USGS Science⌕ Search

SEARCH · USGS Science

Results for “Journal of Environmental Management”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

1,661 records · Page 60Linked to original sources
USGS2025

The 3D National Topography Model Call for Action—Part 2: The Next Generation 3D Elevation Program

The three-dimensional (3D) National Topography Model initiative to integrate elevation and hydrography data includes the next generation of hydrography data from the 3D Hydrography Program and the next generation of elevation data from the 3D Elevation Program (3DEP). The first-ever collection of light detection and ranging (lidar) data for the nation (IfSAR for Alaska) provides a critical baseline reference, and the addition of multiple repeat elevation mapping projects as part of the next generation of 3DEP would substantially expand analysis capabilities. As the U.S. Geological Survey (USGS) is closing in on our goal of complete coverage with 3DEP data available or in progress for 98.3 percent of the Nation at the end of fiscal year 2024, the USGS is already transitioning to the next generation of 3DEP. Based on the 3D Nation Study results and input from a broad range of stakeholders, the USGS National Geospatial Program has finalized a new design for 3DEP that provides increased lidar quality levels and refresh rates. The new program is designed with more flexibility to meet changing user needs and take advantage of improvements in mapping technologies. The program will aim to expand the level of interagency coordination for topobathymetric lidar acquisition for inland rivers. The next generation of 3DEP will also aim to emphasize research, including advancing program design, products, and services and engaging and leveraging the evolving 3D industry. Research goals also include becoming more flexible in meeting user needs and taking advantage of evolving remote-sensing technologies. The program also plans to move from focusing on producing standard products to producing a concept of a 3D Nation Ecosystem with a variety of inputs, products, and services.

Circular↗
USGS2026

Forecasting volcanic activity in Germany—A multi-criteria approach

Igneous activity, including shallow intrusions and volcanism, has the potential to disrupt underground critical infrastructure. Notably, future underground infrastructure projects like high-level radioactive waste repositories must be sited in areas of extremely low disruption probability by igneous activity. In Germany, according to the Repository Site Selection Act of 2017 (Standortauswahlgesetz, or StandAG), areas in which Quaternary volcanism is either present or future volcanic activity is expected within the next 1 million years (m.y.) must be excluded from the site selection process. Although the locations of regions with Quaternary volcanism are reasonably well known in Germany, forecasting potential igneous activity at intraplate volcanic fields is challenging, as many processes and their interactions control the spatial distribution of volcanic centers. Here, a semi-quantitative, multi-criteria approach is proposed for a regional evaluation of the relative potential of future igneous activity in Germany. A variety of geoscientific indicators are used, including seismic anomalies in Earth’s mantle, gravity data, tectonic activity, sutures, ground motion, earthquakes, mantle degassing centers, and geochronological data of volcanic rocks. The indicators describe the sequence of processes from potential melt generation in Earth’s mantle, through ascent and accumulation of melt within the lithosphere, to eruption at Earth’s surface. In total, 15 out of 30 proposed geoscientific indicators are selected and quantified using 20 total assigned parameters. Defined threshold values are used to spatially delimit relevant parameter properties to focus on areas with higher potential of future magmatic activity. To consider uncertainties of parameters and their underlying processes, which are usually more spatially extensive below ground, buffer zones are defined in which values of relevance decrease with increasing distance from the initial lateral shape of a parameter. Normalized parameters are combined into an index, whose spatial value distribution is used to differentiate the relative potential of future igneous activity (within the next 1 m.y.). The sensitivity of the results is shown by varying the weighting factors for the relevant parameters in country-wide index maps. Thereby, profiles illustrate the distribution of the resulting index values and respective index fractions of various parameters. Different index maps for the relative potential of future igneous activity are presented and can be used for hazard assessments.

