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At least 1,801 records · Page 100Linked to original sources
USGS2009

Sedimentology and hydrodynamic implications of a coarse-grained hurricane sequence in a carbonate reef setting

Storms and associated surges are major coast-shaping processes. Nevertheless, no typical sequences for storm surge deposits in different coastal settings have been established. This study interprets a coarse-grained hurricane ridge deposit on the island of Bonaire, Netherlands Antilles. The sequence was deposited during Hurricane Lenny in November 1999. Insight is gained into the hydrodynamics of surge flow by interpreting textural trends, particle imbrication, and deposit geometry. Vertical textural variations, caused by time-dependent hydrodynamic changes, were used to subdivide the deposit into depositional units that correspond to different stages of the surge, such as setup, peak, and return flow. Particle size and imbrication trends and geometry of the units reflect landward bed-load transport of components during the setup, a nondirectional flow with sediment falling out of suspension during the peak, and a seaward bedload transport during the return flow. Formation of a ridge during setup affected the texture of the return flow unit. Changing angles of imbrication reflect alternating flow velocities during each phase. Normal grading during setup and inverse grading during return flow are caused by decelerating and accelerating flow, respectively. Hence, the interpreted deposit seems to represent the first described complete hurricane surge sequence from a carbonate environment. ?? 2009 Geological Society of America.

Geology↗
USGS2002

Sources, fate, and effects of PAHs in shallow water environments: a review with special reference to small watercraft

Polycyclic aromatic hydrocarbons (PAHs) are aromatic hydrocarbons with two to seven fused carbon (benzene) rings that can have substituted groups attached. Shallow coastal, estuarine, lake, and river environments receive PAHs from treated wastewater, stormwater runoff, petroleum spills and natural seeps, recreational and commercial boats, natural fires, volcanoes, and atmospheric deposition of combustion products. Abiotic degradation of PAHs is caused by photooxidation, photolysis in water, and chemical oxidation. Many aquatic microbes, plants, and animals can metabolize and excrete ingested PAHs; accumulation is associated with poor metabolic capabilities, high lipid content, and activity patterns or distributions that coincide with high concentrations of PAHs. Resistance to biological transformation increases with increasing number of carbon rings. Four- to seven-ring PAHs are the most difficult to metabolize and the most likely to accumulate in sediments. Disturbance by boating activity of sediments, shorelines, and the surface microlayer of water causes water column re-entry of recently deposited or concentrated PAHs. Residence time for PAHs in undisturbed sediment exceeds several decades. Toxicity of PAHs causes lethal and sublethal effects in plants and animals, whereas some substituted PAHs and metabolites of some PAHs cause mutations, developmental malformations, tumors, and cancer. Environmental concentrations of PAHs in water are usually several orders of magnitude below levels that are acutely toxic, but concentrations can be much higher in sediment. The best evidence for a link between environmental PAHs and induction of cancerous neoplasms is for demersal fish in areas with high concentrations of PAHs in the sediment.

Book chapter↗
USGS1983

Geological setting of oil shales in the Permian phosphoria formation and some of the geochemistry of these rocks

