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Results for “Journal of Applied Physics”

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USGS2003

Importance of a stochastic distribution of floods and erosion thresholds in the bedrock river incision problem

Fluvial erosion of bedrock occurs during occasional flood events when boundary shear stress exceeds a critical threshold to initiate incision. Therefore efforts to model the evolution of topography over long timescales should include an erosion threshold and should be driven by a stochastic distribution of erosive events. However, most bedrock incision models ignore the threshold as a second‐order detail. In addition, climate is poorly represented in most landscape evolution models, so the quantitative relationship between erosion rate and measurable climatic variables has been elusive. Here we show that the presence of an erosion threshold, when combined with a well‐constrained, probabilistic model of storm and flood occurrence, has first‐order implications for the dynamics of river incision in tectonically active areas. First, we make a direct calculation of the critical shear stress required to pluck bedrock blocks for a field site in New York. Second, we apply a recently proposed stochastic, threshold, bedrock incision model to a series of streams in California, with known tectonic and climatic forcing. Previous work in the area has identified a weak relationship between channel gradient or relief and rock uplift rate that is not easily explained by simpler detachment‐limited models. The results with the stochastic threshold model show that even low erosion thresholds, which are exceeded in steep channels during high‐frequency flood events, fundamentally affect the predicted relationship between gradient and uplift rate in steady state rivers, in a manner consistent with the observed topography. This correspondence between theory and data is, however, nonunique; models in which a thin alluvial cover may act to inhibit channel incision in the low uplift rate zone also provide plausible explanations for the observed topography. Third, we explore the broader implications of the stochastic threshold model to the development of fluvial topography in active tectonic settings. We suggest that continued field applications of geomorphic models, including physically meaningful thresholds and stochastic climate distributions, are required to advance our knowledge of interactions among surficial, climatic, and crustal processes.

California↗

USGS1996

Factors affecting suspended-solids concentrations in South San Francisco Bay, California

Measurements of suspended-solids concentration (SSC) were made at two depths at three sites in South San Francisco Bay (South Bay) to determine the factors that affect SSC. Twenty-eight segments of reliable and continuous SSC time series data longer than 14 days were collected from late 1991 or 1992 through September 1993. Spectral analysis and singular spectrum analysis were used to relate these data segments to time series of several potential forcing factors, including diurnal and semidiurnal tides, the spring-neap tidal cycle, wind shear, freshwater runoff, and longitudinal density differences. SSC is greatest during summer, when a landward wind shear is applied to South Bay by the afternoon sea breeze. About one half the variance of SSC is caused by the spring-neap cycle, and SSC lags the spring-neap cycle by about 2 days. Relatively short duration of slack water limits the duration of deposition of suspended solids and consolidation of newly deposited bed sediment during the tidal cycle, so suspended solids accumulate in the water column as a spring tide is approached and slowly deposit as a neap tide is approached. Perturbations in SSC caused by wind and local runoff from winter storms during the study period were usually much smaller than SSC variations caused by the spring-neap cycle. Variations of SSC at the study sites at tidal timescales are tidally forced, and nonlinear physical processes are significant. Advective transport dominates during spring tides, when water with higher SSC due to wind wave resuspension is advected to the main channel from shallow water, but, during neap tides, advective transport is less significant. The findings of this and other studies indicate that the tidally averaged transport of suspended solids responds to seasonal variations of wind shear in South Bay.

Journal of Geophysical Research C: Oceans↗

USGS2017

Benchmarking computational fluid dynamics models of lava flow simulation for hazard assessment, forecasting, and risk management