Professional Paper↗
USGS2024

Classification of lakebed geologic substrate in autonomously collected benthic imagery using machine learning

Mapping benthic habitats with bathymetric, acoustic, and spectral data requires georeferenced ground-truth information about habitat types and characteristics. New technologies like autonomous underwater vehicles (AUVs) collect tens of thousands of images per mission making image-based ground truthing particularly attractive. Two types of machine learning (ML) models, random forest (RF) and deep neural network (DNN), were tested to determine whether ML models could serve as an accurate substitute for manual classification of AUV images for substrate type interpretation. RF models were trained to predict substrate class as a function of texture, edge, and intensity metrics (i.e., features) calculated for each image. Models were tested using a manually classified image dataset with 9-, 6-, and 2-class schemes based on the Coastal and Marine Ecological Classification Standard (CMECS). Results suggest that both RF and DNN models achieve comparable accuracies, with the 9-class models being least accurate (~73–78%) and the 2-class models being the most accurate (~95–96%). However, the DNN models were more efficient to train and apply because they did not require feature estimation before training or classification. Integrating ML models into benthic habitat mapping process can improve our ability to efficiently and accurately ground-truth large areas of benthic habitat using AUV or similar images.

Michigan, Wisconsin↗
USGS2025

Hydrogeologic characterization of the Cahuilla Valley and Terwilliger Valley Groundwater Basins, Riverside County, California

The relation between the groundwater and the amount of natural recharge to the Cahuilla Valley and Terwilliger Valley groundwater basins is not well understood. During the 20th century, the reliance on groundwater near Anza, California, used for agricultural, domestic, and municipal reasons has increased, and there is the potential for changes in groundwater availability related to climate change. Several types of existing data were evaluated, and new data were collected for this study, with the goal of characterizing the region’s hydrogeology. The study’s scope included constructing a geologic framework model to show where the groundwater-bearing units are present and their relation to each other, estimating the major components of the groundwater budget, and understanding local short-term and regional long-term groundwater flow and how that has changed since the early 1900s. Two electrical resistivity tomography surveys were done in the Durasno Valley about 2,150 feet apart to identify the thickness of the alluvium, its horizontal extent, and the depth-to-basement along two profiles perpendicular to Cahuilla Creek. The subsurface sediments were mostly horizontally layered and the transitional boundary between the alluvium and basement was thinner and shallower along the upgradient profile where the depth-to-basement was about 70 feet below land surface; the depth-to-basement at the downgradient profile was more than about 140 feet below land surface. The results from the surveys were used to place four monitoring wells at two sites along the survey profiles. Artesian flow from the deepest well at the downgradient site indicated that the decomposed and competent basement likely contributed some groundwater to the overlying alluvium, laterally, from below, or both. A digital three-dimensional geologic framework model was constructed using EarthVision software to represent the subsurface geometry of the alluvium, decomposed basement, and competent basement. Maps and cross sections of the modeled thicknesses of the alluvium and decomposed basement, and the modeled elevation of the top of the competent basement, were made to show the subsurface geometry of vertical faults, selected wells, and the groundwater-bearing units. Because natural recharge is related to the variable cycles of precipitation, estimates are difficult to quantify. Recharge and runoff have extreme interannual variability in the study area; recharge and runoff can be sporadic, and a substantive amount may not occur in some years. Estimates of recharge from a previous study and the regional-scale Basin Characterization Model for California for four different periods ranged from 3,800 acre-feet/year for 1897–1947 to 5,900 acre-feet/year for 1971–2000. Potential recharge from the disposal of domestic septic systems may have been as much as 500 acre-feet in 2020. It was estimated that between about 400 and 2,400 acre-feet/year of groundwater is lost through evapotranspiration by vegetation and evaporation from open water bodies, but the main source of discharge is through pumpage, mainly used for agriculture from the alluvium in the Cahuilla Valley and Terwilliger Valley groundwater basins. The estimated total pumpage for 1991–2021 ranged from about 1,140 acre-feet in 2019 to about 3,450 acre-feet in 1994. When summed, the cumulative amount of estimated pumpage between 1991 and 2021 was about 81,400 acre-feet. The general direction of groundwater flow is from the northeast along the San Jacinto fault zone at the headwaters of Cahuilla and Hamilton Creeks, to the surface-water outlets at the west and southeast parts of the study area. Groundwater-level data from the 1950s and earlier indicate that there was a natural groundwater divide between the Cahuilla Valley and Terwilliger Valley groundwater basins, but the changing magnitude and extent of the groundwater depressions caused by pumping since about 1950 indicate that the location of the natural groundwater boundary between the Cahuilla Valley and Terwilliger Valley groundwater basins has migrated over time. Flow from the upper to the lower parts of the Cahuilla Valley groundwater basin roughly follows the course of Cahuilla Creek through the narrow Durasno Valley where an estimated volume of flow in April 2019 was about 10–150 acre-feet/year. Short-term trends in groundwater levels, particularly in wells where groundwater is shallow and in the basement unit, show how some areas respond quickly to recharge and discharge. Wells located further to the east within the Cahuilla Valley groundwater basin in the alluvium show much less of a response to recharge events; areas of sustained pumpage from the alluvium, primarily for agriculture, show long-term declines in groundwater levels and generally do not show the effects of storm events or recent runoff. Groundwater levels in wells that are farthest from where most of the recharge occurs and where pumping has been the greatest, had some of the largest long-term groundwater-level declines at a rate of about 0.8 foot/year between 1971 and 2021.