Recent studies of the Meade Peak and the Retort Phosphatic Shale Members of the Phosphoria Formation have investigated the organic carbon content and some aspects of hydrocarbon generation from these rocks. Phosphorite has been mined from the Retort and Meade Peak members in southeastern Idaho, northern Utah, western Wyoming and southwestern Montana. Organic carbon-rich mudstone beds associated with the phosphorite in these two members also were natural sources of petroleum. These mudstone beds were differentially buried throughout the region so that heating of these rocks has been different from place to place. Most of the Phosphoria source beds have been deeply buried and naturally heated to catagenetically form hydrocarbons. Deepest burial was in eastern Idaho and throughout most of the northeastern Great Basin where high ambient temperatures have driven the catagenesis to its limit and beyond to degrade or to destroy the hydrocarbons. In southwest Montana, however, burial in some areas has been less than 2 km, ambient temperatures remained low and the kerogen has not produced hydrocarbons (2). In these areas in Montana, the kerogen in the carbonaceous mudstone has retained the potential for hydrocarbon generation and the carbon-rich Retort Member is an oil shale from which hydrocarbons can be synthetically extracted. The Phosphoria Formation was deposited in a foreland basin between the Cordilleran geosyncline and the North American craton. This foreland basin, which coincides with the area of deposition of the two organic carbon-rich mudstone members of the Phosphoria, has been named the Sublett basin (Maughan, 1979). The basin has a northwest-southeast trending axis and seems to have been deepest in central Idaho where deep-water sedimentary rocks equivalent to the Phosphoria Formation are exceptionally thick. The depth of the basin was increasingly shallower away from central Idaho toward the Milk River uplift - a land area in Montana, the ancestral Rocky Mountains. The basin is composed of land areas in Colorado, the Humboldt highland in northeastern Nevada and intervening carbonate shelves in Utah and Wyoming. The phosphorites and the carbonaceous mudstones were deposited on the foreslope between the carbonate and littoral sand deposits on the shelf and the dominantly cherty mudstone sediments in the axial part of the basin. Paleomagnetic evidence indicates that in the Permian the region would have been within the northern hemispheric trade wind belt; and wind-direction studies determined from studies of sand dunes, indicate that the prevailing winds from the Milk River uplift would have blown offshore across the Phosphoria sea. Offshore winds would have carried surface water away from the shore and generated upwelling in the sea in eastern Idaho and adjacent areas in Montana, Wyoming and Utah. Prior to deposition of the Phosphoria, the region was the site of extensive deposition of shallow-water carbonate sediments. Equivalent rocks in the northern part of the basin are dominantly sandstone derived from the adjacent Milk River uplift and similar sandstone strata in the southeastern sector were derived from the ancestral Rocky Mountains uplift. Tectonic subsidence of the Sublett basin in part of the region seems to have provided a sea-floor profile favorable for upwelling circulation and the shift in deposition from regional carbonates and local sandstone into a more complex depositional pattern that included the accumulation of the mudstone-chert-phosphorite facies that comprises the Phosphoria Formation. High biological productivity and the accumulation of sapropel on the sea floor is associated with contemporary coastal upwelling (1) and similar environmental and depositional conditions are attributed to the rich accumulations of organic matter in the Phosphoria Formation. Sapropelic mudstone and phosphorite composing the Meade Peak Member are approximately 60 m thick near the center of the Sublett basin. The Meade

Conference Paper↗
USGS2003

Morphological impacts of extreme storms on sandy beaches and barriers

Historical extreme storms that struck the Gulf Coast and Atlantic Coast regions of the United States caused several different styles of morphological response and resulted in a wide range of washover penetration distances. The post- storm erosional responses included dune scarps, channel incisions, and washouts, whereas depositional responses included perched fans, washover terraces, and sheetwash lineations. Maximum inland extent of washover penetration ranged from approximately 100 to 1000 m and estimated sediment volumes associated with these deposits ranged from about 10 to 225 m 3/m of beach. Unusual styles of morphological response (sheetwash lineations and incised channels) and maximum washover penetration distances are closely correlated, and they also correspond to storm intensity as denned by the Saffir-Simpson wind-speed scale. The regional morphological responses and washover penetration distances are controlled primarily by the interactions among heights and durations of storm surge relative to adjacent land elevations, differences in water levels between the ocean and adjacent lagoon, constructive and destructive interference of storm waves, and alongshore variations in nearshore bathymetry. For barrier segments that are entirely submerged during the storm, impacts can be enhanced by the combined influences of shallow water depths and organized flow within the wind field. The greatest washover penetrations and sediment accumulations are products of shallow water, confined flow, and high wind stress. Transport and deposition of washover sediments across barrier islands and into the adjacent lagoon are common processes along the Gulf of Mexico but not along the western Atlantic Ocean. This fundamental difference in storm impact underscores how microtidal and mesotidal barriers respond respectively to extreme storms, and provides insight into how different types of barrier islands will likely respond to future extreme storms and to a relative rise in sea level.

