William C. Schwab

• United States Geological Survey

Integrated terrain models covering 16,357 square kilometers of the Massachusetts coastal zone and offshore waters were built to provide a continuous elevation and bathymetry terrain model for ocean planning purposes. The area is divided into the following four geographical areas to reduce file size and facilitate publishing: Massachusetts Bay from...

Mechanisms relating offshore geologic framework to shoreline evolution are determined through geologic investigations, oceanographic deployments, and numerical modeling. Analysis of shoreline positions from the past 50 years along Fire Island, New York, a 50 km long barrier island, demonstrates a persistent undulating shape along the western half o...

Seafloor mapping investigations conducted on the lower shoreface and inner continental shelf offshore of Fire Island, New York in 2011 and 2014, the period encompassing the impacts of Hurricanes Irene and Sandy, provide an unprecedented perspective regarding regional inner continental shelf sediment dynamics during large storm events. Analyses of t...

Hurricane Sandy was one of the most destructive hurricanes in US history, making landfall on the New Jersey coast on October 30, 2012. Storm impacts included several barrier island breaches, massive coastal erosion, and flooding. While changes to the subaerial landscape are relatively easily observed, storm-induced changes to the adjacent shoreface...

Behavior of coastal systems on time scales ranging from single storm events to years and decades is controlled by both small-scale sediment transport processes and large-scale geologic, oceanographic, and morphologic processes. Improved understanding of coastal behavior at multiple time scales is required for refining models that predict potential...

We investigate the impact of superstorm Sandy on the lower shoreface and inner shelf offshore the barrier island system of Fire Island, NY using before-and-after surveys involving swath bathymetry, backscatter and CHIRP acoustic reflection data. As sea level rises over the long term, the shoreface and inner shelf are eroded as barrier islands migra...

Locations along the inner-continental shelf offshore of Fire Island, NY, are characterized by a series of shoreface-connected ridges (SFCRs). These sand ridges have approximate dimensions of 10 km in length, 3 km spacing, and up to ∼8 m ridge to trough relief and are oriented obliquely at approximately 30° clockwise from the coastline. Stability an...

The inner-continental shelf off Fire Island, New York was mapped in 2011 using interferometric sonar and high-resolution chirp seismic-reflection systems. The area mapped is approximately 50 km long by 8 km wide, extending from Moriches Inlet to Fire Island Inlet in water depths ranging from 8-32 m. The morphology of this inner-continental shelf re...

Federal, state, and local agencies mounted a massive preparation and response to post–tropical storm Sandy, which made landfall along the northern New Jersey coast on 29 October 2012. The data collected and knowledge gained in response to Sandy are unprecedented and provide critical information to agencies, local emergency responders, and coastal m...

Sediment budget analyses along the south shore of Fire Island, New York, have been conducted and debated in the scientific and coastal engineering literature for decades. It is well documented that a primary component of sediment transport in this system is directed alongshore from E to W, but discrepancies in volumetric sediment budget calculation...

High-resolution geophysical and sediment sampling surveys were conducted offshore of the Grand Strand, South Carolina to define the shallow geologic framework of the inner shelf. Results are used to identify and map Holocene sediment deposits, infer sediment transport pathways, and discuss implications for the regional coastal sediment budget.The t...

The mechanism of sediment exchange between offshore sand ridges and the beach at Fire Island, New York is largely unknown. However, recent evidence from repeat nearshore bathymetry surveys, coupled with the complex but consistent bar morphology and patterns of shoreline change demonstrate that there is a feedback occurring between the regional geol...

Sediment budget analyses conducted for annual to decadal timescales report variable magnitudes of littoral transport along the south shore of Long Island, New York. It is well documented that the primary transport component is directed alongshore from east to west, but relatively little information has been reported concerning the directions or mag...

CHIRP seismic and swath bathymetry data acquired offshore La Jolla, California provide an unprecedented three-dimensional view of the La Jolla and Scripps submarine canyons. Shore-parallel patterns of tectonic deformation appear to control nearshore sediment thickness and distribution around the canyons. These shore-parallel patterns allow the impa...

Two cores from the Permian (Guadalupian) Yates Formation in Winkler County, Texas, were analyzed using thin-section petrography, scanning electron microscopy/energy dispersive X-ray, stable-isotope geochemistry, and ⁴⁰Ar/³⁹Ar laser step heating. The Yates was deposited in a coastal-sabkha environment. The sandstone facies is the hydrocarbon reservo...

