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USGS2020

Simulation of groundwater-level changes from projected groundwater withdrawals in the Truxton basin, northwestern Arizona

A three-dimensional, numerical groundwater flow model of the Hualapai Plateau and Truxton basin was developed to assist water-resource managers in understanding the potential effects of projected groundwater withdrawals on groundwater levels and storage in the basin. The Truxton Basin Hydrologic Model (TBHM) is a transient model that simulates the hydrologic system for the years 1976 through 2139, including hypothetical low-, medium-, and high-groundwater withdrawal scenarios beginning in 2020. The simulated effects of these withdrawal scenarios are presented as groundwater-level changes from the year 2020 to 2070, and from 2020 to 2140. Hydrologic properties in the TBHM are derived from calibration of a steady-state model of the predevelopment (before 1976) groundwater system. The future pumping scenarios are each simulated with three different interpretations of basin depth supported by geophysical data. For each of the resulting nine transient models, a Monte Carlo approach is used to produce a range of possible and probable groundwater-level changes at points throughout the basin given probabilistic ranges of hydrologically reasonable aquifer property values supported by the model calibration results. The ensemble of models that simulate the future pumping scenarios include pumping from the existing well field (three wells) plus additional pumping from a proposed new well. Simulated high future pumping increases progressively to 1,840 acre-feet per year in 2120 and produces a range of drawdowns between 20 and 39 feet (ft) near the pumping center, with a median drawdown of 28 ft. The low future pumping scenario, which increases progressively to 650 acre-ft per year in 2120, produces a range of drawdowns between 5 and 15 ft, with a median drawdown of 10 ft at the same location over the same period of time.

Arizona↗

USGS1989

The significance of sediment transport in arroyo development

Arroyo widening dominates postincisional arroyo development, and the manner of widening is dependent on the grain size of bed material transported by the channel. When bed material is predominantly gravel, subaqueous bars that alternate from one side of the channel to the other form during high flows in initially narrow, often straight, arroyos. These alternate bars grow and become coarse-grained point bars. Moderate and low flows cannot rework these coarse bars, and the channel meanders around them. Arroyo walls opposite the bars are undercut and eroded. With progressive arroyo widening by erosion of cut banks, high-flow channel width increases, and depth decreases, reducing channel competence. Gravel is deposited in midchannel bars, point bars are reworked, and the channel becomes braided. As braiding becomes dominant, both arroyo walls are eroded. This conceptual model of coarse-grained arroyo development is based on observations of arroyo development through time using physical models and interpretation of the channel and arroyo morphology and sedimentology during a short period along the San Simon, San Pedro, and Santa Cruz Rivers in southeast Arizona. When bed material is predominantly sand, the channel pattern within initial arroyos is typically braided, and both arroyo walls are actively eroded. Alternate bars may form within single-thread, high-flow channels, but they are reworked during recessional flows, and the .low-flow channel is again braided. With progressive arroyo widening, fine sand, silt, and clay carried in suspension are deposited across a flood plain within the wide arroyo, causing the channel to meander. This fine-grained arroyo development model is based on observations of arroyo development through time using physical models and interpretation of the channel and arroyo morphology and sedimentology during a short period along the Rio Puerco, New Mexico. Experimental investigations using physical models in which incised channels were monitored through time indicate that the rate of arroyo widening is dependent on the amount of bedload transported through a reach. This is documented by the relations between the rate of arroyo erosion and the observed sediment transport, the channel slope, the channel width and the channel width-to-depth ratio. When a small amount of bed material is being transported, arroyos do not widen whether they are narrow (arroyo width-to-depth ratios between 1.5 and 3.1), intermediate (between 2.5 and 4.8), or wide (greater than 4.9). Arroyo widening resumes when a larger supply of bed material is introduced. Arroyo widening decreases through time because with progressive increases of arroyo width, the frequency with which unstable channels within the arroyo impinge upon arroyo walls decreases. Arroyos become wider in a downstream direction in response to the cumulative effect of upstream sediment production.