Numerical simulations of lava flow emplacement are valuable for assessing lava flow hazards, forecasting active flows, designing flow mitigation measures, interpreting past eruptions, and understanding the controls on lava flow behavior. Existing lava flow models vary in simplifying assumptions, physics, dimensionality, and the degree to which they have been validated against analytical solutions, experiments, and natural observations. In order to assess existing models and guide the development of new codes, we conduct a benchmarking study of computational fluid dynamics (CFD) models for lava flow emplacement, including VolcFlow, OpenFOAM, FLOW-3D, COMSOL, and MOLASSES. We model viscous, cooling, and solidifying flows over horizontal planes, sloping surfaces, and into topographic obstacles. We compare model results to physical observations made during well-controlled analogue and molten basalt experiments, and to analytical theory when available. Overall, the models accurately simulate viscous flow with some variability in flow thickness where flows intersect obstacles. OpenFOAM, COMSOL, and FLOW-3D can each reproduce experimental measurements of cooling viscous flows, and OpenFOAM and FLOW-3D simulations with temperature-dependent rheology match results from molten basalt experiments. We assess the goodness-of-fit of the simulation results and the computational cost. Our results guide the selection of numerical simulation codes for different applications, including inferring emplacement conditions of past lava flows, modeling the temporal evolution of ongoing flows during eruption, and probabilistic assessment of lava flow hazard prior to eruption. Finally, we outline potential experiments and desired key observational data from future flows that would extend existing benchmarking data sets.

Journal of Applied Volcanology↗

USGS2011

Estimating detection and density of the Andean cat in the high Andes

The Andean cat ( Leopardus jacobita ) is one of the most endangered, yet least known, felids. Although the Andean cat is considered at risk of extinction, rigorous quantitative population studies are lacking. Because physical observations of the Andean cat are difficult to make in the wild, we used a camera-trapping array to photo-capture individuals. The survey was conducted in northwestern Argentina at an elevation of approximately 4,200 m during October-December 2006 and April-June 2007. In each year we deployed 22 pairs of camera traps, which were strategically placed. To estimate detection probability and density we applied models for spatial capture-recapture using a Bayesian framework. Estimated densities were 0.07 and 0.12 individual/km 2 for 2006 and 2007, respectively. Mean baseline detection probability was estimated at 0.07. By comparison, densities of the Pampas cat ( Leopardus colocolo ), another poorly known felid that shares its habitat with the Andean cat, were estimated at 0.74–0.79 individual/km 2 in the same study area for 2006 and 2007, and its detection probability was estimated at 0.02. Despite having greater detectability, the Andean cat is rarer in the study region than the Pampas cat. Properly accounting for the detection probability is important in making reliable estimates of density, a key parameter in conservation and management decisions for any species.

High Andes↗

USGS2013

Seismicity around Parkfield correlates with static shear stress changes following the 2003 M w 6.5 San Simeon earthquake

Earthquakes trigger other earthquakes, but the physical mechanism of the triggering is currently debated. Most studies of earthquake triggering rely on earthquakes listed in catalogs, which are known to be incomplete around the origin times of large earthquakes and therefore missing potentially triggered events. Here we apply a waveform matched-filter technique to systematically detect earthquakes along the Parkfield section of the San Andreas Fault from 46 days before to 31 days after the nearby 2003 M w 6.5 San Simeon earthquake. After removing all possible false detections, we identify ~8 times more earthquakes than in the Northern California Seismic Network catalog. The newly identified events along the creeping section of the San Andreas Fault show a statistically significant decrease following the San Simeon main shock, which correlates well with the negative static stress changes (i.e., stress shadow) cast by the main shock. In comparison, the seismicity rate around Parkfield increased moderately where the static stress changes are positive. The seismicity rate changes correlate well with the static shear stress changes induced by the San Simeon main shock, suggesting a low friction in the seismogenic zone along the Parkfield section of the San Andreas Fault.

California↗

USGS2006

Cometary impact and amino acid survival - Chemical kinetics and thermochemistry

The Arrhenius parameters for the initiating reactions in butane thermolysis and the formation of soot, reliable to at least 3000 K, have been applied to the question of the survival of amino acids in cometary impacts on early Earth. The pressure/temperature/time course employed here was that developed in hydrocode simulations for kilometer-sized comets (Pierazzo and Chyba, 1999), with attention to the track below 3000 K where it is shown that potential stabilizing effects of high pressure become unimportant kinetically. The question of survival can then be considered without the need for assignment of activation volumes and the related uncertainties in their application to extreme conditions. The exercise shows that the characteristic times for soot formation in the interval fall well below the cooling periods for impacts ranging from fully vertical down to about 9?? above horizontal. Decarboxylation, which emerges as more rapid than soot formation below 2000-3000 K, continues further down to extremely narrow impact angles, and accordingly cometa??ry delivery of amino acids to early Earth is highly unlikely. ?? 2006 American Chemical Society.

