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At least 991 records · Page 55Linked to original sources

USGS2017

Hydrologic and geomorphic changes resulting from episodic glacial lake outburst floods: Rio Colonia, Patagonia, Chile

Glacial lake outburst floods (GLOFs) are a prominent but poorly understood cryospheric hazard in a warming climate. We quantify the hydrologic and geomorphic response to 21 episodic GLOFs that began in April 2008 using multitemporal satellite imagery and field observations. Peak discharge exiting the source lake became progressively muted downstream. At ~40–60 km downstream, where the floods entered and traveled down the main stem Rio Baker, peak discharges were generally < 2000 m 3 s −1 , although these flows were still >1–2 times the peak annual discharge of this system, Chile's largest river by volume. As such, caution must be applied to empirical relationships relating lake volume to peak discharge, as the latter is dependent on where this observation is made along the flood path. The GLOFs and subsequent periods of free drainage resulted in > 40 m of incision, the net removal of ~25 × 10 6 m 3 of sediment from the source lake basin, and a nonsteady channel configuration downstream. These results demonstrate that GLOFs sourced from low‐order tributaries can produce significant floods on major main stem rivers, in addition to significantly altering sediment dynamics.

Cachet‐Colonia‐Baker Valley, Patagonia, Rio Coloni↗

USGS2012

Crustal resistivity structure from magnetotelluric soundings in the Colorado Plateau-Basin and Range provinces, central and western Arizona

Resistivity structure to about 25 km depth is defined from two-dimensional modeling of 29 magnetotelluric (MT) soundings (0.002–5 Hz) that traverse 280 km of the southwestern Colorado Plateau, transition zone, and Basin and Range provinces in Arizona. From the surface to 5 km depth, the MT model suggests structural relationships between low-resistivity sedimentary and volcanic rocks (50–300 ohm m) and high-resistivity granitic and gneissic basement (500–9000 ohm m). In the Basin and Range province, the MT model and a seismic reflection section show a generally consistent distribution of supracrustal rocks that have relatively low to moderate resistivity (MT) and relatively strong, locally coherent reflectivity. The supracrustal zone defined by these physical properties is inferred to be composed of upper plate rocks above a middle Tertiary detachment fault system which has been mapped in surrounding ranges. Some low-angle fault zones inferred from seismic reflections to extend into high resistivity basement below the supracrustal rocks are not resolved by the MT model. A low-resistivity zone with a conductance of 500 S or more is modeled in the crust at an average depth of about 15 km in the Basin and Range province and transition zone and may deepen below the southwestern part of the Colorado Plateau. In the Basin and Range province, the top of the low resistivity may correspond to a reflective layer with a 6-s two-way-travel time. This deep low-resistivity zone might be caused by a small fraction of connected hydrous solutions or silicic melts.

Journal of Geophysical Research↗

USGS2008

Aeromagnetic evidence for a buried Early Cretaceous magmatic arc, northeast Japan

Positive aeromagnetic anomalies, recent drilling, and models constructed from these data delineate the plutonic roots of the Early Cretaceous Kitakami magmatic arc in northeast Japan. Buried plutons, mostly offshore, produce belts of positive magnetic anomalies. These anomalies and magnetotelluric data suggest that the plutons form a batholith 70–120 km wide, nearly 800 km long, and 10–15 km thick. The batholith may mark the location of the main Kitakami arc. Most of the exposed Kitakami plutons are 2–20 km in diameter; some are 3 km thick. The small plutons line up along NW trending faults; some may have been satellite vents that tapped into the magma supply of the main arc. The batholithic roots of the main arc now compose almost half of the modern Japan forearc basement. Steep magnetic gradients, offset anomalies, and basin stratigraphy portray extensive faulting of the Kitakami batholith during oblique subduction in the Late Cretaceous and rifting in the Miocene. The eastern boundary of the Kitakami batholith lies between 90 and 140 km west of the modern trench, much closer than the 300-km distance between the active arc and trench. The Early Cretaceous forearc basin and accretionary prism may underlie the modern forearc basin east of the batholith, but clear evidence is lacking. Much of the Early Cretaceous margin, including most of its forearc therefore is missing. How the material was removed is unknown: it could have been strike-slip faulted, eroded by subduction-related processes, or both.