Water Supply Paper↗

USGS2025

Foundational uncertainties in terminal Ediacaran chronostratigraphy revealed by high-precision zircon U-Pb geochronology of the Nama Group, Namibia

The Nama Group of southern Namibia and northwestern South Africa hosts the best-dated mixed carbonate-siliciclastic foreland basin succession of the terminal Ediacaran [ca. 551 million years (Ma) ago to <538 Ma] and is key for resolving the chronology of early metazoan evolution. Numerous silicified volcanic tuff interbeds are present, but differing interpretations regarding the fidelity of their ages lead to different regional stratigraphic correlations, especially for the Urusis Formation of the Schwarzrand Subgroup. An expanded record of the Urusis Formation is found in the Swartpunt area of southern Namibia, which has yielded an important metazoan biota. But the succession in this area is preserved as a series of thrusts at the leading edge of the Gariep orogenic belt and zircon U-Pb data show systematic age repetition. We use regional stratigraphic and structural mapping, integrated with carbonate carbon isotope (δ 13 C carb ) chemostratigraphy and high-precision radioisotope U-Pb zircon geochronology from outcrop and recently acquired drill core to develop a temporally calibrated basin-wide depositional model. This integrated dataset either reflects complex zircon reworking, inheritance, or potential analytical biases (Scenario 1) or the presence of a Gariep-related cryptic décollement within the Spitskop Member that has resulted in stratigraphic repetition (Scenario 2). We investigate the evidence for and against both scenarios and consider their implications for stratigraphic and δ 13 C carb correlations between the Swartpunt area and coeval exposures along the Orange River border with South Africa. Given that these issues are in an area that hosts numerous silicified ash beds and extensive exposure, an inability to confidently discount either scenario highlights a level of compounding uncertainty in zircon U-Pb geochronology that must be considered when attempting to build global chronostratigraphic frameworks. Scenario 1 implies that some of the weighted mean ages and Bayesian eruption ages from the Swartpunt area may be >1 Myr older than the depositional age of their respective ash beds when assuming existing stratigraphic correlations. If this scenario is preferred, then a cautious approach would be to consider all weighted mean zircon U-Pb ages from ash beds to reflect maximum depositional ages. Both scenarios support deposition of the Huns Member >540 Ma in the Swartpunt area if the oldest weighted mean age reported here represents a near-depositional age, which has significant implications for the temporal calibration of important terminal Ediacaran ichnofossil assemblages and future cyclostratigraphic studies. Stratigraphic correlations common to both scenarios allow us to temporally calibrate a basin evolution model for the Nama Group. Temporal trends in initial hafnium isotope (εHf) compositions of zircon grains from ash beds throughout the succession may support progressive crustal thickening associated with underplating of the Damara orogenic belt along the northern periphery of the Kalahari craton from ca. 547 Ma to ca. 538 Ma. The compilation of new and published zircon U-Pb ages may also imply that the locus of carbonate platform development migrated from north to south (present co-ordinates), tracking the migration of foredeep subsidence.

Earth-Science Reviews↗

USGS2012

Impacts of climate change on biodiversity, ecosystems, and ecosystem services: technical input to the 2013 National Climate Assessment

Ecosystems, and the biodiversity and services they support, are intrinsically dependent on climate. During the twentieth century, climate change has had documented impacts on ecological systems, and impacts are expected to increase as climate change continues and perhaps even accelerates. This technical input to the National Climate Assessment synthesizes our scientific understanding of the way climate change is affecting biodiversity, ecosystems, ecosystem services, and what strategies might be employed to decrease current and future risks. Building on past assessments of how climate change and other stressors are affecting ecosystems in the United States and around the world, we approach the subject from several different perspectives. First, we review the observed and projected impacts on biodiversity, with a focus on genes, species, and assemblages of species. Next, we examine how climate change is affecting ecosystem structural elements—such as biomass, architecture, and heterogeneity—and functions—specifically, as related to the fluxes of energy and matter. People experience climate change impacts on biodiversity and ecosystems as changes in ecosystem services; people depend on ecosystems for resources that are harvested, their role in regulating the movement of materials and disturbances, and their recreational, cultural, and aesthetic value. Thus, we review newly emerging research to determine how human activities and a changing climate are likely to alter the delivery of these ecosystem services. This technical input also examines two cross-cutting topics. First, we recognize that climate change is happening against the backdrop of a wide range of other environmental and anthropogenic stressors, many of which have caused dramatic ecosystem degradation already. This broader range of stressors interacts with climate change, and complicates our abilities to predict and manage the impacts on biodiversity, ecosystems, and the services they support. The second cross-cutting topic is the rapidly advancing field of climate adaptation, where there has been significant progress in developing the conceptual framework, planning approaches, and strategies for safeguarding biodiversity and other ecological resources. At the same time, ecosystem-based adaptation is becoming more prominent as a way to utilize ecosystem services to help human systems adapt to climate change. In this summary, we present key findings of the technical input, focusing on themes that can be found throughout the report. Thus, this summary takes a more integrated look at the question of how climate change is affecting our ecological resources, the implications for humans, and possible response strategies. This integrated approach better reflects the impacts of climate in the real world, where changes in ecosystem structure or function will alter the viability of different species and the efficacy of ecosystem services. Likewise, adaptation to climate change will simultaneously address a range of conservation goals. Case studies are used to illustrate this complete picture throughout the report; a snapshot of one case study, 2011 Las Conchas, New Mexico Fire , is included in this summary.

