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At least 19 recordsLinked to original sources
USGS1980

Visitor use patterns in Yosemite National Park

After several years of dramatic increases, visitor use in Yosemite National Park has leveled off to an average of 2.4 million visits per year. Coincident with this decline in the growth rate, there have been some changes in visitation trends and patterns. Data collected in the park show that the average length of stay has decreased to less than 32 hours and that the average number of visitors per vehicle has dropped to slightly less than three.

Journal of Travel Research↗
USGS2022

How shall we meet? Embracing the opportunities of virtual conferencing

The SARS-CoV-2 (COVID-19) pandemic triggered dramatic shifts in the way that ecologists teach, research, and interact (e.g., Cooke et al. 2021 ). As the world now adjusts to a “new normal” era, there is notable and open discussion about the merits or desire to return to practices used prior to the pandemic (e.g., Roulson 2021 ). A dominant aspect of these discussions is when and how researchers can return to the practice of large, centralized, in-person conferences that have been the primary mode of professional interaction for decades. While questions of safety are naturally paramount and will guide decision making for some time, there remains the broader question of whether and how to implement virtual and hybrid formats in the future. Discussions about the return to in-person meetings and expressed resentment about the use of virtual formats (Stevens and Murphy 2021 ) that we routinely see circulated by professional organizations and on social media assume that the latter is a lesser-quality version of the former. However, we put forward that these sentiments neglect the diversity of opinions among scientists and evidence of prevalent, positive attitudes about the use of virtual (and possibly, as yet undeveloped) modes of conferences. For example, 74% of more than 900 researchers surveyed by the journal Nature during the initial phase of the pandemic expressed a desire for virtual conferences to remain in practice even when travel restrictions were eased (Remmel 2021 ). Other surveys have shown that scientists are highly interested in alternative conference formats due to concerns about climate change (Nursey-Bray et al. 2019 ; Haage 2020 ) and access (Niner and Wassermann 2021 ). These data indicate most researchers have personal circumstances or perspectives that recognize the value of a broader discussion about how conferences and interactions among researchers can be shaped.

Fisheries Magazine↗
USGS1974

Generalization of stream travel rates and dispersion characteristics from time-of-travel measurements

Prediction of travel rates of water in streams is important for pollution control and for warning systems where contaminant spillage is possible. A method of estimating traveltime and dispersion of solutes in streams where such data are not available is provided in this report. Generalized relations for travel rates and dispersion indices as functions of stream-channel and discharge characteristics are developed using available time-of-travel data and the multiple-regression technique.

Journal of Research of the U.S. Geological Survey↗
USGS1998

Detrital zircon U-Pb geochronology of Cambrian to Triassic miogeoclinal and eugeoclinal strata of Sonora, Mexico

One hundred and eighty two individual detrital zircon grains from Cambrian through Permian miogeoclinal strata, Ordovician eugeoclinal rocks, and Triassic post-orogenic sediments in northwestern Sonora have been analyzed. During Cambrian, Devonian, Permian, and Triassic time, most zircons accumulating along this part of the Cordilleran margin were shed from 1.40–1.45 and 1.62–1.78 Ga igneous rocks that are widespread in the southwestern United States and northwestern Mexico. Zircons with ages of approximately 1.11 Ga are common in Cambrian strata and were apparently shed from granite bodies near the sample site. The sources of 225–280 Ma zircons in our Triassic sample are more problematic, as few igneous rocks of these ages are recognized in northwestern Mexico. Such sources may be present but unrecognized, or the grains could have been derived from igneous rocks of the appropriate ages to the northwest in the Mojave Desert region, to the east in Chihuahua and Coahuila, or to the south in accreted(?) arc-type terranes. Because the zircon grains in our Cambrian and Devonian to Triassic samples could have accumulated in proximity to basement rocks near their present position or in the Death Valley region of southern California, our data do not support or refute the existence of the Mojave-Sonora megashear. Ordovician strata of both miogeoclinal and eugeoclinal affinity are dominated by >1.77 Ga detrital zircons, which are considerably older than most basement rocks in the region. Zircon grains in the miogeoclinal sample were apparently derived from the Peace River arch area of northwestern Canada and transported southward by longshore currents. The eugeoclinal grains may also have come from the Peace River arch region, with southward transport by either sedimentary or tectonic processes, or they may have been shed from off-shelf slivers of continents (perhaps Antarctica?) removed from the Cordilleran margin during Neoproterozoic rifting. It is also possible that the Ordovician eugeoclinal strata are far traveled and exotic to North America.

