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At least 1,441 records · Page 80Linked to original sources
USGS2012

Field experiment provides ground truth for surface nuclear magnetic resonance measurement

The need for sustainable management of fresh water resources is one of the great challenges of the 21st century. Since most of the planet's liquid fresh water exists as groundwater, it is essential to develop non-invasive geophysical techniques to characterize groundwater aquifers. A field experiment was conducted in the High Plains Aquifer, central United States, to explore the mechanisms governing the non-invasive Surface NMR (SNMR) technology. We acquired both SNMR data and logging NMR data at a field site, along with lithology information from drill cuttings. This allowed us to directly compare the NMR relaxation parameter measured during logging, T 2 , to the relaxation parameter T 2 * measured using the SNMR method. The latter can be affected by inhomogeneity in the magnetic field, thus obscuring the link between the NMR relaxation parameter and the hydraulic conductivity of the geologic material. When the logging T 2 data were transformed to pseudo- T 2 * data, by accounting for inhomogeneity in the magnetic field and instrument dead time, we found good agreement with T 2 * obtained from the SNMR measurement. These results, combined with the additional information about lithology at the site, allowed us to delineate the physical mechanisms governing the SNMR measurement. Such understanding is a critical step in developing SNMR as a reliable geophysical method for the assessment of groundwater resources.

Geophysical Research Letters↗
USGS2012

Holocene aridification of India

Spanning a latitudinal range typical for deserts, the Indian peninsula is fertile instead and sustains over a billion people through monsoonal rains. Despite the strong link between climate and society, our knowledge of the long‐term monsoon variability is incomplete over the Indian subcontinent. Here we reconstruct the Holocene paleoclimate in the core monsoon zone (CMZ) of the Indian peninsula using a sediment core recovered offshore from the mouth of Godavari River. Carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the CMZ and document a gradual increase in aridity‐adapted vegetation from ∼4,000 until 1,700 years ago followed by the persistence of aridity‐adapted plants after that. The oxygen isotopic composition of planktonic foraminifer Globigerinoides ruber detects unprecedented high salinity events in the Bay of Bengal over the last 3,000 years, and especially after 1,700 years ago, which suggest that the CMZ aridification intensified in the late Holocene through a series of sub‐millennial dry episodes. Cultural changes occurred across the Indian subcontinent as the climate became more arid after ∼4,000 years. Sedentary agriculture took hold in the drying central and south India, while the urban Harappan civilization collapsed in the already arid Indus basin. The establishment of a more variable hydroclimate over the last ca. 1,700 years may have led to the rapid proliferation of water‐conservation technology in south India.

Geophysical Research Letters↗
USGS2011

Estimates of stress drop and crustal tectonic stress from the 27 February 2010 Maule, Chile, earthquake: Implications for fault strength

The great 27 February 2010 M w 8.8 earthquake off the coast of southern Chile ruptured a ∼600 km length of subduction zone. In this paper, we make two independent estimates of shear stress in the crust in the region of the Chile earthquake. First, we use a coseismic slip model constrained by geodetic observations from interferometric synthetic aperture radar (InSAR) and GPS to derive a spatially variable estimate of the change in static shear stress along the ruptured fault. Second, we use a static force balance model to constrain the crustal shear stress required to simultaneously support observed fore‐arc topography and the stress orientation indicated by the earthquake focal mechanism. This includes the derivation of a semianalytic solution for the stress field exerted by surface and Moho topography loading the crust. We find that the deviatoric stress exerted by topography is minimized in the limit when the crust is considered an incompressible elastic solid, with a Poisson ratio of 0.5, and is independent of Young's modulus. This places a strict lower bound on the critical stress state maintained by the crust supporting plastically deformed accretionary wedge topography. We estimate the coseismic shear stress change from the Maule event ranged from −6 MPa (stress increase) to 17 MPa (stress drop), with a maximum depth‐averaged crustal shear‐stress drop of 4 MPa. We separately estimate that the plate‐driving forces acting in the region, regardless of their exact mechanism, must contribute at least 27 MPa trench‐perpendicular compression and 15 MPa trench‐parallel compression. This corresponds to a depth‐averaged shear stress of at least 7 MPa. The comparable magnitude of these two independent shear stress estimates is consistent with the interpretation that the section of the megathrust fault ruptured in the Maule earthquake is weak, with the seismic cycle relieving much of the total sustained shear stress in the crust.

