Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Journal of Interpretation”

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

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

At least 397 records · Page 22Linked to original sources
USGS2012

Crustal structure of accreted terranes in southern Alaska, Chugach Mountains and Copper River Basin, from seismic refraction results

Seismic refraction data were collected along a 320-km-long "transect' line in southern Alaska, crossing the Prince William, Chugach, Peninsular, and Wrangellia terranes, and along several shorter lines within individual terranes. Velocity structure in the upper crust (less than 9-km depth) differs among the four terranes. In contrast, layers in the middle crust (9- to 25-km depth) in some case extend across projected terrane boundaries. The top of a gently north dipping sequence of low- and high-velocity layers (5.7-7.8 km/s), more than 10 km thick, extends from near the surface in the southern Chugach terrane to more than 20-km depth beneath the southern Peninsular terrane. This sequence, truncated by the suture between the Prince William and Chugach terranes, is interpreted to be an underplated "terrane' made up of fragments of the Kula plate and its sedimentary overburden that were accreted during subduction in the late Mesozoic and/or early Tertiary, during or between times of accretion of the Prince William and Chugach terranes.

Alaska↗
USGS2012

Geology of the Mount St. Helens area: Record of discontinuous volcanic and plutonic activity in the Cascade Arc of southern Washington

The Quaternary edifice of Mount St. Helens volcano was built upon a deeply eroded terrane of gently folded and altered volcanic and plutonic rocks that represent the core of the Tertiary Cascade magmatic arc. These rocks constitute an east dipping homoclinal sequence, several kilometers thick, of subaerially erupted mafic to silicic flows and volcaniclastic strata; K‐Ar ages from this section range from about 28 to 23 Ma (late Oligocene and earliest Miocene), which corresponds to an apparent lull in Cascade volcanism to the north of Mount Rainier. Volcanism was essentially continuous during this period of time, and neither a well‐defined base nor top of the section is exposed within the mapped area. Basalt and basaltic andesite dominate the lower part of the mid‐Tertiary section, whereas andesitic and dacitic rocks comprise most of the upper part. This section was intruded by numerous mafic to silicic dikes, sills, and irregular plutonic bodies, most no more than a few million years younger than their host rocks, and subjected to pervasive burial metamorphism and widespread hydrothermal alteration. Large areas of hornfelsed rock surrounding even relatively small intrusions indicate that the proportion of plutonic rock becomes significantly greater at shallow depth beneath the existing erosion surface. A large granitic pluton intruded the mid‐Tertiary section north of Spirit Lake at about 21 Ma. The Earl porphyry copper deposit occurs within the pluton but appears too young (17 Ma) to be genetically related to it. In contrast to the rather continuous and voluminous Oligocene to early Miocene activity, volcanism since then in the Mount St. Helens area has been localized and Volumetrically minor. Products of three younger eruptive periods have been recognized: a sequence of 15 m.y. old pyroxene andesite flows resting unconformably on mid‐Tertiary strata south of Mount St. Helens, widespread shallow dikes and sills of pyroxene andesite between 10 and 8 m.y. old, and compositionally diverse rocks erupted during the past 3 m.y. The Quaternary lavas are more potassic than the Tertiary lavas and typically contain phenocrysts of hornblende and biotite, which are absent from the older rocks. A number of Tertiary structures define a broad NNE trending zone that may reflect a deep‐seated lithospheric flaw that has controlled the locus of Cascade magmatism in southern Washington for the past 25 m.y. Mount St. Helens lies within this zone at the intersection of the NNW striking St. Helens seismic zone (SHZ) and an ENE trending alignment of Pleistocene silicic plug‐domes. No surface breakage has been detected along the SHZ, which is apparently very young. The linear zone of silicic vents is probably controlled by a fault that has been interpreted from seismic records to occur directly beneath the volcano. This zone parallels the directions of regional maximum horizontal compressive stress and North America/Juan de Fuca plate convergence. Mount St. Helens is an example of a low‐volume tectonically controlled magmatic system in an early stage of development.