Journal of Geophysical Research B: Solid Earth↗
USGS2021

Hydrate formation on marine seep bubbles and the implications for water column methane dissolution

Methane released from seafloor seeps contributes to a number of benthic, water column, and atmospheric processes. At seafloor seeps within the methane hydrate stability zone, crystalline gas hydrate shells can form on methane bubbles while the bubbles are still in contact with the seafloor or as the bubbles begin ascending through the water column. These shells reduce methane dissolution rates, allowing hydrate-coated bubbles to deliver methane to shallower depths in the water column than hydrate-free bubbles. Here, we analyze seafloor videos from six deepwater seep sites associated with a diverse range of bubble-release processes involving hydrate formation. Bubbles that grow rapidly are often hydrate-free when released from the seafloor. As bubble growth slows and seafloor residence time increases, a hydrate coating can form on the bubble's gas-water interface, fully coating most bubbles within ∼10 s of the onset of hydrate formation at the seafloor. This finding agrees with water-column observations that most bubbles become hydrate-coated after their initial ∼150 cm of rise, which takes about 10 s. Whether a bubble is coated or not at the seafloor affects how much methane a bubble contains and how quickly that methane dissolves during the bubble's rise through the water column. A simplified model shows that, after rising 150 cm above the seafloor, a bubble that grew a hydrate shell before releasing from the seafloor will have ∼5% more methane than a bubble of initial equal volume that did not grow a hydrate shell after it traveled to the same height.

Journal of Geophysical Research - Oceans↗
USGS2003

Tsunamis generated by subaerial mass flows

Tsunamis generated in lakes and reservoirs by subaerial mass flows pose distinctive problems for hazards assessment because the domain of interest is commonly the "near field," beyond the zone of complex splashing but close enough to the source that wave propagation effects are not predominant. Scaling analysis of the equations governing water wave propagation shows that near-field wave amplitude and wavelength should depend on certain measures of mass flow dynamics and volume. The scaling analysis motivates a successful collapse (in dimensionless space) of data from two distinct sets of experiments with solid block "wave makers." To first order, wave amplitude/water depth is a simple function of the ratio of dimensionless wave maker travel time to dimensionless wave maker volume per unit width. Wave amplitude data from previous laboratory investigations with both rigid and deformable wave makers follow the same trend in dimensionless parameter space as our own data. The characteristic wavelength/water depth for all our experiments is simply proportional to dimensionless wave maker travel time, which is itself given approximately by a simple function of wave maker length/water depth. Wave maker shape and rigidity do not otherwise influence wave features. Application of the amplitude scaling relation to several historical events yields "predicted" near-field wave amplitudes in reasonable agreement with measurements and observations. Together, the scaling relations for near-field amplitude, wavelength, and submerged travel time provide key inputs necessary for computational wave propagation and hazards assessment.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

Crustal resistivity structure from magnetotelluric soundings in the Colorado Plateau-Basin and Range provinces, central and western Arizona

Resistivity structure to about 25 km depth is defined from two-dimensional modeling of 29 magnetotelluric (MT) soundings (0.002–5 Hz) that traverse 280 km of the southwestern Colorado Plateau, transition zone, and Basin and Range provinces in Arizona. From the surface to 5 km depth, the MT model suggests structural relationships between low-resistivity sedimentary and volcanic rocks (50–300 ohm m) and high-resistivity granitic and gneissic basement (500–9000 ohm m). In the Basin and Range province, the MT model and a seismic reflection section show a generally consistent distribution of supracrustal rocks that have relatively low to moderate resistivity (MT) and relatively strong, locally coherent reflectivity. The supracrustal zone defined by these physical properties is inferred to be composed of upper plate rocks above a middle Tertiary detachment fault system which has been mapped in surrounding ranges. Some low-angle fault zones inferred from seismic reflections to extend into high resistivity basement below the supracrustal rocks are not resolved by the MT model. A low-resistivity zone with a conductance of 500 S or more is modeled in the crust at an average depth of about 15 km in the Basin and Range province and transition zone and may deepen below the southwestern part of the Colorado Plateau. In the Basin and Range province, the top of the low resistivity may correspond to a reflective layer with a 6-s two-way-travel time. This deep low-resistivity zone might be caused by a small fraction of connected hydrous solutions or silicic melts.

