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At least 829 records · Page 46Linked to original sources
USGS1981

Depositional sequences in clastic continental slope deposits, Gulf of Mexico

Tertiary and Quaternary sediments, overlying diapiric older Tertiary shales and Louann Salt on the continental slope in the western Gulf of Mexico, show cyclicity based on seismic-reflection patterns. A set of indistinct parallel reflections or an acoustically semi-transparent zone, normally onlapping onto diapir flanks, alternates with a set of distinct parallel reflections that drape the sea bottom. The indistinct reflections represent deposits employed by bottom transport during a lowering of sea level. Sea level rise and hight stand are characterized by hemipelagic sediments that form blanket-type deposits. Differential sediment loading causes diapiric activity that may reach maximum upward velocities when sea level rises. ?? 1981 A.M. Dowden, Inc.

Geo-Marine Letters↗
USGS2005

Suspended sediment fluxes in a tidal wetland: Measurement, controlling factors, and error analysis

Suspended sediment fluxes to and from tidal wetlands are of increasing concern because of habitat restoration efforts, wetland sustainability as sea level rises, and potential contaminant accumulation. We measured water and sediment fluxes through two channels on Browns Island, at the landward end of San Francisco Bay, United States, to determine the factors that control sediment fluxes on and off the island. In situ instrumentation was deployed between October 10 and November 13, 2003. Acoustic Doppler current profilers and the index velocity method were employed to calculate water fluxes. Suspended sediment concentrations (SSC) were determined with optical sensors and cross-sectional water sampling. All procedures were analyzed for their contribution to total error in the flux measurement. The inability to close the water balance and determination of constituent concentration were identified as the main sources of error; total error was 27% for net sediment flux. The water budget for the island was computed, with an unaccounted input of 0.20 m 3 s −1 (22% of mean inflow), after considering channel flow, change in water storage, evapotranspiration, and precipitation. The net imbalance may be a combination of groundwater seepage, overland flow, and flow through minor channels. Change of island water storage, caused by local variations in water surface elevation, dominated the tidally averaged water flux. These variations were mainly caused by wind and barometric pressure change, which alter regional water levels throughout the Sacramento-San Joaquin River Delta. Peak instantaneous ebb flow was 35% greater than peak flood flow, indicating an ebbdominant system, though dominance varied with the spring-neap cycle. SSC were controlled by wind-wave resuspension adjacent to the island and local tidal currents that mobilized sediment from the channel bed. During neap tides sediment was imported onto the island but during spring tides sediment was exported because the main channel became ebb dominant. Over the 34-d monitoring period 14,000 kg of suspended sediment were imported through the two channels. The water imbalance may affect the sediment balance if the unmeasured water transport pathways are capable of transporting large amounts of sediment. We estimate a maximum of 2,800 kg of sediment may have been exported through unmeasured pathways, giving a minimum ent import of 11,200 kg. Sediment flux measurements provide insight on tidal to fortnightly marsh sedimentation processes, especially in complex systems where sedimentation is spatially and temporally variable.

California↗
USGS2003

Volcano seismology

A fundamental goal of volcano seismology is to understand active magmatic systems, to characterize the configuration of such systems, and to determine the extent and evolution of source regions of magmatic energy. Such understanding is critical to our assessment of eruptive behavior and its hazardous impacts. With the emergence of portable broadband seismic instrumentation, availability of digital networks with wide dynamic range, and development of new powerful analysis techniques, rapid progress is being made toward a synthesis of high-quality seismic data to develop a coherent model of eruption mechanics. Examples of recent advances are: (1) high-resolution tomography to image subsurface volcanic structures at scales of a few hundred meters; (2) use of small-aperture seismic antennas to map the spatio-temporal properties of long-period (LP) seismicity; (3) moment tensor inversions of very-long-period (VLP) data to derive the source geometry and mass-transport budget of magmatic fluids; (4) spectral analyses of LP events to determine the acoustic properties of magmatic and associated hydrothermal fluids; and (5) experimental modeling of the source dynamics of volcanic tremor. These promising advances provide new insights into the mechanical properties of volcanic fluids and subvolcanic mass-transport dynamics. As new seismic methods refine our understanding of seismic sources, and geochemical methods better constrain mass balance and magma behavior, we face new challenges in elucidating the physico-chemical processes that cause volcanic unrest and its seismic and gas-discharge manifestations. Much work remains to be done toward a synthesis of seismological, geochemical, and petrological observations into an integrated model of volcanic behavior. Future important goals must include: (1) interpreting the key types of magma movement, degassing and boiling events that produce characteristic seismic phenomena; (2) characterizing multiphase fluids in subvolcanic regimes and determining their physical and chemical properties; and (3) quantitatively understanding multiphase fluid flow behavior under dynamic volcanic conditions. To realize these goals, not only must we learn how to translate seismic observations into quantitative information about fluid dynamics, but we also must determine the underlying physics that governs vesiculation, fragmentation, and the collapse of bubble-rich suspensions to form separate melt and vapor. Refined understanding of such processes—essential for quantitative short-term eruption forecasts—will require multidisciplinary research involving detailed field measurements, laboratory experiments, and numerical modeling.