Report↗

USGS2002

Digital mapping techniques '02, workshop proceedings : May 19-22, 2002, Salt Lake City, Utah

The Digital Mapping Techniques '02 (DMT'02) workshop was attended by 101 technical experts from 43 agencies, universities, and private companies, including representatives from 25 state geological surveys (see Appendix A). This workshop was similar in nature to the previous five meetings, held in Lawrence, Kansas (Soller, 1997), in Champaign, Illinois (Soller, 1998a), in Madison, Wisconsin (Soller, 1999), in Lexington, Kentucky (Soller, 2000), and in Tuscaloosa, Alabama (Soller, 2001). This year's meeting was hosted by the Utah Geological Survey, from May 19 to 22, 2002, on the University of Utah campus in Salt Lake City. As in the previous meetings, the objective was to foster informal discussion and exchange of technical information. When an attendee adopts or modifies a newly learned technique on the basis of discussions at the workshop, the workshop clearly has met that objective. Evidence of learning and cooperation among participating agencies continued to be a highlight of the DMT workshops (see example in Soller, 1998b, and various papers in this volume). All the DMT workshops have been coordinated by the Association of American State Geologists (AASG) and the U.S. Geological Survey (USGS) Data Capture Working Group, which was formed in August 1996 to support the AASG and the USGS in their effort to build a National Geologic Map Database (see Soller and Berg, this volume, and http://ncgmp.usgs.gov/ngmdbproject/standards/datacapt/ ). The Working Group was formed because increased production efficiencies, standardization, and quality of digital map products were needed for the database--and the State and Federal geological surveys--to provide more high-quality digital maps to the public. At the 2002 meeting, oral and poster presentations and special discussion sessions emphasized (1) methods for creating and publishing map products (here, "publishing" includes Web-based release); (2) techniques for scanning already published maps and managing and delivering them on the Web; (3) continued development of the National Geologic Map Database; and (4) progress toward building a standard geologic map data model. In addition, special presentations were provided on building a statewide GIS council, incorporating geology as a NSDI Framework layer, and resolving the roles of surveyors and GIS professionals.

Open-File Report↗

USGS2026

Advancing outreach effectiveness to improve conservation practice adoption

Agricultural conservation practices are central to achieving Chesapeake Bay watershed restoration goals, yet long-term adoption remains challenging even when practices are technically effective and financial assistance is available. Adoption is not a single decision, but a staged and context-dependent process. Awareness and willingness to commitment, implementation, and persistence, are all important. Progress along this pathway is influenced by interacting factors such as knowledge, attitudes, beliefs, social norms, trust, perceived risk, farm characteristics, and practical constraints. Improving adoption requires outreach strategies that respond to the specific factors limiting progress at each stage rather than relying on a one-size-fits-all approach.

Chesapeake Bay watershed↗

USGS2023

2023 PyLith Hackathon report

The 3rd Pylith Hackathon was held June 12–17, 2023, at the Colorado School of Mines in Golden, Colorado with funding from the Computational Infrastructure for Geodynamics (CIG). The hackathon involved 17 participants working on 5 different projects to implement new features and create new examples for the PyLith crustal deformation modeling software. The projects included (1) spontaneous rupture using fault friction, (2) extending the poroelasticity implementation, (3) developing 2D and 3D examples involving strike-slip faults, (4) integrating PyLith with the cascading adaptive transitional metropolis in parallel (CATMIP) Bayesian inversion framework for use in studies inverting for static fault slip, and (5) adding self-gravitation using the current multiphysics formulation in PyLith. Participants learned how to navigate the PyLith code base, implement point-wise functions for governing equations and bulk and fault rheologies using the finite-element method, extend the code using the modular, object-oriented design, write examples that demonstrate how to use the new features in PyLith simulations, and implement method of manufactured solutions tests and full-scale tests. The PyLith development team benefitted from discussions with the other participants (contributors) about the technical aspects of the various projects as well as general discussions about PyLith design. The in-person format and 6-day duration allowed the groups to make significant progress. Participants appreciated the project-based organization of the hackathon and recommended that future hackathons include online meetings of the various projects before the in-person gathering to self-organize and prepare. Sarah Minson (remote) provided technical advice on the use of the CATMIP Bayesian inversion framework, and this type of participation could be expanded to allow additional technical presentations and advice on various topics in future hackathons.