Maule↗
USGS2012

A low-cost method to measure the timing of post-fire flash floods and debris flows relative to rainfall

Data on the specific timing of post-fire flash floods and debris flows are very limited. We describe a method to measure the response times of small burned watersheds to rainfall using a low-cost pressure transducer, which can be installed quickly after a fire. Although the pressure transducer is not designed for sustained sampling at the fast rates ({less than or equal to}2 sec) used at more advanced debris-flow monitoring sites, comparisons with high-data rate stage data show that measured spikes in pressure sampled at 1-min intervals are sufficient to detect the passage of most debris flows and floods. Post-event site visits are used to measure the peak stage and identify flow type based on deposit characteristics. The basin response timescale (tb) to generate flow at each site was determined from an analysis of the cross correlation between time series of flow pressure and 5-min rainfall intensity. This timescale was found to be less than 30 minutes for 40 post-fire floods and 11 post-fire debris flows recorded in 15 southern California watersheds ({less than or equal to} 1.4 km 2 ). Including data from 24 other debris flows recorded at 5 more instrumentally advanced monitoring stations, we find there is not a substantial difference in the median tb for floods and debris flows (11 and 9 minutes, respectively); however, there are slight, statistically significant differences in the trends of flood and debris-flow tb with basin area, which are presumably related to differences in flow speed between floods and debris flows.

Water Resources Research↗
USGS2013

Enhanced transfer of terrestrially derived carbon to the atmosphere in a flooding event

Rising CO 2 concentration in the atmosphere, global climate change, and the sustainability of the Earth's biosphere are great societal concerns for the 21st century. Global climate change has, in part, resulted in a higher frequency of flooding events, which allow for greater exchange between soil/plant litter and aquatic carbon pools. Here we demonstrate that the summer 2011 flood in the Mississippi River basin, caused by extreme precipitation events, resulted in a “flushing” of terrestrially derived dissolved organic carbon (TDOC) to the northern Gulf of Mexico. Data from the lower Atchafalaya and Mississippi rivers showed that the DOC flux to the northern Gulf of Mexico during this flood was significantly higher than in previous years. We also show that consumption of radiocarbon-modern TDOC by bacteria in floodwaters in the lower Atchafalaya River and along the adjacent shelf contributed to northern Gulf shelf waters changing from a net sink to a net source of CO 2 to the atmosphere in June and August 2011. This work shows that enhanced flooding, which may or may not be caused by climate change, can result in rapid losses of stored carbon in soils to the atmosphere via processes in aquatic ecosystems.

Geophysical Research Letters↗
USGS2012

Drivers of change in estuarine-coastal ecosystems: Discoveries from four decades of study in San Francisco Bay

Poised at the interface of rivers, ocean, atmosphere and dense human settlement, estuaries are driven by a large array of natural and anthropogenic forces. San Francisco Bay exemplifies the fast-paced change occurring in many of the world's estuaries, bays and inland seas in response to these diverse forces. We use observations from this particularly well-studied estuary to illustrate responses to six drivers that are common agents of change where land and sea meet: water consumption and diversion; human modification of sediment supply; introduction of non-native species; sewage input; environmental policy; and climate shifts. In San Francisco Bay, responses to these drivers include, respectively, shifts in the timing and extent of freshwater inflow and salinity intrusion; decreasing turbidity; restructuring of plankton communities; nutrient enrichment; elimination of hypoxia and reduced metal contamination of biota; and food web changes that decrease resistance of the estuary to nutrient pollution. Detection of these changes and discovery of their causes through environmental monitoring have been essential for establishing and measuring outcomes of environmental policies that aim to maintain high water quality and sustain services provided by estuarine-coastal ecosystems. The wide range of variability time scales and the multiplicity of interacting drivers place heavy demands on estuarine monitoring programs. But the San Francisco Bay case study illustrates why the imperative for monitoring has never been greater.