Journal of Geophysical Research B: Solid Earth↗

USGS2011

Development of a pan-Arctic monitoring plan for polar bears: Background paper

Polar bears (Ursus maritimus), by their very nature, and the extreme, remote environment in which they live, are inherently difficult to study and monitor. Monitoring polar bear populations is both arduous and costly and, to be effective, must be a long-term commitment. There are few jurisdictional governments and management boards with a mandate for polar bear research and management, and many have limited resources. Although population monitoring of polar bears has been a focus to some degree within most jurisdictions around the Arctic, of the 19 subpopulations recognised by the IUCN/Species Survival Commission Polar Bear Specialist Group (PBSG), adequate scientific trend data exist for only three of the subpopulations, fair trend data for five and poor or no trend data for the remaining 11 subpopulations (PBSG 2010a). There are especially critical knowledge gaps for the subpopulations in East Greenland, in the Russian Kara and Laptev seas, and in the Chukchi Sea, which is shared between Russia and the United States. The range covered by these subpopulations represents a third of the total area (approx. 23 million km2) of polar bears’ current range, and more than half if the Arctic Basin is included. If we use popular terms, we know close to nothing about polar bears in this portion of their range. As summer sea-ice extent, and to a lesser degree, spring-time extent, continues to retreat, outpacing model forecasts (Stroeve et al. 2007, Pedersen et al. 2009), polar bears face the challenge of adapting to rapidly changing habitats. There is a need to use current and synthesised information across the Arctic, and to develop new methods that will facilitate monitoring to generate new knowledge at a pan-Arctic scale. The circumpolar dimension can be lost when efforts are channelled into regional monitoring. Developing and implementing a plan that harmonises local, regional and global efforts will increase our power to detect and understand important trends for polar bears, with particular emphasis on how climate warming may differentially affect populations and habitats. Current knowledge is inadequate for a comprehensive understanding of the present and future impact of climate warming and its interaction with other stressors. The cumulative effects are unknown (Laidre et al. 2008). An integrated pan-Arctic research and monitoring plan will improve the ability to detect future trends, identify the most vulnerable subpopulations and guide effective conservation. There is a need to direct attention and resources where data are deficient to understand the mechanisms that drive trends, and to facilitate more effective and timely conservation response.

Report↗

USGS2008

Compilation of Stratigraphic Thicknesses for Caldera-Related Tertiary Volcanic Rocks, East-Central Nevada and West-Central Utah

The U.S. Geological Survey (USGS), the Desert Research Institute (DRI), and a designee from the State of Utah are currently conducting a water-resources study of aquifers in White Pine County, Nevada, and adjacent areas in Nevada and Utah, in response to concerns about water availability and limited geohydrologic information relevant to ground-water flow in the region. Production of ground water in this region could impact water accumulations in three general types of aquifer materials: consolidated Paleozoic carbonate bedrock, and basin-filling Cenozoic volcanic rocks and unconsolidated Quaternary sediments. At present, the full impact of extracting ground water from any or all of these potential valley-graben reservoirs is not fully understood. A thorough understanding of intermontane basin stratigraphy, mostly concealed by the youngest unconsolidated deposits that blanket the surface in these valleys, is critical to an understanding of the regional hydrology in this area. This report presents a literature-based compilation of geologic data, especially thicknesses and lithologic characteristics, for Tertiary volcanic rocks that are presumably present in the subsurface of the intermontane valleys, which are prominent features of this area. Two methods are used to estimate volcanic-rock thickness beneath valleys: (1) published geologic maps and accompanying descriptions of map units were used to compile the aggregate thicknesses of Tertiary stratigraphic units present in each mountain range within the study areas, and then interpolated to infer volcanic-rock thickness in the intervening valley, and (2) published isopach maps for individual out-flow ash-flow tuff were converted to digital spatial data and thickness was added together to produce a regional thickness map that aggregates thickness of the individual units. The two methods yield generally similar results and are similar to volcanic-rock thickness observed in a limited number of oil and gas exploration drill holes in the region, although local geologic complexity and the inherent assumptions in both methods allow only general comparison. These methods serve the needs of regional ground-water studies that require a three-dimensional depiction of the extent and thickness of subsurface geologic units. The compilation of geologic data from published maps and reports provides a general understanding of the distribution and thickness of tuffs that are presumably present in the subsurface of the intermontane valleys and are critical to understanding the ground-water hydrology of this area.

