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At least 1,009 records · Page 56Linked to original sources
USGS1988

Hydrocarbon gas in sediment of the Southern Pacific Ocean

Methane, ethane, ethene, propane, and propene are common hydrocarbon gases in near-surface sediment from offshore areas in the southern Pacific Ocean near Papua New Guinea, the Solomon Islands, Vanuatu, Tonga, New Zealand, and Antarctica. Sea floor sites for sampling of sediment were selected on the basis of anomalies in marine seismic records, and the samples were intentionally biased toward finding possible thermogenic hydrocarbon gases. In none of the areas, however, were thermogenic hydrocarbons clearly identified. The hydrocarbon gases that were found appear to be mainly the products of in situ microbial processes. ?? 1988 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS1979

Geologic implications and potential hazards of scour depressions on bering shelf, Alaska

Flat-bottomed depression 50-150 m in diameter and 60-80 cm deep occur in the floor of Norton Sound, Bering Sea. These large erosional bedforms and associated current ripples are found in areas where sediment grain size is 0.063-0.044 mm (4-4.5 ??), speeds of bottom currents are greatest (20-30 cm/s mean speeds under nonstorm conditions, 70 cm/s during typical storms), circulation of water is constricted by major topographic shoals (kilometers in scale), and small-scale topographic disruptions, such as ice gouges, occur locally on slopes of shoals. These local obstructions on shoals appear to disrupt currents, causing separation of flow and generating eddies that produce large-scale scour. Offshore artificial structures also may disrupt bottom currents in these same areas and have the potential to generate turbulence and induce extensive scour in the area of disrupted flow. The size and character of natural scour depressions in areas of ice gouging suggest that large-scale regions of scour may develop from enlargement of local scour sites around pilings, platforms, or pipelines. Consequently, loss of substrate support for pipelines and gravity structures is possible during frequent autumn storms. ?? 1979 Springer-Verlag New York Inc.

Environmental Geology↗
USGS1984

Delgada Fan: Preliminary interpretation of channel development

The Delgada Fan, an irregularly shaped turbidite deposit extending more than 350 km offshore from northern California, consists of two large leveed-valley units each fed by a separate complex of coalescing submarine canyons and slope gullies. Although the leveed-valley units head within 25 km of each other, both appear to have developed independently during fan growth. The larger southern leveed-valley system has not developed middle-fan distributary channels and appears to illustrate a period of progressive valley abandonment. Although the lower-fan area is underlain by sandy sediments, little sand has been recovered in piston cores from the leveed-valley unit. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS1982

Erosional channels on the shoreface of Nauset Beach, Cape Cod, Massachusetts

Many channels (1 to 3 m relief)_are located offshore of Nauset Beach, Cape Cod, Massachusetts, in water 4 to 18 m deep. The channels are oblique to the shoreline, are spaced approximately 260 m apart, and deepen seaward. The southern flank of each channel is rippled whereas the northern flank and interchannel areas are smooth. The origin of the channels is unknown. They probably formed by erosion of the shoreface, perhaps by rip-current circulation during storm conditions or by rip-current circulation under quiet conditions. The channels may control current flow and thereby maintain themselves even though formative conditions may no longer exist.

Massachusetts↗
USGS1981

Storm-built sand ridges on the Maryland inner shelf: a preliminary report

Several aspects of the Maryland ridge field are pertinent to the problem of ridge genesis in response to Holocene sea-level rise. There is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges, which reflects the changing hydraulic regime. Grain size is 90?? out of phase with topography, so that the coarsest sand lies between the axis of each trough and the adjacent seaward ridge crest, while the finest sand lies between each ridge crest and the axis of the adjacent seaward trough. Finally, analysis over a 43-year period on an outer ridge reveals a systematic pattern of landward flank erosion, seaward flank deposition, and seaward crest migration. These relationships support a model which explains the ridges as consequences of the up-current shift of maximum bottom shear stress with respect to the crests of initial bottom irregularities. The oblique orientation of the ridges with respect to the beach may be at least partly due to the more rapid migration rate of the ridges' inshore ends. ?? 1981 A.M. Dowden, Inc.