Journal of Geophysical Research↗
USGS1975

Norman Creek, a source of recharge to Maramec Spring, Phelps County, Missouri

Rhodamine WT dye was used to trace the subsurface movement of water from Norman Creek, a losing Ozark stream, to Maramec Spring, a straight-line distance of 8.7 mi (14.0 km). Grab samples and activated charcoal packets were used to check possible emergent points of the dye. The leading edge of the dye reached Maramec Spring 68-75 days after the dye injection, and the peak concentration reached the spring 82-93 d after injection. Small quantities of dye were still being recovered at the spring 114 d after injection and 39-46 d after the dye first arrived at the spring. Computed average velocities, assuming straight-line travel, are 0.47-0.42 ft(0.14-0.13 m)/min for the leading edge and 0.39- 0.34 ft(0.12-0.10 m)/min for the peak. This apparent rate of travel compares favorably with other recent subsurface tracing studies in southern Missouri which generally range from 0.4 to 25 ft(0.12 to 7.6 m)/min.

Missouri↗
USGS2017

Numerical simulation of large-scale bed load particle tracer advection-dispersion in rivers with free bars

Asymptotic characteristics of the transport of bed load tracer particles in rivers have been described by advection-dispersion equations. Here we perform numerical simulations designed to study the role of free bars, and more specifically single-row alternate bars, on streamwise tracer particle dispersion. In treating the conservation of tracer particle mass, we use two alternative formulations for the Exner equation of sediment mass conservation: the flux-based formulation, in which bed elevation varies with the divergence of the bed load transport rate, and the entrainment-based formulation, in which bed elevation changes with the net deposition rate. Under the condition of no net bed aggradation/degradation, a 1-D flux-based deterministic model that does not describe free bars yields no streamwise dispersion. The entrainment-based 1-D formulation, on the other hand, models stochasticity via the probability density function (PDF) of particle step length, and as a result does show tracer dispersion. When the formulation is generalized to 2-D to include free alternate bars, however, both models yield almost identical asymptotic advection-dispersion characteristics, in which streamwise dispersion is dominated by randomness inherent in free bar morphodynamics. This randomness can result in a heavy-tailed PDF of waiting time. In addition, migrating bars may constrain the travel distance through temporary burial, causing a thin-tailed PDF of travel distance. The superdiffusive character of streamwise particle dispersion predicted by the model is attributable to the interaction of these two effects.

Journal of Geophysical Research F: Earth Surface↗
USGS2012

Dust deposition in southern Nevada and California, 1984–1989: Relations to climate, source area, and source lithology

Dust samples collected annually for 5 years from 55 sites in southern Nevada and California provide the first regional source of information on modern rates of dust deposition, grain size, and mineralogical and chemical composition relative to climate and to type and lithology of dust source. The average silt and clay flux (rate of deposition) in southern Nevada and southeastern California ranges from 4.3 to 15.7 g/m 2 /yr, but in southwestern California the average silt and clay flux is as high as 30 g/m 2 /yr. The climatic factors that affect dust flux interact with each other and with the factors of source type (playas versus alluvium), source lithology, geographic area, and human disturbance. Average dust flux increases with mean annual temperature but is not correlated to decreases in mean annual precipitation because the regional winds bring dust to relatively wet areas. In contrast, annual dust flux mostly reflects changes in annual precipitation (relative drought) rather than temperature. Although playa and alluvial sources produce about the same amount of dust per unit area, the total volume of dust from the more extensive alluvial sources is much larger. In addition, playa and alluvial sources respond differently to annual changes in precipitation. Most playas produce dust that is richer in soluble salts and carbonate than that from alluvial sources (except carbonate‐rich alluvium). Gypsum dust may be produced by the interaction of carbonate dust and anthropogenic or marine sulfates. The dust flux in an arid urbanizing area may be as much as twice that before disturbance but decreases when construction stops. The mineralogic and major‐oxide composition of the dust samples indicates that sand and some silt is locally derived and deposited, whereas clay and some silt from different sources can be far‐traveled. Dust deposited in the Transverse Ranges of California by the Santa Ana winds appears to be mainly derived from sources to the north and east.

