Search USGS⌕ Search

Geology topics

William C. Schwab

Publications and source records attributed to William C. Schwab.

At least 55 records · Page 3Linked to original sources
USGS2000

Archive of water gun subbottom data collected during USGS cruise SEAX 96004, New York Bight, 1 May - 9 June 1996

Beginning in 1995, the USGS, in cooperation with the U.S Army Corps of Engineers (USACE), New York District, began a program to generate reconnaissance maps of the sea floor offshore of the New York-New Jersey metropolitan area, one of the most populated coastal regions of the United States. The goal of this mapping program is to provide a regional synthesis of the sea-floor environment, including a description of sedimentary environments, sediment texture, seafloor morphology, and geologic history to aid in understanding the impacts of anthropogenic activities, such as ocean dumping. This mapping effort differs from previous studies of this area by obtaining digital, sidescan sonar images that cover 100 percent of the sea floor. This investigation was motivated by the need to develop an environmentally acceptable solution for the disposal of dredged material from the New York - New Jersey Port, by the need to identify potential sources of sand for renourishment of the southern shore of Long island, and by the opportunity to develop a better understanding of the transport and long-term fate of contaminants by investigations of the present distribution of materials discharged into the New York Bight over the last 100+ years (Schwab and others, 1997). Data collected in 1996, USGS cruise SEAX 96004, augments data collected in 1995 with sidescan sonar and seismic reflection data collected within the New York Bight Apex region. This report is an archive of the water gun seismic reflection data collected in 1996.

Open-File Report↗
USGS1999

Stratigraphic framework maps of the nearshore area of southern Long Island from Fire Island to Montauk Point, New York

The maps presented in this report (depth to Coastal Plain unconformity, Quaternary sediment thickness, paleochannel thickness, and modern sand thickness) are helpful for determining sand-resource availability for beach nourishment programs and understanding the influence that the inner-shelf framework of southern Long Island has on coastal processes and evolution. The maps showing structure of the Coastal Plain unconformity and thickness of overlying Quaternary sediment delineate the framework of the coastal region. The map showing the distribution and thickness of paleochannel fill indicates areas not suitable as sources for beach nourishment, assuming the channels contain muddy estuarine deposits. The areas between channels are Pleistocene glacial deposits and probably consist of coarse sediment that may be suitable for beach nourishment. These coarser-grained glacial deposits are the source for modern sand deposits. The modern sands have been reworked primarily from glacial deposits and a Cretaceous outcrop off Watch Hill. These reworked deposits provide well-sorted clean sand that have and will provide nourishment for southern Long Island beaches.

Open-File Report↗
USGS1999

Tracing sediment dispersal on nourished beaches: Two case studies

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 sediment and can be used to identify sediment transport pathways and infer mechanisms for across-shelf transport. The data from both sites demonstrate that significant quantities of nourishment sediment are being transported seaward onto the inner continental shelf. The time and space scales of this transport are of engineering interest for the planning, design and long-term maintenance of nourished beaches.

North Carolina, South Carolina↗
USGS1996

Breaching the levee of a channel on the Mississippi Fan

GLORIA images of the youngest channel on the Mississippi Fan indicate that it has not been a stable feature, but instead has shifted its course several times. A detailed study of a site of channel shifting found a complex stratigraphy that resulted from one episode of channel avulsion. The channel avulsion appears to have been initiated by a large mass flow that choked the channel below the point where the levee was breached and additionally spilled a large volume of material through the breach in the levee onto the adjacent fan. Subsequent flows were redirected through this breach in the levee and built a channel-levee complex over the mass movement deposits. A second phase of mass movement resulted from another large mass flow that came down the channel and triggered the collapse of part of the newly developed levee. In this case, locally derived levee sediment was mixed with allochthonous sediment from farther up the fan and was spread northward from the levee. This localized study suggests that fan stratigraphy is complex and variable at several scales, not just at the scale resolved in seismic stratigraphic studies (Weimer 1989) and that large mass flows capable of choking the channel system have been an important mechanism in redirecting sedimentation on the Mississippi Fan.

Mississippi Fan↗
USGS1994

Acoustic mapping as an environmental management tool: I. detection of barrels of low-level radioactive waste, Gulf of the Farallones National Marine Sanctuary, California

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 not known. Acoustic mapping of the seafloor with sidescan sonar is a very effective technique for locating and monitoring dredge-spoil material and other debris. Sidescan sonar provides an acoustic image or sonograph of the sea floor that is similar to a satellite image of the Earth's land surface. In effect sidescan sonar allows the water column to be stripped from the sea floor, thereby providing a clear, unobstructed view of the sea bed. An example of the potential of this technique is summarized herein for the Gulf of the Farallones region. More than 47 800 drums (55 gallon) and other containers of low-level radioactive waste were dumped on the continental margin offshore the San Francisco Bay between 1946 and 1970. These drums now litter a large area (1200 km 2 ) of the sea floor within the Gulf of the Farallones National Marine Sanctuary (GFNMS). The exact location of the drums and the potential hazard the drums pose to the environment are unknown. To evaluate the risk, samples of the sediment, biota and water must be collected near and distant from the concentrations of barrels. To do this the exact location of the barrels must be known prior to sampling. The USGS, through a cooperative research agreement with GFNMS, used sidescan sonar to map two areas within the sanctuary. Total sea-floor coverage was obtained and computer-processed sonographic mosaics were constructed on board ship. Many small nongeologic targets were distributed throughout the survey areas that covered about 70 km 2 on the shelf and 120 km 2 on the slope. Analysis of the sidescan data suggests that the targets are 55-gallon drums. This interpretation was confirmed at one site with an underwater video and 35-mm camera system. Data were collected with both a 30-kHz and a 120-kHz sidescan system within a 15-km 2 area on the shelf. We found that the barrels were more easily detected with the mid-range 30-kHz system than with the higher resolution 120-kHz system. Maps of barrel distribution derived from the sonographs are being used to design sampling schemes to evaluate the risk that the radioactivity may have on the biota and environment.

California↗
USGS1992

Characteristics of a sandy depositional lobe on the outer Mississippi fan from SeaMARC IA sidescan sonar images

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 and deposition of the sandy and silty sediment found on this fan. The dendritic distributary pattern and the high order of splaying of the channels, only one of which appears to have been active at a time, suggest that coarse-grained deposits on this fan are laterally discontinuous.

Mississippi↗