Journal of Physical Chemistry A↗

USGS2020

Natural and anthropogenic processes affecting radon releases during mining and early stage reclamation activities, Pinenut uranium mine, Arizona, USA

Radon (Rnair) was monitored in open air in publicly accessible areas surrounding the Pinenut uranium (U) mine during mining and reclamation activities in 2015–16 to address concerns about mining related effects to areas surrounding Grand Canyon National Park (GCNP) in Arizona, USA. During July 2015, Rnair concentrations associated with the ore storage pile monitoring site were larger than those at the mine vent monitoring site and likely resulted from the relatively large amount of ore stored on site during this period. Higher wind velocities at the ore pile monitoring site generally resulted in lower Rnair concentrations; however, wind velocity did not appear to be an important factor in controlling Rnair concentrations at the mine vent monitoring site. Physical disturbances of the ore pile by heavy equipment did not coincide with elevated Rnair concentrations at the ore storage pile or mine vent monitoring sites. The relative size of the ore storage pile showed a positive trend with the daily mean Rnair concentration measured at the ore pile monitoring site. Principal component analysis (PCA) was applied to the ore pile and mine vent multivariate data sets for simultaneous comparison of all measured variables during 230 days of the study period. A significant positive coefficient for Rnair was associated with a significant negative coefficient for wind speed for principal component (PC) 2ore pile. Significant, positive PC2mine vent coefficients included Rnair, wind direction, and relative ore pile size indicating that Rnair variations at the mine vent monitoring site may be affected by Rn sourced from the ore pile. The ore pile is located about 200 m south of the mine vent Rn monitor with the prevalent wind direction coming from the south. All data generated during the field study and laboratory verification tests were published by Naftz et al. (2018) and are available online at:

Journal of Environmental Radioactivity↗

USGS2007

Physical and hormonal examination of Missouri River shovelnose sturgeon reproductive stage: A reference guide

From May 2001 to June 2002 Wildhaber et al. (2005) conducted monthly sampling of Lower Missouri River shovelnose sturgeon ( Scaphirhynchus platorynchus ) to develop methods for determination of sex and the reproductive stage of sturgeons in the field. Shovelnose sturgeon were collected from the Missouri River and ultrasonic and endoscopic imagery and blood and gonadal tissue samples were taken. The full set of data was used to develop monthly reproductive stage profiles for S. platorynchus that could be compared to data collected on pallid sturgeon ( Scaphirhynchus albus ). This paper presents a comprehensive reference set of images, sex steroids, and vitellogenin (VTG, an egg protein precursor) data for assessing shovelnose sturgeon sex and reproductive stage. This reference set includes ultrasonic, endoscopic, histologic, and internal images of male and female gonads of shovelnose sturgeon at each reproductive stage along with complementary data on average 17- β estradiol, 11-ketotestosterone, VTG, gonadosomatic index, and polarization index.

Missouri↗

USGS2009

Pilot- and bench-scale testing of faecal indicator bacteria survival in marine beach sand near point sources

Aim: Factors affecting faecal indicator bacteria (FIB) and pathogen survival/persistence in sand remain largely unstudied. This work elucidates how biological and physical factors affect die-off in beach sand following sewage spills. Methods and Results: Solar disinfection with mechanical mixing was pilot-tested as a disinfection procedure after a large sewage spill in Los Angeles. Effects of solar exposure, mechanical mixing, predation and/or competition, season, and moisture were tested at bench scale. First-order decay constants for Escherichia coli ranged between -0??23 and -1??02 per day, and for enterococci between -0??5 and -1??0 per day. Desiccation was a dominant factor for E. coli but not enterococci inactivation. Effects of season were investigated through a comparison of experimental results from winter, spring, and fall. Conclusions: Moisture was the dominant factor controlling E. coli inactivation kinetics. Initial microbial community and sand temperature were also important factors. Mechanical mixing, common in beach grooming, did not consistently reduce bacterial levels. Significance and Impact of the Study: Inactivation rates are mainly dependent on moisture and high sand temperature. Chlorination was an effective disinfection treatment in sand microcosms inoculated with raw influent. ?? 2009 The Society for Applied Microbiology.