California↗
USGS2015

Agencies collaborate, develop a cyanobacteria assessment network

Cyanobacteria are a genetically diverse group of photosynthetic microorganisms that occupy a broad range of habitats on land and water all over the world. They release toxins that can cause lung and skin irritation, alter the taste and odor of potable water, and cause human and animal illness. Cyanobacteria blooms occur worldwide, and climate change may increase the frequency, duration, and extent of these bloom events. Rapid detection of potentially harmful blooms is essential to protect humans and animals from exposure. Information about potential for exposure, such as bloom duration, frequency, and extent, is especially critical for developing environmental management decisions during periods of limited resources and funding. The National Research Council (NRC) report Exposure Science in the 21st Century suggested that effectively assessing and mitigating exposures requires techniques for rapid measurement of a stressor, such as an algal bloom, across diverse geographic, temporal, and biologic scales (e.g., various bloom concentrations) and an enhanced infrastructure to address threats [ NRC , 2012]. The report specifically calls for approaches that use diverse information, such as satellite remote sensing, to identify and understand exposures that may pose a threat to ecosystems or human health. A collaborative effort integrates the work of the U.S. Environmental Protection Agency (EPA), NASA, the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Geological Survey (USGS) to provide an approach for using satellite ocean color capabilities in U.S. fresh and brackish water quality management decisions. The overarching goal of this collaborative project is to detect and quantify cyanobacteria blooms using satellite data records in order to support the environmental management and public use of U.S. lakes and reservoirs. Satellite remote sensing tools may enable policy makers and environmental managers to assess the sustainability of watershed ecosystems and the services they provide, now and in the future. Satellite technology allows us to develop early-warning indicators of cyanobacteria blooms at the local scale while maintaining continuous national coverage.

Eos, Earth and Space Science News↗
USGS2015

What is the Anthropocene?

Since Paul Crutzen and Eugene Stoermer introduced the word “Anthropocene” in 2000, scientists and nonscientists alike have used the word to highlight the concept that we are now living in a time when the global environment, at some level, is shaped by humankind rather than vice versa. Humans have significantly altered Earth’s land surface, oceans, rivers, atmosphere, flora, and fauna. By its emphasis on the here and now and on what humans have done and can do in the future, the word “Anthropocene” has served as a call to action for environmental sustainability and responsibility [ Crutzen and Stoermer , 2000; Waters et al. , 2014; Ruddiman et al. , 2015]. So far, however, the term “Anthropocene” has not been integrated into the official Geologic Time Scale, which geologists use to divide the past into named blocks based on the rock record. In 2016 or thereabouts, the International Commission on Stratigraphy—the scientific body that maintains the official Geologic Time Scale—will consider a proposal to formalize a definition of this term. It’s a decision that has both semantic and scientific implications and may have legal implications as well.

Eos, Earth and Space Science News↗
USGS2017

Cross-scale phenological data integration to benefit resource management and monitoring

Climate change is presenting new challenges for natural resource managers charged with maintaining sustainable ecosystems and landscapes. Phenology, a branch of science dealing with seasonal natural phenomena (bird migration or plant flowering in response to weather changes, for example), bridges the gap between the biosphere and the climate system. Phenological processes operate across scales that span orders of magnitude—from leaf to globe and from days to seasons—making phenology ideally suited to multiscale, multiplatform data integration and delivery of information at spatial and temporal scales suitable to inform resource management decisions. A workshop report: Workshop held June 2016 to investigate opportunities and challenges facing multi-scale, multi-platform integration of phenological data to support natural resource management decision-making.