Data Series↗

USGS2009

Evaluation of LiDAR-Acquired Bathymetric and Topographic Data Accuracy in Various Hydrogeomorphic Settings in the Lower Boise River, Southwestern Idaho, 2007

Elevation data in riverine environments can be used in various applications for which different levels of accuracy are required. The Experimental Advanced Airborne Research LiDAR (Light Detection and Ranging) - or EAARL - system was used to obtain topographic and bathymetric data along the lower Boise River, southwestern Idaho, for use in hydraulic and habitat modeling. The EAARL data were post-processed into bare earth and bathymetric raster and point datasets. Concurrently with the EAARL data collection, real-time kinetic global positioning system and total station ground-survey data were collected in three areas within the lower Boise River basin to assess the accuracy of the EAARL elevation data in different hydrogeomorphic settings. The accuracies of the EAARL-derived elevation data, determined in open, flat terrain, to provide an optimal vertical comparison surface, had root mean square errors ranging from 0.082 to 0.138 m. Accuracies for bank, floodplain, and in-stream bathymetric data had root mean square errors ranging from 0.090 to 0.583 m. The greater root mean square errors for the latter data are the result of high levels of turbidity in the downstream ground-survey area, dense tree canopy, and horizontal location discrepancies between the EAARL and ground-survey data in steeply sloping areas such as riverbanks. The EAARL point to ground-survey comparisons produced results similar to those for the EAARL raster to ground-survey comparisons, indicating that the interpolation of the EAARL points to rasters did not introduce significant additional error. The mean percent error for the wetted cross-sectional areas of the two upstream ground-survey areas was 1 percent. The mean percent error increases to -18 percent if the downstream ground-survey area is included, reflecting the influence of turbidity in that area.

Scientific Investigations Report↗

USGS2021

The formation, transport, and breakup of submerged oil-particle aggregates in Great Lakes riverine environments

The formation, transport, and resuspension of oil-particle aggregates (OPA) in freshwater environments are of much interest to oil spill responders and scientists, especially as transportation of light and heavy crude oils has substantially increased across river corridors and coasts in the Great Lakes Basin. The persistent sheening from accumulated OPA along 60 km of the Kalamazoo River in Michigan’s lower peninsula resulted in a lengthy and expensive cleanup for the 2010 Enbridge Line 6B pipeline rupture. The interaction of oil with river mineral sediment and organic matter and its long-term fate depend on the physical properties of the oil and particles as well as the environmental setting of river, its climate, morphology, currents and mixing opportunities. This research brief describes the expanded work conducted for the cleanup for the 2010 Enbridge Line 6B pipeline rupture and includes laboratory experiments of aggregate characteristics with Cold Lake Blend and a range of sediment particle sizes, addition of an OPA formation algorithm to an existing sediment contaminant transport model, and development of a simplified, particle-tracking based rapid response model of OPA formation, transport, and deposition. A description of formulas developed for mixing energy in rivers in terms of river properties is also included.

Michigan↗

USGS2015

Colonial waterbird predation on Lost River and shortnose suckers based on recoveries of passive integrated transponder tags

We evaluated predation on Lost River suckers ( Deltistes luxatus ) and shortnose suckers ( Chasmistes brevirostris ), both listed under the Endangered Species Act (ESA), from American white pelicans ( Pelecanus erythrorhynchos ) and double-crested cormorants ( Phalacrocorax auritus ) nesting at mixed species colonies on Clear Lake Reservoir, CA and Upper Klamath Lake, OR during 2009-2014. Predation was evaluated by recovering passive integrated transponder (PIT) tags that were implanted in suckers, subsequently consumed by pelicans or cormorants, and deposited on the birds’ nesting colonies. Data from PIT tag recoveries were used to estimate predation rates (proportion of available tagged suckers consumed) by birds to evaluate the relative susceptibility of suckers to avian predation in Upper Klamath Basin. Data on the size of pelican and cormorant colonies (number of breeding adults) at Clear Lake and Upper Klamath Lake were also collected and reported in the context of predation on suckers. Results indicate that predation rates varied by sucker species (Lost River, shortnose), sucker age-class (adult, juvenile), bird colony location (Upper Klamath Lake, Clear Lake), and year (2009-2014), demonstrating that predator-prey interactions in the system were dynamic during the study period. Tagged suckers ranging from 72 mm to 730 mm were susceptible to cormorant or pelican predation; all but the largest of the tagged Lost River suckers were susceptible to avian predation. Estimates of minimum, annual predation rates ranged from <0.1% to 4.6% of the available Lost River suckers and from <0.1% to 4.2% of the available shortnose suckers during the study period. Of the two colony locations evaluated, predation rates on suckers in Clear Lake were generally higher by birds nesting at mixed-species colonies on Clear Lake. Birds nesting on Clear Lake also commuted over 75 kilometers to forage on suckers in Upper Klamath Lake. Conversely, there was no evidence that birds nesting in Upper Klamath Lake foraged on tagged suckers in Clear Lake. Although sample sizes of tagged juvenile suckers were small and limited to fish tagged in Upper Klamath Lake, there was evidence that bird predation on juvenile suckers was higher than on adult suckers, with annual predate rate estimates on juvenile suckers ranging from 5.7% to 8.4% of available fish. The minimum annual predation rates presented here suggests that avian predation may be a factor limiting recovery of populations of Lost River and shortnose suckers, particularly juvenile suckers in Upper Klamath Lake and adult suckers in Clear Lake. Additional research is needed, however, to better assess the impacts of avian predation on sucker populations by (1) recovering PIT tags in a manner so that the species of avian predator is known (i.e., pelican vs. cormorant), (2) measuring predator-specific PIT tag deposition probabilities at each colony, (3) increasing the sample of juvenile suckers in the population that are PIT-tagged, and (4) recovering sufficient sample sizes of PIT tags on bird colonies to describe how various biotic and abiotic factors (e.g., fish size and condition, water levels and quality, and other factors) contribute to sucker susceptibility to avian predation in the Upper Klamath Basin.