Washington↗
USGS2016

Misapplied survey data and model uncertainty result in incorrect conclusions about the role of predation on alewife population dynamics in Lake Huron: a comment on He et al. (2015)

Drastic recent and ongoing changes to fish populations and food webs in the Great Lakes have been well-described ( Riley et al. 2008 ; Barbiero et al. 2009 ; Nalepa et al. 2009 ; Fahnenstiel et al. 2010 ; Evans et al. 2011 ; Gobin et al. 2015 ), and uncertainty regarding their potential effects on fisheries has caused concern among scientists and fishery managers (e.g., Dettmers et al. 2012 ). In particular, the relative importance of “bottom-up” (e.g., lower trophic level changes) versus “top-down” (e.g., predation) factors to fish community changes in the Great Lakes have been widely debated (e.g., Barbiero et al. 2011 ; Eshenroder and Lantry 2012 ; Bunnell et al. 2014 ). In Lake Huron, recent ecosystem changes have been particularly profound, and populations of alewife ( Alosa pseudoharengus ), an offshore pelagic prey fish, collapsed in 2003 and have yet to recover ( Riley et al. 2008 , 2014 ). He et al. (2015) recently used a series of linked ecological models to assess the role of predation in the dynamics of the offshore prey fish community in Lake Huron. While we believe that they provide a novel method for combining bioenergetics and stock assessment modeling, we question the validity of their conclusions because of the misapplication of survey data and the lack of critical interpretation of their modeling efforts. Here we describe how He et al. (2015) have misapplied bottom trawl data from Lake Huron, and we provide examples of how this has resulted in erroneous conclusions regarding the importance of predation to the population dynamics and collapse of alewife in Lake Huron.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1984

Distribution of Eurasian watermilfoil, Myriophyllum spicatum , in the St. Clair-Detroit River system in 1978

Submersed macrophytes were surveyed at 595 stations located throughout the St. Clair-Detroit River system between Lakes Huron and Erie, 23 August to 13 October 1978. Eurasian watermilfoil ( Myriophyllum spicatum ), first recorded in the system in 1974, became the fourth most common submersed macrophyte in the system by 1978. However, it has not been reported as a widespread nuisance in this system as it has in many other large water bodies in the United States. Observations made during the present study, and interpretation of an aerial photograph, suggest that M. spicatum was a minor nuisance to small boat navigation in portions of the system. Information presented in this study provides a baseline against which future changes in the occurrence of M. spicatum in the St. Clair-Detroit River system can be measured.

Journal of Great Lakes Research↗
USGS2012

Rapid extension recorded by cooling‐age patterns and brittle deformation, Naxos, Greece

The metamorphic core complex exposed as the island of Naxos in the Aegean Sea records an unusually complete sequence of structures developed as a result of continental extension. The structures formed during Miocene rise and cooling from ductile, upper amphibolite facies and anatectic conditions to brittle near‐surface conditions beneath the Naxos detachment fault. Top‐to‐the‐north ductile fabrics in the footwall, which initially developed during amphibolite facies prograde metamorphism, were overprinted by a succession of north directed, normal sense lower‐temperature brittle structures as the footwall was tectonically unloaded and unroofed. Pseudotachylite and cataclasite formation, brittle faulting, alteration, and erosion of the footwall occurred during continued slip and tectonic denudation. Neogene conglomerate and megabreccia, in part derived from exhumation of this footwall, lie structurally above the peripheral Naxos fault. Published K‐Ar and 40 Ar/ 39 Ar ages for hornblende, white mica, and biotite in the footwall decrease northwestward; apparent ages 17–50 Ma in the southeast correspond to areas of low metamorphic grade where preextension argon was partially retained. Published ages 16–10 Ma in higher‐grade rocks of the domal core in the north are cooling ages that for each of the three minerals show a component of younging in the NNE direction of extension. Assuming this is the direction of unroofing, we interpret the rate of this younging as the fault slip rate as the footwall rocks moved >20 km SSW relative to their hanging wall along the base of the Naxos detachment fault. The calculated rates of slip average 5–8 mm/yr, comparable to maximum rates reported in the Basin and Range province.