California↗
USGS2024

From exploration to production: Understanding the development dynamics of lithium mining projects

Recently, there has been considerable recent controversy whether current and new lithium mines will be able to supply the rapidly growing needs of the electromobility transition. Mineral exploration projects are typically active for many years, and only some become operational mines. From exploration to production, the projects go through several stages of characterisation and evaluation. At each stage, decisions are made by companies and stakeholders to advance, continue or stop the project. This is a complex process, and even projects with very similar geological and technical characteristics may take very different trajectories, depending on external factors such as global market conditions and local regulatory environments. The present study investigates the dynamics of this process for lithium exploration projects. A global database of 397 lithium projects was compiled, covering their progression through major development stages between 2004 and 2022. Ordinal logistic regression was used for the statistical analysis of this data. Different explanatory variables were tested, including economic, geological, technical, and geographic factors, to identify the best predictors for project progress at each development stage. The results suggest an essential role for lithium carbonate prices, and a variable role for other factors at each stage. Critically, the already elapsed lead time and project economics, which are traditionally considered important for the prediction of the start-up of individual mines, do not appear to be relevant in all cases. The results provide important insights into the dynamics of lithium supply and may eventually allow more realistic forecasts to be made for future lithium market dynamics.

Resources Policy↗
USGS2025

A regional model comparison between MODPATH and MT3D of groundwater travel time distributions

Groundwater quality changes in wells and streams lag behind changes to land use due to groundwater travel times. Two contaminant transport methods were compared to assess differences in their simulated travel time distributions (TTDs) to streams and wells in the Wisconsin Central Sands. MODPATH simulates advective groundwater flow with particle tracking, while MT3D simulates age-mass using a finite difference solution without dispersion to allow for direct comparison of the two methods. MODPATH appropriately simulates groundwater TTDs from the water table to surface discharge but is subject to inaccuracies at weak-sink well cells due to the flow-model grid discretization and imprecise location of well discharge within well cells. MT3D better represents weak-sink well cells since it removes mass in proportion to the prescribed pumping rate, although travel time within well cells is neglected. Conversely, MT3D's treatment of surface water boundary cells is not as accurate as MODPATH because mass should be removed from the water table rather than the full cell volume. MT3D simulations of TTDs can also be confounded by the instantaneous vertical distribution of mass introduced throughout recharge cells instead of at the water table, which initiates mass along deeper flow paths. We evaluated 9 MODPATH and 13 MT3D implementations, generating differences in median travel times of up to 18 years. Both methods have strengths and weaknesses, with MT3D better representing weak-sink well cell behavior and MODPATH better representing surficial recharge and discharge. The effect of these characteristics on simulated TTDs, along with ideas for ameliorating method weaknesses, is discussed.

Wisconsin↗
USGS2024

Fairweather transform boundary Oligocene to present orogenesis: Fairweather Range vertical extrusion and rotation of the Yakutat microplate at ca. 3 Ma