California, Oregon↗

USGS2014

Hydrogeology of the Old Faithful area, Yellowstone National Park, Wyoming, and its relevance to natural resources and infrastructure

A panel of leading experts (The Old Faithful Science Review Panel) was convened by Yellowstone National Park (YNP) to review and summarize the geological and hydrological understanding that can inform National Park Service management of the Upper Geyser Basin area. We give an overview of present geological and hydrological knowledge of the Old Faithful hydrothermal (hot water) system and related thermal areas in the Upper Geyser Basin. We prioritize avenues for improving our understanding of key knowledge gaps that limit informed decision-making regarding human use in this fragile natural landscape. Lastly, we offer guidelines to minimize impacts to the hydrothermal system that could be used to aid decisions by park management. Old Faithful sits within the Upper Geyser Basin, an area of abundant hydrothermal activity where boiling waters extend from the surface to significant depth within glacial sediments and underlying volcanic rocks. The geyser systems are directly fed by waters recharged decades to millennia ago, which are surrounded by colder, younger waters. Activity of the geysers is controlled by complex subsurface plumbing with fractures and conduits separated by regions of low permeability. Observations over the past century indicate that the thermal areas and their features are both fragile and highly dynamic. Although Old Faithful has erupted regularly for the past 150 years, it exhibits changes in eruptive behavior over time, and the average interval between eruptions has increased by about 50 percent over the past 50 years. It is clear that human activity has modified the hydrothermal system in the past; conversely, natural features pose ongoing hazards to humans and human infrastructure. Current (2014) long-term programs to measure heat discharge by chloride-flux monitoring, and more recently by thermal-infrared imaging, are crucial for assessing the status of the hydrothermal system. Complementary studies could include airborne resistivity, environmental tracers, numerical modeling, and greater emphasis on measuring the discharge of water during geyser eruptions. Such data are needed to better understand the subsurface plumbing systems that feed the geysers. Further understanding can be gained through installation of shallow groundwater observation wells, surface geophysical studies, and direct measurement of temperature gradients near the surface. It also is critical to archive existing data from all studies in a manner that will be readily accessible to scientists and decision makers. Monitoring and data collection can be achieved through the YNP geology program, by direct funding to other groups, or by encouraging and facilitating externally funded research. There are many documented examples at YNP and elsewhere where human infrastructure and natural thermal features have negatively affected each other. Unless action is taken, human conflicts with the Old Faithful hydrothermal system are likely to increase over the coming years. This is partly because of the increase in park visitation over the past decades, but also because the interval between eruptions of Old Faithful has increased, lengthening the time spent (and services needed) for each visitor at Old Faithful. To avoid an increase in visitor impacts, the National Park Service should consider 2 alternate strategies to accommodate people, vehicles, and services in the Upper Geyser Basin, such as shuttle services from staging (parking and dining) areas with little or no recent hydrothermal activity. We further suggest that YNP consider a zone system to guide maintenance and development of infrastructure in the immediate Old Faithful area. A “red” zone includes hydrothermally active land where new development is discouraged and existing infrastructure is modified with great care. An outer “green” zone represents areas where cooler temperatures and less hydrothermal flow are thought to exist, and where development and maintenance could proceed as occurs elsewhere in the park. An intermediate “yellow” zone would require preliminary assessment of subsurface temperatures and gas concentrations to assess suitability for infrastructure development. The panel recommends that YNP management follow the lead of the National Park System Advisory Board Science Committee (2012) by applying the “precautionary principle” when making decisions regarding the interaction of hydrothermal phenomena and park infrastructure in the Old Faithful area and other thermal areas within YNP.