Conference Paper↗
USGS2019

Hydroacoustic, seismic, and bathymetric observations of the 2014 submarine eruption at Ahyi Seamount, Mariana Arc

Ahyi seamount, a shallow submarine volcano in the Northern Mariana Islands, began erupting on April 23, 2014. Hydroacoustic eruption signals were observed on the regional Mariana seismic network and on distant hydrophones, and NOAA scuba divers working in the area soon after the eruption began heard and felt underwater explosion sounds. The NOAA crew observed yellow orange bubble mats along the shore of neighboring Farallon de Pájaros island, but no other surface manifestations of the eruption were reported by the crew or observed in satellite data. Here, we detail the eruption chronology and its morphologic impacts through analysis of seismic and hydroacoustic recordings and repeat bathymetric mapping. Throughout the 2-week-long eruption, Ahyi produced several thousand short, impulsive hydroacoustic signals that we interpret as underwater explosions as well as tremor near the beginning and end of the sequence. The initial tremor, which occurred for 2 hours, is interpreted as small phreatomagmatic explosions. This tremor was followed by a 90 min pause before the characteristic impulsive signals began. Occasional tremor (lasting up to a few minutes) during the last 1.5 days of the eruption is interpreted as more sustained eruptive activity. Bathymetric changes show that a new crater, about 150 m deep, formed near the former summit and a large landslide chute formed on the southeastern flank. Comparing to other geophysically-detected submarine eruptions, we find that the signals from the 2014 Ahyi eruption were more similar to those from other shallow or at surface submarine eruptions than those at deep (>500 m) eruptions.

Geochemistry, Geophysics, Geosystems↗
USGS2019

Mechanics of inflationary deformation during Caldera collapse: Evidence from the 2018 Kīlauea Eruption

During the 2018 Kilauea eruption the caldera ffloor dropped 500 meters in 62 nearly periodic events of up to 8 meters. Caldera collapse maintains pressure in the magma reservoir necessary to sustain high-rate eruptions. The 2018 collapses were accompanied by inflationary tilts and displacements, similar to observations at other basaltic calderas. Collapse is modeled in 2D by uniform slip dislocations intersecting a magma chamber. Collapses occurred rapidly, such that mass within the chamber was constant. For vertical faults surface deformation outside the collapse results only from chamber pressurization with displacements anti-parallel to pre-collapse deflation, similar to observations. For inward dipping faults the predicted ratio of horizontal to vertical displacements during collapse is greater than for the pre-collapse deflation, as observed. For outward dipping faults the horizontal displacements are inward, contrary to data. The average deformation trends during the eruption depend on fault dip and whether stress required to trigger collapses was constant or changed with time.

Hawaii↗
USGS2019

Post-collapse gravity increase at the summit of Kīlauea Volcano, Hawaiʻi

We conducted gravity surveys of the summit area of Kīlauea Volcano, Hawaiʻi, in November 2018 and March 2019, with the goal of determining whether there was any mass change at depth following the volcano's May–August 2018 caldera collapse. Surface deformation between the two surveys was minimal, but we measured a gravity increase (maximum 44 μGal) centered on the caldera that can be modeled as mass accumulation in a region ~1 km beneath the surface. We interpret this mass increase to be mostly magma accumulation in void space that was created during the summit collapse. Caldera uplift was evident by April 2019, indicating that the magma volume had reached a point where pressurization could be sustained. Modeled gravity change suggests a maximum magma storage rate at Kīlauea's summit during November 2018 to March 2019 that is much less than the pre‐2018 magma supply rate to the volcano.

Hawaii↗
USGS2020

The future of sediment transport and streamflow under a changing climate and the implications for long-term resilience of the San Francisco Bay-Delta

Sedimentation and turbidity have effects on habitat suitability in the San Francisco Bay‐Delta (Bay‐Delta), concerning key species in the bay as well as the ability of the delta marshes to keep pace with sea level rise. A daily rainfall runoff and transport model of the Sacramento River Basin of northern California was developed to simulate streamflow and suspended sediment transport to the Bay‐Delta for the next century (water years, WY2010–2099). The model was calibrated to historical streamflow and sediment data and applied using 10 Global Climate Models with two representative concentration pathways (RCP) each for WY1980–2099 from the IPCC 5th Assessment Report. Results indicate average increases in peak streamflow of +58% and +66% for the RCP 4.5 and 8.5 ensembles, respectively, by mid‐century and +62 and +96% by end‐of‐century. Sediment loads increased by +39% and +69% by end‐of‐century. Suspended sediment concentrations (SSC) increased on average by +4.6% and +6.7% for RCP 4.5 and 8.5, respectively, by end‐of‐century. Individual scenario results varied, and statistically significant increasing trends of sediment loads to the Bay‐Delta were found for the RCP 4.5 and 8.5 ensembles and five individual scenarios. Increased suspended sediment loads may have negative effects such as contaminant transport but also have positive effects that help protect against sea level rise, increase turbidity and fish habitat, and sustain wetland habitats in the Bay‐Delta.

