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At least 811 records · Page 45Linked to original sources
USGS2009

Simulating and understanding sand wave variation: A case study of the Golden Gate sand waves

In this paper we present a detailed comparison between measured features of the Golden Gate sand wave field and the results of a nonlinear sand wave model. Because the Golden Gate sand waves exhibit large variation in their characteristics and in their environmental physics, this area gives us the opportunity to study sand wave variation between locations, within one well-measured, large area. The nonlinear model used in this paper is presently the only tool that provides information on the nonlinear evolution of large-amplitude sand waves. The model is used to increase our understanding of the coupling between the variability in environmental conditions and the sand wave characteristics. Results show that the model is able to describe the variation in the Golden Gate sand waves well when both the local oscillating tidal current and the residual current are taken into account. Current and water depth seem to be the most important factors influencing sand wave characteristics. The simulation results give further confidence in the underlying model hypothesis and assumptions. Copyright 2009 by the American Geophysical Union.

Journal of Geophysical Research F: Earth Surface↗
USGS2009

Assessing reservoir operations risk under climate change

Risk-based planning offers a robust way to identify strategies that permit adaptive water resources management under climate change. This paper presents a flexible methodology for conducting climate change risk assessments involving reservoir operations. Decision makers can apply this methodology to their systems by selecting future periods and risk metrics relevant to their planning questions and by collectively evaluating system impacts relative to an ensemble of climate projection scenarios (weighted or not). This paper shows multiple applications of this methodology in a case study involving California's Central Valley Project and State Water Project systems. Multiple applications were conducted to show how choices made in conducting the risk assessment, choices known as analytical design decisions, can affect assessed risk. Specifically, risk was reanalyzed for every choice combination of two design decisions: (1) whether to assume climate change will influence flood-control constraints on water supply operations (and how), and (2) whether to weight climate change scenarios (and how). Results show that assessed risk would motivate different planning pathways depending on decision-maker attitudes toward risk (e.g., risk neutral versus risk averse). Results also show that assessed risk at a given risk attitude is sensitive to the analytical design choices listed above, with the choice of whether to adjust flood-control rules under climate change having considerably more influence than the choice on whether to weight climate scenarios. Copyright 2009 by the American Geophysical Union.

Water Resources Research↗
USGS2011

The influence of the Atlantic Warm Pool on the Florida panhandle sea breeze

In this paper we examine the variations of the boreal summer season sea breeze circulation along the Florida panhandle coast from relatively high resolution (10 km) regional climate model integrations. The 23 year climatology (1979–2001) of the multidecadal dynamically downscaled simulations forced by the National Centers for Environmental Prediction–Department of Energy (NCEP‐DOE) Reanalysis II at the lateral boundaries verify quite well with the observed climatology. The variations at diurnal and interannual time scales are also well simulated with respect to the observations. We show from composite analyses made from these downscaled simulations that sea breezes in northwestern Florida are associated with changes in the size of the Atlantic Warm Pool (AWP) on interannual time scales. In large AWP years when the North Atlantic Subtropical High becomes weaker and moves further eastward relative to the small AWP years, a large part of the southeast U.S. including Florida comes under the influence of relatively strong anomalous low‐level northerly flow and large‐scale subsidence consistent with the theory of the Sverdrup balance. This tends to suppress the diurnal convection over the Florida panhandle coast in large AWP years. This study is also an illustration of the benefit of dynamic downscaling in understanding the low‐frequency variations of the sea breeze.