Wyoming↗

USGS2017

A reevaluation of the timing and causes of high lake phases in the Lake Michigan basin

Radiocarbon age control on the type Glenwood, Calumet, and Toleston shoreline features and on the abandoned Chicago outlet at the south end of the Lake Michigan basin provides a basis for reevaluating the timing and causes of high lake phases in the basin. Radiocarbon dates suggest that Glenwood-level (195 m) shoreline features formed between 14,100 and 12,700 yr B.P. (Glenwood I and II phases), Calumet-level (189 m) between 12,700 and 11,000 yr B.P. (Calumet I and II phases), and Toleston-level (184.5 m) between 5000 and 4000 yr B.P. (Nipissing phase), and that the Chicago outlet was cut to its present level (180 m) on bedrock while the lake was at the Glenwood level. This new chronology is inconsistent with J H. Bretz' hypothesis ((1951) American Journal of Science249, 401-429) that the progressive lowering of lake level resulted from episodic down-cutting of the outlet. Instead, the changes in lake level appear to relate to changes in the amount of glacial meltwater and precipitation entering the basin. We hypothesize that the Glenwood phases correspond with times when discharge from the Huron and Erie basins also entered the Lake Michigan basin (Lake Border and early Port Huron glacial phases), the Calumet phases with times when drainage was from the Lake Michigan basin alone (late Port Huron and Two Rivers glacial phases), and the Nipissing phase with the postglacial middle Holocene transgression caused by differential uplift in the basin. Estimates of relative net inputs to the basin during the Glenwood, Calumet, and Nipissing lake phases are consistent with estimates of relative outputs (i.e., discharge through the Chicago outlet); the magnitude of relative differences in inputs and outputs between phases is sufficient to explain lake-level changes of 4.5 to 6 m. ?? 1988.

Quaternary Research↗

USGS2013

Investigating the effects of point source and nonpoint source pollution on the water quality of the East River (Dongjiang) in South China

Understanding the physical processes of point source (PS) and nonpoint source (NPS) pollution is critical to evaluate river water quality and identify major pollutant sources in a watershed. In this study, we used the physically-based hydrological/water quality model, Soil and Water Assessment Tool, to investigate the influence of PS and NPS pollution on the water quality of the East River (Dongjiang in Chinese) in southern China. Our results indicate that NPS pollution was the dominant contribution (>94%) to nutrient loads except for mineral phosphorus (50%). A comprehensive Water Quality Index (WQI) computed using eight key water quality variables demonstrates that water quality is better upstream than downstream despite the higher level of ammonium nitrogen found in upstream waters. Also, the temporal (seasonal) and spatial distributions of nutrient loads clearly indicate the critical time period (from late dry season to early wet season) and pollution source areas within the basin (middle and downstream agricultural lands), which resource managers can use to accomplish substantial reduction of NPS pollutant loadings. Overall, this study helps our understanding of the relationship between human activities and pollutant loads and further contributes to decision support for local watershed managers to protect water quality in this region. In particular, the methods presented such as integrating WQI with watershed modeling and identifying the critical time period and pollutions source areas can be valuable for other researchers worldwide.

Dongjiang↗

USGS2026

Spawning habitat suitability models for Lake Erie cisco (Coregonus artedi) during the historical period of pre- and post-population declines 1877–1957

Coregonine fishes play a key role in the food webs and fisheries of the Laurentian Great Lakes and are a major focus of basin-wide conservation efforts. In Lake Erie, management goals prioritize rebuilding spawning populations of cisco ( Coregonus artedi ). However, the historical distribution of cisco spawning habitat and the environmental conditions that influence early life-stage success remain poorly defined. We used a novel database of historical coregonine spawning observations as well as novel habitat variables to describe historical conditions to model and determine where and what habitat was historically most suitable for spawning cisco in Lake Erie. The environmental predictors that produced the best model included reefs, distance to rivers, historical substrate, coefficient of variation of ice duration, fetch, and circulation. The highest suitability occurred in areas of high reef probability, near river mouths, in rocky and sandy substrate, and in areas of low variability in historical ice, fetch, and circulation. Suitable spawning habitat is predicted mostly around reefs in the western basin as well as along the coast and near rivers lake-wide. Our model identifies important habitat features and allows managers to envision relevant scales and locations at which to focus restoration efforts.