Oblique-slip along transform fault boundaries is often partitioned between a strike-slip system and thrust faults that accommodate contraction. However, topography along the Yakutat-North American transform (Fairweather fault), is asymmetric with low-terrain above active thrusts on the western, Yakutat side of the transform and high topography on the continental side with peaks >4500 m (Mount Fairweather: 4671 m) to the west of the Border Ranges fault, limited recorded earthquakes >M4, and no apparent reverse faults to generate the highest terrain. In this study we compile, for the first time, published U-Pb zircon, 40 Ar/ 39 Ar and K-Ar (hornblende, muscovite, and biotite) and U-Th/He and fission-track (zircon and apatite) bedrock ages (109) from 75 samples to investigate the exhumation history of the Fairweather Range region, complemented by a published detrital sample (ZFT and AFT) and 13 new 40 Ar/ 39 Ar (hornblende, biotite, and K-feldspar) ages on 9 bedrock samples from both sides of the Fairweather fault. Additionally, we examined published seismicity and geodetic data of the Fairweather region and assessed if plate paleo-vectors correlate with the cooling history of the Fairweather Range. Cooling age, seismic, and block-motion patterns indicate the Fairweather Range has been vertically extruded between the Fairweather and the Border Ranges faults as a coherent block since ca. 25 Ma. The pre-6 Ma Pacific plate motion (N30°W) aligns with the N33°W strike of the Fairweather Fault whereas a hypothetical pre-6 Ma Yakutat microplate paleo-vector of (N39°W) does not: indicating a post-6 Ma timing for Yakutat microplate counter-clockwise rotation (9°). We infer that rotation and impingement of the Yakutat microplate along the Fairweather fault at ca. 3 Ma led to the development of the Fairweather restraining bend and increased cooling rates. The resultant thickened Fairweather welt and the ∼30 km thick southeast end of the Yakutat microplate compounded double-indenter tectonics into Alaska's southeast convergent corner

Tectonophysics↗
USGS2024

Precariously balanced rocks in northern New York and Vermont, U.S.A.: Ground-motion constraints and implications for fault sources

Precariously balanced rocks (PBRs) and other fragile geologic features have the potential to constrain the maximum intensity of earthquake ground shaking over millennia. Such constraints may be particularly useful in the eastern United States (U.S.), where few earthquake‐source faults are reliably identified, and moderate earthquakes can be felt at great distances due to low seismic attenuation. We describe five PBRs in northern New York and Vermont—a region of elevated seismic hazard associated with historical seismicity. These boulders appear to be among the most fragile PBRs in the region, based on reports from hobbyists. The PBRs are glacial erratics, best evidenced by glacial striations on bedrock pedestals. The pedestals themselves are locally high knobs, often situated on regionally high topography; this setting limits soil development and indicates that any outwash deposits were likely ephemeral. As a result, PBR ages can be reliably established by the retreat of the last continental ice sheet, ∼15–13 ka. To quantify the fragility of the PBRs, we surveyed them with ground‐based light detection and ranging and calculated geometric parameters from the point clouds, field observations, and seismic responses. Preliminary validation of the 2023 time‐independent U.S. National Seismic Hazard Model (NSHM) shows that the existence of PBRs is generally consistent with the median site‐specific hazard curves. Only the Blue Ridge Road site suggests a modest reduction in hazard. To visualize the ensemble of data, we mapped the minimum permissible distance to potential source faults around each PBR site as a function of source magnitude by using the ground‐motion models from the 2023 NSHM. Viewed in this manner, our data are consistent with potential M ∼6.5 earthquake‐source faults in many parts of the Lake Champlain Valley and northern Adirondack Mountains. Our work illustrates a potential pathway for better constraining earthquake‐source faults in regions of cryptic faults.

Bulletin of the Seismological Society of America↗
USGS2025

Measurement of in situ-produced cosmogenic nuclides in fine-grained quartz from shale

In situ -produced 10 Be in quartz is widely used to constrain exposure ages and denudation rates, traditionally measured in sand-sized grains. Here we report a new method for isolating fine-grained quartz from shale and demonstrate its reliability for grain sizes down to single microns. Sequential dissolution tests and analyses of grain size separates show that meteoric 10 Be is eliminated and that recoil losses during cosmogenic nuclide production are balanced by implantation from other mineral grains. High-temperature combustion leads to diffusion of meteoric 10 Be into fine-grained quartz and must be used with caution.

Nuclear Instruments and Methods in Physics Researc↗
USGS2025

Groundwater surveillance of swine pathogens from private wells supplying swine farms in Iowa

Biosecurity practices are essential for maintaining pig health and productivity. Despite these measures, pathogen spread still occurs. Water is one of the largest daily inputs on swine farms by volume and is not routinely tested or disinfected before it is consumed by the animals [1-3], making it a poorly understood biosecurity risk. Groundwater from privately-owned wells is a common water source for swine farms. Pathogens in the landscape, such as bacteria, viruses, and protozoa, can reach groundwater more rapidly through soil macropores, maintaining viability and facilitating transmission of pathogens into aquifers [3-13].