Journal of Applied Microbiology↗

USGS2024

Improved efficient physics-based computational modeling of regional wave-driven coastal flooding for reef-lined coastlines

Coastal flooding affects low-lying communities worldwide and is expected to increase with climate change, especially along reef-lined coasts, where wave-driven flooding is particularly prevalent. However, current regional modeling approaches are either insufficient or too computationally expensive to accurately assess risks in these complex environments. This study introduces and validates an improved computationally efficient and physics-based approach to compute dynamic wave-driven regional flooding on reef-lined coasts. We coupled a simplified-physics flood model (SFINCS) with a one-dimensional wave transformation model (XBeach-1D). To assess the performance of the proposed approach, we compared its results with results from a fully resolving two-dimensional wave transformation model (XBeach-2D). We applied this approach for a range of storms and sea-level rise scenarios for two contrasting reef-lined coastal geomorphologies: one low relief area and one high relief area. Our findings reveal that SFINCS coupled with XBeach-1D generates flood extents comparable to those produced by XBeach-2D, with a hit rate of 92%. However, this method tends to underpredict the flood extent of weaker, high-frequency storms and overpredict stronger, low-frequency storms. Across scenarios, our approach overpredicted the mean flood water depth, with a positive bias of 7 cm and root mean square difference of 15 cm. Offering approximately 100 times greater computational efficiency than its two-dimensional XBeach counterpart, this flood modeling technique is recommended for wave-driven flood modeling in scenarios with high computational demands, such as modeling numerous scenarios or undertaking detailed regional-scale modeling.

Journal of Marine Science & Engineering↗

USGS2019

Effects of infiltration characteristics on the spatial-temporal evolution of stability of an interstate highway embankment

Infiltration-induced landslides are among the most common natural disasters threatening modern civilization, but conventional methods for studying the triggering mechanisms and predicting the occurrence of these slides are limited by incomplete consideration of underlying physical processes and the lack of precision inherent in limit-equilibrium analyses. To address this problem the spatial-temporal evolution of failure is investigated in a seasonally unstable section of interstate highway embankment, known as the Straight Creek landslide, Colorado. The study includes multi-year site investigation, monitoring, and numerical simulation using a rigorous hydromechanical framework along with a field of local factor of safety method. The sensitivity of episodic landslide reactivation to infiltration characteristics is evaluated. Results indicate that annual cumulative snowmelt infiltration, which typically accounts for approximately 75% of total annual cumulative infiltration and occurs over a short period in the spring, has the most substantial impact on slide activation. The rate of snowmelt infiltration varies independently of annual cumulative snowmelt infiltration and cumulative infiltration in the previous year, but still affects antecedent soil moisture conditions at the onset of snowmelt infiltration and therefore also the level of slide activation. These findings are used to establish specific thresholds for exacerbated slide movement using annual snowpack accumulation, forecasted snowmelt rate, and the previous year’s snowmelt, an approach which may be applied for predicting movement at this and other recurring or potential slide sites.

Colorado↗

USGS2003

Ductile flow of methane hydrate

Compressional creep tests (i.e., constant applied stress) conducted on pure, polycrystalline methane hydrate over the temperature range 260-287 K and confining pressures of 50-100 MPa show this material to be extraordinarily strong compared to other icy compounds. The contrast with hexagonal water ice, sometimes used as a proxy for gas hydrate properties, is impressive: over the thermal range where both are solid, methane hydrate is as much as 40 times stronger than ice at a given strain rate. The specific mechanical response of naturally occurring methane hydrate in sediments to environmental changes is expected to be dependent on the distribution of the hydrate phase within the formation - whether arranged structurally between and (or) cementing sediments grains versus passively in pore space within a sediment framework. If hydrate is in the former mode, the very high strength of methane hydrate implies a significantly greater strain-energy release upon decomposition and subsequent failure of hydrate-cemented formations than previously expected.

