SEARCH · Geology Reports

Results for “Processes”

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

SourceResearch connectionFrom yearThrough year

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

At least 217 records · Page 12Linked to original sources

USGS2018

Overview and progress of the pallid sturgeon assessment framework redesign process

The Pallid Sturgeon Population Assessment Program (PSPAP) was initiated in 2003, and full implementation began in 2006, to monitor the trend of Scaphirhynchus albus (pallid sturgeon) and native fish communities in the Upper and Lower Missouri River Basins. The original PSPAP (v. 1.0) was a catch-effort based monitoring program where population abundance and trend were monitored using a relative index, catch per unit effort. In 2013, the Missouri River Recovery Program (MRRP), led by the U.S. Army Corps of Engineers (USACE) and the U.S. Fish and Wildlife Service (USFWS), began a reassessment of science and monitoring approaches to support a new river management plan. The need to redesign the PSPAP was triggered by the recognition that the PSPAP v. 1.0 would not be optimally effective in contributing information needed to make decisions about the pallid sturgeon fundamental management objective—to avoid jeopardizing the continued existence of the pallid sturgeon from USACE actions in the Missouri River—identified in the Missouri River Science and Adaptive Management Plan. The fundamental management objective includes two management subobjectives: (1) increase pallid sturgeon recruitment to age 1 and (2) maintain or increase numbers of pallid sturgeon as an interim measure until sufficient and sustained natural recruitment occurs. These two management subobjectives motivated the development of two fundamental information objectives for PSPAP v. 2.0: (1) to provide information needed to quantify recruitment to age 1 and (2) to quantify pallid sturgeon population abundance and trend. The charge to the authors of this report was to develop an approach to monitoring the pallid sturgeon population in the Missouri River that would contribute information toward gauging overall performance of management actions to achieve the fundamental objectives of the MRRP and to potentially improve understanding of linkages from the management activities to population responses. We used transparent and robust processes to identify alternative monitoring designs that meet the fundamental objectives for managing pallid sturgeon in the MRRP, with a focus on simulation models to evaluate the performance of varying monitoring. This report documents the process of comparing potential alternative monitoring design abilities to provide decision-relevant information for management of the species. The process includes evaluation of information content and attendant uncertainties and considers tradeoffs in types of information valued by stakeholders. The anticipated end product of this process will be synthesized in a decision-support tool that can be used to facilitate learning and iterative revisions of the monitoring roadmap.

Open-File Report↗

USGS1992

Digital mapping of side-scan sonar data with the Woods Hole Image Processing System software

Since 1985, the Branch of Atlantic Marine Geology has been involved in collecting, processing and digitally mosaicking high and low resolution sidescan sonar data. In the past, processing and digital mosaicking has been accomplished with a dedicated, shore-based computer system. Recent development of a UNIX-based image-processing software system includes a series of task specific programs for pre-processing sidescan sonar data. To extend the capabilities of the UNIX-based programs, development of digital mapping techniques have been developed. This report describes the initial development of an automated digital mapping procedure. Included is a description of the programs and steps required to complete the digital mosaicking on a UNIXbased computer system, and a comparison of techniques that the user may wish to select.

Open-File Report↗

USGS2015

Arctic Alaska’s Lower Cretaceous (Hauterivian and Barremian) mudstone succession—Linking lithofacies, texture, and geochemistry to marine processes