Report↗

USGS2018

The size, distribution, and mobility of landslides caused by the 2015 Mw7.8 Gorkha earthquake, Nepal

Coseismic landslides pose immediate and prolonged hazards to mountainous communities, and provide a rare opportunity to study the effect of large earthquakes on erosion and sediment budgets. By mapping landslides using high-resolution satellite imagery, we find that the 25 April 2015 M w 7.8 Gorkha earthquake and aftershock sequence produced at least 25,000 landslides throughout the steep Himalayan Mountains in central Nepal. Despite early reports claiming lower than expected landslide activity, our results show that the total number, area, and volume of landslides associated with the Gorkha event are consistent with expectations, when compared to prior landslide-triggering earthquakes around the world. The extent of landsliding mimics the extent of fault rupture along the east-west trace of the Main Himalayan Thrust and increases eastward following the progression of rupture. In this event, maximum modeled Peak Ground Acceleration (PGA) and the steepest topographic slopes of the High Himalaya are not spatially coincident, so it is not surprising that landslide density correlates neither with PGA nor steepest slopes on their own. Instead, we find that the highest landslide density is located at the confluence of steep slopes, high mean annual precipitation, and proximity to the deepest part of the fault rupture from which 0.5–2 Hz seismic energy originated. We suggest that landslide density was determined by a combination of earthquake source characteristics, slope distributions, and the influence of precipitation on rock strength via weathering and changes in vegetation cover. Determining the relative contribution of each factor will require further modeling and better constrained seismic parameters, both of which are likely to be developed in the coming few years as post-event studies evolve. Landslide mobility, in terms of the ratio of runout distance to fall height, is comparable to small volume landslides in other settings, and landslide volume-runout scaling is consistent with compilations of data on larger slope failures. In general, the size ratios of landslide source area to full landslide area are smaller than global averages, and hillslope length seems to largely control runout distance, which we propose reflects a topographic control on landslide mobility in this setting. We find that landslide size dictates runout distance and that more than half of the landslide debris was deposited in direct connection with stream channels. Connectivity, which is defined as the spatial proximity of landslides to fluvial channels, is greatest for larger landslides in the high-relief part of the High Himalaya. Although these failures are less abundant than those at lower elevations, they may have a disproportionate impact on sediment dynamics and cascading hazards, such as landslide reactivation by monsoon rainfall and landslide dams that lead to outburst floods. The overall high fluvial connectivity of coseismic landsliding in the Gorkha event suggests coupling between the earthquake cycle and sediment/geochemical budgets of fluvial systems in the Himalaya.

Geomorphology↗

USGS2011

Plan for living on a restless planet sets NASA's solid Earth agenda

What are the most important challenges facing solid Earth science today and over the next two decades? And what is the best approach for NASA, in partnership with other agencies, to address those challenges? A new report, Living on a Restless Planet, provides a blueprint for answering these questions. The top priority for a new spacecraft mission in the area of solid Earth science over the next 5 years, according to this report, is a satellite dedicated to Interferometric Synthetic Aperture Radar (InSAR). At the request of NASA, the Solid Earth Science Working Group (SESWG) developed a strategy for the highest priority objectives in solid Earth science for the space agency over the next 25 years. The strategy addresses six challenges that are of fundamental scientific importance, have strong implications for society, and are amenable to substantial progress through a concerted series of scientific observations from space.

Eos Science News↗

USGS2022

Stormwater quantity and quality in selected urban watersheds in Hampton Roads, Virginia, 2016–2020