Canadian Journal of Physics↗

USGS2008

Distributed energy balance modeling of South Cascade Glacier, Washington and assessment of model uncertainty

We have developed a physically based, distributed surface energy balance model to simulate glacier mass balance under meteorological and climatological forcing. Here we apply the model to estimate summer ablation on South Cascade Glacier, Washington, for the 2004 and 2005 mass balance seasons. To arrive at optimal mass balance simulations, we investigate and quantify model uncertainty associated with selecting from a range of physical parameter values that are not commonly measured in glaciological mass balance field studies. We optimize the performance of the model by varying values for atmospheric transmissivity, the albedo of surrounding topography, precipitation-elevation lapse rate, surface roughness for turbulent exchange of momentum, and snow albedo aging coefficient. Of these the snow aging parameter and precipitation lapse rates have the greatest influence on the modeled ablation. We examined model sensitivity to varying parameters by performing an additional 103 realizations with parameters randomly chosen over a ??5% range centered about the optimum values. The best fit suite of model parameters yielded a net balance of -1.69??0.38 m water equivalent (WE) for the 2004 water year and -2.10??0.30 m WE up to 11 September 2005. The 2004 result is within 3% of the measured value. These simulations account for 91% and 93% of the variance in measured ablation for the respective years. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research F: Earth Surface↗

USGS2012

Testing alternative conceptual models of seawater intrusion in a coastal aquifer using computer simulation, southern California, USA

Two alternative conceptual models of the physical processes controlling seawater intrusion in a coastal basin in California, USA, were tested to identify a likely principal pathway for seawater intrusion. The conceptual models were tested by using a two-dimensional, finite-element groundwater flow and transport model. This pathway was identified by the conceptual model that best replicated the historical data. The numerical model was applied in cross section to a submarine canyon that is a main avenue for seawater to enter the aquifer system underlying the study area. Both models are characterized by a heterogeneous, layered, water-bearing aquifer. However, the first model is characterized by flat-lying aquifer layers and by a high value of hydraulic conductivity in the basal aquifer layer, which is thought to be a principal conduit for seawater intrusion. The second model is characterized by offshore folding, which was modeled as a very nearshore outcrop, thereby providing a shorter path for seawater to intrude. General conclusions are that: 1) the aquifer system is best modeled as a flat, heterogeneous, layered system; 2) relatively thin basal layers with relatively high values of hydraulic conductivity are the principal pathways for seawater intrusion; and 3) continuous clay layers of low hydraulic conductivity play an important role in controlling the movement of seawater.

Hydrogeology Journal↗

USGS2012

Reoccupation of floodplains by rivers and its relation to the age structure of floodplain vegetation

River channel dynamics over many decades provide a physical control on the age structure of floodplain vegetation as a river occupies and abandons locations. Floodplain reoccupation by a river, in particular, determines the interval of time during which vegetation can establish and mature. A general framework for analyzing floodplain reoccupation and a time series model are developed and applied to five alluvial rivers in the United States. Channel dynamics in these rivers demonstrate time-scale dependence with short-term oscillation in active channel area in response to floods and subsequent vegetation growth and progressive lateral movement that accounts for much of the cumulative area occupied by the rivers over decades. Rivers preferentially reoccupy locations recently abandoned causing a decreasing probability of reoccupation with time since abandonment. For a typical case, a river is 10 times more likely to reoccupy an area it abandoned in the past decade than it is to reoccupy an area it abandoned 30 yrs ago. The decreasing probability of reoccupation over time is consistent with observations of persistent stands of late seral stage floodplain forest. A power function provides a robust approach for estimating the cumulative area occupied by a river and the age structure of riparian forests resulting from a specific historical sequence of streamflow in comparison to either linear or exponential alternatives.

