsive volcano-tectonic events, but experiences shallow (<3 km) low-frequency events likely related to glacier activity, as well as deep (>10 km) long-period earthquakes. Reviewing the observations from the 1975 unrest in combination with geophysical and geochemical data collected in the decades that followed, we infer that elevated gas and thermal emissions at Mount Baker in 1975 resulted from magmatic activity beneath the volcano: either the emplacement of magma at mid-crustal levels, or opening of a conduit to a deep existing source of magmatic volatiles. Decadal-timescale, multi-parameter observations were essential to this assessment of magmatic activity.

Mount Baker Volcano↗

USGS1999

Permit application and approval chronology for a small airgun survey offshore southern California, June 1999

Offshore geophysical surveys are subject to increased restrictions resulting from new or revised Federal legislation and increased authority of State agencies that deal with environmental issues. This report reviews the process followed by the U.S. Geological Survey to obtain necessary approvals for a marine geophysical survey conducted in June, 1999, offshore Southern California. Discussions and negotiations between the USGS, National Marine Fisheries Service, the California Coastal Commission, the California State Lands Commission, and various other interested parties during six months prior to the survey are documented. A suggested timeframe that should be followed for obtaining the approvals and permits for future work offshore California is based on the outcome of the permitting process for the 1999 cruise, as well as continuing dialog with representatives of the Federal and State entities involved.

California↗

USGS2014

Source and progression of a submarine landslide and tsunami: The 1964 Great Alaska earthquake at Valdez

Like many subduction zone earthquakes, the deadliest aspects of the 1964 M = 9.2 Alaska earthquake were the tsunamis it caused. The worst of these were generated by local submarine landslides induced by the earthquake. These caused high runups, engulfing several coastal towns in Prince William Sound. In this paper, we study one of these cases in detail, the Port Valdez submarine landslide and tsunami. We combine eyewitness reports, preserved film, and careful posttsunami surveys with new geophysical data to inform numerical models for landslide tsunami generation. We review the series of events as recorded at Valdez old town and then determine the corresponding subsurface events that led to the tsunami. We build digital elevation models of part of the pretsunami and posttsunami fjord‐head delta. Comparing them reveals a ~1500 m long region that receded 150 m to the east, which we interpret as the primary delta landslide source. Multibeam imagery and high‐resolution seismic reflection data identify a ~400 m wide chute with hummocky deposits at its terminus, which may define the primary slide path. Using these elements we run hydrodynamic models of the landslide‐driven tsunamis that match observations of current direction, maximum inundation, and wave height at Valdez old town. We speculate that failure conditions at the delta front may have been influenced by manmade changes in drainage patterns as well as the fast retreat of Valdez and other glaciers during the past century.

Alaska↗

USGS2006

Speculations on continental crustal evolution

The evolution of the continental crust is a topic that has challenged Earth scientists since the earliest hypotheses of crustal evolution were put forth by such luminaries as Hutton, the 18th century Scottish scientist, and later by Stille (Germany), Argand (France), and Dana (United States). Recent geophysical observations provide important constraints on hypotheses of crustal evolution, and the most important of these observations are reviewed in a companion paper [ Mooney and Meissner , 1991], henceforth referred to as Paper 1. In this article we briefly speculate on crustal evolution using both geological and geophysical data as guidelines. For the past 25 years, the basic framework for models of the evolution of the Earth's crust and lithosphere has been plate tectonics. This framework has been particularly successful in explaining the processes that form and modify the oceanic crust but has had somewhat more limited success in its application to the continental crust. Some of the basic tenets of plate tectonics, as applied to the continental crust, are listed below. Continental masses coalesce and disperse as ocean basins open and close in the Wilson cycle.

Eos, Earth and Space Science News↗

USGS2006

Mapping ground water in three dimensions: An analysis of airborne geophysical surveys of the Upper San Pedro River Basin, Cochise County, southeastern Arizona