Urbanization can substantially alter sediment and nutrient loadings to streams. Although a growing body of literature has documented these processes, conditions may vary widely by region and physiographic province (PP). Substantial investments are made by localities to meet federal, state, and local water-quality goals and locally relevant monitoring data are needed to appropriately set standards and track progress. In 2016, a long-term stormwater monitoring program was initiated to characterize water-quality and streamflow conditions and compute average annual nutrient- and sediment-loading rates across the three dominant land-use types—commercial (COM), high-density residential, and single-family residential (SFR)—in the Hampton Roads metropolitan region within the Coastal Plain PP in southeastern Virginia. This report summarizes the first five years of data collection to (1) assess patterns in streamflow and water chemistry across the three major land-use types in the region; (2) compute annual sediment and nutrient loads; and (3) compare annual loading rates to those in other urbanized regions. Patterns in watershed hydrology characteristics and conditions were similar to those observed in other urban monitoring studies. Base-flow indices were lower and stream flashiness indices were higher in the study watersheds compared to those in less developed reference watersheds. These patterns reflect a decrease in infiltration and consequent increase in storm runoff as a result of urbanization. Stream flashiness was strongly positively related to degree of impervious land cover and negatively to watershed area. Hydrologic metrics varied across the land-use gradient, reflecting greater and more rapid runoff in the COM watersheds than in SFR watersheds. Event-based analyses conducted exclusively on periods of runoff highlight longer duration events, longer time-to-peak streamflow, and a longer lag between peak precipitation and peak streamflow in SFR watersheds, and higher stormflow yields, runoff ratios, and peak flows in COM watersheds. Event-based metrics varied seasonally because of regional meteorological patterns. Concentrations of total suspended solids (TSS) and total phosphorus (TP) were positively correlated to streamflow, whereas concentrations of total nitrogen (TN) varied little across the hydrologic regime. Phosphorus composition varied spatially and seasonally—the proportion of orthophosphate (PO 4 3- ) was highest in samples collected from stations draining residential land-use types and was elevated in summer and fall. Nitrogen composition varied with hydrologic condition: nitrate plus nitrite (NO 3 - ) dominance during base flow shifted to total organic nitrogen (TON) dominance during periods of runoff. For all three major constituents (TSS, TP, and TN), concentrations were highest in SFR watersheds, whereas yields were greatest in COM watersheds. This seeming contradiction in concentration and yield across land-use types occurred because of spatial differences in streamflow yield. The network average TSS yield in Hampton Roads was lower than that in comparable networks in Fairfax County, Virginia, and Gwinnett County, Georgia, a difference that may reflect dissimilarities in the topographic and soil characteristics of the Coastal Plain versus those in Piedmont PPs, as well as differences in engineered concrete stormwater conveyances versus earthen streams. The average annual TP yield in Hampton Roads was higher than averages reported in comparison studies and was primarily driven by elevated PO 4 3- . Elevated PO 4 3- yields may be related to unique soil and geological features of the Coastal Plain PP that limit phosphorus retention. Total nitrogen yields in the Hampton Roads and Fairfax County networks were similar; however, composition did vary, with greater total organic nitrogen yields in Hampton Roads and greater NO 3 - yields in Fairfax County. Cross-correlation analyses and mass-volume curves were used to assess the timing of sediment and nutrient loadings. The majority of TSS and TP was typically transported during the initial phase of a storm-runoff event, a phenomenon commonly termed the “first flush.” Although TN concentrations typically peaked within an hour of peak streamflow, reflecting the particulate dominance of TN during stormflows, and loadings were greater during the early phase of most storm events, the stricter first-flush criterion was rarely met. This suggests that the most abundant sources of TN in these watersheds are not as directly connected to the stormwater-conveyance system as are TSS and TP.

Virginia↗

USGS2005

Early to middle Jurassic salt in Baltimore Canyon trough

A pervasive, moderately deep (5-6 s two-way traveltime), high-amplitude reflection is traced on multichannel seismic sections over an approximately 7500 km² area of Baltimore Canyon Trough. The layer associated with the reflection is about 25 km wide, about 60 m thick in the center, and thins monotonically laterally, though asymmetrically, at the edges. Geophysical characteristics are compatible with an interpretation of this negative-polarity reflector as a salt lens deposited on the top of a synrift evaporite sequence. However, alternative interpretations of the layer as gas-saturated sediments, an overpressured shale, or a weathered igneous intrusion are also worthy of consideration. Geophysical analyses were made on three wavelet- and true-amplitude processed multichannel seismic dip lines. The lens-shaped layer demarked by the reflection has a velocity of 4.4 km/s; the lens lies within strata having velocities of 5.3 to 5.7 km/s. A trough marking the onset of the lens has an amplitude that is 10 to 20 db greater than reflections from the encasing layers and an apparent reflection coefficient of -0.24. Using amplitude versus offset analysis methods, we determined that observed reflection coefficients, though variable, decrease consistently with respect to increasing offset. Linear inversion yields a low density, about 2.2 g/cc . Integration of one of the true-amplitude-processed lines and one-dimensional modeling of the layer provide data on the impedance contrast and interference patterns that further reinforce the salt lens interpretation. The thin, horizontal salt lens was probably deposited or precipitated during the Jurassic in a shallow, narrow (peripheral) rift basin, as rifting progressed down the North Atlantic margin. Unlike thicker deposits in other areas that deformed and flowed, often into diapir structures, this thin lens has remained relatively undisturbed since deposition.