Geo-Marine Letters↗
USGS2003

Erosion and sedimentation from the 17 July, 1998 Papua New Guinea tsunami

This paper describes erosion and sedimentation associated with the 17 July 1998 Papua New Guinea tsunami. Observed within two months of the tsunami, distinct deposits of a layer averaging 8-cm thick of gray sand rested on a brown muddy soil. In most cases the sand is normally graded, with more coarse sand near the base and fine sand at the top. In some cases the deposit contains rip-up clasts of muddy soil and in some locations it has a mud cap. Detailed measurements of coastal topography, tsunami flow height and direction indicators, and deposit thickness were made in the field, and samples of the deposit were collected for grain-size analysis in the laboratory. Four shore-normal transects were examined in detail to assess the shore-normal and along shore distribution of the tsunami deposit. Near the shoreline, the tsunami eroded approximately 10-25 cm of sand from the beach and berm. The sandy layer deposited by the tsunami began 50-150 m inland from the shoreline and extended across the coastal plain to within about 40 m of the limit of inundation; a total distance of up to 750 m from the beach. As much as 2/3 of the sand in the deposit originated from offshore. Across most of the coastal plain the deposit thickness and mean grain size varied little. In the along-shore direction the deposit thickness varied with the tsunami wave height; both largest near the entrance to Sissano Lagoon.

Pure and Applied Geophysics↗
USGS2010

Field survey of the March 28, 2005 Nias-Simeulue earthquake and Tsunami

On the evening of March 28, 2005 at 11:09 p.m. local time (16:09 UTC), a large earthquake occurred offshore of West Sumatra, Indonesia. With a moment magnitude (Mw) of 8.6, the event caused substantial shaking damage and land level changes between Simeulue Island in the north and the Batu Islands in the south. The earthquake also generated a tsunami, which was observed throughout the source region as well as on distant tide gauges. While the tsunami was not as extreme as the tsunami of December 26th, 2004, it did cause significant flooding and damage at some locations. The spatial and temporal proximity of the two events led to a unique set of observational data from the earthquake and tsunami as well as insights relevant to tsunami hazard planning and education efforts. ?? 2010 Springer Basel AG.

Pure and Applied Geophysics↗
USGS2017

Introduction to “Global tsunami science: Past and future, Volume II”

Twenty-two papers on the study of tsunamis are included in Volume II of the PAGEOPH topical issue “Global Tsunami Science: Past and Future”. Volume I of this topical issue was published as PAGEOPH, vol. 173, No. 12, 2016 (Eds., E. L. Geist, H. M. Fritz, A. B. Rabinovich, and Y. Tanioka). Three papers in Volume II focus on details of the 2011 and 2016 tsunami-generating earthquakes offshore of Tohoku, Japan. The next six papers describe important case studies and observations of recent and historical events. Four papers related to tsunami hazard assessment are followed by three papers on tsunami hydrodynamics and numerical modelling. Three papers discuss problems of tsunami warning and real-time forecasting. The final set of three papers importantly investigates tsunamis generated by non-seismic sources: volcanic explosions, landslides, and meteorological disturbances. Collectively, this volume highlights contemporary trends in global tsunami research, both fundamental and applied toward hazard assessment and mitigation.

Pure and Applied Geophysics↗
USGS2019

Migration routes, foraging behavior, and site fidelity of loggerhead sea turtles (Caretta caretta) satellite tracked from a globally important rookery

The Archie Carr National Wildlife Refuge, Florida, USA (27.946°N, − 80.494°W) represents one of the largest loggerhead turtle ( Caretta caretta ) nesting sites in the Western Hemisphere. Surprisingly, little work has been conducted to determine females’ post-nesting migratory behavior and characteristics of their foraging areas. Between 2008 and 2017, satellite telemetry was used to trace the locations and movements of 45 post-nesting loggerhead turtles. A switching state-space model was employed to estimate the behavioral state of each location. Internesting, migrating and foraging activity periods were determined for 38 loggerheads based on the SSSM. Seven environmental variables were extracted from remote sensing imagery for each location to compare values among behaviors. Core primary foraging areas ranged in size from 5.89 to 4572.80 km 2 . Four foraging types (primary, secondary, seasonal, and loops) were observed. Most turtles resided at a primary foraging area year round. A few individuals conducted foraging loops away from a primary foraging area. Both seasonal and loop movements were associated with changes in sea surface temperature as turtles moved to avoid temperatures that could cause cold-stunning or mortality. Turtle size and nesting beach offshore currents may play a role in foraging area selection, and date of departure from the nesting beach may be linked to foraging destination. By making the connection among oceanic features, foraging areas, and the influence of environmental variables on these areas, it is possible to identify and characterize critically important feeding areas and migration corridors for loggerheads nesting on the east coast of Florida.