We present new images and descriptions of the lithofacies and organic facies of the pebble shale unit and lower part of the Hue Shale (Lower Cretaceous) of Arctic Alaska at a high magnification that illustrates their textural characteristics. Our aims were to describe and determine the distribution of facies in these petroleum source rocks and to identify the processes that formed them. We sampled at high-resolution and applied new petrographic techniques combined with scanning electron microscopy and geochemical analyses to samples collected from three widely spaced sections—located in exposures along the Canning River and continuous core from the Mikkelsen Bay State 1 and Orion 1 wells. Results from these three locations indicate that this succession consists primarily of clay-rich mudstones that are variously silt- or sand-bearing and clay-dominated mudstones that exhibit mainly relict, 2–5 millimeter thick bedding and common but variable microbioturbation, rare macrobioturbation, and common fabrics of pelleted clay and silt. These mudstones contain rare, poorly sorted, silt-rich basal laminae that are often discontinuous and have wavy, sharp bases and crude upward fining. In addition, mud-supported, outsized clasts (dropstones) of fine sand to pebble size are present throughout the succession as isolated clasts or in clusters. We interpret these textures and much of this succession to result from intermittent deposition by suspension settling from melting seasonal sea ice—sometimes sediment-laden—and associated primary productivity. Overall, this mudstone succession fines and deepens upward from the pebble shale unit into the Hue Shale. In the Hue Shale of the Orion well, however, different processes intermittently deposited thin, discrete intervals of coarser sediment that probably represent deposition from density currents. Also in the Hue Shale of the Orion well, several thicker sandstone and silt-dominated mudstone units with discordant, scoured bases and cut and fill structures represent erosion during higher energy events such as major storms. Other lithofacies within the succession are graded tuffs/bentonites and tuffaceous/bentonitic mudstones from episodic volcanic ash falls; these are abundant in the Hue Shale, and very rare in the pebble shale unit of the two wells. Organic-carbon rich strata associated with volcanic ash intervals of the pebble shale unit and Hue Shale in the Mikkelsen 1 well have some of the best petroleum source rock potential determined for this succession. Authigenic pyrite and carbonate-cement-dominated mudstone are also present in both units of all three sections. The carbonate-cemented units indicate breaks in sedimentation and are common in the Hue Shale and in sections of the pebble shale unit interpreted to be more distal, such as along the Canning River. Our results document the variation in facies and textures of the Hauterivian and Barremian Lower Cretaceous mudstone succession of Arctic Alaska. Comparison of these characteristics to the products of modern processes on the North Slope of Alaska, in the Beaufort Sea, and elsewhere suggest that this succession formed primarily from depositional processes related to seasonal sea ice with intermittent fluvial-sourced sediment deposited by density currents and episodic erosion and reworking by storms and other currents.

Alaska↗

USGS2009

Evaluation of Sources of Nitrate Beneath Food Processing Wastewater-Application Sites near Umatilla, Oregon

Water samples from wells were collected beneath and downgradient of two food-processing wastewater-application sites near Umatilla, Oregon. These samples were analyzed for nitrate stable isotopes, nutrients, major ions, and age-dating constituents to determine if nitrate-stable isotopes can be used to differentiate food-processing waste from other potential sources of nitrate. Major-ion data from each site were used to determine which samples were associated with the recharge of the food-processing wastewater. End-member mixing analysis was used to determine the relative amounts of each identified end member within the samples collected from the Terrace Farm site. The delta nitrogen-15 (delta 15N) of nitrate generally ranged between +2 and +9 parts per thousand and the delta oxygen-18 (delta 18O) of nitrate generally ranged between -2 and -7 parts per thousand. None of the samples that were determined to be associated with the wastewater were different from the samples that were not affected by the wastewater. The nitrate isotope values measured in this study are also characteristic of ammonium fertilizer, animal and human waste, and soil nitrate; therefore, it was not possible to differentiate between food-processing wastewater and the other nitrate sources. Values of delta 15N and delta 18O of nitrate provided no more information about the sources of nitrate in the Umatilla River basin than did a hydrologic and geochemical understanding of the ground-water system derived from interpreting water-level and major-ion chemistry data.

Scientific Investigations Report↗

USGS1979

Arctic stream processes--an annotated bibliography

This bibliography selectively summarizes investigations to date (1978) dealing with the physical processes of streams in the Arctic. The specialized annotations include aspects of stream processes described in subordinate parts of general papers on the arctic environment and therefore not evident in author-abstract bibliographies. Foreign contributions--Canadian, Scandinavian, and Russian--are summarized, in the case of Russian literature primarily by means of papers in translation journals. Until 1970 the role of streams in development of the arctic landscape was commonly considered subordinate to that of glacial and frost-related processes. This conclusion changed, however, with the findings of the many new studies begun in response to oil and gas discoveries in the late 1960's. The conclusions of these studies, made to provide both the engineering data for resource development and the information to assess the impacts of that development, were in general agreement that stream processes throughout most of the Arctic were significantly more important than previously had been thought.