Pure and Applied Geophysics↗
USGS2014

Laboratory generated M -6 earthquakes

We consider whether mm-scale earthquake-like seismic events generated in laboratory experiments are consistent with our understanding of the physics of larger earthquakes. This work focuses on a population of 48 very small shocks that are foreshocks and aftershocks of stick–slip events occurring on a 2.0 m by 0.4 m simulated strike-slip fault cut through a large granite sample. Unlike the larger stick–slip events that rupture the entirety of the simulated fault, the small foreshocks and aftershocks are contained events whose properties are controlled by the rigidity of the surrounding granite blocks rather than characteristics of the experimental apparatus. The large size of the experimental apparatus, high fidelity sensors, rigorous treatment of wave propagation effects, and in situ system calibration separates this study from traditional acoustic emission analyses and allows these sources to be studied with as much rigor as larger natural earthquakes. The tiny events have short (3–6 μs) rise times and are well modeled by simple double couple focal mechanisms that are consistent with left-lateral slip occurring on a mm-scale patch of the precut fault surface. The repeatability of the experiments indicates that they are the result of frictional processes on the simulated fault surface rather than grain crushing or fracture of fresh rock. Our waveform analysis shows no significant differences (other than size) between the M -7 to M -5.5 earthquakes reported here and larger natural earthquakes. Their source characteristics such as stress drop (1–10 MPa) appear to be entirely consistent with earthquake scaling laws derived for larger earthquakes.

Pure and Applied Geophysics↗
USGS2026

Accounting for emigration reveals high survival and bimodal size at departure from a loggerhead sea turtle (Caretta caretta) foraging area

The life history of hard-shelled sea turtles includes several ontogenetic shifts in habitat use and these complex permanent emigration patterns can impact estimates of stage-specific population rates, including survival. We developed several multistate mark recapture models to estimate survival of adult and juvenile loggerhead turtles from a coastal bay in the northern Gulf of America (also commonly referred to as the Gulf of Mexico) while, in some cases, accounting for permanent emigration and transient individuals. Our mark-recapture dataset consisted of 228 individual turtles with 37 total recaptures from 2011 to 2024. Of the models we fit, those that incorporated emigration produced higher estimates for annual survival than models that did not, and higher estimates than what is commonly seen in the literature for loggerheads. All models suggested a major permanent emigration pulse at the typical size of sexual maturity (70 cm straight carapace length) and another major pulse at > 90 cm. This bimodal pattern of departure may reflect differences in size at sexual maturity among loggerheads, possible genetic variability within the assemblage, or both. To assess the models’ ability to effectively recover true parameter values, we developed a simulation study of 50 randomly generated independent data sets under our specified models of similar sample size to our study dataset. Simulation results suggested that models that accounted for permanent emigration and transient individuals produced relatively unbiased estimates of survival, while models that did not often underestimated survival rates. Mark-recapture studies that may exhibit emigration and suffer from low recapture rates would benefit from auxiliary data collection such as acoustic telemetry detections to better estimate true rates of emigration and survival. Obtaining unbiased estimates of true survival by accounting for processes like emigration can support effective conservation of endangered long-lived species like loggerheads.