Iowa↗
USGS2026

Using a temporary emigration model to estimate abundance of stream fishes from hybrid removal surveys with and without block nets

Monitoring programs are often faced with a decision to allocate resources into either robust spatiotemporal coverage to estimate a population index (e.g., not true abundance) or confirming closed sampling conditions (e.g., with block nets) for an unbiased population estimate at the cost of spatiotemporal coverage. However, making accurate and precise abundance estimates at robust spatiotemporal scales is possible when combining open and closed sampling designs with integrated modeling techniques. We used simulations and a case study of backpack electrofishing surveys in the Santa Ana River, California to test the efficacy of an integrated abundance model (temporary emigration model, TE) to estimate abundance of fishes using removal sampling methods with a hybrid sampling design (sampling with and without block nets during removal sampling). We found that the TE model performed well under most modeling scenarios (sample size, amount of closure violation, number of samples collected during closure), although at least a few samples with block nets were necessary for all parameters to be estimable. When applied to fish surveys in the Santa Ana River, we found that catch of the fishes fit to the TE model (Santa Ana Sucker, Arroyo Chub, Channel Catfish, Largemouth Bass, Yellow Bullhead) showed little evidence that the closure assumption was violated when block nets were not used. Additionally, we found that the abundance of non-native fishes negatively affected the abundance of the native Santa Ana Sucker, which was also found to adversely affect the native fish’s access to critical habitat consisting of gravel and cobble substrate. Our results indicate that the TE model presents a viable solution to common sampling problems that impact many monitoring programs, where precise and accurate population estimates can be made at large spatiotemporal scales even when most samples violate the closure assumption.

California↗
USGS2025

Multi-scale geophysical imaging of a hydrothermal system in Yellowstone National Park, USA

Little is known about the local plumbing systems that fuel Yellowstone’s famous hot springs, geysers and mud pots. A multi-method, multi-scale geophysical investigation was carried out in the Obsidian Pool Thermal Area (OPTA) to: (i) delineate the lateral extent of the hydrothermal area and associated surface features; (ii) estimate the dimensions of the upflow zone and identify its main controlling structures; (iii) assess fluids circulation pathways from depth to surface. Ground and airborne geophysical data were acquired to connect local and regional scales, from shallow to large depths. Maps of surface electrical resistivity show a strong correlation with hydrothermal features. At in-termediate depths, electrical resistivity permits delineating the upper limit of the upflow zone, while Poisson’s ratio highlights differences in subsurface fluid content. Combining these results with surface observations and topographic information, we speculate that differential mixing of hydrothermal and fresh water could explain the wide diversity of features observed at OPTA. Low electrical resistivity observed at large depths also suggest that a vast upflow zone, controlled by rhyolite flows and conjugate faults, underlies the OPTA. We speculate that hydrothermal fluids rise along fractures and reach the surface in topographic lows to form hydrothermal features. Our results show that synoptic, multi-scale geophysical measurements provide a roadmap for understanding where and how geologic heterogeneity, topography, fluid-gas separation, and the mixing of thermal and meteoric waters conspire to produce the wide variety of Yellowstone’s renowned hydrothermal features.

Wyoming↗
USGS2026

Bottom-up characterization of geologic methane emissions in the San Juan Basin in the southwestern USA

Methane is a potent greenhouse gas that plays an important role in atmospheric chemistry and global warming. The current global methane budget has large uncertainties, and a better understanding of the budget would help to guide strategies for reducing anthropogenic emissions to fight climate change. Natural geologic methane emissions are a particularly poorly constrained source, with top-down estimates from 14 C in ice cores suggesting much lower geologic emissions than bottom-up scaling of direct flux measurements. Our study aims to contribute to resolving this discrepancy through improved bottom-up characterization of geologic methane seepage in the San Juan Basin in southwestern Colorado and northwestern New Mexico, USA. We performed 983 new flux chamber measurements in this basin during summer 2022 and winter 2023 field campaigns. Our results, in combination with prior measurements, suggest that natural seepage in the San Juan Basin only occurs on or near the Fruitland coal outcrop. Specifically, our new measurements confirm previous measurements of seepage along the northwestern exposure of the Fruitland outcrop in Colorado (a known hydrodynamic overpressure region) and for the first time, identified seepage locations along the southernmost Fruitland outcrop exposure in New Mexico, in association with a coal cleat and a fault. Overall, seepage along the Fruitland coal outcrop is heterogeneously distributed, with both positive and negative (interpreted as microbial soil sink) methane fluxes. Features that are hypothesized to be predictive of seepage (e.g., faults) were not associated with positive methane fluxes in areas outside of the Fruitland outcrop. Our best estimate for total geologic methane seepage in the San Juan Basin from spatial interpolation and statistical upscaling is approximately 0.14 Tg CH 4 /yr, with a range from 0.029 to 0.48 Tg CH 4 /yr. This best-estimate value is lower than a previous bottom-up estimate from a gridded seepage inventory, but higher than a previous top-down estimate.