Lake Erie↗

USGS2021

Globally prevalent land nitrogen memory amplifies water pollution following drought years

Enhanced riverine delivery of terrestrial nitrogen (N) has polluted many freshwater and coastal ecosystems, degrading drinking water and marine resources. An emerging view suggests a contribution of land N memory effects—impacts of antecedent dry conditions on land N accumulation that disproportionately increase subsequent river N loads. To date, however, such effects have only been explored for several relatively small rivers covering a few episodes. Here we introduce an index for quantifying land N memory effects and assess their prevalence using regional observations and global terrestrial-freshwater ecosystem model outputs. Model analyses imply that land N memory effects are globally prevalent but vary widely in strength. Strong effects reflect large soil dissolved inorganic N (DIN) surpluses by the end of dry years. During the subsequent wetter years, the surpluses are augmented by soil net mineralization pulses, which outpace plant uptake and soil denitrification, resulting in disproportionately increased soil leaching and eventual river loads. These mechanisms are most prominent in areas with high hydroclimate variability, warm climates, and ecosystem disturbances. In 48 of the 118 basins analyzed, strong memory effects produce 43% (21%–88%) higher DIN loads following drought years than following average years. Such a marked influence supports close consideration of prevalent land N memory effects in water-pollution management efforts.

Environmental Research Letters↗

USGS2003

Earthquake recordings from the 2002 Seattle Seismic Hazard Investigation of Puget Sound (SHIPS), Washington state

This report describes seismic data obtained during the fourth Seismic Hazard Investigation of Puget Sound (SHIPS) experiment, termed Seattle SHIPS . The experiment was designed to study the influence of the Seattle sedimentary basin on ground shaking during earthquakes. To accomplish this, we deployed seismometers over the basin to record local earthquakes, quarry blasts, and teleseisms during the period of January 26 to May 27, 2002. We plan to analyze the recordings to compute spectral amplitudes at each site, to determine the variability of ground motions over the basin. During the Seattle SHIPS experiment, seismometers were deployed at 87 sites in a 110-km-long east-west line, three north-south lines, and a grid throughout the Seattle urban area (Figure 1). At each of these sites, an L-22, 2-Hz velocity transducer was installed and connected to a REF TEK Digital Acquisition System (DAS), both provided by the Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL) of the Incorporated Research Institutes for Seismology (IRIS). The instruments were installed on January 26 and 27, and were retrieved gradually between April 18 and May 27. All instruments continuously sampled all three components of motion (velocity) at a sample rate of 50 samples/sec. To ensure accurate computations of amplitude, we calibrated the geophones in situ to obtain the instrument responses. In this report, we discuss the acquisition of these data, we describe the processing and merging of these data into 1-hour long traces and into windowed events, we discuss the geophone calibration process and its results, and we display some of the earthquake recordings.

Washington↗

USGS2012

History of surface displacements at the Yellowstone Caldera, Wyoming, from leveling surveys and InSAR observations, 1923-2008