Florida↗
USGS2011

Opportunity Mars Rover mission: Overview and selected results from Purgatory ripple to traverses to Endeavour crater

Opportunity has been traversing the Meridiani plains since 25 January 2004 (sol 1), acquiring numerous observations of the atmosphere, soils, and rocks. This paper provides an overview of key discoveries between sols 511 and 2300, complementing earlier papers covering results from the initial phases of the mission. Key new results include (1) atmospheric argon measurements that demonstrate the importance of atmospheric transport to and from the winter carbon dioxide polar ice caps; (2) observations showing that aeolian ripples covering the plains were generated by easterly winds during an epoch with enhanced Hadley cell circulation; (3) the discovery and characterization of cobbles and boulders that include iron and stony-iron meteorites and Martian impact ejecta; (4) measurements of wall rock strata within Erebus and Victoria craters that provide compelling evidence of formation by aeolian sand deposition, with local reworking within ephemeral lakes; (5) determination that the stratigraphy exposed in the walls of Victoria and Endurance craters show an enrichment of chlorine and depletion of magnesium and sulfur with increasing depth. This result implies that regional-scale aqueous alteration took place before formation of these craters. Most recently, Opportunity has been traversing toward the ancient Endeavour crater. Orbital data show that clay minerals are exposed on its rim. Hydrated sulfate minerals are exposed in plains rocks adjacent to the rim, unlike the surfaces of plains outcrops observed thus far by Opportunity. With continued mechanical health, Opportunity will reach terrains on and around Endeavour's rim that will be markedly different from anything examined to date.

Journal of Geophysical Research E: Planets↗
USGS2012

Advances in the simulation and automated measurement of well-sorted granular material: 1. Simulation

1. In this, the first of a pair of papers which address the simulation and automated measurement of well-sorted natural granular material, a method is presented for simulation of two-phase (solid, void) assemblages of discrete non-cohesive particles. The purpose is to have a flexible, yet computationally and theoretically simple, suite of tools with well constrained and well known statistical properties, in order to simulate realistic granular material as a discrete element model with realistic size and shape distributions, for a variety of purposes. The stochastic modeling framework is based on three-dimensional tessellations with variable degrees of order in particle-packing arrangement. Examples of sediments with a variety of particle size distributions and spatial variability in grain size are presented. The relationship between particle shape and porosity conforms to published data. The immediate application is testing new algorithms for automated measurements of particle properties (mean and standard deviation of particle sizes, and apparent porosity) from images of natural sediment, as detailed in the second of this pair of papers. The model could also prove useful for simulating specific depositional structures found in natural sediments, the result of physical alterations to packing and grain fabric, using discrete particle flow models. While the principal focus here is on naturally occurring sediment and sedimentary rock, the methods presented might also be useful for simulations of similar granular or cellular material encountered in engineering, industrial and life sciences.

Journal of Geophysical Research F: Earth Surface↗
USGS2020

Planetary sensor models interoperability using the community sensor model specification

This paper presents the photogrammetric foundations upon which the Community Sensor Model specification depends, describes common coordinate system and reference frame transformations that support conversion between image sensor (charge‐coupled device) coordinates to some arbitrary body coordinate, and describes the U.S. Geological Survey Astrogeology Community Sensor Model implementation ( https://github.com/USGS-Astrogeology/usgscsm ). We present a new image support data specification that provides the position, pointing, timing, and metadata information necessary to properly locate a pixel or observations location on a body and describe a system architecture designed to explicitly identify the responsibilities of software components within a larger pipeline or analytical environment. This paper concludes with a set of experiments that illustrate positional and pointing error in the sensor location and the impact on the computed surface location.

Earth and Space Science↗
USGS2006

Speculations on continental crustal evolution

The evolution of the continental crust is a topic that has challenged Earth scientists since the earliest hypotheses of crustal evolution were put forth by such luminaries as Hutton, the 18th century Scottish scientist, and later by Stille (Germany), Argand (France), and Dana (United States). Recent geophysical observations provide important constraints on hypotheses of crustal evolution, and the most important of these observations are reviewed in a companion paper [ Mooney and Meissner , 1991], henceforth referred to as Paper 1. In this article we briefly speculate on crustal evolution using both geological and geophysical data as guidelines. For the past 25 years, the basic framework for models of the evolution of the Earth's crust and lithosphere has been plate tectonics. This framework has been particularly successful in explaining the processes that form and modify the oceanic crust but has had somewhat more limited success in its application to the continental crust. Some of the basic tenets of plate tectonics, as applied to the continental crust, are listed below. Continental masses coalesce and disperse as ocean basins open and close in the Wilson cycle.