The regional geologic framework of the inner shelf off Fire Island, New York is well-documented. Ridges of reworked Holocene sand derived from erosion of a headland of Cretaceous coastal-plain strata overlie Pleistocene sediment. Coastal geomorphology of the barrier and imbalances in the regional sediment budget together suggest that material, like...

The inner continental shelf off northern South Carolina is a sediment-limited environment characterized by extensive hardground areas, where coastal plain strata and ancient channel-fill deposits are exposed at the sea floor. Holocene sand is concentrated in large shoals associated with active tidal inlets, an isolated shore-detached sand body, and...

The U.S. Geological Survey (USGS) has been involved in geological mapping of the sea floor for the past thirty years. Early geophysical and acoustic mapping efforts using GLORIA (Geologic LOng Range Inclined ASDIC) a long-range sidescan-sonar system, provided broad-scale imagery of deep waters within the U.S. Exclusive Economic Zone (EEZ). In the e...

The Hudson Shelf Valley (HSV) is the largest physiographic feature on the U.S. mid-Atlantic continental shelf. The 150-km long valley is the submerged extension of the ancestral Hudson River Valley that connects to the Hudson Canyon. Unlike other incised valleys on the mid-Atlantic shelf, it has not been infilled with sediment during the Holocene....

Shoreline behavior along the coast of Long Bay, South Carolina is dictated by waves, tidal currents, and sediment supply that act within the overall constraints of the regional geologic setting. This study examined the influence of the geologic framework on coastal evolution through the interpretation of high-resolution geophysical data (swath bath...

Several generations of the ancestral Pee Dee River system have been mapped beneath the South Carolina Grand Strand coastline and adjacent Long Bay inner shelf. Deep boreholes onshore and high-resolution seismic-reflection data offshore allow for reconstruction of these paleochannels, which formed during glacial lowstands, when the Pee Dee River sys...

Glacial freshwater discharge to the Atlantic Ocean during deglaciation may have inhibited oceanic thermohaline circulation, and is often postulated to have driven climatic fluctuations. Yet attributing meltwater-discharge events to particular climate oscillations is problematic, because the location, timing, and amount of meltwater discharge are of...

Meltwater discharge to the North Atlantic during deglaciation likely influenced global oceanic circulation and climate. However, directly linking meltwater discharge events with individual climate oscillations has been difficult because of challenges in determining the location, timing and amount of meltwater discharge. New evidence from the Hudson...

Naturally occurring hard bottom areas provide the geological substrate that can support diverse assemblages of sessile benthic organisms, which in turn, attract many reef-dwelling fish species. Alternatively, defining the location and extent of bottom sand bodies is relevant for potential nourishment projects as well as to ensure that transient sed...

Integrated high-resolution geophysical surveys of the northern South Carolina shoreface have been linked to similar surveys of the inner shelf and a range of onshore data types defining the structure and behavior of the modern beach. Together they characterize patterns of coastal erosion and evolution on a range of temporal and spatial scales. The...

A portion of the USGS-SC Sea Grant Consortium coastal erosion program, this study presents a comparison of historical shorelines, LIDAR and coastal geomorphology to the geologic framework of the lower Coastal Plain and inner Continental Shelf of South Carolina. Shoreline change trends of historical data of Anders et al. (1990) and recent aerial pho...

Located in the transition between the more extensively studied wave-dominated barrier islands of North Carolina and the mixed-energy barrier islands of Central South Carolina, Waites Island is a 5 km long and 0.5 km wide barrier island situated at the northern end of South Carolina's Grand Strand arcuate coastal system. Building upon previous strat...

This study presents a statistical comparison of historical shoreline changes to framework geology and coastal geomorphology along a portion of the South Carolina coast. Situated along a dominantly mainland attached barrier system, we utilize a wide array of directly and remotely sensed geological framework data collected as part of a larger coastal...

The barrier island complexes of northeastern South Carolina are located between the more extensively studied wave-dominated barrier complexes of North Carolina and the classic mixed-energy (drumstick) barrier complexes of South Carolina. As part of the United States Geological Survey-South Carolina Sea Grant Consortium Coastal Erosion Program, this...

Orrin Pilkey has brought conceptual simplifications of beach behavior used to model/manage beach change to national attention and debate. A regional program of beach profiling, shoreline mapping and geologic framework studies provide the perspective of beach behavior along the northern coast of South Carolina necessary to assess the assertions of P...

The lower Coastal Plain and inner Continental Shelf of the United States East Coast vary coherently in both pre-Holocene and modern morphology, in long-term trends of coastal change, and in respect to critical areas of beach erosion. As a portion of the USGS-SC Sea Grant Consortium coastal erosion program, this study presents a comparison of histor...