California, Nevada↗
USGS1987

Origin of the lethal gas burst from Lake Monoun, Cameroun

On 15 August, 1984, a lethal gas burst issued from a submerged 96-m-deep crater in Lake Monoun in Cameroun, western Africa, killing 37 people. The event was associated with a landslide from the eastern crater rim, which slumped into deep water. Waters below 50 m are anoxic, dominated by high Fe2+ (???600 mg/l) and HCO3- (??? 1900 mg/l), anoxic and supersaturated with siderite, which is a major component of the crater floor sediments. The unusually high Fe2+ levels are attributed to reduction of laterite-derived ferric iron gradually brought into the lake as loess and in river input. Sulfur compounds are below detection limits in both water and gas. Gases effervescing from depressurized deep waters are dominantly CO2 with minor CH4, having ??13C of -7.18 and -54.8 per mil, respectively. Bacterial decomposition of organic matter may account for the methane, but 14C of lake water indicates that only 10% of the carbon is modern, giving an apparent age of 18,000 years. The dominant source of carbon is therefore attributed to long-term emission of CO2 as volcanic exhalation from vents within the crater, which led to gradual build-up of HCO3- in the lake. The density stratification of the lake may have been upset by an earthquake and underwater landslide on 15 August, which triggered overturn of the lake and caused nucleation of CO2 in the deep water. The resultant ebullition of CO2 from deep lake waters led to a gas burst at the surface and locally generated a water wave up to 5 m high. People travelling through the gas cloud were asphyxiated, presumably from CO2, and suffered skin discoloration from unidentified components. ?? 1987.

Journal of Volcanology and Geothermal Research↗
USGS2022

Introduction to the special issue of the Consortium of Organizations for Strong Motion Observation Systems (COSMOS) international guidelines for applying noninvasive geophysical techniques to characterize seismic site conditions

Knowledge about local seismic site conditions provides critical information to account for site effects that are commonly observed in strong motion recordings. Certainly, other wave propagation effects can influence these observations, which are attributable to variations in material properties of the paths traveled by the waves, as well as the characteristics of the seismic source. However, local geologic conditions, particularly, when under shear-wave excitation, are known to have a strong influence on the behavior of ground shaking in the frequency range that is expected to directly affect the built environment. Thus, shear waves traveling in the shallow subsurface—defined here as tens to hundreds of meters beneath the ground surface—are the main foci for application and research in the earthquake engineering community.

Journal of Seismology↗
USGS2018

Travel time variation on backcountry trails

Numerous interrelated factors influence the travel times of hikers and riders on backcountry trails. This study sought to quantify those factors which were thought to be most important in affecting trail speeds. The travel times of 897 backpacking parties, 634 day hiking parties, and 111 riding parties were obtained from gentle (0.75%), moderate (5.0%), and steep (12.5%) trail segments one mile in length. The significance of party size, direction of travel, and slope class were tested for each type of party. It took an average of 34.8 minutes for backpacking parties, 36.4 minutes for day hiking parties, and 27.3 minutes for horse parties to travel all of the sample trail segments. Party size was not significant for all three types of parties, and slope-direction class was significant for only backpacking parties. For these parties, average times for uphill travel were greater than downhill travel and time increased as the slope increased. Regression equations were developed for backpacker travel times as a function of direction of travel and slope. The application of these data are discussed in relation to a wilderness use simulation model developed by the Forest Service and Resources for the Future.

Journal of Leisure Research↗
USGS2015

Rafinesque’s names for western American mammals, including the earliest scientific name for the coyote ( Canis latrans Say, 1822), based on the apocryphal journal of Charles Le Raye

In 1817, the naturalist Constantine S. Rafinesque named nine new species of mammals from the American West, indicating the recently published journal of Charles Le Raye as the primary source for his descriptions. Le Raye was purported to be a French Canadian fur trader who, as a captive of the Sioux, had traveled across broad portions of the Missouri and Yellowstone river drainages a few years before the Lewis and Clark Expedition (1804-1806) traversed much of the same region. Le Raye's journal was relied upon by generations of scholars as a valuable source documenting the native peoples and natural history of the Upper Missouri river in the era just prior to European settlement. Subsequent research, however, has shown that Le Raye never existed, and his purported journal is fraudulent. Despite this, Rafinesque's creation of the names followed conventional and accepted practice at the time, and they are porentially available. Fortunately, much of the Le Raye journal was based on verifiable sources, such as Patrick Gass's published account of the Lewis and Clark Expedition. Identification of the original source materials makes it possible to establish the correct application of Rafinesque's names and to determine their current status. This process reveals that the earliest scientific name for the coyote ( Canis latrans Say, 1822) was Canis chlorops Rafinesque, 1817; this name is now a nomen oblitum , however, and is no longer available.