Naxos↗
USGS2009

Deciphering hydrological systems by means of geochemical processes

Interpretation of geochemical reactions and isotopic composition of groundwater provides a method to determine hydrological parameters such as porosity, hydraulic conductivity, and groundwater flow rates. This geochemical method is largely independent of the more conventional approach of determining these parameters by an evaluation of physical properties of aquifer systems. -from Authors

Hydrological Sciences Journal↗
USGS1978

Morphology of chasma walls, Mars

The landforms developed on the walls of the Valles Marineris system of chasmas are of three major types, which are locally transitional. The most common type is composed of steep spurs and gullies. The dominant process in the formation or modification of this type appears to be the downslope movement of. material under the influence of gravity, resulting in the accumulation of extensive talus deposits. The type is morphologically similar to high, steep terrestrial scarps in desert or alpine environments. The second morphologic type consists of walls dissected by tributary canyons with characteristic V-shaped cross profiles and blunt canyon heads that locally contain lobate deposits. The tributary canyons may be relict features of the time, when the existence of running water was possible on the surface of Mars. The third morphologic type consists of landslide scars forming broad curved or straight recessed sections of chasma wall. This type is accompanied by landslide deposits that form hummocky floors at the base of the recessed sections. The landslides developed at the expense of other wall morphologies. Chains of rimless depressions and craters that parallel the main structural trends of the chasmas are best interpreted as collapse holes. The origin of the chasmas on Mars is conjectural and may have been structural (grabens), but, on the basis of morphologic studies of their walls, it is suggested that most of the present wall configuration is the result of erosional scarp retreat, where erosion follows preestablished structural planes of weakness.

Journal of Research of the U.S. Geological Survey↗
USGS1977

Chemical structure of humic acids - Part 2, the molecular aggregation of some humic acid fractions in N, N-dimethylformamide

Humic acid fractions form molecular aggregates in solution. In previous studies we have shown by small angle X-ray scattering that the size of these aggregates is a function of pH. In this study we have found that the size of the aggregates of two humic acid fractions in water and buffers and in dimethylformamide solutions can be changed by oxidation with molecular oxygen and air. These results cast new light on the bonding mechanisms that cause aggregation of the humic acid particles in solution. We have interpreted the changes in aggregation sizes as being brought about by changes in intermolecular and intramolecular hydrogen bonding of the humic particles. Solvation of the humic molecules by dimethylformamide interferes with some of the hydrogen bonding reactions between proton donor and acceptor groups on the same humic acid molecules or on different molecules.

Journal of Research of the U.S. Geological Survey↗
USGS1978

Potassium-argon ages of basement rocks from Saint George Island, Alaska

Potassium-argon ages from basement granitic rocks that intrude serpentinized peridotite on St. George Island, Alaska, range from 50 to 57 million years, with an initial argon isochron age. interpreted as a minimum figure, of 52 ± 2 m.y. The age of the granitic rocks and their association with serpentinized peridotite near the continental margin, which apparently marks the site of a Mesozoic subduction zone, suggest that the position of the subduction zone shifted southward to the Aleutian Trench in early Tertiary time.

Alaska↗
USGS1989

Geochemistry of placer gold, Koyukuk-Chandalar mining district, Alaska

The Koyukuk-Chandalar mining district of the Brooks Range mineral belt in north-central Alaska contains numerous placer gold deposits but few known lode gold sources. Gold grains, collected from 46 placer localities and 6 lode gold sites in the district, were analyzed for Ag and 37 trace elements utilizing direct current-arc optical emission spectroscopy. When possible, several measurements were made on each sample and averaged. Gold content was calculated by the summation of the 38 elements determined and subtracting from 100. The objectives of our study were to characterize the deposits by defining the type and number of distinct geochemical characteristics for the Au, to determine relationships of Au in placer deposits to possible lode sources (placer and lode), to identify possible primary sources of placer gold, and to study processes of placer formation. Interpretation of results emphasize that the Au grains are almost invariably ternary (Au-Ag-Cu) alloys. The average Cu content is 0.040% and the average Ag content and fineness [(Au/Au+Ag)×1,000] are 10.5% and 893 parts per thousand, respectively, for the 46 placer localities.