Journal of Coastal Research↗
USGS1988

Cobalt in ferromanganese crusts as a monitor of hydrothermal discharge on the Pacific sea floor

Ferromanganese oxide crusts, which accumulate on unsedimented surfaces in the open ocean 1–6 , derive most of their metal content from dissolved and particulate matter in ambient bottom water 7,8 , in proportions modified by the variable scavenging efficiency of the oxide phase for susceptible ions 9 . They differ in this respect from abyssal nodules, much of whose metals are remobilized from host sediments. Here we present maps of cobalt concentration and inferred accumulation rate of ferromanganese crusts from the Pacific Ocean. We propose that depletion of cobalt in Pacific crusts measures the location and intensity of submarine hydrothermal discharge. Use of the 'cobalt chronometer', an algorithm inversely relating cobalt content and crust growth rate, permits mapping of the accumulation rate of ferromanganese crusts with only indirect recourse to radioactivity-based dating methods. These maps show that crusts in hydrothermal areas grow from two to more than four orders of magnitude faster than in the Central Pacific Ocean. Cobalt-enriched crusts are found where water masses are most isolated from continental-coastal and hydrothermal sources of metals, now and in the past. This relationship can resolve the problem of cobalt enrichment in crusts without recourse to hypotheses invoking special cobalt sources or enrichment mechanisms.

Nature↗
USGS2001

Factors controlling navigation-channel Shoaling in Laguna Madre, Texas

Shoaling in the Gulf Intracoastal Waterway of Laguna Madre, Tex., is caused primarily by recycling of dredged sediments. Sediment recycling, which is controlled by water depth and location with respect to the predominant wind-driven currents, is minimal where dredged material is placed on tidal flats that are either flooded infrequently or where the water is extremely shallow. In contrast, nearly all of the dredged material placed in open water >1.5 m deep is reworked and either transported back into the channel or dispersed into the surrounding lagoon. A sediment flux analysis incorporating geotechnical properties demonstrated that erosion and not postemplacement compaction caused most sediment losses from the placement areas. Comparing sediment properties in the placement areas and natural lagoon indicated that the remaining dredged material is mostly a residual of initial channel construction. Experimental containment designs (shallow subaqueous mound, submerged levee, and emergent levee) constructed in high-maintenance areas to reduce reworking did not retain large volumes of dredged material. The emergent levee provided the greatest retention potential approximately 2 years after construction.

Journal of Waterway, Port, Coastal and Ocean Engin↗
USGS2005

A note on the comparative turbidity of some estuaries of the Americas

Field data from 27 estuaries of the Americas are used to show that, in broad terms, there is a large difference in turbidity between the analyzed east and west-coast estuaries and that tidal range and tidal length have an important influence on that turbidity. Generic, numerical sediment-transport modeling is used to illustrate this influence, which exists over a range of space scales from, e.g., the Rogue River Estuary (few km, few mg l-1) to the Bay of Fundy (hundreds of km, few g l-1). The difference in Pacific and Atlantic seaboard estuarine turbidity for the analyzed estuaries is ultimately related to the broad-scale geomorphology of the two continents.

Journal of Coastal Research↗
USGS2010

Hydrology, water quality, and causes of changes in vegetation in the vicinity of the Spring Bluff Nature Preserve, Lake County, Illinois, May 2007–August 2008

Agriculture and urbanization have altered the hydrology and water quality of the coastal wetland complex along the shore of Lake Michigan at the Spring Bluff Nature Preserve and Illinois Beach State Park in northeastern Lake County, Ill., and the adjacent Chiwaukee Prairie State Natural Area in southeastern Wisconsin. Culverts, roads, ditches, and berms installed within the wetland complex have altered the natural directions of surface-water flow and likely have increased the natural hydroperiod in the Spring Bluff Nature Preserve and decreased it in the northern part of the Illinois Beach State Park. Relative to presettlement conditions, surface-water runoff into the wetlands likely is greater in quantity and higher in concentrations of several constituents, including chloride, nitrate, phosphorous, and suspended sediment. These constituent concentrations are affected by a variety of factors, including the amount of agricultural and urban land use in the watersheds. Hydrologic, chemical, and biologic processes within the wetland communities reduce the concentrations of these constituents in surface water before the water discharges to Lake Michigan by as much as 75 percent for chloride, 85 percent for nitrate, 66 percent for phosphorous, and more than an order of magnitude for suspended sediment. However, concentrations of phosphorous and suspended sediment in surface water increased within parts of the wetland complex. Given these changes, the floristic quality of these wetlands has been altered from the historic condition. Specifically, Typha spp. and Phragmites australis occur in greater numbers and over a larger area than in the past. The spread of Typha spp. and Phragmites australis appears to be enhanced by anthropogenic alterations within the wetland complex, such as increased water levels and duration of inundation and, possibly, increases in the total concentration of dissolved constituents in water.