Modern geodetic studies of the Yellowstone caldera, Wyoming, and its extraordinary tectonic, magmatic, and hydrothermal systems date from an initial leveling survey done throughout Yellowstone National Park in 1923 by the U.S. Coast and Geodetic Survey. A repeat park-wide survey by the U.S. Geological Survey (USGS) and the University of Utah during 1975-77 revealed that the central part of the caldera floor had risen more than 700 mm since 1923, at an average rate of 14±1 mm/yr. From 1983 to 2007, the USGS conducted 15 smaller surveys of a single level line that crosses the northeast part of the caldera, including the area where the greatest uplift had occurred from 1923 to 1975-77. The 1983 and 1984 surveys showed that uplift had continued at an average rate of 22±1 mm/yr since 1975-77, but no additional uplift occurred during 1984-85 (-2±5 mm/yr), and during 1985-95 the area subsided at an average rate of 19±1 mm/yr. The change from uplift to subsidence was accompanied by an earthquake swarm, the largest ever recorded in the Yellowstone area (as of March 2012), starting in October 1985 and located near the northwest rim of the caldera. Interferometric synthetic aperture radar (InSAR) images showed that the area of greatest subsidence migrated from the northeast part of the caldera (including the Sour Creek resurgent dome) during 1992-93 to the southwest part (including the Mallard Lake resurgent dome) during 1993-95. Thereafter, uplift resumed in the northeast part of the caldera during 1995-96, while subsidence continued in the southwest part. The onset of uplift migrated southwestward, and by mid-1997, uplift was occurring throughout the entire caldera (essentially rim to rim, including both domes). Consistent with these InSAR observations, leveling surveys indicated 24±3 mm of uplift in the northeast part of the caldera during 1995-98. The beginning of uplift was coincident with or followed shortly after an earthquake swarm near the north caldera rim during June-July 1995 - the strongest swarm since 1985. Rather than a single deformation source as inferred from leveling surveys, the InSAR images revealed two distinct sources - one beneath each resurgent dome on the caldera floor. Subsequently, repeated GPS surveys (sometimes referred to as "campaign" surveys to distinguish them from continuous GPS observations) and InSAR images revealed a third deformation source beneath the north caldera rim. The north-rim source started to inflate in or about 1995, resulting in as much as 80 mm of surface uplift by 2000. Meanwhile, motion of the caldera floor changed from uplift to subsidence during 1997-8. The north rim area rose, while the entire caldera floor (including both domes) subsided until 2002, when both motions paused. Uplift in the northeast part of the caldera resumed in mid-2004 at a historically unprecedented rate of as much as 70 mm/yr, while the north rim area subsided at a lesser rate. Resurveys of the level line across the northeast part of the caldera in 2005 and 2007 indicated the greatest average uplift rate since the initial survey in 1923-53±3 mm/yr. Data from a nearby continuous GPS (CGPS) station showed that the uplift rate slowed to 40-50 mm/yr during 2007-8 and to near zero by September 2009. Following an intense earthquake swarm during January-February 2010, this one near the northwest caldera rim and the strongest since the 1985 swarm in the same general area, CGPS stations recorded the onset of subsidence throughout the entire caldera. Any viable model for the cause(s) of ground deformation at Yellowstone should account for (1) three distinct deformation sources and their association with both resurgent domes and the north caldera rim; (2) interplay among these sources, as suggested by the timing of major changes in deformation mode; (3) migration of the area of greatest subsidence or uplift from the northeast part of the caldera to the southwest part during 1992-95 and 1995-97, respectively; (4) repeated cycles of uplift and subsidence and sudden changes from uplift to subsidence or vice versa; (5) spatial and temporal relationships between changes in deformation mode and strong earthquake swarms; and (6) lateral dimensions of all three deforming areas that indicate source depths in the range of 5 to 15 km. We prefer a conceptual model in which surface displacements at Yellowstone are caused primarily by variations in the flux of basaltic magma into the crust beneath the caldera. Specifically, we envision a magmatic conduit system beneath the northeast part of the caldera that supplies basalt from a mantle source to an accumulation zone at 5-10 km depth, perhaps at a rheological boundary within a crystallizing rhyolite body remnant from past eruptions. Increases in the magma flux favor uplift of the caldera and decreases favor subsidence. A delicate equilibrium exists among the mass and heat flux from basaltic intrusions, heat and volatile loss from the crystallizing rhyolite body, and the overlying hydrothermal system. In the absence of basalt input, steady subsidence occurs mainly as a result of fluid loss from crystallizing rhyolite. At times when a self-sealing zone in the deep hydrothermal system prevents the escape of magmatic fluid, the resulting pressure increase contributes to surface uplift within the caldera; such episodes end when the seal ruptures during an earthquake swarm. To account for the north rim deformation source, we propose that magma or fluid exsolved from magma episodically escapes the caldera system at the three-way structural intersection of (1) the northern caldera boundary, (2) an active seismic belt to the north-northwest that is associated with the Hebgen Lake fault zone, and (3) the Norris - Mammoth corridor - a zone of faults, volcanic vents, and thermal activity that strikes north from the north rim of the caldera near Norris Geyser Basin to Mammoth Hot Springs near the northern boundary of Yellowstone National Park. Increased fluid flux out of the caldera by way of this intersection favors subsidence of the north rim area, and decreased flux favors uplift. This model does not account for poroelastic and thermoelastic effects, nonelastic rheology, or heat and mass transport in the hot and wet subcaldera crust. Such effects almost surely play a role in caldera deformation and are an important topic of ongoing research.

Wyoming↗

USGS2012

Structure of the lower crust beneath the Carolina Trough, U.S. Atlantic continental margin

Data from three large-offset seismic profiles provide information on the crustal structure beneath the Carolina trough. The profiles, obtained by the U.S. Geological Survey, the Naval Oceanographic Research Development Agency, and the Scripps Institution of Oceanography in 1985, were oriented parallel to the trough and were located (1) seaward of the East Coast Magnetic Anomaly (ECMA), which is generally thought to represent the boundary between oceanic and continental crust; (2) along the axis of the trough between the ECMA and the hinge zone, which is thought to reflect the landward limit of highly stretched and altered transitional crust; and (3) along the Carolina platform landward of the basement hinge zone on crust thought to have been thinned only slightly during rifting. These data constrain the velocity structure of the lower crust and provide evidence for a thick lens of high-velocity (>7.1 km/s) lower crustal material that extends beneath the Carolina trough and the adjacent ocean basin. This lens reaches a maximum thickness of about 13 km beneath the deepest part of the trough, thins to about 5 km seaward of the ECMA, and is either very thin or absent landward of the hinge zone. It is interpreted to represent material that was underplated beneath and/or intruded into the crust during the late stage of continental rifting and that led to an anomalously thick plutonic layer during the early seafloor spreading phase. These data thus support the recent conclusions of White et al. (1987b) and Mutter et al. (1988) that the initiation of seafloor spreading is attended in many, if not most, cases by the generation of an anomalously large volume of melt.