Water Supply Paper↗

USGS2018

Development of a species status assessment process for decisions under the U.S. Endangered Species Act

Decisions under the U.S. Endangered Species Act (ESA) require scientific input on the risk that the species will become extinct. A series of critiques on the role of science in ESA decisions have called for improved consistency and transparency in species risk assessments and clear distinctions between science input and policy application. To address the critiques and document the emerging practice of the U.S. Fish and Wildlife Service (USFWS), we outline an assessment process based on principles and practices of risk and decision analyses that results in a scientific report on species status. The species status assessment (SSA) process has three successive stages: 1) document the life history and ecological relationships of the species in question to provide the foundation for the assessment, 2) describe and hypothesize causes for the current condition of the species, and 3) forecast the species' future condition. The future condition refers to the ability of a species to sustain populations in the wild under plausible future scenarios. The scenarios help explore the species' response to future environmental stressors and to assess the potential for conservation to intervene to improve its status. The SSA process incorporates modeling and scenario planning for prediction of extinction risk and applies the conservation biology principles of representation, resiliency, and redundancy to evaluate the current and future condition. The SSA results in a scientific report distinct from policy application, which contributes to streamlined, transparent, and consistent decision-making and allows for greater technical participation by experts outside of the USFWS, for example, by state natural resource agencies. We present two case studies based on assessments of the eastern massasauga rattlesnake Sistrurus catenatus and the Sonoran Desert tortoise Gopherus morafkai to illustrate the process. The SSA builds upon the past threat-focused assessment by including systematic and explicit analyses of a species' future response to stressors and conservation, and as a result, we believe it provides an improved scientific analysis for ESA decisions.

Journal of Fish and Wildlife Management↗

USGS2017

Community tools for cartographic and photogrammetric processing of Mars Express HRSC images

The High Resolution Stereo Camera (HRSC) on the Mars Express orbiter (Neukum et al. 2004) is a multi-line pushbroom scanner that can obtain stereo and color coverage of targets in a single overpass, with pixel scales as small as 10 m at periapsis. Since commencing operations in 2004 it has imaged ~ 77 % of Mars at 20 m/pixel or better. The instrument team uses the Video Image Communication And Retrieval (VICAR) software to produce and archive a range of data products from uncalibrated and radiometrically calibrated images to controlled digital topographic models (DTMs) and orthoimages and regional mosaics of DTM and orthophoto data (Gwinner et al. 2009; 2010b; 2016). Alternatives to this highly effective standard processing pipeline are nevertheless of interest to researchers who do not have access to the full VICAR suite and may wish to make topographic products or perform other (e. g., spectrophotometric) analyses prior to the release of the highest level products. We have therefore developed software to ingest HRSC images and model their geometry in the USGS Integrated Software for Imagers and Spectrometers (ISIS3), which can be used for data preparation, geodetic control, and analysis, and the commercial photogrammetric software SOCET SET (® BAE Systems; Miller and Walker 1993; 1995) which can be used for independent production of DTMs and orthoimages. The initial implementation of this capability utilized the then-current ISIS2 system and the generic pushbroom sensor model of SOCET SET, and was described in the DTM comparison of independent photogrammetric processing by different elements of the HRSC team (Heipke et al. 2007). A major drawback of this prototype was that neither software system then allowed for pushbroom images in which the exposure time changes from line to line. Except at periapsis, HRSC makes such timing changes every few hundred lines to accommodate changes of altitude and velocity in its elliptical orbit. As a result, it was necessary to split observations into blocks of constant exposure time, greatly increasing the effort needed to control the images and collect DTMs. Here, we describe a substantially improved HRSC processing capability that incorporates sensor models with varying line timing in the current ISIS3 system (Sides 2017) and SOCET SET. This enormously reduces the work effort for processing most images and eliminates the artifacts that arose from segmenting them. In addition, the software takes advantage of the continuously evolving capabilities of ISIS3 and the improved image matching module NGATE (Next Generation Automatic Terrain Extraction, incorporating area and feature based algorithms, multi-image and multi-direction matching) of SOCET SET, thus greatly reducing the need for manual editing of DTM errors. We have also developed a procedure for geodetically controlling the images to Mars Orbiter Laser Altimeter (MOLA) data by registering a preliminary stereo topographic model to MOLA by using the point cloud alignment ( pc_align ) function of the NASA Ames Stereo Pipeline (ASP; Moratto et al. 2010). This effectively converts inter-image tiepoints into ground control points in the MOLA coordinate system. The result is improved absolute accuracy and a significant reduction in work effort relative to manual measurement of ground control. The ISIS and ASP software used are freely available; SOCET SET, is a commercial product. By the end of 2017 we expect to have ported our SOCET SET HRSC sensor model to the Community Sensor Model (CSM; Community Sensor Model Working Group 2010; Hare and Kirk 2017) standard utilized by the successor photogrammetric system SOCET GXP that is currently offered by BAE. In early 2018, we are also working with BAE to release the CSM source code under a BSD or MIT open source license.