Baltimore Canyon trough↗

USGS2023

Blue snowflakes in a warming world: Karner blue butterfly climate change vulnerability synthesis and best practices for adaptation

This report—developed at the request of the United States Fish and Wildlife Service-led Karner Blue Butterfly Recovery Team by Recovery Team members and partners—provides a Karner blue butterfly climate change vulnerability synthesis, explores a range of potential responses, and presents best practices for climate change-informed conservation of the species. The three decades since the Karner blue butterfly’s (Lycaeides [Plebejus] melissa samuelis Nabokov) listing as federally endangered in the United States have seen a diverse and dedicated research and management community coalesce around the species’ recovery. This geographically expansive conservation collaboration has broken new ground for threatened and endangered species recovery. Many Karner blue recovery areas are making steady progress towards recovery goals, but some are not. An extremely hot and dry 2012, perhaps aided by adverse longer-term climate trends such as declining snow cover, extirpated the Karner blue from Indiana Dunes National Park and the surrounding Indiana Dunes Karner Blue Butterfly Recovery Unit—the southernmost recovery unit and once host to one of the species’ largest populations—as well as from northwest Ohio. Because of the fundamental challenge that climate change represents to Karner blue butterfly recovery and of the general need for endangered species conservation plans to better address climate change, the United States Fish and Wildlife Service-led Karner Blue Butterfly Recovery Team tasked a subset of the team to: Explore the species’ climate change sensitivity and adaptive capacity, review ongoing and projected climate change across the Karner blue range and associated uncertainties, and develop and suggest best practices concerning long-term adaptation strategies. Consistent with that mandate, this report synthesizes what is known about Karner blue climate change vulnerability and applies current thinking in climate change adaptation to help foster strategic, long-term, climate change-informed Karner blue recovery and conservation. It develops and explores a range of potential climate change-informed butterfly- and habitat-stewardship responses, using the resist-accept-direct (RAD) framework to foster a broad range of approaches, and provides guidance regarding how they may be pursued. The report also provides suggestions for improving the climate change-exposure component of Karner blue vulnerability assessment.

Natural Resource Report↗

USGS1999

The effect of temperature on experimental and natural chemical weathering rates of granitoid rocks

The effects of climatic temperature variations (5-35??C) on chemical weathering are investigated both experimentally using flow-through columns containing fresh and weathered granitoid rocks and for natural granitoid weathering in watersheds based on annual solute discharge. Although experimental Na and Si effluent concentrations are significantly higher in the fresh relative to the weathered granitoids, the proportional increases in concentration with increasing temperature are similar. Si and Na exhibit comparable average apparent activation energies (E(a)) of 56 and 61 kJ/mol, respectively, which are similar to those reported for experimental feldspar dissolution measured over larger temperature ranges. A coupled temperature-precipitation model, using an expanded database for solute discharge fluxes from a global distribution of 86 granitoid watersheds, produces an apparent activation energy for Si (51 kJ/mol), which is also comparable to those derived from the experimental study. This correlation reinforces evidence that temperature does significantly impact natural silicate weathering rates. Effluent K concentrations in the column study are elevated with respect to other cations compared to watershed discharge due to the rapid oxidation/dissolution of biotite. K concentrations are less sensitive to temperature, resulting in a lower average E(a) value (27 kJ/mol) indicative of K loss from lower energy interlayer sites in biotite. At lower temperatures, initial cation release from biotite is significantly faster than cation release from plagioclase. This agrees with reported higher K/Na ratios in cold glacial watersheds relative to warmer temperate environments. Increased release of less radiogenic Sr from plagioclase relative to biotite at increasing temperature produces corresponding decreases in 87Sr/86Sr ratios in the column effluents. A simple mixing calculation using effluent K/Na ratios, Sr concentrations and 87Sr/86Sr ratios for biotite and plagioclase approximates stoichiometric cation ratios from biotite/plagioclase dissolution at warmer temperatures (35??C), but progressively overestimates the relative proportion of biotite with decreasing temperature. Ca, Mg, and Sr concentrations closely correlate, exhibit no consistent trends with temperature, and are controlled by trace amounts of calcite or exchange within weathered biotite. The inability of the watershed model to differentiate a climate signal for such species correlates with the lower temperature dependence observed in the experimental studies.