This report summarizes the results of two airborne geophysical surveys conducted in the upper San Pedro Valley of southeastern Arizona in 1997 and 1999. The combined surveys cover about 1,000 square kilometers and extend from the Huachuca Mountains on the west to the Mule Mountains and Tombstone Hills on the east and from north of the Babocomari River to near the Mexican border on the south. The surveys included the acquisition of high-resolution magnetic data, which were used to map depth to the crystalline basement rocks underlying the sediments filling the basin. The magnetic inversion results show a complex basement morphology, with sediment thickness in the center of the valley ranging from ~237 meters beneath the city of Sierra Vista to ~1,500 meters beneath Huachuca City and the Palominas area near the Mexican border. The surveys also included acquisition of 60-channel time-domain electromagnetic (EM) data. Extensive quality analyses of these data, including inversion to conductivity vs. depth (conductivity-depth-transform or CDT) profiles and comparisons with electrical well logs, show that the electrical conductor mapped represents the subsurface water-bearing sediments throughout most of the basin. In a few places (notably the mouth of Huachuca Canyon), the reported water table lies above where the electrical conductor places it. These exceptions appear to be due to a combination of outdated water-table information, significant horizontal displacement between the wells and the CDT profiles, and a subtle calibration issue with the CDT algorithm apparent only in areas of highly resistive (very dry) overburden. These occasional disparities appear in less than 5 percent of the surveyed area. Observations show, however, that wells drilled in the thick unsaturated zone along the Huachuca Mountain front eventually intersect water, at which point the water rapidly rises high into the unsaturated zone within the wellbore. This rising of water in a wellbore implies some sort of confinement below the thick unsaturated zone, a confinement that is not identified in the available literature. Occasional disparities notwithstanding, maps of the electrical conductor derived from the airborne EM system provide a synoptic view of the presence of water underlying the upper San Pedro Valley, including its three-dimensional distribution. The EM data even show faults previously only inferred from geologic mapping. The magnetic and electromagnetic data together appear to show the thickness of the sediments, the water in the saturated sediments down to a maximum of about 400 meters depth, and even places where the main ground-water body is not in direct contact with the San Pedro River. However, the geophysical data cannot reveal anything directly about hydraulic conductivity or ground-water flow. Estimating these characteristics requires new hydraulic modeling based in part on this report. One concern to reviewers of this report is the effect that clays may have on the electrical conductor mapped with the airborne geophysical system. Although the water in the basin is unusually conductive, averaging 338 microsiemens per centimeter, reasoning cited below suggests that the contribution of clays to the overall conductivity would be relatively small. Basic principles of sedimentary geology suggest that silts and clays should dominate the center of the basin, while sands and gravels would tend to dominate the margins. Although clay content may increase the amplitude of the observed electrical conductors somewhat, it will not affect the depths to the conductor derived from depth inversions. Further, fine-grained sediments generally have higher porosity and tend to lie toward a basin center, a fact in general agreement with the observed geophysical data.

Arizona↗

USGS2026

Understanding the resource potential of natural hydrogen on Earth: Scientific gaps, uncertainties and recommendations

A comprehensive scientific research roadmap is essential to bridge knowledge gaps and deepen the understanding of key geological, geochemical, and geophysical aspects of natural hydrogen (H 2 ) as a potential new energy resource. This paper reviews major scientific uncertainties on natural H 2 , suggesting research priorities, as a guide for defining exploration strategies, techniques, and data interpretation. The uncertainties concern all phases of the natural H 2 cycle, from generation (source rocks) through migration (advection and diffusion) and accumulation (reservoir and cap rocks) to the application and interpretation of subsurface and surface geochemical and geophysical exploration techniques. Understanding H 2 sources and generation rates (the amount of H 2 generated by a given volume of rock over time) is crucial for determining whether a geological H 2 system operates as a short-term dynamic system with rapid H 2 production and release, or as a conventional gas system with long-term accumulations, analogous to petroleum reservoirs. Preliminary estimates for serpentinisation, radiolysis, and organic matter degradation suggest that H 2 generation is not inherently fast, especially for non-hydrothermal continental systems (crystalline basement of shields, ophiolites, peridotite massifs, sedimentary basins), and long-term accumulations, like those of fossil natural gas systems, represent the most likely scenario. The mechanisms of H 2 migration through geological formations require application of fundamental principles of fluid-flow physics, distinguishing advection and diffusion, as well as their forms (from gas-phase, bubble flows to aqueous solutions). Additional studies of H 2 accumulation and retention in subsurface reservoirs could improve understanding of mechanisms of H 2 migration by focusing on the rock fluid-bearing properties and the factors affecting H 2 preservation, such as the presence of cap rocks impermeable to H 2 , pressure conditions, residence times, and microbial or abiotic consumption. Advanced techniques, including reservoir modelling, flow simulations, 3D imaging (micro-CT) of H 2 -bearing rocks, and extraction and analysis of gas occluded in rocks, can provide insights into the stability and potential recoverability of H 2 accumulations. The interpretation of surface exploration techniques, including gas geochemistry, geophysics, and remote sensing, long employed in mineral and energy resource exploration, is now being adapted for natural H 2 studies, but challenges remain in the data interpretation. Distinguishing H 2 seepage due to geological degassing from H 2 produced near the surface by modern microbial processes or artificial sources, such as hammering or drilling for soil-gas sampling, drilling into aquifers, and corrosion in boreholes, is an essential step in exploration. The simple detection of H 2 in soils, even in morphological structures like sub-circular depressions or “fairy circles”, cannot be cursorily interpreted as a signal of natural H 2 seepage from a deep source. A holistic geochemical approach, including isotopic analyses of gases associated with H 2 , is recommended to distinguish among the variety of possible H 2 origins. Observations of H 2 in wells should be interrogated to rule out possible artifacts such as corrosion and drill bit metamorphism. The integration of multiple geophysical methods, including seismic, gravimetric, magnetic, and electro-magnetic surveys, is recommended to mitigate interpretation ambiguities regarding the structure of a subsurface H 2 system (source and reservoir rocks, including fluid and gas storage), due to the non-uniqueness of rock-specific physical properties.