Proceedings of the Biological Society of Washingto↗
USGS2023

Bayesian hierarchical modeling for probabilistic estimation of tsunami amplitude from far-field earthquake sources

Evaluation of tsunami disaster risk for a coastal region requires reliable estimation of tsunami hazard, for example, wave amplitude close to the shore. Observed tsunami data are scarce and have poor spatial coverage, and for this reason probabilistic tsunami hazard analysis (PTHA) traditionally relies on numerical simulation of “synthetic” tsunami generation and propagation toward the coast. Such an approach has been extensively studied in the past and it is widely recognized as an important disaster-risk mitigation tool. PTHA can not only provide less uncertain and spatially coherent hazard estimates in comparison with classical empirical data analysis which is restricted at the tide gauge stations, but also local inundation information. In this paper, we explore a purely statistical alternative to traditional PTHA for evaluation of tsunami amplitude hazard. Here, we use tide gauge measurements of tsunami amplitude along the western United States, specifically California and Oregon, and develop a spatial Bayesian hierarchical model (BHM) to assess tsunami hazard from far-field earthquake sources at various recurrence intervals. The configuration of our model incorporates latent Gaussian fields that utilize information on the distance between tide gauges as well as on the continental shelf width, that is, a covariate linked to potential dissipative effects on wave energy as the tsunami travels over shallow water. Through our BHM, we produce spatially continuous probabilistic maps of far-field tsunami hazard which can aid comprehensive tsunami disaster risk reduction and management.

California, Oregon, Washington↗
USGS1991

Distribution and dispersal of the zebra mussel ( Dreissena polymorpha ) in the Great Lakes region

Dreissena polymorpha (Pallas), a small mussel common throughout most of Europe, was discovered in June of 1988 in the southern part of Lake St. Clair. Length–frequency analyses of populations from the Great Lakes and review of historical benthic studies suggest that the mussel was introduced into Lake St. Clair in late 1986, probably as a result of the discharge of ballast water from an ocean-crossing vessel. Following the 1990 reproductive season, Dreissena populations ranged from the head of the St. Clair River, through Lake St. Clair, the Detroit River, Lake Erie, the Welland Canal, and the Niagara River to the western basin and southern shoreline of Lake Ontario. Isolated populations were found in the St. Lawrence River and in harbours in Lakes Huron, Michigan, and Superior. The rapid dispersal of this organism has resulted from its high fecundity, pelagic larval stage, bysso-pelagic drifting ability of juveniles, and human activities associated with commercial shipping, fishing, and boating (research and pleasure). Virtually any waterbody that can be reached by boaters and fisherman within a few days travel of the lower Great Lakes, particularly Lake Erie, seems to be at risk of being invaded by this nuisance species.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2012

Crustal and upper mantle structure of the northern and central Sierra Nevada

Teleseismic data were recorded within the Sierra Nevada to look for lateral variations in the upper mantle. The data were collected at both temporary and permanent stations, and P wave residuals were computed. After correcting the P residual data for crustal and topographic effects, there is still a variation of as much as 0.5-0.6 s from the north end of the Sierra Nevada to Mono Lake, located east of the central part of the range. In addition, there are significant variations in travel time patterns, depending on the azimuth of wave arrivals. Two simple modeling approaches have been used to infer the upper mantle velocity structure from the observed variations in travel time. In the first, it is assumed that the velocity variations are distributed throughout a depth range of about 60–160 km. One model that fits the data indicates a north-to-south trend in upper mantle P velocities from about 7.9 km/s at the north end of the Sierra to 7.6 km/s near Mono Lake. Superimposed is a west-to-east trend from 7.85 km/s under the Sierra Nevada crest to 7.7 km/s east of Lake Tahoe. In the second modeling approach, a fixed velocity contrast is assumed between the lithosphere and asthenosphere with variations in travel time resulting from variations in lithospheric thickness. One model, consistent with the observations, indicates a thinning of the lithosphere from 110 km at the north end of the Sierra to 60 km near Mono Lake.

Journal of Geophysical Research Solid Earth↗
USGS2008

Compositional trends in aeolian dust along a transect across the southwestern United States

Aeolian dust strongly influences ecology and landscape geochemistry over large areas that span several desert ecosystems of the southwestern United States. This study evaluates spatial and temporal variations and trends of the physical and chemical properties of dust in the southwestern United States by examining dust deposited in natural depressions on high isolated surfaces along a transect from the Mojave Desert to the central Colorado Plateau. Aeolian dust is recognized in these depressions on the basis of textural, chemical, isotopic, and mineralogical characteristics and comparisons of those characteristics to the underlying bedrock units. Spatial and temporal trends suggest that although local dust sources are important to the accumulated material in these depressions, Mojave Desert dust sources may also contribute. Depth trends in the depressions suggest that Mojave sources may have contributed more dust to the Colorado Plateau recently than in the past. These interpretations point to the important roles of far-traveled aeolian dust for landscape geochemistry and imply future changes to soil geochemistry under changing conditions in far-distant dust source areas. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research F: Earth Surface↗