This GIS overlay is a component of the U.S. Geological Survey, Woods Hole Science Center's, Gulf of Mexico GIS database. The Gulf of Mexico GIS database is intended to organize and display USGS held data and provide on-line (WWW) access to the data and/or metadata. A two week cruise aboard the R/V GYRE focused on mapping surficial sedimentary processes and their connection to the subsurface geology. The study area was on the upper continental slope in the northwestern Gulf of Mexico; an area of active hydrocarbon exploration. Active salt movement, hydrocarbon movement up faults, the presence of gas hydrates associated with biogenic and thermogenic methane, and overpressured sand deposits all present hazards to oil exploration in this area. This study used sidescan sonar and high-resolution chirp subbottom profiling techniques to map the surficial and shallow subsurface expression of these processes in two areas roughly 15 by 25 km in size. High-resolution multi-channel seismic-reflection data were collected simultaneously with the sidescan imagery to provide a link to the deeper subsurface. Additional multi-channel and Huntec seismic data were collected along regional lines between the detailed study areas to tie these studies to other areas of known hydrates and to wells where shallow overpressured sands have been drilled. The detailed studies attempted to map entire geological systems in this upper slope environment to provide a broader perspective than can be seen from studying a single lease block. One study area focused on two adjacent salt withdrawal basins to assess the processes that are shaping the flanks of the basins, the processes affecting sedimentation in the basin floors, and to compare the deeper structures and surficial processes between the basins. The second study area focused on three salt domes, the processes associated with them, and how they affect the shallow subsurface stratigraphy. Initial observations suggest that most of the surface and shallow subsurface geohazards are associated with the flanks of salt structures. Here active salt movement generates faults along which hydrocarbons can escape to the seafloor, and tectonic oversteepenning generates slope failures.

This GIS overlay is a component of the U.S. Geological Survey, Woods Hole Science Center's, Gulf of Mexico GIS database. The Gulf of Mexico GIS database is intended to organize and display USGS held data and provide on-line (WWW) access to the data and/or metadata. A two week cruise aboard the R/V GYRE focused on mapping surficial sedimentary processes and their connection to the subsurface geology. The study area was on the upper continental slope in the northwestern Gulf of Mexico; an area of active hydrocarbon exploration. Active salt movement, hydrocarbon movement up faults, the presence of gas hydrates associated with biogenic and thermogenic methane, and overpressured sand deposits all present hazards to oil exploration in this area. This study used sidescan sonar and high-resolution chirp subbottom profiling techniques to map the surficial and shallow subsurface expression of these processes in two areas roughly 15 by 25 km in size. High-resolution multi-channel seismic-reflection data were collected simultaneously with the sidescan imagery to provide a link to the deeper subsurface. Additional multi-channel and Huntec seismic data were collected along regional lines between the detailed study areas to tie these studies to other areas of known hydrates and to wells where shallow overpressured sands have been drilled. The detailed studies attempted to map entire geological systems in this upper slope environment to provide a broader perspective than can be seen from studying a single lease block. One study area focused on two adjacent salt withdrawal basins to assess the processes that are shaping the flanks of the basins, the processes affecting sedimentation in the basin floors, and to compare the deeper structures and surficial processes between the basins. The second study area focused on three salt domes, the processes associated with them, and how they affect the shallow subsurface stratigraphy. Initial observations suggest that most of the surface and shallow subsurface geohazards are associated with the flanks of salt structures. Here active salt movement generates faults along which hydrocarbons can escape to the seafloor, and tectonic oversteepenning generates slope failures.

This GIS overlay is a component of the U.S. Geological Survey, Woods Hole Science Center's, Gulf of Mexico GIS database. The Gulf of Mexico GIS database is intended to organize and display USGS held data and provide on-line (WWW) access to the data and/or metadata. A two week cruise aboard the R/V GYRE focused on mapping surficial sedimentary processes and their connection to the subsurface geology. The study area was on the upper continental slope in the northwestern Gulf of Mexico; an area of active hydrocarbon exploration. Active salt movement, hydrocarbon movement up faults, the presence of gas hydrates associated with biogenic and thermogenic methane, and overpressured sand deposits all present hazards to oil exploration in this area. This study used sidescan sonar and high-resolution chirp subbottom profiling techniques to map the surficial and shallow subsurface expression of these processes in two areas roughly 15 by 25 km in size. High-resolution multi-channel seismic-reflection data were collected simultaneously with the sidescan imagery to provide a link to the deeper subsurface. Additional multi-channel and Huntec seismic data were collected along regional lines between the detailed study areas to tie these studies to other areas of known hydrates and to wells where shallow overpressured sands have been drilled. The detailed studies attempted to map entire geological systems in this upper slope environment to provide a broader perspective than can be seen from studying a single lease block. One study area focused on two adjacent salt withdrawal basins to assess the processes that are shaping the flanks of the basins, the processes affecting sedimentation in the basin floors, and to compare the deeper structures and surficial processes between the basins. The second study area focused on three salt domes, the processes associated with them, and how they affect the shallow subsurface stratigraphy. Initial observations suggest that most of the surface and shallow subsurface geohazards are associated with the flanks of salt structures. Here active salt movement generates faults along which hydrocarbons can escape to the seafloor, and tectonic oversteepenning generates slope failures.