California↗
USGS2020

A one‐dimensional model for turbulent mixing in the benthic biolayer of stream and coastal sediments

In this paper, we develop and validate a rigorous modeling framework, based on Duhamel's Theorem, for the unsteady one-dimensional vertical transport of a solute across a flat sediment-water interface (SWI) and through the benthic biolayer of a turbulent stream. The modeling framework is novel in capturing the two-way coupling between evolving solute concentrations above and below the SWI and in allowing for a depth-varying diffusivity. Three diffusivity profiles within the sediment (constant, exponentially decaying, and a hybrid model) are evaluated against an extensive set of previously published laboratory measurements of turbulent mass transfer across the SWI. The exponential diffusivity profile best represents experimental observations and its reference diffusivity scales with the permeability Reynolds number, a dimensionless measure of turbulence at the SWI. The depth over which turbulence-enhanced diffusivity decays is of the order of centimeters and comparable to the thickness of the benthic biolayer. Thus, turbulent mixing across the SWI may serve as a universal transport mechanism, supplying the nutrient and energy fluxes needed to sustain microbial growth, and nutrient processing, in the benthic biolayer of stream and coastal sediments.

Water Resources Research↗
USGS2020

Lessons from a post-eruption landscape

From March to May 1980, magma rose high into Mount St. Helens (MSH), swelling and—as it turned out—destabilizing its north flank. Scientists knew the volcano had been highly active at times over the past 40,000 years, but the mountain, located amid the Cascade Range in southwestern Washington, had been mostly quiet since the mid-19th century. The collapse of the north flank on 18 May shattered that quiet, triggering a cascade of events that left resounding impressions not only on those who witnessed and studied them but also on the surrounding landscape [Lipman and Mullineaux, 1981; Waitt, 2015]. The eruption of MSH also provided unparalleled opportunities for advancing several disciplines [e.g., Shore et al., 1986; Newhall, 2000; Franklin and MacMahon, 2000]. Although not as conspicuously as in volcanology, the eruption and its aftermath led to an intensification of research investigating biophysical impacts of eruptions and subsequent responses [e.g., Dale et al., 2005; Pierson and Major, 2014; Crisafulli and Dale, 2018]. Long-term research on the biophysical responses at MSH has provided important new insights, challenged long-standing ideas, and provided many societal benefits. The fortieth anniversary of the eruption this year offers a timely opportunity to reflect on these insights and influences. This long-term vantage is important because sustained, place-based studies following landscape disturbances are rare; because the MSH eruption spurred the greatest depth and breadth of multidisciplinary studies of biophysical responses to landscape disturbance; and because these responses created some of the most significant societal challenges to emerge after the eruption. We summarize key biophysical disturbances and responses, highlight salient insights, and suggest actions that can extend the usefulness of these insights to volcanically vulnerable communities worldwide.