Assessment of the extent and variability of benthic habitats is an important mission of biologists and marine scientists, and has supreme relevance in monitoring and maintaining the offshore resources of coastal nations. Mapping `hard bottoms', in particular, is of critical importance because these are the areas that support sessile benthic habitat...

A regional geophysical mapping survey of Long Bay provides a comprehensive image of sea-floor character, bathymetry and shallow subbottom stratigraphy within the shoreface and across the inner shelf along 90 kilometers of the northern South Carolina coast. Chirp subbottom profiles, sidescan-sonar imagery and interferometric swath-bathymetry imaged...

Many channels are preserved on the Carolinas continental shelf, and they are widely distributed with a marked variability in form. Preserved channels are largely believed to be excavated by rivers during sea-level low stands, however, they also can be created and modified by processes (e.g., waves and tides) active during high-stand, falling, and r...

High-resolution seismic reflection profiles, sidescan-sonar imagery and interferometric swath-bathymetry, groundtruthed with surficial sediment samples and vibracores, allow for a detailed interpretation of the shallow geologic framework within South Carolina's Long Bay. This mapping provides a better understanding of the area's nearshore geology b...

The event-to decade-scale patterns of sediment dispersal on two artificially nourished beaches have been mapped using a combination of geophysical surveys, closely-spaced vibracores, and repeated beach profiles. At both Wrightsville Beach, NC and Folly Island, SC the sediment used for beach nourishment is macroscopically distinct from native sedime...

As exploration for hydrocarbons moves toward subtler traps, channel-end sand deposits of deep-sea fans and related turbidite systems are among the key targets. SeaMARC 1A sidescan-sonar imagery and cores from the distal reaches of a depositional lobe on the Mississippi Fan show that channelized mass flow as the dominant mechanism for transport of s...

Sidescan sonar provides a map of the seafloor that has greatly improved the understanding of depositional processes on modern deep-sea fans (e.g. Mutti and Normark 1991). Here, we present a sidescan-sonar mosaic from the eastern Gulf of Mexico that images the distal reaches of a channel on the Mississippi Fan and the deposits associated with it (Fi...

The oceans have been and will continue to be disposal sites for a wide variety of waste products. Often these wastes are not dumped at the designated sites or transport occurs during or after dumping, and, subsequent attempts to monitor the effects the waste products have on the environment are inadequate because the actual location of the waste is...

The locations of these landslides are distributed fairly uniformly around the United States. The goal is to show the variety of landslides that have been found, the associations of the landslides with other features, methods that have been used to understand the causes and mechanisms of the landslides, and the potential that some of these features...

SeaMARC IA sidescan sonar images of the distal reaches of a depositional lobe on the Mississippi Fan show that channelized rather than unconfined transport was the dominant transport mechanism for coarse-grained sediment during the formation of this part of the deep-sea fan. Overbank sheet flow of sands was not an important process in the transport...

Cores from a Mississippi outer-fan depositional lobe demonstrate that sublobes at the distal edge contain a complex local network of channelized-turbidite beds of graded sand and debris-flow beds of chaotic silt. Off-lobe basin plains lack siliciclastic coarse-grained beds. The basin-plain mud facies exhibit low acoustic backscatter on SeaMARC IA s...

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A large amphitheater-shaped scarp, approximately 55 km across, was imaged on the northern insular slope of Puerto Rico using long-range sidescan sonar and bathymetric data. This scarp results from the removal of more than 1500 km3 of Tertiary strata. A review of seismic-reflection profiles, stratigraphic data, and subsidence models of the northern...

The concept of the steady‐state of deformation can be applied to predicting the ultimate form a landslide will take. The steady‐state condition, defined by a line in void ratio‐effective stress space, exists at large levels of strain and remolding. Conceptually, if sediment initially exists with void ratio‐effective stress conditions above the stea...

An amphitheater-shaped scarp, approximately 55 km across in water depths from about 3,000 m to 6,700 m was imaged on the northern insular slope of Puerto Rico (southern slope of the Puerto Rico Trench) using the GLORIA side-scan sonar system. This scarp represents the removal of more than 1,500 m³ of Tertiary Arecibo basin strata. The head of the...

Slope failure and subsequent mass movement have been identified on a slope of 1.6° to 2.0° on the pelagic sediment cap of Horizon Guyot, Mid-Pacific Mountains, in a zone of strong bottom-current activity. A seismic-reflection survey and submersible investigation of this slope failure shows it to be a slump that contains discrete blocks which have...