Marine Biology↗
USGS2004

Sediment resuspension and transport patterns on a fringing reef flat, Molokai, Hawaii

Corals are known to flourish in various turbid environments around the world. The quantitative distinction between clear and turbid water in coral habitats is not well defined nor are the amount of sediment in suspension and rates of sedimentation used to evaluate the condition of reef environments well established. This study of sediment resuspension, transport, and resulting deposition on a fringing reef flat off Molokai, Hawaii, uses a year of time-series data from a small, instrumented tripod. It shows the importance of trade winds and ocean wave heights in controlling the movement of sediment. Sediment is typically resuspended daily and the dominant controls on the magnitude of events (10-25 mg/l) are the trade-wind-generated waves and currents and tidal elevation on the reef flat. The net flux of sediment on this reef is primarily along the reef flat in the direction of the prevailing trade winds (to the west), with a secondary direction of slightly offshore, towards a zone of low coral abundance. These results have application to reef studies and reef management in other areas in several ways. First, the observed resuspension and turbidity results from fine-grained terrigenous sediment that appears to be trapped and recycled on the reef flat. Thus corals are subjected to light attenuation by the same particles repeatedly, however small the amount. Secondly, the measurements show high temporal variability (from daily to seasonal scales) of sediment resuspension, indicating that single measurements are inadequate to accurately describe conditions on a reef flat. ?? Springer-Verlag 2004.

Coral Reefs↗
USGS2011

Numerical modeling of the impact of sea-level rise on fringing coral reef hydrodynamics and sediment transport

Most climate projections suggest that sea level may rise on the order of 0.5-1.0 m by 2100; it is not clear, however, how fluid flow and sediment dynamics on exposed fringing reefs might change in response to this rapid sea-level rise. Coupled hydrodynamic and sediment-transport numerical modeling is consistent with recent published results that suggest that an increase in water depth on the order of 0.5-1.0 m on a 1-2 m deep exposed fringing reef flat would result in larger significant wave heights and setup, further elevating water depths on the reef flat. Larger waves would generate higher near-bed shear stresses, which, in turn, would result in an increase in both the size and the quantity of sediment that can be resuspended from the seabed or eroded from adjacent coastal plain deposits. Greater wave- and wind-driven currents would develop with increasing water depth, increasing the alongshore and offshore flux of water and sediment from the inner reef flat to the outer reef flat and fore reef where coral growth is typically greatest. Sediment residence time on the fringing reef flat was modeled to decrease exponentially with increasing sea-level rise as the magnitude of sea-level rise approached the mean water depth over the reef flat. The model results presented here suggest that a 0.5-1.0 m rise in sea level will likely increase coastal erosion, mixing and circulation, the amount of sediment resuspended, and the duration of high turbidity on exposed reef flats, resulting in decreased light availability for photosynthesis, increased sediment-induced stress on the reef ecosystem, and potentially affecting a number of other ecological processes.