Colorado, New Mexico↗
USGS2024

Evidence of nitrate attenuation in intertidal and subtidal groundwater in a subterranean estuary at a Cape Cod embayment, East Falmouth, Massachusetts, 2015–16

Nitrogen dynamics in intertidal and nearshore subtidal groundwater (subterranean estuary) adjacent to the Seacoast Shores peninsula, Falmouth, Massachusetts, were investigated during 2015–16 by the U.S. Geological Survey. The peninsula is a densely populated residential area with septic systems and cesspools that are substantial sources of nitrogen to groundwater. The study area is in the Eel River, an estuarine saltwater embayment connected to the ocean adjacent to the western shore of the peninsula, that was the subject of an earlier study by Colman and others (2018, https://doi.org/10.3133/sir20185095 ) on nitrogen transport and transformations in groundwater between onshore and offshore locations. The previous study documented the distribution of nitrate concentrations and nitrate attenuation reactions in fresh groundwater beneath the peninsula and the estuary. The current study extended those observations with more detailed sampling and analysis of shallow groundwater from wells near discharge sites beneath the estuary. The current field investigation included sampling of existing wells and installation and sampling of clusters of wells and temporary sampling points in the subterranean estuary, including (1) shallow transects 0.3 to 1.2 meters (m) deep extending from 1 to 13.5 m offshore and (2) deeper wells (from 1.83 to 4.88 m deep) extending from 4.3 to 14.3 m offshore. Measurements of hydraulic-head gradients 2–5 m below the sediment/water interface in the intertidal and nearshore subtidal zones indicated that groundwater flow generally was upwards (towards the estuary) under all tide conditions in October 2016. The magnitude of the gradient was greatest during low tide conditions, indicating that groundwater discharge likely decreased during high tides. Measurements of specific conductance in shallow groundwater in the subterranean estuary in three transects perpendicular to shore were consistent with the existence of saltwater flow cells (infiltration of overlying saline water, mixing with fresh groundwater, and discharge to the overlying saline water) in the intertidal and nearshore subtidal regions. The size of these flow cells was variable in space and time and dependent on the elevation of the tide (spring or neap). At this location in the Eel River subterranean estuary, and offshore to at least 13.5 m, offshore flow of fresh groundwater apparently prevented a deeper saltwater wedge from discharging to the surface. Nitrate concentrations in shallow groundwater (30 to 122 centimeters [cm] depth) were variable in space and time, ranging from not detectable to 600 micromoles per liter (μmol/L) (8.4 milligrams per liter as N), and were highest in June 2016 at depths from 61 to 122 cm below the sediment/water interface and from 4 to 9 m offshore. Nitrate generally was not detectable in saline shallow groundwater at 30-cm depth or at any depth from 30 to 122 cm from 10 to 13.5 m offshore. Dissolved oxygen concentrations were suboxic (less than 16 μmol/L) in 60 percent of the sampled subterranean groundwater beneath the intertidal and subtidal zones. In the remaining sites, the range of dissolved oxygen concentrations was from 18 to 272 μmol/L and the median concentration was 43 μmol/L. Evidence for microbial nitrate reduction (denitrification and possibly anammox) was provided by the distribution of the reaction product nitrogen gas (excess N 2 , or N 2MIC ), as determined from analysis of the dissolved nitrogen gas and argon gas (Ar) concentrations in groundwater samples. Excess nitrogen gas provided evidence for nitrate reduction in shallow groundwater below the subtidal and, to a lesser extent, intertidal zones adjacent to the Seacoast Shores peninsula. These zones, where evidence for nitrate reduction was detected, were in fresh and brackish groundwater near subtidal or intertidal saltwater cells where discharging fresh groundwater mixed with infiltrating saline water. Infiltrating seawater may have supplied organic carbon, one of several potential electron donors that are required for denitrification. Other potential electron donors, such as organic carbon, iron, manganese, hydrogen, methane, ammonium, elemental sulfur, or sulfide phases, may have been supplied by the estuarine sediments. Drainage from surface runoff near the shore also may have supplied organic carbon to fresh groundwater near the intertidal saltwater cell. The highest amounts of nitrate converted to excess nitrogen gas were estimated to be in the range of 230 to 430 μmol/L in nearly fresh groundwater near the subtidal saltwater cell at depths of 61 to 122 cm below the sediment/water interface and from 10 to 13.5 m offshore. Evidence of denitrification within 10 m of the shore was sparse (generally limited to less than 50 μmol/L of N 2 -N) despite the presence of high nitrate concentrations. The spatial distribution of estimated nitrate reduction in the intertidal and nearshore subtidal fresh and brackish groundwater may be related to local variability in the distribution of reactive electron donors in those zones. Variations in the amount of nitrate reduction to nitrogen gas were not clearly related to potential aqueous electron donors such as dissolved organic carbon, nor to potential reaction products such as alkalinity, but may have been controlled by combinations of aqueous and solid-phase reactants. The distribution of relatively shallow fresh groundwater containing nitrate could indicate potential nitrate discharge areas in the lower intertidal zone and uncertain locations farther offshore; however, the data did not extend all the way to the sediment/water interface or to the offshore freshwater limit. This study confirmed substantial loss of nitrate from some of the fresh and brackish groundwater in shallow subestuarine sediments prior to discharge but did not quantify how much nitrate eventually discharged to the estuary.