Illinois↗
USGS2009

Neogene collision and deformation of convergent margins along the backbone of the Americas

Along Pacific convergent margins of the Americas, high-standing relief on the subducting oceanic plate "collides" with continental slopes and subducts. Features common to many collisions are uplift of the continental margin, accelerated seafloor erosion, accelerated basal subduction erosion, a flat slab, and a lack of active volcanism. Each collision along America's margins has exceptions to a single explanation. Subduction of an ???600 km segment of the Yakutat terrane is associated with >5000-m-high coastal mountains. The terrane may currently be adding its unsubducted mass to the continent by a seaward jump of the deformation front and could be a model for docking of terranes in the past. Cocos Ridge subduction is associated with >3000-m-high mountains, but its shallow subduction zone is not followed by a flat slab. The entry point of the Nazca and Juan Fernandez Ridges into the subduction zone has migrated southward along the South American margin and the adjacent coast without unusually high mountains. The Nazca Ridge and Juan Fernandez Ridges are not actively spreading but the Chile Rise collision is a triple junction. These collisions form barriers to trench sediment transport and separate accreting from eroding segments of the frontal prism. They also occur at the separation of a flat slab from a steeply dipping one. At a smaller scale, the subduction of seamounts and lesser ridges causes temporary surface uplift as long as they remain attached to the subducting plate. Off Costa Rica, these features remain attached beneath the continental shelf. They illustrate, at a small scale, the processes of collision. ?? 2009 The Geological Society of America. All rights reserved.

Conference Paper↗
USGS1978

Susceptibility of coastal plain aquifers to contamination, Fairfax County, Virginia; a computer composite map

A map is presented that classifies the Coastal Plain of Fairfax County, Virginia according to the susceptibility of the principal sand aquifers to contamination from surface sources. The following classification is used: (1) areas where leachate can readily enter the principal sand aquifers, (2) areas offering great natural protection against migration of leachate into the aquifers, and, (3) areas where the contamination risk is uncertain and onsite investigations are needed. Approximately 20 percent of the area is in the high-risk category. The map is computer generated and was made by combining four source maps depicting those hydrogeologic factors related to movement of contaminants into the aquifers. These factors are (1) lithologic character of the upper 25 feet of sediments, (2) clay thickness above uppermost sand aquifer, (3) hydraulic gradient direction and head difference between water table and artesian head in principal aquifer, and (4) areal occurrence of moderate to high transmissiviry aquifers. The map is designed to be used by planners with little or no earth-science background, however, a technical discussion for hydrologists and geologists is also provided. (Woodard-USGS)

Open-File Report↗
USGS1986

Configuration and hydrology of the Pre-Cretaceous rocks underlying the southeastern Coastal Plain aquifer system

An investigation was conduced to define the configuration and hydrology of the rock surface upon which the sand aquifers and confining beds of the Southeastern Coastal Plain aquifer system were deposited. The base of the Southeastern Coastal Plain aquifer system consists of crystalline rocks, saprolite, Paleozoic rocks, Triassic sedimentary rocks (some of which are intruded by basalt), and Jurassic sedimentary rocks. The permeability of these rocks is extremely low and little exchange of water occurs upward to the overlying Cretaceous aquifers. Porosity values are in the range of 10% or less in some of the rocks, indicating little water is stored in them. The transmissivity values are extremely low, indicating very slow movement of water in these rocks. The small volume of water moving at a very slow rate has a long residence time and is usually mineralized to a greater degree than water in the more permeable overlying sediments. (Peters-PTT)

Water-Resources Investigations Report↗
USGS2006

Enhanced submarine ground water discharge form mixing of pore water and estuarine water