Journal of Geochemical Exploration↗
USGS2002

Measurement error associated with surveys of fish abundance in Lake Michigan

In fisheries, imprecise measurements in catch data from surveys add uncertainty to the results of fishery stock assessments. The USGS Great Lakes Science Center (GLSC) began to survey the fall fish community of Lake Michigan in 1962 with bottom trawls. The measurement error was evaluated at the level of individual tows for nine fish species collected in this survey by applying a measurementerror regression model to replicated trawl data. It was found that the estimates of measurement-error variance ranged from 0.37 (deepwater sculpin, Myoxocephalus thompsoni ) to 1.23 (alewife, Alosa pseudoharengus ) on a logarithmic scale corresponding to a coefficient of variation = 66 to 156%. The estimates appeared to increase with the range of temperature occupied by the fish species. This association may be a result of the variability in the fall thermal structure of the lake. The estimates may also be influenced by other factors, such as pelagic behavior and schooling. Measurement error might be reduced by surveying the fish community during other seasons and/or by using additional technologies, such as acoustics. Measurement-error estimates should be considered when interpreting results of assessments that use abundance information from USGS-GLSC surveys of Lake Michigan and could be used if the survey design was altered. This study is the first to report estimates of measurement-error variance associated with this survey.

Lake Michigan↗
USGS2006

Dislocation pileup as a representation of strain accumulation on a strike-slip fault

The conventional model of strain accumulation on a vertical transform fault is a discrete screw dislocation in an elastic half-space with the Burgers vector of the dislocation increasing at the rate of relative plate motion. It would be more realistic to replace that discrete dislocation by a dislocation distribution, presumably a pileup in which the individual dislocations are in equilibrium. The length of the pileup depends upon the applied stress and the amount of slip that has occurred at depth. I argue here that the dislocation pileup (the transition on the fault from no slip to slip at the full plate rate) occupies a substantial portion of the lithosphere thickness. A discrete dislocation at an adjustable depth can reproduce the surface deformation profile predicted by a pileup so closely that it will be difficult to distinguish between the two models. The locking depth (dislocation depth) of that discrete dislocation approximation is substantially (???30%) larger than that (depth to top of the pileup) in the pileup model. Thus, in inverting surface deformation data using the discrete dislocation model, the locking depth in the model should not be interpreted as the true locking depth. Although dislocation pileup models should provide a good explanation of the surface deformation near the fault trace, that explanation may not be adequate at greater distances from the fault trace because approximating the expected horizontally distributed deformation at subcrustal depths by uniform slip concentrated on the fault is not justified.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

Thermal regime of the State 2-14 well, Salton Sea Scientific Drilling Project

Temperature logs were made repeatedly during breaks in drilling and both during and after flow tests in the Salton Sea Scientific Drilling Project well (State 2–14). The purpose of these logs was to assist in identifying zones of fluid loss or grain and to characterize reservoir temperatures. At the conclusion of the active phase of the project, a series of logs was begun in an attempt to establish the equilibrium temperature profile. Initially, we were able to log to depths below 3 km, but beginning in late May of 1986, it was impossible to log below about 1.8 km owing to casing failure. Our best estimates of formation temperature below 1.8 km are 305° ± 5°C at 1890 m and 355° ± 10°C at 3170 m. For the upper 1.8 km the latest temperature log (October 24, 1986), using a digital “slickline” (heat-shielded downhole recording) device, was within a few degrees Celsius of equilibrium, as confirmed by a more recent log (July 31, 1987) to a depth of ∼ 1 km. As in most other wells in the Salton Sea geothermal field, there is an impermeable, thermally conductive “cap” on the hydrothermal system; this cap extends to a depth of more than 900 m at the State 2–14 well. Thermal conductivities of 19 samples of drill cuttings from this interval were measured at room temperature. The conductivity values were corrected for in situ porosity as determined from geophysical logs and for the effects of elevated temperature. Thermal gradients decrease from about 250 mK m −1 (same as degrees Celsius per kilometer) in the upper few hundred meters to just below 200 mK m −1 near the base of the conductive cap. Using one interpretation, thermal conductivities increase with depth (mainly because of decreasing porosity), resulting in component heat flows that agree reasonably well with the mean of about 450 m W m −2 . This value agrees well with heat flow data from shallow wells within the Salton Sea geothermal field. A second interpretation, in which measured temperature coefficients of quartz- and carbonate-rich rocks are used to correct thermal conductivity, results in lower mean conductivities that are roughly constant with depth and, consequently, systematically decreasing heat flux averaging about 350 mW m −2 below 300 m. This interpretation is consistent with the inference (from fluid inclusion studies) that the rocks in this part of the field were once several tens of degrees Celsius hotter than they are now. The age of this possible disturbance is estimated at a few thousand years.