Florida↗
USGS2010

Geomorphology of mesophotic coral ecosystems: Current perspectives on morphology, distribution, and mapping strategies

This paper presents a general review of the distribution of mesophotic coral ecosystems (MCEs) in relationship to geomorphology in US waters. It was specifically concerned with the depth range of 30–100 m, where more than 186,000 km2 of potential seafloor area was identified within the US Gulf of Mexico/Florida, Caribbean, and main Hawaiian Islands. The geomorphology of MCEs was largely inherited from a variety of pre-existing structures of highly diverse origins, which, in combination with environmental stress and physical controls, restrict the distribution of MCEs. Sea-level history, along with depositional and erosional processes, played an integral role in formation of MCE settings. However, mapping the distribution of both potential MCE topography/substrate and existing MCE habitat is only beginning. Mapping techniques pertinent to understanding morphology and MCE distributions are discussed throughout this paper. Future investigations need to consider more cost-effective and remote methods (such as autonomous underwater vehicles (AUVs) and acoustics) in order to assess the distribution and extent of MCE habitat. Some understanding of the history of known MCEs through coring studies would help understand their initiation and response to environmental change over time, essential for assessing how they may be impacted by future environmental change.

Alabama, Florida, Georgia, Hawai'i, Louisiana, Mis↗
USGS2025

Complex sound scattering layer and water-column dynamics over a mesophotic coral ecosystem: Southwest Puerto Rico, U.S.A.

A nearly 5-month record of high-resolution temperature and acoustic backscatter profiles from the upper insular slope off southwest Puerto Rico reveals complex sound scattering layer (SSL) dynamics over a mesophotic coral ecosystem (MCE). The SSLs exhibited both diel and reverse diel vertical migration, thin layer (< 5 m) and multiple layer formations, depth modulation due to internal waves, and vertical layering in the absence of water column stratification. The long-term observations also capture SSL and water column dynamics across changing seasons and two category five hurricanes, Irma and María. The SSLs, likely comprosed of zooplankton, represent an important food source for both the sessile ( e.g. , corals and sponges) and mobile ( e.g. , fish) MCE taxa, and their effective vertical mobility underscores their importance to trophic connectivity between the upper and lower slope MCEs, as well as the shelf. Our results also underscore the challenges in adequately resolving zooplankton aggregations using conventional sampling techniques.

Puerto Rico↗
USGS2016

Seasonal changes in atmospheric noise levels and the annual variation in pigeon homing performance

Repeated releases of experienced homing pigeons from single sites were conducted between 1972 and 1974 near Cornell University in upstate New York and between 1982 and 1983 near the University of Pittsburgh in western Pennsylvania, USA. No annual variation in homing performance was observed at these sites in eastern North America, in contrast to results from a number of similar experiments in Europe. Assuming pigeons home using low-frequency infrasonic signals (~0.1–0.3 Hz), as has been previously proposed, the annual and geographic variability in homing performance within the northern hemisphere might be explained, to a first order, by seasonal changes in low-frequency atmospheric background noise levels related to storm activity in the North Atlantic Ocean, and by acoustic waveguides formed between the surface and seasonally reversing stratospheric winds. In addition, increased dispersion among departure bearings of test birds on some North American release days was possibly caused by infrasonic noise from severe weather events during tornado and Atlantic hurricane seasons.

Journal of Comparative Physiology A↗
USGS2018

A reinterpretation of “Homing pigeons’ flight over and under low stratus” based on atmospheric propagation modeling of infrasonic navigational cues

Pigeons flying above temperature inversion and related low-stratus layers appear to lack important navigational cues, and a reinterpretation of Wagner’s 1978 study suggests that these cues are low-frequency acoustic signals (infrasound). Wagner released homing pigeons above opaque stratus over the Swiss Plateau to determine whether they could locate their loft beneath it. Birds above the clouds appeared lost, while those that descended beneath them returned home directly. Atmospheric propagation modeling of infrasonic waves virtually transmitted from the loft area shows that these signals would have been ducted beneath the inversion layer, and would not have reached the release sites above it. The absence of homeward infrasonic cues above temperature inversions could explain the disorientation of Wagner’s birds, especially if such signals are the predominant cues used by pigeons to home. The possible generation of infrasonic navigational signals in the loft area and recent queries concerning the infrasound navigational “map” hypothesis are also discussed.