The International Archives of the Photogrammetry, ↗

USGS2024

Rapid simulation of wave runup on morphologically diverse, reef-lined coasts with the BEWARE-2 (Broad-range Estimator of Wave Attack in Reef Environments) meta-process model

Low-lying, tropical, coral-reef-lined coastlines are becoming increasingly vulnerable to wave-driven flooding due to population growth, coral reef degradation, and sea-level rise. Early-warning systems (EWSs) are needed to enable coastal authorities to issue timely alerts and coordinate preparedness and evacuation measures for their coastal communities. At longer timescales, risk management and adaptation planning require robust assessments of future flooding hazard considering uncertainties. However, due to diversity in reef morphologies and complex reef hydrodynamics compared to sandy shorelines, there have been no robust analytical solutions for wave runup to allow for the development of large-scale coastal wave-driven flooding EWSs and risk assessment frameworks for reef-lined coasts. To address the need for fast, robust predictions of runup that account for the natural variability in coral reef morphologies, we constructed the BEWARE-2 (Broad-range Estimator of Wave Attack in Reef Environments) meta-process modeling system. We developed this meta-process model using a training dataset of hydrodynamics and wave runup computed by the XBeach Non-Hydrostatic process-based hydrodynamic model for 440 combinations of water level, wave height, and wave period with 195 representative reef profiles that encompass the natural diversity in real-world fringing coral reef systems. Through this innovation, BEWARE-2 can be applied in a larger range of coastal settings than meta-models that rely on a parametric description of the coral reef geometry. In the validation stage, the BEWARE-2 modeling system produced runup results that had a relative root mean square error of 13% and relative bias of 5% relative to runup simulated by XBeach Non-Hydrostatic for a large range of oceanographic forcing conditions and for diverse reef morphologies (root mean square error and bias 0.63 and 0.26 m, respectively, relative to mean simulated wave runup of 4.85 m). Incorporating parametric modifications in the modeling system to account for variations in reef roughness and beach slope allows for systematic errors (relative bias) in BEWARE-2 predictions to be reduced by a factor of 1.5–6.5 for relatively coarse or smooth reefs and mild or steep beach slopes. This prediction provided by the BEWARE-2 modeling system is faster by 4–5 orders of magnitude than the full, process-based hydrodynamic model and could therefore be integrated into large-scale EWSs for tropical, reef-lined coasts and used for large-scale flood risk assessments.

Natural Hazards and Earth System Sciences↗

USGS2005

The five elements process: Designing optimal landscapes to meet bird conservation objectives

In February 2004 at Port Aransas, Texas, Partners in Flight (PIF) and representatives from the other NABCI bird initiative met to discuss the process of stepping down PIF continental population objectives (Rich et al. 2004) to regional and local scales. Participants also discussed rolling up local population estimates and targets to assess the feasibility of the landscape changes necessary to meet continental objectives. Since the process of stepping-down/rolling-up population objectives shifts focus from identifying priority species to formulating quantitative estimates of how much habitat was needed, where, and by when the Port Aransas group called the stepping-down/rolling-up process a??stepping forward.a?? Participants agreed that stepping forward objectives was the beginning of an inevitably iterative dialog necessary to evaluate the assumptions of PIF population estimates and objectives as well as the methods used to monitor local implementation. To facilitate the translation of continental population objectives into biologically sound, measurable regional and local population-based habitat targets the Port Aransas group recommended a process no commonly referred to as the Five Elements Processa?|