Journal of Geophysical Research Solid Earth↗
USGS2007

Coseismic and post-seismic signatures of the Sumatra 2004 December and 2005 March earthquakes in GRACE satellite gravity

The GRACE satellite mission has been measuring the Earth's gravity field and its temporal variations since 2002 April. Although these variations are mainly due to mass transfer within the geofluid envelops, they also result from mass displacements associated with phenomena including glacial isostatic adjustment and earthquakes. However, these last contributions are difficult to isolate because of the presence of noise and of geofluid signals, and because of GRACE's coarse spatial resolution (>400 km half-wavelength). In this paper, we show that a wavelet analysis on the sphere helps to retrieve earthquake signatures from GRACE geoid products. Using a wavelet analysis of GRACE geoids products, we show that the geoid variations caused by the 2004 December ( M w = 9.2) and 2005 March ( M w = 8.7) Sumatra earthquakes can be detected. At GRACE resolution, the 2004 December earthquake produced a strong coseismic decrease of the gravity field in the Andaman Sea, followed by relaxation in the area affected by both the Andaman 2004 and the Nias 2005 earthquakes. We find two characteristic timescales for the relaxation, with a fast variation occurring in the vicinity of the Central Andaman ridge. We discuss our coseismic observations in terms of density changes of crustal and upper-mantle rocks, and of the vertical displacements in the Andaman Sea. We interpret the post-seismic signal in terms of the viscoelastic response of the Earth's mantle. The transient component of the relaxation may indicate the presence of hot, viscous material beneath the active Central Andaman Basin.

Geophysical Journal International↗
USGS2005

Modeling of site occupancy dynamics for northern spotted owls, with emphasis on the effects of barred owls

Northern spotted owls ( Strix occidentalis caurina ) have been studied intensively since their listing as a threatened species by the U.S. Fish and Wildlife Service in 1990. Studies of spotted owl site occupancy have used various binary response measures, but most of these studies have made the assumption that detectability is perfect, or at least high and not variable. Further, previous studies did not consider temporal variation in site occupancy. We used relatively new methods for open population modeling of site occupancy that incorporated imperfect and variable detectability of spotted owls and allowed modeling of temporal variation in site occupancy, extinction, and colonization probabilities. We also examined the effects of barred owl ( S. varia ) presence on these parameters. We used spotted owl survey data from 1990 to 2002 for 3 study areas in Oregon, USA, and we used program MARK to develop and analyze site occupancy models. We found per visit detection probabilities averaged <0.70 and were highly variable among study years and study areas. Site occupancy probabilities for owl pairs declined greatly on 1 study area and slightly on the other 2 areas. For all owls, including singles and pairs, site occupancy was mostly stable through time. Barred owl presence had a negative effect on spotted owl detection probabilities, and it had either a positive effect on local-extinction probabilities or a negative effect on colonization probabilities. We conclude that further analyses of spotted owls must account for imperfect and variable detectability and barred owl presence to properly interpret results. Further, because barred owl presence is increasing within the range of northern spotted owls, we expect to see further declines in the proportion of sites occupied by spotted owls.

Journal of Wildlife Management↗
USGS2024

Visual interpretation of high-resolution aerial imagery: A tool for land managers