Coral Reefs↗
USGS2020

Annual outbreaks of coral disease coincide with extreme seasonal warming

Reef-building corals living in extreme environments can provide insight into the negative effects of future climate scenarios. In hot environments, coral communities experience disproportionate thermal stress as they live very near or at their upper thermal limits. This results in a high frequency of bleaching episodes, but it is unknown whether temperature-driven outbreaks of coral disease follow a similar trajectory. Here we tracked outbreaks of a white-syndrome (WS) disease over three years in the hottest region inhabited by reef-building corals, the southern Persian Gulf. From 2014 to 2016, WS affected 10 of the 16 scleractinian genera recorded at inshore and offshore sites. Intra- and inter-specific transmission of lesions was frequently observed, indicative of a single contagious disease infecting multiple coral taxa. Colonies of Acropora were the most susceptible to WS disease and were more than twice as likely to experience lesions than any other genera. Prevalence reached 42% of Acropora colonies and lesions progressed at an average rate of 1 mm day −1 . Platygyra colonies were the second most susceptible to WS disease, where prevalence reached 33% and lesions progressed at 0.3 mm day −1 . Affected colonies of both of these genera suffered considerable partial mortality that was not recovered between years, promoting the fragmentation of larger colonies into smaller size classes. Across the 3 years of our study, the onset of WS outbreaks occurred early in summer and prevalence increased exponentially with cumulative heat exposure (coral community r 2 = 0.55, Acropora r 2 = 0.72, Platygyra r 2 = 0.75). Peak levels of community-wide prevalence occurred in August (10% of all coral colonies) to September (14%) when preceding 4-week and 8-week average temperatures exceeded 34.5 °C and 34 °C, respectively. Outbreaks ceased following the return of cooler temperatures with prevalence remaining below 0.5% between December and June. Levels of bleaching remained relatively low (< 5% prevalence), despite exposure to daily temperatures ≥ 35 °C each summer. These findings demonstrate that thermal stress on coral reefs does not always manifest as coral bleaching and diseases can present as a primary sign of thermal stress. Consequently, temperature-driven outbreaks of coral disease are expected to become more widespread as climate warming pushes corals to be living increasingly closer to their upper thermal limits.

Saadiyat Island, Sir Bu Nair Island↗
USGS2004

Dispersal forcing of a southern California river plumes, based on field and remote sensing observations

River plumes are important pathways of terrestrial materials entering the sea. In southern California, rivers are known to be the dominant source of littoral, shelf and basin sediment and coastal pollution, although a basic understanding of the dynamics of these river inputs does not exist. Here we evaluate forcing parameters of a southern California river plume using ship-based hydrographic surveys and satellite remote sensing measurements to provide the first insights of river dispersal dynamics in southern California. Our results suggest that plumes of the Santa Clara River are strongly influenced by river inertia, producing jet-like structures ~10 km offshore during annual recurrence (~two-year) flood events and ~30 km during exceptional (~10-year recurrence) floods. Upwelling-favorable winds may be strong following stormwater events and can alter dispersal pathways of thse plumes. Due to similar runoff relationships and other reported satellite observations, we hypothesize that interia-dominated dispersal may be an important characteristic of the small, mountainous rivers throughout southern California.

California↗
USGS2010

Distribution patterns of wintering sea ducks in relation to the North Atlantic Oscillation and local environmental characteristics

Twelve species of North American sea ducks (Tribe Mergini) winter off the eastern coast of the United States and Canada. Yet, despite their seasonal proximity to urbanized areas in this region, there is limited information on patterns of wintering sea duck habitat use. It is difficult to gather information on sea ducks because of the relative inaccessibility of their offshore locations, their high degree of mobility, and their aggregated distributions. To characterize environmental conditions that affect wintering distributions, as well as their geographic ranges, we analyzed count data on five species of sea ducks (black scoters Melanitta nigra americana, surf scoters M. perspicillata, white-winged scoters M. fusca, common eiders Somateria mollissima, and long-tailed ducks Clangula hyemalis) that were collected during the Atlantic Flyway Sea Duck Survey for ten years starting in the early 1990s. We modeled count data for each species within ten-nautical-mile linear survey segments using a zero-inflated negative binomial model that included four local-scale habitat covariates (sea surface temperature, mean bottom depth, maximum bottom slope, and a variable to indicate if the segment was in a bay or not), one broad-scale covariate (the North Atlantic Oscillation), and a temporal correlation component. Our results indicate that species distributions have strong latitudinal gradients and consistency in local habitat use. The North Atlantic Oscillation was the only environmental covariate that had a significant (but variable) effect on the expected count for all five species, suggesting that broad-scale climatic conditions may be directly or indirectly important to the distributions of wintering sea ducks. Our results provide critical information on species-habitat associations, elucidate the complicated relationship between the North Atlantic Oscillation, sea surface temperature, and local sea duck abundances, and should be useful in assessing the impacts of climate change on seabirds.