Journal of Comparative Physiology A↗
USGS2025

Avian navigation: Comparing the olfactory navigational “map” and the infrasound direction-finding hypotheses to aeronautics

Animal navigation has long been a fascinating but bewildering subject. Humans and animals might well share similar navigational strategies because they developed within the same physical environments. A “map-and-compass” model has been proposed to explain the two-step avian navigational process, but the “map” step has remained elusive. Although scalar values from bicoordinate geomagnetic or atmospheric olfactory gradients have been considered foundational to the avian map, neither has proved convincing engendering decades of controversy. The olfactory map, and an alternative infrasound direction-finding (IDF) hypothesis, are discussed in this review. The olfactory map hypothesis currently requires extensive stable gradients of trace-odor ratios, but such gradients are highly unlikely within a turbulent and rapidly mixed lower atmosphere. The IDF hypothesis, on the other hand, postulates a two-step navigational model analogous to the maritime and aeronautical radio direction-finding technique. This review was also written to encourage further investigation, and direct testing, of the acoustic navigational process. The IDF hypothesis, at present, appears the better explanation of observed avian navigational behavior and accuracy within the atmosphere’s physical environment.

Journal of Comparative Physiology A↗
USGS2007

Understanding shallow gas occurrences in the Gulf of Lions

New coring data have been acquired along the western Gulf of Lions showing anomalous concentrations of methane (up to 95,700 ppm) off the Rhône prodelta and the head of the southern canyons Lacaze-Duthiers and Cap de Creus. Sediment cores were acquired with box and kasten cores during 2004–2005 on several EuroSTRATAFORM cruises. Anomalous methane concentrations are discussed and integrated with organic carbon data. Sampled sites include locations where previous surveys identified acoustic anomalies in high-resolution seismic profiles, which may be related to the presence of gas. Interpretation of the collected data has enabled us to discuss the nature of shallow gas along the Gulf of Lions, and its association with recent sedimentary dynamics. The Rhône prodelta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried, effectively removing this organic matter from aerobic oxidation and biological uptake, and leading to the potential for methanogenesis with burial. Away from the flood-related sediments off the Rhône delta, the organic matter is being reworked and remineralized on its way along the western coast of the Gulf of Lions, with the result that the recent deposits in the canyon contain little reactive carbon. In the southernmost canyons, Lacaze-Duthiers and Cap de Creus, the gas analyses show relatively little shallow gas in the core samples. Samples with anomalous gas (up to 5,000 ppm methane) are limited to local areas where the samples also show higher amounts of organic matter. The anomalous samples at the head of the southern canyons may be related to methanogenesis of recent drape or of older sidewall canyon infills.

Gulf of Lions↗
USGS2016

Observations of pockmark flow structure in Belfast Bay, Maine, Part 1: current-induced mixing

Field observations of current profiles and temperature, salinity, and density structure were used to examine vertical mixing within two pockmarks in Belfast Bay, Maine. The first is located in 21 m water depth (sea level to rim), nearly circular in shape with a 45 m rim diameter and 12 m rim-to-bottom relief. The second is located in 25 m water depth, more elongated in shape with an approximately 80 m (36 m) major (minor) axis length at the rim, and 17 m relief. Hourly averaged current profiles were acquired from bottom-mounted acoustic Doppler current profilers deployed on the rim and center of each pockmark over successive 42 h periods in July 2011. Conductivity–temperature–depth casts at the rim and center of each pockmark show warmer, fresher water in the upper water column, evidence of both active and fossil thermocline structure 5–8 m above the rim, and well-mixed water below the rim to the bottom. Vertical velocities show up- and down-welling events that extend into the depths of each pockmark. An observed temperature change at both the rim and center occurs coincident with an overturning event below the rim, and suggests active mixing of the water column into the depths of each pockmark. Vertical profiles of horizontal velocities show depth variation at both the center and rim consistent with turbulent logarithmic current boundary layers, and suggest that form drag may possibly be influencing the local flow regime. While resource limitations prevented observation of the current structure and water properties at a control site, the acquired data suggest that active mixing and overturning within the sampled pockmarks occur under typical benign conditions, and that current flows are influenced by upstream bathymetric irregularities induced by distant pockmarks.