Remotely sensed imagery from various collection platforms (e.g., satellites, crewed and uncrewed aircraft) are used by biologists and other conservation personnel to support management activities ranging from monitoring invasive species to assessing land cover and vegetation characteristics. Although remote sensing–based vegetation indices and models have been developed and used for some management applications, straightforward visual interpretation of imagery by on-the-ground personnel may be a pragmatic approach for obtaining time-sensitive and spatially relevant information to support and guide local management activities. Our primary objective was to qualitatively assess our ability to identify patches of target invasive plant species based on simple visual interpretation of high-resolution aerial imagery. We also sought to compare the high-resolution imagery to widely available imagery (e.g., National Agriculture Imagery Program) to determine the efficacy of each for assessing vegetation communities and land-cover features in support of management activities. To accomplish these objectives, we obtained high-resolution imagery and visually scanned and assessed the imagery by using standard geographic information system software. We were able to differentiate patches of crownvetch Securigera varia (L.) Lassen and wild parsnip Pastinaca sativa L., but not spotted knapweed Centaurea stoebe L. or leafy spurge Euphorbia esula L. The relative success in identifying these species had a relationship to plant characteristics (e.g., flower color and morphology, height), time of year (phenology), patch size and density, and potentially site characteristics such density of the underlying vegetation (e.g., grasses), substrate color characteristics (i.e., color contrast with flowers), and physical disturbance. Our straightforward, qualitative assessment suggests that visual interpretation of high-resolution imagery, but not some lower-resolution imagery, may be an efficient and effective tool for supporting local invasive species management through activities such as monitoring known patches, identifying undetected infestations, assessing management actions, guiding field work, or prioritizing on-the-ground monitoring activities.

Journal of Fish and Wildlife Management↗
USGS2025

Detection probabilities of Flathead Catfish in small Kansas impoundments

A primary challenge of Flathead Catfish Pylodictis olivaris management is uncertainty associated with sampling strategies and resulting ambiguity in population-level information. Assessment of impoundment and environmental conditions that affect detection probability may aid in reducing sample variance and benefit inferences regarding changes to Flathead Catfish populations. We sampled eight small impoundments in Kansas (37–114 surface ha) using low-frequency electrofishing in summer, 2021. We revisited sites nine times over three months using an occupancy modeling framework to estimate the influence of impoundment and environmental conditions on detection probability of Flathead Catfish. We employed an information theoretic approach and ranked models built with impoundment as a random effect and three environmental variables predicted to influence detection of Flathead Catfish in small impoundments. Detection probability across all populations was 0.526 (SE = 0.020) and was influenced by water temperature, mean depth of the impoundment, and proportion of impoundment sampled. Generally, detection probability increased with all measured variables. The inclusion of detection probability in assessments of Flathead Catfish in small impoundments can inform interpretation of catch-related metrics. Further, variable detection suggests collection of multiple samples during a defined sampling period might be more suitable for characterizing populations than a single sample.

Kansas↗
USGS2009

Compositional changes in sediments of subalpine lakes, Uinta Mountains (Utah): Evidence for the effects of human activity on atmospheric dust inputs

Sediments in Marshall and Hidden Lakes in the Uinta Mountains of northeastern Utah contain records of atmospheric mineral-dust deposition as revealed by differences in mineralogy and geochemistry of lake sediments relative to Precambrian clastic rocks in the watersheds. In cores spanning more than a thousand years, the largest changes in composition occurred within the past approximately 140 years. Many elements associated with ore deposits (Ag, As, Bi, Cd, Cu, In, Mo, Pb, S, Sb, Sn, and Te) increase in the lake sediments above depths that correspond to about AD 1870. Sources of these metals from mining districts to the west of the Uinta Mountains are suggested by (1) the absence of mining and smelting of these metals in the Uinta Mountains, and (2) lower concentrations of most of these elements in post-settlement sediments of Hidden Lake than in those of Marshall Lake, which is closer to areas of mining and the densely urbanized part of north-central Utah that is termed the Wasatch Front, and (3) correspondence of Pb isotopic compositions in the sediments with isotopic composition of ores likely to have been smelted in the Wasatch Front. A major source of Cu in lake sediments may have been the Bingham Canyon open-pit mine 110 km west of Marshall Lake. Numerous other sources of metals beyond the Wasatch Front are likely, on the basis of the widespread increases of industrial activities in western United States since about AD 1900. In sediment deposited since ca. AD 1945, as estimated using 239+240 Pu activities, increases in concentrations of Mn, Fe, S, and some other redox-sensitive metals may result partly from diagenesis related to changes in redox. However, our results indicate that these elemental increases are also related to atmospheric inputs on the basis of their large increases that are nearly coincident with abrupt increases in silt-sized, titanium-bearing detrital magnetite. Such magnetite is interpreted as a component of atmospheric dust, because it is absent in catchment bedrock. Enrichment of P in sediments deposited after ca. AD 1950 appears to be caused largely by atmospheric inputs, perhaps from agricultural fertilizer along with magnetite-bearing soil.

Utah↗