Oecologia↗
USGS2004

Emplacement mechanisms of the South Kona slide complex, Hawaii Island: Sampling and observations by remotely operated vehicle Kaiko

Emplacement of a giant submarine slide complex, offshore of South Kona, Hawaii Island, was investigated in 2001 by visual observation and in-situ sampling on the bench scarp and a megablock, during two dives utilizing the Remotely Operated Vehicle (ROV) Kaiko and its mother ship R/V Kairei. Topography of the bench scarp and megablocks were defined in 3-D perspective, using high-resolution digital bathymetric data acquired during the cruise. Compositions of 34 rock samples provide constraints on the landslide source regions and emplacement mechanisms. The bench scarp consists mainly of highly fractured, vesiculated, and oxidized a-a lavas that slumped from the subaerial flank of ancestral Mauna Loa. The megablock contains three units: block facies, matrix facies, and draped sediment. The block facies contains hyaloclastite interbedded with massive lava, which slid from the shallow submarine flank of ancestral Mauna Loa, as indicated by glassy groundmass of the hyaloclastite, low oxidation state, and low sulfur content. The matrix facies, which directly overlies the block facies and is similar to a lahar deposit, is thought to have been deposited from the water column immediately after the South Kona slide event. The draped sediment is a thin high-density turbidite layer that may be a distal facies of the Alika-2 debris-avalanche deposit; its composition overlaps with rocks from subaerial Mauna Loa. The deposits generated by the South Kona slide vary from debris avalanche deposit to turbidite. Spatial distribution of the deposits is consistent with deposits related to large landslides adjacent to other Hawaiian volcanoes and the Canary Islands. ?? Springer-Verlag 2004.

Bulletin of Volcanology↗
USGS2021

Lava effusion rate evolution and erupted volume during the 2018 Kīlauea lower East Rift Zone eruption

The 2018 eruption on the lower East Rift Zone of Kīlauea Volcano produced one of the largest and most destructive lava flows in Hawai’i during the past 200 years. Over the course of more than 3 months, twenty-four fissures erupted, and the rate of lava effusion varied by two orders of magnitude, with significant implications for evolving flow behavior and hazards. Syn-eruptive data were collected to quantify these changes in lava effusion rate, including video of flow through channels and digital elevation models acquired using small unoccupied aircraft systems, airborne lidar, and airborne single-pass interferometric synthetic aperture radar. Topographic data through time allowed calculation of subaerial lava flow volume and time-averaged discharge rate over the course of the eruption, which we integrated with pre- and post-eruption bathymetric surveys. Repeat videos of the near-vent channel were analyzed with particle velocimetry to extract flow velocities, and these were combined with open channel flow theory to calculate a time series of instantaneous effusion rates. Results show a general increase in dense rock equivalent (DRE) effusion rate from ~7 to ~100 m 3 /s from early to late May for the whole flow field and ≥ 200 m 3 /s by mid-June after the eruption had focused at a primary vent. By the end of the eruption in August, 0.9–1.4 km 3 DRE of lava had erupted, with 0.4 km 3 deposited on land and at least 0.5 km 3 offshore. The trends in effusion rate through time reflect magmatic processes in the connected summit and rift zone system that controlled eruption rate, with resulting implications for lava flow dynamics and hazards.