Carolina Trough↗

USGS2024

Ecology of Lake Erie - Chemistry, plankton & planktivory: A synthesis

As with other large lake ecosystems worldwide, Lake Erie can be considered a moving target for management, owing to physicochemical and biological changes brought on by anthropogenic change, both planned (e.g. nutrient and fisheries management) and unplanned (e.g. climate change, invasive species, modified land-use activities). These changes have challenged efforts to conserve biodiversity, sustain exploitable resources, and maintain the integrity of services valued by society both within the Lake Erie basin and (Fraker et al., 2022; Fussell et al., 2016; Sinclair et al., 2021; Sinclair et al., 2023) and outside of it (Allan et al., 2013; Jenny et al., 2020; Sterner et al., 2017). Some of these changes and their ramifications for management were documented in the first of four AEHM special issues devoted to the Lake Erie ecosystem (the fourth issue of 2023, volume 26, issue 4; see overview by Ludsin et al., 2023). That special issue focused explicitly on nutrient inputs and availability in Lake Erie and the lower food web, including planktonic and benthic microbial (including cyanobacteria), algal, and invasive dreissenid mussel communities. Similar to the previous Lake Erie special issue, this second one has focused on documenting the state of the lake, providing ecological understanding that could potentially benefit management. While some overlap in topics exists between issues, the studies conducted herein were completely independent of those previous investigations and offer unique insights. Specifically, the contributions to this current issue center on: 1) dynamics of water chemistry in Lake Erie’s central basin (i.e. bottom hypoxia; Ackerman et al., 2024) and western basin (i.e. mercury; Starr et al., 2024); 2) changes in primary producer biomass (Lesht et al., 2024), cyanotoxins (i.e. microcystin; Zastepa et al., 2024), and water quality (e.g. water clarity and dissolved nutrients; Howell et al., 2024); and 3) larval fish foraging (i.e. Lake Whitefish; Coregonus clupeaformis; Amidon et al., 2024) and community structure and phenology (DeBruyne et al., 2024). Below we summarize the major findings of these papers and offer a synthetic perspective on the value of this research for understanding the state of Lake Erie and enhancing management.

Aquatic Ecosystem Health and Management↗

USGS1992

An aeromagnetic survey over the northwestern Ross Ice Shelf and the McMurdo Sound area

As part of the expedition GANOVEX VI 1990/91, the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), the Alfred Wegener Institute for Polar and Marine Research (AWI), and the United States Geological Survey (USGS) carried out an airborne magnetic survey over the northwestern Ross Ice Shelf and McMurdo Sound between Ross Island, the Transantarctic Mountains, and Minna Bluff. The area planned for the aeromagnetic survey connects directly with the GANOVEX IV survey area (BGR & USGS 1987, BACHEM et al. 1989a) which terminated along an approximately cast-west line at about the latitude of Cape Bird. The GANOVEX IV survey covered the Victoria Land Basin - which is the westernmost of the three north/south striking basins in the Ross Sea - from its northern end in the Terra Nova Bay region to its known southern end at Ross Island. A possible southem extension of the Victoria Land Basin and its central graben structure (the Terror Rift as found from seismic surveys (COOPER et al. 1987) and what has been referred to as Victoria Graben in the aeromagnetic interpretation of the GANOVEX IV data (BOSUM et al. 1989) was one of the major targets for this survey. The survey was laid out in the form of blocks. A 135 km wide transect from the Transantarctic Mountains to about 175° W formed the focal block of the survey (Fig. 1) in which all major scientific objectives could be covered. Other survey blocks were planned to the south of this. During the course of the survey it turned out that in the time available no further area could be covered. Indeed, the unfavourable weather conditions made it impossible to complete even the above described main section fully. In detail, the lay-out of the survey area was closely following that of the GANOVEX IV survey to assure compatibility and direct continuation between the two data sets. The line spacing was chosen again to 4.4 km with a tic-line separation of 22 km. The survey altitude of 2,000 ft (610 m) corresponds to that of the Ross Sea section of the GANOVEX IV survey to which this survey area is directly adjacent. The profile lines were aligned approximately E-W, the tie-lines N-S. As part of the survey area is covered by the maps of the USGS Antarctica Reconnaissance Series 1:250,000 the Lambert conformal conic projection used for these maps was also used for the preparation of a flight line grid.

Polarforschung↗