Submarine ground water discharge is suggested to be an important pathway for contaminants from continents to coastal zones, but its significance depends on the volume of water and concentrations of contaminants that originate in continental aquifers. Ground water discharge to the Banana River Lagoon, Florida, was estimated by analyzing the temporal and spatial variations of Cl − concentration profiles in the upper 230 cm of pore waters and was measured directly by seepage meters. Total submarine ground water discharge consists of slow discharge at depths > ∼70 cm below seafloor (cmbsf) of largely marine water combined with rapid discharge of mixed pore water and estuarine water above ∼70 cmbsf. Cl − profiles indicate average linear velocities of ∼0.014 cm/d at depths > ∼70 cmbsf. In contrast, seepage meters indicate water discharges across the sediment-water interface at rates between 3.6 and 6.9 cm/d. The discrepancy appears to be caused by mixing in the shallow sediment, which may result from a combination of bioirrigation, wave and tidal pumping, and convection. Wave and tidal pumping and convection would be minor because the tidal range is small, the short fetch of the lagoon limits wave heights, and large density contacts are lacking between lagoon and pore water. Mixing occurs to ∼70 cmbsf, which represents depths greater than previously reported. Mixing of oxygenated water to these depths could be important for remineralization of organic matter.

Florida↗
USGS2014

Bathymetry of the waters surrounding the Elizabeth Islands, Massachusetts

The Elizabeth Islands in Massachusetts that separate Vineyard Sound from Buzzards Bay are the remnants of a moraine (unconsolidated glacial sediment deposited at an ice sheet margin; Oldale and O’Hara, 1984). The most recent glacial ice retreat in this region occurred between 25,000 and 20,000 years ago, and the subsequent rise in sea level that followed deglaciation caused differences in the seafloor character between Buzzards Bay and Vineyard Sound. The relatively rough seafloor of Vineyard Sound reflects widespread exposure of glacial material. Shoals mark the location of recessional ice contact material, and deep channels illustrate where meltwater drainage incised glacial deposits. Following ice retreat from the Elizabeth Islands, a glacial lake formed across the mouth of Buzzards Bay, when the lake drained, it scoured two deep channels at the southern end of the bay. Sea level rise began to inundate Vineyard Sound and Buzzards Bay about 8,000 years ago and continues to modify the modern seafloor (Robb and Oldale, 1977). Fine-grained marine and estuarine sediments were deposited in the partially protected setting of Buzzards Bay. These deposits, up to 10 meters in thickness, buried the high-relief glacial landscape and created the generally smooth modern seafloor. In contrast, the Vineyard Sound of today experiences strong tidal currents, which largely prevent the deposition of fine-grained material and constantly rework the glacial sand and gravel within shoals. The seafloor of the sound largely reflects the contours of the ancient glaciated landscape that existed before sea level began to rise. The bathymetric data used to create the hillshaded relief image of the seafloor were collected by the U.S. Geological Survey (USGS) in cooperation with the Massachusetts Office of Coastal Zone Management and supplemented with National Oceanic and Atmospheric Administration hydrographic survey data. The map shows the detailed bathymetry of Buzzards Bay and Vineyard Sound with depth soundings shown on a 5-meter-per-pixel grid. Depths are coded by color where the deepest areas are in blue and the shallowest areas are in orange. The aerial photography for the Elizabeth Islands and Massachusetts mainland were obtained from the Massachusetts Office of Geographic Information. Data collected during this statewide cooperative project have been released in a series of USGS open-file reports. These publications and information regarding geologic mapping in Massachusetts can be obtained from the Coastal and Marine Geology Program’s Web site (http://woodshole.er.usgs.gov/project-pages/coastal_mass/).

Massachusetts↗
USGS2021

Does geomorphology determine vulnerability of mangrove coasts to sea-level rise?