Journal of Geophysical Research↗

USGS2021

Postwildfire soil‐hydraulic recovery and the persistence of debris flow hazards

Deadly and destructive debris flows often follow wildfire, but understanding of changes in the hazard potential with time since fire is poor. We develop a simulation‐based framework to quantify changes in the hydrologic triggering conditions for debris flows as postwildfire infiltration properties evolve through time. Our approach produces time‐varying rainfall intensity‐duration thresholds for runoff‐ and infiltration‐generated debris flows with physics‐based hydrologic simulations that are parameterized with widely available hydroclimatic, vegetation reflectance, and soil texture data. When we apply our thresholding protocol to a test case in the San Gabriel Mountains (California, USA), the results are consistent with existing regional empirical thresholds and rainstorms that caused runoff‐ and infiltration‐generated debris flows soon after and three years following a wildfire, respectively. We find that the hydrologic triggering mechanisms for the two observed debris flow types are coupled with the effects of fire on the soil saturated hydraulic conductivity. Specifically, the rainfall intensity needed to generate debris flows via runoff increases with time following wildfire while the rainfall duration needed to produce debris flows via subsurface pore‐water pressures decreases. We also find that variations in soil moisture, rainfall climatology, median grain size, and root reinforcement could impact the median annual probability of postwildfire debris flows. We conclude that a simulation‐based method for calculating rainfall thresholds is a tractable approach to improve situational awareness of debris flow hazard in the years following wildfire. Further development of our framework will be important to quantify postwildfire hazard levels in variable climates, vegetation types, and fire regimes.

Journal of Geophysical Research: Earth Surface↗

USGS2011

Discrete choice modeling of shovelnose sturgeon habitat selection in the Lower Missouri River

Substantive changes to physical habitat in the Lower Missouri River, resulting from intensive management, have been implicated in the decline of pallid ( Scaphirhynchus albus ) and shovelnose ( S. platorynchus ) sturgeon. To aid in habitat rehabilitation efforts, we evaluated habitat selection of gravid, female shovelnose sturgeon during the spawning season in two sections (lower and upper) of the Lower Missouri River in 2005 and in the upper section in 2007. We fit discrete choice models within an information theoretic framework to identify selection of means and variability in three components of physical habitat. Characterizing habitat within divisions around fish better explained selection than habitat values at the fish locations. In general, female shovelnose sturgeon were negatively associated with mean velocity between them and the bank and positively associated with variability in surrounding depths. For example, in the upper section in 2005, a 0.5 m s −1 decrease in velocity within 10 m in the bank direction increased the relative probability of selection 70%. In the upper section fish also selected sites with surrounding structure in depth (e.g., change in relief). Differences in models between sections and years, which are reinforced by validation rates, suggest that changes in habitat due to geomorphology, hydrology, and their interactions over time need to be addressed when evaluating habitat selection. Because of the importance of variability in surrounding depths, these results support an emphasis on restoring channel complexity as an objective of habitat restoration for shovelnose sturgeon in the Lower Missouri River.

Kansas, Missouri, Nebraska, South Dakota↗

USGS2012

The high-pressure electronic structure of magnesiowustite (Mg, Fe)O: applications to the physics and chemistry of the lower mantle

The electronic structure of magnesiowustite is investigated using self-consistent field X α scattered wave (SCF- X α-SW) molecular orbital calculations on (FeO 6 ) 10− and (FeMg 12 O 14 ) 2− clusters. Calculated one-electron transition energies are used to interpret the optical spectrum of (Mg, Fe)O. The results are applied to the electrical and thermal conductivity of the lower mantle. The spin pairing of Fe 2+ and the effect of pressure on bonding in magnesiowustite, with some inferences regarding the incorporation of oxygen in the outer core, is also addressed. The approach used here appears to give a reliable description of the energy and pressure dependence of the spin-allowed 5 T 2 g → 5 E g ligand field transition and the spin-pairing transition of Fe 2+ in (Mg, Fe)O. However, the oxygen to metal charge transfer transitions in (Mg, Fe)O are not as reliably determined insofar as the p - d band gap varies with cluster size and the energies of the charge transfer states cannot be found without including configurational interaction. Nevertheless, it is argued that the charge transfer transitions that are intrinsic to (Fe, Mg)O are of a sufficiently high energy to be irrelevant to the electrical and thermal conductivity of the lower mantle. This is especially true if Fe 2+ adopts the low-spin configuration. The geophysically significant properties of (Fe, Mg)O probably result from defect Fe 3+ .

Journal of Geophysical Research↗