Earth-Science Reviews↗

USGS2010

Volcanic hazards and their mitigation: progress and problems

At the beginning of the twentieth century, volcanology began to emerge as a modern science as a result of increased interest in eruptive phenomena following some of the worst volcanic disasters in recorded history: Krakatau (Indonesia) in 1883 and Mont Pelée (Martinique), Soufrière (St. Vincent), and Santa María (Guatemala) in 1902. Volcanology is again experiencing a period of heightened public awareness and scientific growth in the 1980s, the worst period since 1902 in terms of volcanic disasters and crises. A review of hazards mitigation approaches and techniques indicates that significant advances have been made in hazards assessment, volcano monitoring, and eruption forecasting. For example, the remarkable accuracy of the predictions of dome-building events at Mount St. Helens since June 1980 is unprecedented. Yet a predictive capability for more voluminous and explosive eruptions still has not been achieved. Studies of magma-induced seismicity and ground deformation continue to provide the most systematic and reliable data for early detection of precursors to eruptions and shallow intrusions. In addition, some other geophysical monitoring techniques and geochemical methods have been refined and are being more widely applied and tested. Comparison of the four major volcanic disasters of the 1980s (Mount St. Helens, U.S.A. (1980), El Chichón, Mexico (1982); Galunggung, Indonesia (1982); and Nevado del Ruíz, Colombia (1985) illustrates the importance of predisaster geoscience studies, volcanic hazards assessments, volcano monitoring, contingency planning, and effective communications between scientists and authorities. The death toll (>22,000) from the Ruíz catastrophe probably could have been greatly reduced; the reasons for the tragically ineffective implementation of evacuation measures are still unclear and puzzling in view of the fact that sufficient warnings were given. The most pressing problem in the mitigation of volcanic and associated hazards on a global scale is that most of the world's dangerous volcanoes are in densely populated countries that lack the economic and scientific resources or the political will to adequately study and monitor them. This problem afflicts both developed and developing countries, but it is especially acute for the latter. The greatest advances in volcanic hazards mitigation in the near future are most likely to be achieved by wider application of existing technology to poorly understood and studied volcanoes, rather than by refinements or new discoveries in technology alone.

Reviews of Geophysics↗

USGS1983

Ground-followup studies of the 1977 airborne electromagnetic survey in the Assifar and Mulhal areas, Wadi Bidah district, Kingdom of Saudi Arabia

Parts of four airborne electromagnetic (AEM) anomalies were selected for study in order to determine the cause of high conductivity of Precambrian rocks underlying extensive areas in the southern Wadi Bidah district, Kingdom of Saudi Arabia. In the Assifar area, which contains an ancient mine or prospect having the same name, geophysical data suggest that a mineralized body may lie beneath and immediately south of the ancient workings. Many other conductive zones detected during the course of the geophysical survey are thought to be related to metavolcanic rocks containing carbonaceous materials. Detailed geologic mapping, and possibly diamond core drilling, will be necessary to fully evaluate the area. In the Mulhal No. 2 area, located about 2 km south of the Mulhal ancient mine, geophysical studies suggest that mineralized rocks extend about 500 m along strike beneath outcrops of gossanous material. A brief review of the AEM ground-followup studies in the Wadi Bidah district suggests that most, if not all, of the AEM conductors are carbonaceous rocks. Secondary causes of conductivity are intense faulting and shearing.

Open-File Report↗

USGS2024

Methods for quantifying interactions between groundwater and surface water

Driven by the need for integrated management of groundwater (GW) and surface water (SW), quantification of GW–SW interactions and associated contaminant transport has become increasingly important. This is due to their substantial impact on water quantity and quality. In this review, we provide an overview of the methods developed over the past several decades to investigate GW–SW interactions. These methods include geophysical, hydrometric, and tracer techniques, as well as various modeling approaches. Different methods reveal valuable information on GW–SW interactions at different scales with their respective advantages and limitations. Interpreting data from these techniques can be challenging due to factors like scale effects, heterogeneous hydrogeological conditions, sediment variability, and complex spatiotemporal connections between GW and SW. To facilitate the selection of appropriate methods for specific sites, we discuss the strengths, weaknesses, and challenges of each technique, and we offer perspectives on knowledge gaps in the current science.

Annual Review of Environment and Resources↗