Massachusetts↗
USGS2024

A great tsunami earthquake component of the 1957 Aleutian Islands earthquake

The great 1957 Aleutian Islands earthquake ruptured ∼1200 km of the plate boundary along the Aleutian subduction zone and produced a destructive tsunami across Hawaiʻi. Early seismic and tsunami analyses indicated that large megathrust fault slip was concentrated in the western Aleutian Islands, but tsunami waves generated by slip in the west cannot explain the large observed runup in Hawaiʻi far to the southeast. Recently mapped 1957 geologic deposits on eastern Aleutian Islands suggest occurrence of very large nearby slip. Jointly modeling tsunami runup along the eastern Aleutian and Hawaiian Islands together with tide gauge recordings across the Pacific resolves 12-26 m shallow slip along 600 km of the eastern Aleutian Islands in addition to modest, deeper western slip inferred from seismic records. The eastern near-trench slip results in an M W 8.3-8.6 tsunami earthquake component of the M W 8.6-8.8 rupture, comparable in size to the adjacent 1946 Aleutian tsunami earthquake to the east. The reexamination of the 1957 rupture confirms the tsunami hazards posed by the eastern Aleutian subduction zone to Hawaiʻi and lays the groundwork for investigation of large prehistoric earthquakes through modeling tsunami runup inferred from stratigraphic observations to constrain their rupture processes.

Alaska↗
USGS2000

Quality assurance and analysis of water levels in wells on Pahute Mesa and vicinity, Nevada Test Site, Nye County, Nevada

Periodic and continual water-level data from 1963 to 1998 were compiled and quality assured for 65 observation wells on Pahute Mesa and vicinity, Nye County, Nevada. As part of the quality assurance of all water levels, ancillary data pertinent to computing hydraulic heads in wells were compiled and analyzed. Quality-assured water levels that were not necessarily in error but which did not represent static heads in the regional aquifer system, or required some other qualification, were flagged. Water levels flagged include those recovering from recent pumping or well construction, water levels affected by nuclear tests, and measurements affected by borehole deviations. A cursory examination of about 30 wells with available water-level and down-hole temperature data indicate that water levels in most wells on Pahute Mesa would not be significantly affected by temperature if corrected to 95 degrees Fahrenheit. Wells with large corrections (greater than 10 feet) are those with long water columns (greater than 1,500 feet of water above the assumed point of inflow) in combination with mean water-column temperatures exceeding 105 degrees Fahrenheit. Water-level fluctuations in wells on Pahute Mesa are caused by several factors including infiltration of precipitation, barometric pressure, Earth tides, ground-water pumpage, and seismic events caused by tectonic activity and underground nuclear testing. No observed water-level fluctuations were attributed to a naturally occurring earthquake. The magnitude and duration of changes in water levels caused by nuclear tests are affected by the test size and the distance from a well to the test. Identifying water levels that might be affected by past nuclear tests is difficult because pre-testing water-level data are sparse. Hydrologically significant trends were found in 13 of 25 wells with multiple years of water-level record. The largest change in water levels (1,029 feet in 25 years) occurred in well U-19v PS 1D as a result of the Almendro nuclear test. Likely explanations for trends in most of the wells are either changes in precipitation patterns that affect recharge rates to the ground-water system, pumping effects from water-supply well U-20 WW, or a combination of these two factors.