A side-scan mosaic was constructed from an 800 km² bed-form field located in the Gulf of the Farallones on the central shelf between Point Reyes and the Golden Gate. Sediment samples were collected at 1-km grid intervals within a small area (130 km²) of the field. Large-scale bed-formed, broad, shallow (⤠2 m relief) depressions, floored by medi...

The US Geological Survey (USGS) surveyed 1,000 km² of the continental shelf off San Francisco during a 17-day cruise, using a 120-kHz side-scan sonar system, and produced a digitally processed sonar mosaic of the survey area. The data were processed and mosaicked in real time using software developed at the Lamont-Doherty Geological Observatory an...

Mass movement and erosion have been identified on the pelagic sediment cap of Horizon Guyot, a seamount in the Mid-Pacific Mountains. Trends in the size, shape and preservation of bedforms and sediment textural trends on the pelagic cap indicate that bottom-current-generated sediment transport direction is upslope. Slumping of the sediment cap occu...

SeaMARC side-scan sonographs and Argo video and photographic data suggest that the recent sedimentary environment of the floor of the Tongue of the Ocean is controlled by an interplay of turbidity current flow from the south, sediment spill-over from the carbonate platform to the east (windward side), and rock falls from the west carbonate escarpme...

Volcanic rock dredged from the flanks of four volcanic edifices in the Ratak chain of the Marshall Islands consist of alkalic lave that erupted above sea level or in shallow water. Compositions of recovered samples are predominantly differentiated alkalic basalt and hawaiite but include strongly alkalic melilitite. Whole rock 40Ar/39Ar total fusion...

Large semidiurnal current and isotherm oscillations were observed by one current meter continuously for 9 months in the waters above Horizon Guyot, a seamount located in the central Pacific. The M2 tides dominated the current-meter record. The M2 current ellipse was oriented along 142°; the semi-major amplitude was 7.6 cm s−1 and the currents rotat...

Seismic-reflection profiles, sediment cores, and current velocities were assessed to study the impact of erosion and sediment redistribution on the pelagic sediment cap of Horizon Guyot, a flat-topped submarine volcanic ridge in the Mid-Pacific Mountains. These processes seem to concentrate their effect around the rim of the sediment cap. Sediment...

Internal tidal currents are the likely cause of erosional features such as current ripples, sand waves, and truncated bedding horizons on the sediment cap of Horizon Guyot. Current meter data obtained over a 9 month period in 1983–1984 at about 213 m above the guyot show that the tidal currents are anomalously strong for mid-oceanic depths, probabl...

Ferromanganese crusts cover most hard substrates on seafloor edifices in the central Pacific basin. Crust samples and their associated substrates from seven volcanic edifices of Cretaceous age along the Ratak chain of the Marshall Islands are discussed. The two most abundant substrate lithologies recovered were limestone, dominantly fore-reef slope...

Slope failures and subsequent mass movements have been identified in Holocene glaciomarine sediment on declivities less than 1.3° on the Alsek prodelta, Gulf of Alaska. Isolated collapse features cover less than 10 percent of a nearshore sand deposit, in water depths less than 40 m. In contrast, sediment gravity flow deposits (disintegrative failur...

Side-scan sonar records collected over an area of the North Aleutian Shelf, approximately 250 km west of the head of Bristol Bay, Alaska, identified widespread evidence of active sea floor erosion processes, including sediment transport. Thousands of sea floor depressions, many linear and some containing rippled floors, were identified in water dep...

Ferromanganese crusts coat most hard substrates on seamounts, ridges, and plateaus in the central Pacific basin. Crusts from less than 2500 m water depth are rich in Mn, Co, Ni, Pb, and Pt. Samples we collected from the EEZ of the Hawaiian, Johnston, Palmyra, and Marshall Islands are discussed. Necker Ridge in the Hawaiian EEZ has the greatest aver...

Necker Ridge, Horizon Guyot and S.P. Lee Guyot in the Central Pacific were sampled, seismically surveyed, and photographed by bottom cameras in order to better understand the distribution, origin, and evolution of ferromanganese crusts. Necker Ridge is over 600 km long with a rugged crest, pods of sediment to 146 m thick, slopes that average 12° to...

The 150-km-long Hudson Shelf Valley, the largest physiographic feature on the mid- Atlantic continental shelf, bisects the New York Bight region. The Valley is the submerged seaward extension of the ancestral Hudson River drainage system that, unlike other valleys on the Atlantic shelf, has not been filled with sediment. A survey of the topography...