Eos, Earth and Space Science News↗
USGS2010

A solute flux approach to transport in heterogeneous formations: 1. The general framework

It is common to represent solute tranport in heterogeneous formations in terms of the resident concentration C (x, t), regarded as a random space function. The present study investigates the alternative representation by q , the solute mass flux at a point of a control plane normal to the mean flow. This representation is appropriate for many field applications in which the variable of interest is the mass of solute discharged through a control surface. A general framework to compute the statistical moments of q and of the associated total solute discharge Q and mass M is established. With x the direction of the mean flow, a solute particle is crossing the control plane at y = η, z = ζ and at the travel (arrival) time τ. The associated expected solute flux value is proportional to the joint probability density function (pdf) g 1 of η, ζ and τ, whereas the variance of q is shown to depend on the joint pdf g 2 of the same variables for two particles. In turn, the statistical moments of η, ζ and τ depend on those of the velocity components through a system of stochastic ordinary differential equations. For a steady velocity field and neglecting the effect of pore‐scale dispersion, a major simplification of the problem results in the independence of the random variables η, ζ and τ. As a consequence, the pdf of η and ζ can be derived independently of τ. A few approximate approaches to derive the statistical moments of η, ζ and τ are outlined. These methods will be explored in paper 2 in order to effectively derive the variances of the total solute discharge and mass, while paper 3 will deal with the nonlinear effect of the velocity variance upon the moments of η, ζ and τ

Water Resources Research↗
USGS2012

Recent advances in understanding the interaction of groundwater and surface water

The most common image of the interaction of groundwater and surface water is that of the interaction of streams with a contiguous alluvial aquifer. This type of system has been the focus of study for more than 100 years, from the work of Boussinesq (1877) to the present, and stream-aquifer interaction continues to be the most common topic of papers discussing the interaction of groundwater and surface water. However, groundwater and surface water interact in a wide variety of landscapes from alpine to coastal. Within these landscapes, ground-water systems range in scale from local to regional, and the types of surface water include streams, lakes, wetlands, and oceans. Given the broad spectrum of the topic of groundwater and surface water interaction, an overview of studies of this topic could be organized according to surface water type, landscape type, scale of hydrologic systems, or field and analytical methods. All these factors are discussed, but this paper is organized according to landscape type because of the great increase in studies of the interaction of groundwater and surface water in landscapes other than riverine systems in the last 15 years. Furthermore, discussing studies by landscape type facilitates comparison of methods and results from different geologic and climatic settings. The general landscapes discussed are mountain terrane, riverine systems, coastal terrane, hummocky terrane, and karst terrane.

Reviews of Geophysics↗
USGS2010

Estimating 14C groundwater ages in a methanogenic aquifer

This paper addresses the problem of 14 C age dating of groundwaters in a confined regional aquifer affected by methanogenesis. Increasing CH 4 concentrations along the groundwater flow system and 13 C and 14 C isotopic data for dissolved inorganic carbon, dissolved organic carbon, and CH 4 clearly show the effect of methanogenesis on groundwater chemistry. Inverse reaction path modeling using NETPATH indicates the predominant geochemical reactions controlling the chemical evolution of groundwater in the aquifer are incongruent dissolution of dolomite, ion exchange, methanogenesis, and oxidation of sedimentary organic matter. Modeling of groundwater 14 C ages using NETPATH indicates that a significant part of groundwater in the Alliston aquifer is less than 13,000 years old; however, older groundwater in the range of 15,000–23,000 years is also present in the aquifer. This paper demonstrates that 14C ages calculated using NETPATH, incorporating the effects of methanogenesis on the carbon pools, provide reasonable groundwater ages that were not possible by other isotopic methods.