Geochimica et Cosmochimica Acta↗

USGS1963

Effects of drought in central and south Texas

The effects of drought upon ground-water storage and discharge, and upon streamflow, vary tremendously in the central third of Texas (the area from the Panhandle to the Gulf of Mexico). Extremes are represented by (a) the Llano Estacado, where the drought had negligible effect upon ground-water resources, which are being progressively depleted by pumping for irrigation; and (b) the Balcones fault-zone aquifer west of San Antonio, whose storage and natural discharge declined substantially during the drought, but increased even more rapidly during succeeding years of more abundant precipitation.

Texas↗

USGS2006

Geohydrology and water chemistry of the Alexander Valley, Sonoma County, California

This study of the geohydrology and water chemistry of the Alexander Valley, California, was done to provide an improved scientific basis for addressing emerging water-management issues, including potential increases in water demand and changes in flows in the Russian River. The study tasks included (1) evaluation of existing geohydrological, geophysical, and geochemical data; (2) collection and analysis of new geohydrologic data, including subsurface lithologic data, ground-water levels, and streamflow records; and (3) collection and analysis of new water-chemistry data. The estimated total water use for the Alexander Valley for 1999 was approximately 15,800 acre-feet. About 13,500 acre-feet of this amount was for agricultural use, primarily vineyards, and about 2,300 acre-feet was for municipal/industrial use. Ground water is the main source of water supply for this area. The main sources of ground water in the Alexander Valley are the Quaternary alluvial deposits, the Glen Ellen Formation, and the Sonoma Volcanics. The alluvial units, where sufficiently thick and saturated, comprise the best aquifer in the study area. Average recharge to the Alexander Valley is estimated from a simple, basinwide water budget. On the basis of an estimated annual average of 298,000 acre-feet of precipitation, 160,000 acre-feet of runoff, and 113,000 to 133,000 acre-feet of evapotranspiration, about 5,000 to 25,000 acre-feet per year is available for ground-water recharge. Because this estimate is based on differences between large numbers, there is significant uncertainty in this recharge estimate. Long-term changes in ground-water levels are evident in parts of the study area, but because of the sparse network and lack of data on well construction and lithology, it is uncertain if any significant changes have occurred in the northern part of the study area since 1980. In the southern half of the study area, ground-water levels generally were lower at the end of the 2002 irrigation season than at the end of the 1980 season, which suggests that a greater amount of ground water is being pumped in the southern half of the study area in recent years compared with that pumped in the early 1980s. Water-chemistry data for samples collected from 11 wells during 2002-04 indicate that water quality in the study area generally is acceptable for potable use. Two wells, however, each contained one constituent (241 ?g/L of manganese and 1,350 ?g/L of boron) in excess of the recommended standards for drinking water (50 ?g/L and 1,000 ?g/L, respectively). The chemical composition of water from most of the wells sampled for major ions plot as a mixed cation-bicarbonate, magnesium-bicarbonate, or calcium-bicarbonate type water. The ionic composition of the historical and recent samples from wells in the Alexander Valley is similar to that of the historical surface-water samples collected from the Russian River near Healdsburg. This suggests a similar source of water, particularly for wells that are less than 200 feet total depth and perforated in Quaternary alluvial deposits. Water from deeper, non-alluvial wells may contain slightly higher concentrations of sodium as a result of cation exchange. Water samples collected from several wells over an approximately 30-year period suggest a progressive change in water chemistry over time. Samples from the southern part of the valley show a trend towards higher ionic concentrations and increasing concentrations of particular constituents such as sulfate.

California↗

USGS2026

Improving offshore 3D splay fault geometries and slip histories using seismic data reprocessing and structural modeling