Maine↗
USGS1997

Benthic boundary layer processes in the Lower Florida Keys

This special issue of Geo-Marine Letters, "Benthic Boundary Layer Processes in the Lower Florida Keys," includes 12 papers that present preliminary results from the Key West Campaign. The Dry Tortugas and Marquesas Keys test sites were selected by a group of 115 scientists and technicians to study benthic boundary layer processes in a carbonate environment controlled by bioturbation and biogeochemical processes. Major activities included remote sediment classification; high-frequency acoustic scattering experiments; sediment sampling for radiological, geotechnical, biological, biogeochemical, physical, and geoacoustic studies; and hydrodynamic studies using an instrumented tetrapod. All these data are being used to improve our understanding of the effects of environmental processes on sediment structure and behavior.

Florida↗
USGS2023

Spatiotemporal segregation by migratory phenotype indicates potential for assortative mating in lake sturgeon

Migratory diversity can promote population differentiation if sympatric phenotypes become temporally, spatially, or behaviorally segregated during breeding. In this study, the potential for spatiotemporal segregation was tested among three migratory phenotypes of lake sturgeon ( Acipenser fulvescens ) that spawn in the St. Clair River of North America’s Laurentian Great Lakes but differ in how often they migrate into the river and in which direction they move after spawning. Acoustic telemetry over 9 years monitored use of two major spawning sites by lake sturgeon that moved north to overwinter in Lake Huron or south to overwinter in Lake St. Clair. Lake St. Clair migrants were further distinguished by whether they migrated into the St. Clair River each year (annual migrants) or intermittently (intermittent migrants). Social network analyses indicated lake sturgeon generally co-occurred with individuals of the same migratory phenotype more often than with different migratory phenotypes. A direct test for differences in space use revealed one site was almost exclusively visited by Lake St. Clair migrants whereas the other site was visited by Lake Huron migrants, intermittent Lake St. Clair migrants, and, to a lesser extent, annual Lake St. Clair migrants. Analysis of arrival and departure dates indicated opportunity for co-occurrence at the site visited by all phenotypes but showed Lake Huron migrants arrived approximately 2 weeks before Lake St. Clair migrants. Taken together, our results indicated partial spatiotemporal segregation of migratory phenotypes that may generate assortative mating and promote population differentiation.

Michigan, Ontario↗
USGS2020

Did ice-charging generate volcanic lightning during the 2016–2017 eruption of Bogoslof volcano, Alaska?

The 2016–2017 shallow submarine eruption of Bogoslof volcano in Alaska injected plumes of ash and seawater to maximum heights of ~ 12 km. More than 4550 volcanic lightning strokes were detected by the World Wide Lightning Location Network (WWLLN) and Vaisala’s Global Lightning Dataset (GLD360) over 9 months. Lightning assisted monitoring efforts by confirming ash-producing explosions in near-real time, but only 32 out of the 70 explosive events produced detectable lightning. What led to electrical activity within some of the volcanic plumes, but not others? And why did the lightning intensity wax and wane over the lifetime of individual explosions? We address these questions using multiparametric observations from ground-based lightning sensors, satellite imagery, photographs, acoustic signals, and 1D plume modeling. Detailed time-series of monitoring data show that the plumes did not produce detectable lightning until they rose higher than the atmospheric freezing level (approximated by − 20 °C temperatures). For example, on 28 May 2017 (event 40), the delayed onset of lightning coincides with modeled ice formation in upper levels of the plume. Model results suggest that microphysical conditions inside the plume rivaled those of severe thunderstorms, with liquid water contents > 5 g m −3 and vigorous updrafts > 40 m s −1 in the mixed-phase region where liquid water and ice coexist. Based on these findings, we infer that ‘thunderstorm-style’ collisional ice-charging catalyzed the volcanic lightning. However, charge mechanisms likely operated on a continuum, with silicate collisions dominating electrification in the near-vent region, and ice charging taking over in the upper-level plumes. A key implication of this study is that lightning during the Bogoslof eruption provided a reliable indicator of sustained, ash-rich plumes (and associated hazards) above the atmospheric freezing level.