Nevada↗
USGS2024

Repeated coseismic uplift of coastal lagoons above the Patton Bay Splay Fault System, Montague Island, Alaska, USA

Coseismic slip on the Patton Bay splay fault system during the 1964 M w 9.2 Great Alaska Earthquake contributed to local tsunami generation and vertically uplifted shorelines as much as 11 m on Montague Island in Prince William Sound (PWS). Sudden uplift of 3.7–4.3 m caused coastal lagoons along the island's northwestern coast to gradually drain. The resulting change in depositional environment from marine lagoon to freshwater muskeg created a sharp, laterally continuous stratigraphic contact between silt and overlying peat. Here, we characterize the geomorphology, sedimentology, and diatom ecology across the 1964 earthquake contact and three similar prehistoric contacts within the stratigraphy of the Hidden Lagoons locality. We find that the contacts signal instances of abrupt coastal uplift that, within error, overlap the timing of independently constrained megathrust earthquakes in PWS—1964 Common Era, 760–870 yr BP, 2500–2700 yr BP, and 4120–4500 yr BP. Changes in fossil diatom assemblages across the inferred prehistoric earthquake contacts reflect ecological shifts consistent with repeated draining of a lagoon system caused by >3 m of coseismic uplift. Our observations provide evidence for four instances of combined megathrust-splay fault ruptures that have occurred in the past ∼4,200 years in PWS. The possibility that 1964-style combined megathrust-splay fault ruptures may have repeated in the past warrants their consideration in future seismic and tsunami hazards assessments.

Alaska↗
USGS2025

Near-surface material and topography generate anomalous high-frequency ground motion amplification in Chugiak, Alaska

An ∼3 km long nodal array oriented approximately east–west was deployed in Chugiak, Alaska, by the U.S. Geological Survey during 2021. The array intersects with the permanent NetQuakes station NP.ARTY, where peak ground acceleration (PGA) value of 1.98 g was recorded during the 2018 M w 7.1 Anchorage, Alaska, earthquake, in sharp contrast to the PGA of ∼0.3 g at a site just 4 km to the west. Seismic data for M w 1.8–4.3 aftershocks from the M w 7.1 event recorded by the nodal array confirm the anomalously large ground motions obtained at NP.ARTY as well as similar amplifications at nodes within ∼1 km to the east. Here, we performed 0–10 Hz 3D finite‐difference simulations, including high‐resolution surface topography, to explore the cause of the unexpectedly large amplification. As expected, the simulations computed with a regional 3D tomography velocity model severely underpredict the 0–10 Hz acceleration records at almost all sites. Adding a near‐surface low‐velocity taper to 300 m depth amplifies the accelerations by up to a factor of 5 and enables a reasonable match between the nodal data and simulations at sites to the west of NP.ARTY. However, this model still underpredicts the spectral energy in the area covered by glacial sediments by up to an order of magnitude. The addition of a till layer using a depth‐dependent shear‐wave velocity ( ⁠⁠ V s ) profile along with a homogeneous, 8 m thick low‐velocity layer with V s = 250 m/s representing the kame terraces improves the fit to data to within a factor of 2 at nodes located on top of the glacial sediments. Our study shows that the anomalously large high‐frequency amplification recorded at and near NP.ARTY can be explained by a combination of topographic effects and near‐surface low‐velocity material with amplification effects on the high‐frequency ground motion by up to about 40% and an order of magnitude, respectively.

Alaska↗