Washington↗
USGS2021

Seasonal controls on sediment delivery and hydrodynamics in a vegetated tidally influenced interdistributary island

River deltas are maintained by a continuous supply of terrestrial sediments that provide critical land building material to help sustain and protect vulnerable ecological communities and serve as natural storm protection barriers. Local hydrodynamics are important in determining the degree to which fluvial sediments are removed from the water column and retained on the delta complex. During 2014, we measured hydrodynamics and sediment transport characteristics at one of the world's most rapidly prograding deltas, the Wax Lake delta in Louisiana, USA. We observed waves to be the dominant source of bottom stress for 70% of our observations. Sediment concentration tended to increase with shear stress, but only after stresses exceeded 0.01–0.02 Pa. Significant wave height and bottom stress were substantially reduced after June, when the emergence of American lotus ( Nelumbo lutea ) formed a dense canopy over the intertidal regions of the island splay. Hydrodynamics during these summer vegetated conditions were much more favorable to floc formation, and by extension particle settling, as shown by trends in the Kolmogorov microscale parameter over the course of the measurement campaign. Together, these findings suggest that the timing between peak river discharge and the emergence of vegetation may have a strong influence on rates of progradation in seasonally vegetated delta splays, whereby sediments delivered by flood events that extend late into summer may be governed by hydrodynamics that favor particle deposition, whereas those delivered prior to the summer may be more prone to remain in suspension and bypass the delta complex.

Louisiana↗
USGS2021

Mars: Abundant recurring slope lineae (RSL) following the planet-encircling dust event (PEDE) of 2018

Recurring slope lineae (RSL) are dark linear markings on Mars that regrow annually and likely originate from the flow of either liquid water or granular material. Following the great dust storm (or planet-encircling dust event, PEDE) of Mars year (MY) 34, Mars Reconnaissance Orbiter/High Resolution Imaging Science Experiment has seen many more candidate RSL than in typical Mars years. They have been imaged at more than 285 unique locations from August 2018 (when the atmosphere was clearing as the PEDE decayed) to August 2019, about half (157) of which are locations where RSL have not been documented previously. In MY34, 150 active RSL sites were identified in the southern middle latitudes (SML, -60° to -30°), whereas an average of 36 active sites were observed in each previous year (MY28–33). Post-PEDE RSL are also present during southern summer over a wider range of latitude, slope aspect, and L s (areocentric longitude of the sun) than in prior years. These RSL sites usually show evidence for recent dust deposition: obscuration of relatively dark areas, an overall brighter and redder surface than in prior years, and dust devil tracks, which indicate dust lifting by several mechanisms. We speculate that dust-lifting processes may initiate and sustain RSL activity. The RSL may form from flows of dust (perhaps clumped) and/or sand that is destabilized by dust movement or directly mobilized by dust devils. If this is the case, then the otherwise puzzling recurrence and year-to-year variability of RSL activity can be at least partly explained. The dust replenishment varies from year to year, which could explain interannual variations in RSL activity.

Journal of Geophysical Research: Planets↗
USGS2021

Characterization of groundwater recharge and flow in California's San Joaquin Valley from InSAR-observed surface deformation

Surface deformation in California's Central Valley (CV) has long been linked to changes in groundwater storage. Recent advances in remote sensing have enabled the mapping of CV deformation and associated changes in groundwater resources at increasingly higher spatiotemporal resolution. Here, we use interferometric synthetic aperture radar (InSAR) from the Sentinel‐1 missions, augmented by continuous Global Positioning System (cGPS) positioning, to characterize the surface deformation of the San Joaquin Valley (SJV, southern two‐thirds of the CV) for consecutive dry (2016) and wet (2017) water years. We separate trends and seasonal oscillations in deformation time series and interpret them in the context of surface and groundwater hydrology. We find that subsidence rates in 2016 (mean −42.0 mm/yr; peak −345 mm/yr) are twice that in 2017 (mean −20.4 mm/yr; peak −177 mm/yr), consistent with increased groundwater pumping in 2016 to offset the loss of surface‐water deliveries. Locations of greatest subsidence migrated outwards from the valley axis in the wetter 2017 water year, possibly reflecting a surplus of surface‐water supplies in the lowest portions of the SJV. Patterns in the amplitude of seasonal deformation and the timing of peak seasonal uplift reveal entry points and potential pathways for groundwater recharge into the SJV and subsequent groundwater flow within the aquifer. This study provides novel insight into the SJV aquifer system that can be used to constrain groundwater flow and subsidence models, which has relevance to groundwater management in the context of California's 2014 Sustainable Groundwater Management Act (SGMA).

California↗