Partners in Flight Technical Series↗

USGS2012

Expanding biological data standards development processes for US IOOS: visual line transect observing community for mammal, bird, and turtle data

The US Integrated Ocean Observing System (IOOS) has recently adopted standards for biological core variables in collaboration with the US Geological Survey/Ocean Biogeographic Information System (USGS/OBIS-USA) and other federal and non-federal partners. In this Community White Paper (CWP) we provide a process to bring into IOOS a rich new source of biological observing data, visual line transect surveys, and to establish quality data standards for visual line transect observations, an important source of at-sea bird, turtle and marine mammal observation data. The processes developed through this exercise will be useful for other similar biogeographic observing efforts, such as passive acoustic point and line transect observations, tagged animal data, and mark-recapture (photo-identification) methods. Furthermore, we suggest that the processes developed through this exercise will serve as a catalyst for broadening involvement by the larger marine biological data community within the goals and processes of IOOS.

Conference Paper↗

USGS2016

Integrated water flow model and modflow-farm process: A comparison of theory, approaches, and features of two integrated hydrologic models

Effective modeling of conjunctive use of surface and subsurface water resources requires simulation of land use-based root zone and surface flow processes as well as groundwater flows, streamflows, and their interactions. Recently, two computer models developed for this purpose, the Integrated Water Flow Model (IWFM) from the California Department of Water Resources and the MODFLOW with Farm Process (MF-FMP) from the US Geological Survey, have been applied to complex basins such as the Central Valley of California. As both IWFM and MFFMP are publicly available for download and can be applied to other basins, there is a need to objectively compare the main approaches and features used in both models. This paper compares the concepts, as well as the method and simulation features of each hydrologic model pertaining to groundwater, surface water, and landscape processes. The comparison is focused on the integrated simulation of water demand and supply, water use, and the flow between coupled hydrologic processes. The differences in the capabilities and features of these two models could affect the outcome and types of water resource problems that can be simulated.

California Natural Resources Agency↗

USGS2017

Permafrost-related processes and recent response to climatic changes

Permafrost-related processes have direct and indirect consequences to northern environments, but the impacts are affected by complex interactions involving positive and negative feedbacks at the surface (Jorgenson et al. 2010), climatic trends and fluctuations (Romanovsky et al. 2010; Konishchev 2011), and terrain and ground ice conditions (French and Shur 2010, Ukraintseva et al. 2012; Murton 2013). The degradation (reduction of thickness and/or lateral extent) of permafrost and the related disturbance of the surface are associated with a diverse set of processes such as thermokarst (the thawing of ice-rich permafrost or the melting of massive ice followed by subsidence of the ground surface and potential formation of a water body), thermal erosion (downwearing from moving water), thermal abrasion (backwearing from moving water), and thermal denudation associated with hillslope processes (downslope movement of soil or rock, such as frost creep, solifluction and cryogenic landslides including active-layer detachments and retrogressive thaw slumps). At the same time, the aggradation of permafrost and related processes (e.g., frost heave and formation of ice wedges and pingos) are still occurring during the observed climatic warming trend in the northern hemisphere. For example, the drainage of thermokarst lakes expose taliks (unfrozen ground beneath the water body) to the negative mean-annual ground surface temperatures in the continuous and discontinuous permafrost zone, which results in talik freezing accompanied by accumulation of ground ice. Both permafrost aggradation and degradation associated with thermokarst and other thaw-related features requires further observation and study to determine the pan-Arctic response of the landscape to climatic trends and fluctuations.