The greatest climate-based threat to coastlines worldwide is sea-level rise. We tested the hypothesis that tropical coasts fringed by mangroves and receiving high inputs of terrigenous sediment are less vulnerable to sea-level rise than biogenic systems dependent upon peat formation for vertical land development. An analysis of published data spanning a range of geomorphic settings showed that mineral accretion was a poor predictor of vulnerability to rising sea level. We additionally compared two oceanic island systems representing two extremes along this sediment gradient to further examine controls on elevation dynamics in minerogenic versus biogenic mangrove systems. Minerogenic systems characterized by intermediate to high rates of mineral sedimentation (Pacific high islands in Micronesia) were not better buffered against sea-level rise because of high subsidence rates. Peat-forming systems (Caribbean low islands in Belize) kept pace with relative sea-level rise (combined ocean and land movements) because of subsurface expansion driven by root matter accumulation. The data were not consistent with the paradigm that tropical coastlines characterized by peat-forming mangroves are generally more vulnerable to sea-level rise compared to minerogenic systems; however, they are not necessarily equally sensitive to the same external and internal forces controlling soil elevations. Our findings demonstrate that reliance on surface accretion data alone can lead to an inaccurate evaluation of coastal vulnerability and why all surface and subsurface land movements must be considered in relation to local sea-level trends to assess risk of submergence. Recognition of such differences is essential to proper management of tropical coastlines to ensure their resilience in the face of future sea-level rise.

Book chapter↗
USGS2024

Late-Quaternary surface displacements on accretionary wedge splay faults in the Cascadia Subduction Zone: Implications for megathrust rupture

Because splay faults branch at a steep dip angle from the plate-boundary décollement in an accretionary wedge, their coseismic displacement can potentially result in larger tsunamis with distinct characteristics compared to megathrust-only fault ruptures, posing an enhanced hazard to coastal communities. Elsewhere, there is evidence of coseismic slip on splay faults during many of the largest subduction zone earthquakes, but our understanding of potentially active splay faults and their hazards at the Cascadia subduction zone remains limited. To identify the most recently active splay faults at Cascadia, we conduct stratigraphic and structural interpretations of near-surface deformation in the outer accretionary wedge for the ~400 km along-strike length of the landward vergence zone. We analyze recently acquired high-frequency sparker seismic data and crustal-scale multi-channel seismic data to examine the record of deformation in shallow slope basins and the upper ~1 km of the surrounding accreted sediments and to investigate linkages to deeper décollement structure. We present a new fault map for widest, most completely locked portion of Cascadia from 45 to 48°N latitude, which documents the distribution of faults that show clear evidence of recent late Quaternary activity. We find widespread evidence for active splay faulting up to 30 km landward of the deformation front, in what we define as the active domain, and diminished fault activity landward outside of this zone. The abundance of surface-deforming splay faults in the active outer wedge domain suggests Cascadia megathrust events may commonly host distributed shallow rupture on multiple splay faults located within 30 km of the deformation front.

British Columbia, California, Oregon, Washington↗
USGS2007

Historical Shoreline Changes at Rincon, Puerto Rico, 1936-2006

The coast from Punta Higuero to Punta Cadena in Rincon, Puerto Rico is experiencing long-term erosion. This study documents historical shoreline changes at Rincon for the period 1936-2006 and constitutes a significant expansion and revision of previous work. The study area extends approximately 8 km from Punta Higuero to Punta Cadena. Fourteen historical shoreline positions were compiled from existing data, new orthophotography, and Global Positioning System (GPS) field surveys. The study area can be divided into four distinct reaches on the basis of observed erosion rates, consistent with previous work. The coast of Reach A, from Punta Higuero to the north end of the Balneario de Rincon, is fairly stable and has a long-term (70 years) average erosion rate of -0.2 ? 0.1 m/yr. The coast of Reach B, from the Balneario de Rincon to 500 m south of the mouth of Quebrada los Ramos, has an average long-term erosion rate of -1.1 ? 0.3 m/yr. The coast of Reach C, from 500 m south of the mouth of Quebrada los Ramos to Corcega, has an average long-term erosion rate of -0.4 ? 0.2 m/yr. The coast of Reach D, from Corcega to Punta Cadena, has an average long-term change rate of -0.2 ? 0.2 m/yr. Previous work (Thieler and others, 1995) identified an apparent increase in erosion rate in Reach B that probably began between 1977 and 1987. New data and statistical analysis suggest that long-term and short-term rates of shoreline change are statistically similar. Nevertheless, the coast in Reach B is eroding at a rapid and statistically significant rate that is 2 to 10 times greater than in the other three reaches. Comparison of the 1994 and 2006 GPS shoreline positions indicates the following erosion rates occurred over the past 12 years: Reach A, -0.3 ? 0.4 m/yr; Reach B, -1.0 ? 0.4 m/yr; Reach C, -0.7 ? 0.4 m/yr; and Reach D, -0.3 ? 0.4 m/yr. Thieler and others (1995) speculated that the increased erosion rate in Reach B could be attributed to the effects of marina construction in 1983 on the local sediment budget. New data and analysis suggest, however, that other factors may be equally or perhaps more important. For example, high-resolution lidar bathymetric data collected in 2001 show a complex nearshore bathymetry that may substantially affect wave refraction, diffraction, and reflection in Reach B where erosion rates are the highest. In addition, several historical photographs dating from 1951 to 2006 show a wide array of complex wave patterns that suggest the bathymetric influence on nearshore processes to be a long-term, rather than recent, phenomenon. In addition, removal of sand from the beach system may be contributing further to the elevated erosion rates in Reach B. Development of potential options for addressing coastal erosion in Rincon was beyond the scope of this study, but the data and interpretations presented here provide a sound scientific foundation for further work to identify the causes of the increased erosion and to develop strategies to mitigate its effect.