Hawaii↗
USGS2000

Formation of submarine flat-topped volcanic cones in Hawai'i

High-resolution bathymetric mapping has shown that submarine flat-topped volcanic cones, morphologically similar to ones on the deep sea floor and near mid-ocean ridges, are common on or near submarine rift zones of Kilauea, Kohala (or Mauna Kea), Mahukona, and Haleakala volcanoes. Four flat-topped cones on Kohala were explored and sampled with the Pisces V submersible in October 1998. Samples show that flat-topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage. Similarly shaped flat-topped cones on the northwest submarine flank of Ni'ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage. Submarine postshield-stage eruptions on Hilo Ridge, Mahukona, Hana Ridge, and offshore Ni'ihau form pointed cones of alkalic basalt and hawaiite. The shield stage flat-topped cones have steep (∼25°) sides, remarkably flat horizontal tops, basal diameters of 1–3 km, and heights <300 m. The flat tops commonly have either a low mound or a deep crater in the center. The rejuvenated-stage flat-topped cones have the same shape with steep sides and flat horizontal tops, but are much larger with basal diameters up to 5.5 km and heights commonly greater than 200 m. The flat tops have a central low mound, shallow crater, or levees that surrounded lava ponds as large as 1 km across. Most of the rejuvenated-stage flat-topped cones formed on slopes <10° and formed adjacent semicircular steps down the flank of Ni'ihau, rather than circular structures. All the flat-topped cones appear to be monogenetic and formed during steady effusive eruptions lasting years to decades. These, and other submarine volcanic cones of similar size and shape, apparently form as continuously overflowing submarine lava ponds. A lava pond surrounded by a levee forms above a sea-floor vent. As lava continues to flow into the pond, the lava flow surface rises and overflows the lowest point on the levee, forming elongate pillow lava flows that simultaneously build the rim outward and upward, but also dam and fill in the low point on the rim. The process repeats at the new lowest point, forming a circular structure with a flat horizontal top and steep pillowed margins. There is a delicate balance between lava (heat) supply to the pond and cooling and thickening of the floating crust. Factors that facilitate construction of such landforms include effusive eruption of lava with low volatile contents, moderate to high confining pressure at moderate to great ocean depth, long-lived steady eruption (years to decades), moderate effusion rates (probably ca. 0.1 km 3 /year), and low, but not necessarily flat, slopes. With higher effusion rates, sheet flows flood the slope. With lower effusion rates, pillow mounds form. Hawaiian shield-stage eruptions begin as fissure eruptions. If the eruption is too brief, it will not consolidate activity at a point, and fissure-fed flows will form a pond with irregular levees. The pond will solidify between eruptive pulses if the eruption is not steady. Lava that is too volatile rich or that is erupted in too shallow water will produce fragmental and highly vesicular lava that will accumulate to form steep pointed cones, as occurs during the post-shield stage. The steady effusion of lava on land constructs lava shields, which are probably the subaerial analogs to submarine flat-topped cones but formed under different cooling conditions.

Hawaii↗
USGS2017

Evaluating stocking efficacy in an ecosystem undergoing oligotrophication

Oligotrophication has negatively affected fisheries production in many freshwater ecosystems and could conceivably reduce the efficacy of stockings used to enhance fisheries. In Lake Michigan, offshore oligotrophication has occurred since the 1970s, owing to reductions in total phosphorus (TP) inputs and nearshore sequestration of TP by nonindigenous dreissenid mussels. We evaluated simultaneous effects of stock enhancement and oligotrophication on salmonine species (Chinook salmon Oncorhynchus tshawytscha , lake trout Salvelinus namaycush , and steelhead O. mykiss ) that support valuable recreational fisheries. We employed a novel application of an Ecopath with Ecosim model by conducting a full factorial simulation experiment. Our design included multiple levels of salmonine stocking, consumption by invasive quagga mussels ( Dreissena bugensis ), and TP that were informed by manager interests. Under all levels of TP and quagga mussel consumption, our results showed that stock enhancement could still increase salmonine biomass, but positive responses were stronger for lake trout and steelhead than Chinook salmon. Simulations showed that quagga mussel consumption has deleterious effects on pelagic-oriented prey fishes and Chinook salmon, which feed almost exclusively on the pelagic-oriented alewife ( Alosa pseudoharengus ). In summary, results from our simulation experiment suggested that lake trout and steelhead are better suited to the current ecosystem than Chinook salmon, and therefore, stock enhancement provides the highest gains for these two species. Furthermore, simulated biomass of all recreational salmonine species increased with increasing TP, indicating the need for managers to consider how potential future oligotrophication will limit the carrying capacity of salmonine biomass in Lake Michigan

Lake Michigan↗