Book chapter↗

USGS2016

Combined use of isotopic and hydrometric data to conceptualize ecohydrological processes in a high-elevation tropical ecosystem

Few high-elevation tropical catchments worldwide are gauged and even fewer are studied using combined hydrometric and isotopic data. Consequently, we lack information needed to understand processes governing rainfall-runoff dynamics and to predict their influence on downstream ecosystem functioning. To address this need, we present a combination of hydrometric and water stable isotopic observations in the wet Andean páramo ecosystem of the Zhurucay Ecohydrological Observatory (7.53 km2). The catchment is located in the Andes of south Ecuador between 3400 and 3900 m a.s.l. Water samples for stable isotopic analysis were collected during 2 years (May 2011 – May 2013), while rainfall and runoff measurements were continuously recorded since late 2010. The isotopic data reveal that Andosol soils predominantly situated on hillslopes drain laterally to Histosols (Andean páramo wetlands) mainly located at the valley bottom. Histosols, in turn, feed water to creeks and small rivers throughout the year, establishing hydrologic connectivity between wetlands and the drainage network. Runoff is primarily comprised of pre-event water stored in the Histosols, which is replenished by rainfall that infiltrates through the Andosols. Contributions from the mineral horizon and the top of the fractured bedrock are small and only seem to influence discharge in small catchments during low flow generation (non-exceedance flows < Q35). Variations in source contributions are controlled by antecedent soil moisture, rainfall intensity, and duration of rainy periods. Saturated hydraulic conductivity of the soils, higher than the year-round low precipitation intensity, indicates that Hortonian overland flow rarely occurs during high intensity precipitation events. Deep groundwater contributions to discharge seem to be minimal. These results suggest that, in this high-elevation tropical ecosystem: 1) subsurface flow is a dominant hydrological process and 2) (Histosols) wetlands are the major source of stream runoff. Our study highlights that detailed isotopic characterization during short time periods provides valuable information about ecohydrological processes in regions where very few basins are gauged.

Zhurucay River Ecohydrological Observatory↗

USGS2024

Evaluating a process-guided deep learning approach for predicting dissolved oxygen in streams

Dissolved oxygen (DO) is a critical water quality constituent that governs habitat suitability for aquatic biota, biogeochemical reactions and solubility of metals in streams. Recently introduced high-frequency sensors have increased our ability to measure DO, but we still lack the capacity to understand and predict DO concentrations at high spatial resolutions or in unmonitored locations. Machine learning (ML) has been a commonly used approach for modelling DO, however, conventional ML models have no representation of the limnological processes governing DO dynamics. Here we implement and evaluate two process-guided deep learning (PGDL) approaches for predicting daily minimum, mean and maximum DO concentrations in rivers from the Delaware River Basin, USA. In both cases, a multi-task approach was taken in which the PGDL models predicted stream metabolism and gas exchange rates in addition to the DO concentrations themselves. Our results showed that for these sites, the PGDL approaches did not improve upon baseline predictions in temporal and spatially similar holdout experiments. One of the approaches did, however, improve predictions when applied to spatially dissimilar sites. Although this particular PGDL approach did not improve predictive accuracy in most cases, our results suggest that process guidance, perhaps a more constrained approach, could benefit a data-driven DO model.

Hydrological Processes↗

USGS2013

Fate of process solution cyanide and nitrate at three Nevada gold mines inferred from stable carbon and nitrogen isotope measurements

Stable isotope methods have been used to identify the mechanisms responsible for cyanide consumption at three heap-leach operations that process Carlin-type gold ores in Nevada, U.S.A. The reagent cyanide had δ 15 N values ranging from -5 to -2‰ and δ 13C values from -60 to -35‰. The wide δ 13 C range reflects the use by different suppliers of isotopically distinct natural-gas feedstocks and indicates that isotopes may be useful in environmental studies where there is a need to trace cyanide sources. In heap-leach circuits displaying from 5 to 98% consumption of cyanide, barren-solution and pregnant-solution cyanide were isotopically indistinguishable. The similarity is inconsistent with cyanide loss predominantly by HCN offgassing (a process that in laboratory experiments caused substantial isotopic changes), but it is consistent with cyanide retention within the heaps as solids, a process that caused minimal isotopic changes in laboratory simulations, or with cyanide oxidation, which also appears to cause minimal changes. In many pregnant solutions cyanide was carried entirely as metal complexes, which is consistent with ferrocyanides having precipitated or cyano-complexes having been adsorbed within the heaps. It is inferred that gaseous cyanide emissions from operations of this type are less important than has generally been thought and that the dissolution or desorption kinetics of solid species is an important control on cyanide elution when the spent heaps undergo rinsing. Nitrate, nitrite and ammonium had δ 15 N values of 1-16‰. The data reflect isotopic fractionation during ammonia offgassing or denitrification of nitrate–particularly in reclaim ponds–but do not indicate the extent to which nitrate is derived from cyanide or from explosive residues.