Alaska↗
USGS2020

Infrasound generated by the 2016-2017 shallow submarine eruption of Bogoslof volcano, Alaska

The 2016–2017 shallow submarine eruption of Bogoslof volcano produced numerous infrasound signals over 9 months that were recorded on six Alaska Volcano Observatory (AVO) arrays at ranges of 59 to over 800 km from the volcano. The lack of geophysical monitoring near Bogoslof and the repeated production of volcanic clouds to flight levels made monitoring by remote infrasound critical during the eruption; for the first time, AVO relied extensively on automated infrasound detections from regional arrays to dispatch timely notifications of the ongoing activity. Most of the 70 eruptive events were detected on at least one array, but no array detected all of the events mainly because atmospheric conditions were highly variable during the eruption. Acoustic propagation modeling helps explain some of the variation in array detections but also highlights limitations in regional propagation models. To our knowledge, this is the first example of well-recorded infrasound from an explosive eruption occurring in shallow seawater, providing extensive insights into eruption dynamics in this unique environment. The dominance of low-frequency infrasound (0.1–1 Hz) is attributed to eruptions occurring beneath tens of meters of seawater. Higher-frequency infrasound signals were mostly limited to eruptions where the vent was isolated from major interaction with seawater or in several cases where a lava dome grew above sea level.

Alaska↗
USGS2022

Infrasound observations and constraints on the 2018 eruption of Kīlauea Volcano, Hawaii

The 2018 eruption of Kīlauea Volcano was a dynamic event involving explosions, collapses, and fountaining at multiple vents spread over tens of kilometers. The permanent infrasound network operated by the USGS Hawaiian Volcano Observatory (HVO) was well prepared to observe the collapse of the summit, and additional deployments permitted infrasound observations during fissuring in the lower East Rift Zone (LERZ). We provide a summary of infrasound observations, including lava lake spattering, collapses, explosions, rockfall, and lava fountaining, using seismicity and tilt at times to help constrain our interpretations. At the summit of Kīlauea Volcano, we document the process of partial caldera collapse and examine a set of “proto-collapse” events that precede the widely observed events but share many of the same qualities as the larger collapses. For the initial twelve collapse events, we compare the timing of collapse onset to other observations and illustrate the repeatable characteristics of the recorded waveforms and infrasound characteristics associated with each episode of caldera collapse. In the LERZ, we match the acoustic signals with visual observations, including fissure migration, explosions near fissures, and littoral explosions. Lastly, we document and discuss the performance of infrasound alarms during the 2018 Kīlauea eruption. In general, alarming became successful in detecting collapse events at the summit of the volcano after tuning and became a key discriminant in the initial determination of collapse events, especially when visual observations were not available.

Hawaii↗
USGS2019

Relaxation response of critically stressed macroscale surficial rock sheets

Rock environments both underground and on Earth’s surface show indications of energetic macroscale fracture. In tunnels and excavations, these manifest as rockbursts—energetic explosions of rock that can damage engineering projects, and may pose ongoing financial and safety risk as rock stresses adjust during post-failure relaxation. In natural settings at the surface, evidence for rockbursts exist in the form of tent-like structures of ruptured exfoliation sheets, but few direct observations of such events exist, precluding the analysis of how natural rock formations may evolve after rupture. Here we investigate the post-failure evolution of a granitic rock dome following rapid fracture events (i.e., surficial rockbursts) that occurred in California, USA during 2014–2016. Building upon previous work that showed a thermal stress origin for the observed fracturing, we investigate the return to background stress conditions (i.e., stress relaxation) observed in both short- (week, month) and long-term (multi-year) rock deformation trends. Acoustic emissions, deformation, and environmental monitoring data indicate that partially detached rock sheets forming the surface of the dome undergo fracture aperture closing during cooling periods, concurrent with reduction of rock stress by the source of forcing (i.e., thermal stress). However, with sufficient critical and/or subcritical fracture, our observations also show that rock sheets can become decoupled from the source of stress, resulting in a long-term return to background stress conditions. Our results provide insight into the cyclic and likely ephemeral nature of rock fracture in surficial rock domes, as well as in underground rockburst environments.

Rock Mechanics and Rock Engineering↗