The goal of this project as written in the CRESCENT seed grant proposal was as follows: 1) reprocess selected profiles along strike from 45° to 48°N from the CASIE21 crustal-scale seismic data to obtain higher-resolution and higher-quality imaging of the uppermost 1-2 km of the accretionary wedge; 2) convert high-resolution USGS sparker seismic data from the time to depth domain to constrain near-surface fault geometries; 3) use kinematic modeling in the MOVE software to derive individual fault slip rates and per-event-displacements; and 4) work with the CFM group to create updated 3D models of identified faults based on the new data sources. At this stage, we have begun the reprocessing of the CASIE21 seismic reflection data (Carbotte et al., 2023). The time-migration reprocessing of the CASIE21 dataset has improved imaging of the near-surface structure by incorporating usable frequencies up to ~220 Hz, in contrast to the ~50 Hz maximum usable content in the currently available pre-stack depth migrated (PSDM) profiles (Fig. 1C). An example of the image quality gained through reprocessing is shown in Fig. 1, where the dominant wavelength of each reflector is reduced to ~10 m (Fig. 1B) from ~20 m in the existing PSDM product (Fig. 1A). The reprocessing work is still currently in progress. While the imaging in the shallow section has been much improved, reprocessing below the first multiple is still needed to create a seamless image from the plate boundary to the surface.

Final Report↗

USGS2007

Hydrology and geomorphology of the Snake River in Grand Teton National Park

The influence of significant tributaries that join the Snake River within 10 km of Jackson Lake Dam (JLD) mitigate some impacts resulting from nearly 100 years of flow regulation in Grand Teton National Park. I analyzed measured and estimated unregulated flow data for all segments of the study area by accounting for tributary flows. The magnitude of the 2-yr recurrence flood immediately downstream from JLD decreased 45% since 1958 relative to estimated unregulated flows, whereas that downstream from Buffalo Fork, the largest tributary, decreased 36%. There has been no long-term progressive geomorphic change on the Snake River resulting from dam regulation. I mapped the bankfull channel on four series of aerial photographs taken in 1945, 1969, 1990/1991, and 2002 and analyzed channel change in a geographic information system. Periods of low-magnitude floods (1945 to 1969) resulted in widespread deposition whereas periods of high-magnitude floods (1969 to 1990/1991 and 1990/1991 to 2002) resulted in widespread erosion; channels narrowed and widened by as much as 31%. I mapped three distinct deposits within the Holocene alluvial valley. The lower floodplain covers 3.5% of the mapped area in the form of abandoned channel and inset, channel-margin facies and has inundating recurrence intervals of one to two years. The upper floodplain covers 36% of the mapped area, is composed of abandoned channels and bars, is higher in elevation than the lower floodplain, and is inundated by floods with recurrence intervals greater than 10 years. The lowest Holocene terrace covers 35% of the mapped area and is approximately 1 m higher in elevation than the upper floodplain. Though the lowest terrace has not been inundated or built since 1945, the two floodplain deposits have been developing since before 1945. Flood magnitudes have decreased throughout the study area as a result of regulation, but these decreases are mitigated downstream from tributaries. Dam operations have not resulted in long-term progressive channel change or the development and abandonment of floodplain deposits. However, channel change is now dependant on the frequency of high-magnitude floods, and the frequency with which the two floodplains are inundated has been reduced.

Wyoming↗

USGS2011

Seasonal flux and assemblage composition of planktic foraminifera from the northern Gulf of Mexico, 2008-2010

The U.S. Geological Survey anchored a sediment trap in the northern Gulf of Mexico to collect seasonal time-series data on the flux and assemblage composition of live planktic foraminifers. This report provides an update of the previous time-series data to include results from 2010. Ten species, or varieties, of planktic foraminifers constituted ~90 percent of the assemblage: Globigerinoides ruber (pink and white varieties), Gs. sacculifer, Globigerina calida, Globigerinella aequilateralis, Globorotalia menardii group, Gt. truncatulinoides, Pulleniatina spp., Orbulina universa, and Neogloboquadrina dutertrei. The mean daily flux was 219 tests per square meter per day (m -2 day -1 ), with maximum fluxes of >600 tests m -2 day -1 during late December and minimum fluxes of <40 tests m-2 day-1 during late August. Globorotalia truncatulinoides showed a clear preference for the winter, consistent with data from 2008 and 2009. Globigerinoides ruber (white variety) flux data for 2010 (average 29 tests m -2 day -1 ) showed a steady increase of about a factor of 3 since 2009 (average 11 tests m -2 day -1 ), and an almost 10-fold increase from the 2008 flux (average 3 tests m-2 day-1). The progressive increase in flux resulted in a relatively large increase in percent abundance of total assemblage from 2008 (1.5 percent) to 2010 (12.4 percent). In addition, though Gs. ruber (white) percent abundance increased from 4.9 percent in 2009 to over 12 percent in 2010, it continued to occur in lower abundance than the 20-30 percent indicated by dead-assemblage records from nearby sediments.

Open-File Report↗