Water Resources Research↗
USGS1998

High-resolution Monte Carlo simulation of flow and conservative transport in heterogeneous porous media: 1. Methodology and flow results

In this, the first of two papers concerned with the use of numerical simulation to examine flow and transport parameters in heterogeneous porous media via Monte Carlo methods, various aspects of the modelling effort are examined. In particular, the need to save on core memory causes one to use only specific realizations that have certain initial characteristics; in effect, these transport simulations are conditioned by these characteristics. Also, the need to independently estimate length scales for the generated fields is discussed. The statistical uniformity of the flow field is investigated by plotting the variance of the seepage velocity for vector components in the x , y , and z directions. Finally, specific features of the velocity field itself are illuminated in this first paper. In particular, these data give one the opportunity to investigate the effective hydraulic conductivity in a flow field which is approximately statistically uniform; comparisons are made with first- and second-order perturbation analyses. The mean cloud velocity is examined to ascertain whether it is identical to the mean seepage velocity of the model. Finally, the variance in the cloud centroid velocity is examined for the effect of source size and differing strengths of local transverse dispersion.

Water Resources Research↗
USGS2013

The age of scarplike landforms from diffusion-equation analysis

The purpose of this paper is to review developments in the quantitative modeling of fault-scarp geomorphology, principally those since 1980. These developments utilize diffusionequation mathematics, in several different forms, as the basic model of fault-scarp evolution. Because solutions to the general diffusion equation evolve with time, as we expect faultscarp morphology to evolve with time, the model solutions carry information about the age of the structure and thus its time of formation; hence the inclusion of this paper in this volume. The evolution of fault-scarp morphology holds a small but special place in the much larger class of problems in landform evolution. In general, landform evolution means the evolution of topography as a function of both space and time. It is the outcome of the competition among those tectonic processes that make topography, erosive processes that destroy topography, and depositional processes that redistribute topography. Deposition and erosion can always be coupled through conservation-of-mass relations, but in general deposition occurs at great distance from the source region of detritus. Moreover, erosion is an inherently rough process whereas deposition is inherently smooth, as is evident from even casual inspection of shaded-relief, digital-elevation maps (e.g., Thelin and Pike, 1990; Simpson and Anders, 1992) and the current fascination with fractal representations oferoding terrains (e.g., Huang and Turcotte, 1989; Newman and Turcotte, 1990). Nevertheless, large-scale landform-evolution modeling, now a computationally intensive, advanced numerical exercise, is generating ever more realistic landforms (e.g., Willgoose and others, 1991a,b; Kooi and Beaumont, 1994; Tucker and Slingerland, 1994), although many of the rate coefficients remain poorly prescribed

Book chapter↗
USGS2014

Pre‐Cambrian and Paleozoic vulcanism of interior Alaska

The history of vulcanism in Alaska is a topic of great universal interest, but one which has had no adequate treatment. For some years the writer has been accumulating comparative data on this subject, and it is hoped that this information may some time be sufficiently amplified and coordinated to justify a general description of the sequential igneous history of Alaska. The scope of such an undertaking, however, can well be appreciated from the statement that Alaska is nearly a fifth the size of the United States, and that geologic studies have shown that igneous rocks have originated in Alaska in every geologic period, excepting perhaps the Cambrian and the Silurian. Therefore, in the present paper, it has seemed best to present only a part of this interesting record, and perhaps in subsequent papers to expand the areal and geologic limits of discussion. ©1935. American Geophysical Union. All Rights Reserved.

Eos, Transactions, American Geophysical Union↗
USGS2014

The channel‐storage method of determining effluent seepage

Some years ago the senior author, in collaboration with Norah Dowell Stearns, undertook to make a monthly inventory of the water‐supply of the Pomperaug River Basin, in Connecticut, from a study of data obtained by A. J. Ellis from 1913 to 1916. For this purpose approximate determinations or estimates were made of the ground‐water runoff, that is, of the part of the daily discharge of the river that consisted of water derived from the zone of saturation by effluent seepage. The determinations or estimates were essentially based on the assumption that after a week of fair weather the storm‐water was all discharged and that until the next rain the runoff was essentially all ground‐water (U.S. Geol, Surv. Water‐Supply Paper 597, pp. 107–116 and pi. 19, 1929). In the discussion of the methods and results of this investigation, the following statement was made (Water‐Supply Paper 597, pp. 145–146): “In this investigation the estimates of ground‐water runoff were based on the discharge of the Pomperaug at Bennetts Bridge—that is, on the discharge during the periods between rains, when there was virtually no direct runoff left in the stream‐system. Much better results could be obtained by basing the estimates on periods beginning as soon after rains as all of the direct runoff has reached the streams. With this method the ground‐water runoff during any particular day would be the total runoff minus the decrease in stream‐storage. The decrease in stream‐storage could be estimated by maintaining gages at several points on the trunk‐stream and on selected tributaries and making surveys of the stream‐system showing the approximate water‐areas of different parts of the system at different gage‐heights.”