Nevada↗

USGS2006

Unsaturated zone flow processes

Water flow in the unsaturated zone is greatly influenced by unsaturated hydrostatics (water content, energy, pressure, and retention) and by unsaturated hydrodynamics (diffuse flow and preferential flow). Important multiphase processes include the transport of gases, nonaqueous liquids, and solid particles. Numerous means are available for determination of unsaturated conditions and properties, both measurement (of moisture state, water retention, and dynamic characteristics) and through various formulas and models that are mostly empirical in nature, but in some cases incorporating insight into unsaturated‐zone physical processes. Applications to practical problems include models and techniques relating to distributions of water and energy, fluxes at the land surface, inputs, outputs, and fluxes within the unsaturated zone, all of which are frequently complicated by heterogeneity and preferential flow. Further scientific advance requires new measurement techniques and theoretical constructs that more adequately represent the important physical processes within practical modeling schemes.

Book chapter↗

USGS2014

Preslip and cascade processes initiating laboratory stick slip

Recent modeling studies have explored whether earthquakes begin with a large aseismic nucleation process or initiate dynamically from the rapid growth of a smaller instability in a “cascade-up” process. To explore such a case in the laboratory, we study the initiation of dynamic rupture (stick slip) of a smooth saw-cut fault in a 76mm diameter cylindrical granite laboratory sample at 40–120MPa confining pressure. We use a high dynamic range recording system to directly compare the seismic waves radiated during the stick-slip event to those radiated from tiny (M _6) discrete seismic events, commonly known as acoustic emissions (AEs), that occur in the seconds prior to each large stick slip. The seismic moments, focal mechanisms, locations, and timing of the AEs all contribute to our understanding of their mechanics and provide us with information about the stick-slip nucleation process. In a sequence of 10 stick slips, the first few microseconds of the signals recorded from stick-slip instabilities are nearly indistinguishable from those of premonitory AEs. In this sense, it appears that each stick slip begins as an AE event that rapidly (~20 μs) grows about 2 orders of magnitude in linear dimension and ruptures the entire 150mm length of the simulated fault. We also measure accelerating fault slip in the final seconds before stick slip. We estimate that this slip is at least 98% aseismic and that it both weakens the fault and produces AEs that will eventually cascade-up to initiate the larger dynamic rupture.

Journal of Geophysical Research B: Solid Earth↗

USGS2016

Processes of multibathyal aragonite undersaturation in the Arctic Ocean

During 3 years of study (2010–2012), the western Arctic Ocean was found to have unique aragonite saturation profiles with up to three distinct aragonite undersaturation zones. This complexity is produced as inflow of Atlantic-derived and Pacific-derived water masses mix with Arctic-derived waters, which are further modified by physiochemical and biological processes. The shallowest aragonite undersaturation zone, from the surface to ∼30 m depth is characterized by relatively low alkalinity and other dissolved ions. Besides local influence of biological processes on aragonite undersaturation of shallow coastal waters, the nature of this zone is consistent with dilution by sea-ice melt and invasion of anthropogenic CO 2 from the atmosphere. A second undersaturated zone at ∼90–220 m depth (salinity ∼31.8–35.4) occurs within the Arctic Halocline and is characterized by elevated p CO 2 and nutrients. The nature of this horizon is consistent with remineralization of organic matter on shallow continental shelves bordering the Canada Basin and the input of the nutrients and CO 2 entrained by currents from the Pacific Inlet. Finally, the deepest aragonite undersaturation zone is at greater than 2000 m depth and is controlled by similar processes as deep aragonite saturation horizons in the Atlantic and Pacific Oceans. The comparatively shallow depth of this deepest aragonite saturation horizon in the Arctic is maintained by relatively low temperatures, and stable chemical composition. Understanding the mechanisms controlling the distribution of these aragonite undersaturation zones, and the time scales over which they operate will be crucial to refine predictive models.

Journal of Geophysical Research: Oceans↗