Open-File Report↗
USGS2014

Bathymetry, acoustic backscatter, and seafloor character of Farallon Escarpment and Rittenburg Bank, northern California

In 2011, scientists from the U.S. Geological Survey’s Coastal and Marine Geology Program acquired bathymetry and acoustic-backscatter data along the upper slope of the Farallon Escarpment and Rittenburg Bank within the Gulf of the Farallones National Marine Sanctuary offshore of the San Francisco Bay area. The surveys were funded by the National Oceanic and Atmospheric Administration’s Deep Sea Coral Research and Technology Program to identify potential deep sea coral habitat prior to planned sampling efforts. Bathymetry and acoustic-backscatter data can be used to map seafloor geology (rock, sand, mud), and slope of the sea floor, both of which are useful for the prediction of deep sea coral habitat. The data also can be used for the prediction of sediment and contaminant budgets and transport, and for the assessment of earthquake and tsunami hazards. The surveys were conducted aboard National Oceanic and Atmospheric Administration’s National Marine Sanctuary Program’s 67-foot-long research vessel Fulmar outfitted with a U.S. Geological Survey 100-kHz Reson 7111 multibeam-echosounder system. This report provides the bathymetry and backscatter data acquired during these surveys, interpretive seafloor character maps in several formats, a summary of the mapping mission, maps of bathymetry and backscatter, and Federal Geographic Data Committee metadata.

California↗
USGS1980

Geology of the Round Bay quadrangle, Anne Arundel County, Maryland

Six Coastal Plain formations and one group crop out in the Round Bay quadrangle near the inner edge of the Atlantic Coastal Plain physiographic province. The quadrangle lies astride the Severn River, in Anne Arundel County, near Annapolis, Md. The seven stratigraphic units aggregate as much as 128 m in outcrop. In ascending order, the units are: the upper part of the Potomac Group and the Magothy, Matawan, and Severn Formations, all of Cretaceous age; the Brightseat and Aquia Formations of Paleocene age and the Calvert Formation of Miocene age. Quaternary deposits are thin and cover only small areas; they are all mapped under one unit. Several small, thin deposits of Tertiary alluvium are mapped separately. The largely unconsolidated Cretaceous and Tertiary formations consist chiefly of quartz, glauconite, clays, muscovite, chlorite, lignite, feldspar, and pyrite. Quaternary sediments are mostly locally derived sands, silts, and clays with some gravel and, in the finer sediments, considerable amounts of organic matter. The Cretaceous and Tertiary units strike generally northeast; the younger the formation, the more easterly it strikes. Dips are gentle, 3.6 to 15 m per kilometer toward the southeast, and decrease upward through the section. The Round Bay quadrangle is near the southern limit of several formations that thin progressively toward the southwest from New Jersey. Some pinch out between Betterton, on the eastern shore of Chesapeake Bay, and Round Bay, on the western shore, whereas others are present only as thin remnants 1-2 m thick. Resources of the quadrangle include abundant ground water, sand, and high land values near water.

Maryland↗

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