Eos, Transactions, American Geophysical Union↗
USGS2014

Part I—History and activities of the section of geophysics of the United States Geological Survey

From the beginning of time, all ingenuity of mankind has been concentrated upon the methods of finding gold and unusual deposits in the earth. An illustration (Fig. 1) from the old treatise by Agricola, “De Re Metallica,” published in 1580, will serve to show the implicit faith of that generation in divining methods. However, it was not until 1920 that real progress was made in prospecting by using the latest advances of the physical sciences. The public interest was stimulated by the successes of these methods on the part of commercial operators, and governmental agencies received many requests for information concerning their reliability. There were also, in the late 1920's, high‐pressure mine‐promotion schemes which used geophysical methods in a very questionable manner, symbolized in Figure 2 as of 1928 by an electrified forked stick. Authoritative information concerning such practices for public protection was needed to curb such notorious undertakings. Dr. Scott Turner, then Director of the United States Bureau of Mines, thoroughly understood the situation and was first in the governmental departments to recognize the possible value of a study of modern prospecting methods. The Bureau of Mines began this investigation by employing Drs. A. S. Eve and D. A. Keys of McGill University for short periods in the summer in 1927. Their first publication [see 1 of “References” at end of paper] served to illustrate the fundamental scientific principles which underlie geophysical prospecting. This was followed by a second publication [2] giving the results of field‐tests. In the light of the rapid improvements during the intervening ten years, these two papers take a historical position.

Eos, Transactions, American Geophysical Union↗
USGS2014

Report of committee on relation of inch and meter

Those of you who attended the annual meeting of this Section on April 27, 1938, heard a paper entitled “A method for introducing a new standard of length” that was presented by Professor Philip Klssara, calling attention to the Bill then in Congress proposing to redefine the length of the inch. The paper has been published in the “Transactions of the American Geophysical Union“ [19th Annual Meeting, 1938, pp. 94–96]. Its closing paragraph is as follows: “As the American Geophysical Union has as one of its functions the duty of offering advice to the Congress on technical matters, I move, Mr. Chairman, that the Chairman be empowered to appoint a committee to study the matter and to report what recommendations should be made to Congress by the Union.”

Eos, Transactions, American Geophysical Union↗
USGS2014

Some features of the Livingston Formation near Nye, Montana

The Livingston Formation is a series of pyroclastic rocks several thousand feet thick cropping out on the north side of the Beartooth Mountains. These pyroclastic rocks grade laterally into the Claggett, Judith River, Bearpaw, and Lennep formations of the Montana Group, according to Stone and Calvert [see 1 of references at end of paper], showing that they were being deposited during much of Montana time; they are therefore of Upper Cretaceous age and antedate the Laramide orogeny. The purpose of this paper is to describe briefly several significant features of the Formation where it is exposed in the Nye No. 2 Quadrangle (Fig. 1) along the southeast edge of its outcrop. It is concluded that much of the Formation was formed by mudflows, and that certain chloritized beds were deposited by hot mudflows.

Montana↗
USGS2014

Early history of the Mexican volcano Parícutin

Owing to the good fortune of being stationed near the new volcano Parícutin when it first erupted, I was able to visit it when it was only a week old. As my observations have been recorded in full in a previous article [see 1 of “References” at end of paper], only a few of the more pertinent features are repeated here, in order to give a setting for the succeeding papers in this symposium.

Michoacan↗