This GIS overlay is a component of the U.S. Geological Survey, Woods Hole Science Center's, Gulf of Mexico GIS database. The Gulf of Mexico GIS database is intended to organize and display USGS held data and provide on-line (WWW) access to the data and/or metadata. A two week cruise aboard the R/V GYRE focused on mapping surficial sedimentary processes and their connection to the subsurface geology. The study area was on the upper continental slope in the northwestern Gulf of Mexico; an area of active hydrocarbon exploration. Active salt movement, hydrocarbon movement up faults, the presence of gas hydrates associated with biogenic and thermogenic methane, and overpressured sand deposits all present hazards to oil exploration in this area. This study used sidescan sonar and high-resolution chirp subbottom profiling techniques to map the surficial and shallow subsurface expression of these processes in two areas roughly 15 by 25 km in size. High-resolution multi-channel seismic-reflection data were collected simultaneously with the sidescan imagery to provide a link to the deeper subsurface. Additional multi-channel and Huntec seismic data were collected along regional lines between the detailed study areas to tie these studies to other areas of known hydrates and to wells where shallow overpressured sands have been drilled. The detailed studies attempted to map entire geological systems in this upper slope environment to provide a broader perspective than can be seen from studying a single lease block. One study area focused on two adjacent salt withdrawal basins to assess the processes that are shaping the flanks of the basins, the processes affecting sedimentation in the basin floors, and to compare the deeper structures and surficial processes between the basins. The second study area focused on three salt domes, the processes associated with them, and how they affect the shallow subsurface stratigraphy. Initial observations suggest that most of the surface and shallow subsurface geohazards are associated with the flanks of salt structures. Here active salt movement generates faults along which hydrocarbons can escape to the seafloor, and tectonic oversteepenning generates slope failures.

This GIS overlay is a component of the U.S. Geological Survey, Woods Hole Science Center's, Gulf of Mexico GIS database. The Gulf of Mexico GIS database is intended to organize and display USGS held data and provide on-line (WWW) access to the data and/or metadata. A two week cruise aboard the R/V GYRE focused on mapping surficial sedimentary processes and their connection to the subsurface geology. The study area was on the upper continental slope in the northwestern Gulf of Mexico; an area of active hydrocarbon exploration. Active salt movement, hydrocarbon movement up faults, the presence of gas hydrates associated with biogenic and thermogenic methane, and overpressured sand deposits all present hazards to oil exploration in this area. This study used sidescan sonar and high-resolution chirp subbottom profiling techniques to map the surficial and shallow subsurface expression of these processes in two areas roughly 15 by 25 km in size. High-resolution multi-channel seismic-reflection data were collected simultaneously with the sidescan imagery to provide a link to the deeper subsurface. Additional multi-channel and Huntec seismic data were collected along regional lines between the detailed study areas to tie these studies to other areas of known hydrates and to wells where shallow overpressured sands have been drilled. The detailed studies attempted to map entire geological systems in this upper slope environment to provide a broader perspective than can be seen from studying a single lease block. One study area focused on two adjacent salt withdrawal basins to assess the processes that are shaping the flanks of the basins, the processes affecting sedimentation in the basin floors, and to compare the deeper structures and surficial processes between the basins. The second study area focused on three salt domes, the processes associated with them, and how they affect the shallow subsurface stratigraphy. Initial observations suggest that most of the surface and shallow subsurface geohazards are associated with the flanks of salt structures. Here active salt movement generates faults along which hydrocarbons can escape to the seafloor, and tectonic oversteepenning generates slope failures.

This GIS overlay is a component of the U.S. Geological Survey, Woods Hole Science Center's, Gulf of Mexico GIS database. The Gulf of Mexico GIS database is intended to organize and display USGS held data and provide on-line (WWW) access to the data and/or metadata. A two week cruise aboard the R/V GYRE focused on mapping surficial sedimentary processes and their connection to the subsurface geology. The study area was on the upper continental slope in the northwestern Gulf of Mexico; an area of active hydrocarbon exploration. Active salt movement, hydrocarbon movement up faults, the presence of gas hydrates associated with biogenic and thermogenic methane, and overpressured sand deposits all present hazards to oil exploration in this area. This study used sidescan sonar and high-resolution chirp subbottom profiling techniques to map the surficial and shallow subsurface expression of these processes in two areas roughly 15 by 25 km in size. High-resolution multi-channel seismic-reflection data were collected simultaneously with the sidescan imagery to provide a link to the deeper subsurface. Additional multi-channel and Huntec seismic data were collected along regional lines between the detailed study areas to tie these studies to other areas of known hydrates and to wells where shallow overpressured sands have been drilled. The detailed studies attempted to map entire geological systems in this upper slope environment to provide a broader perspective than can be seen from studying a single lease block. One study area focused on two adjacent salt withdrawal basins to assess the processes that are shaping the flanks of the basins, the processes affecting sedimentation in the basin floors, and to compare the deeper structures and surficial processes between the basins. The second study area focused on three salt domes, the processes associated with them, and how they affect the shallow subsurface stratigraphy. Initial observations suggest that most of the surface and shallow subsurface geohazards are associated with the flanks of salt structures. Here active salt movement generates faults along which hydrocarbons can escape to the seafloor, and tectonic oversteepenning generates slope failures.

This GIS overlay is a component of the U.S. Geological Survey, Woods Hole Science Center's, Gulf of Mexico GIS database. The Gulf of Mexico GIS database is intended to organize and display USGS held data and provide on-line (WWW) access to the data and/or metadata. A two week cruise aboard the R/V GYRE focused on mapping surficial sedimentary processes and their connection to the subsurface geology. The study area was on the upper continental slope in the northwestern Gulf of Mexico; an area of active hydrocarbon exploration. Active salt movement, hydrocarbon movement up faults, the presence of gas hydrates associated with biogenic and thermogenic methane, and overpressured sand deposits all present hazards to oil exploration in this area. This study used sidescan sonar and high-resolution chirp subbottom profiling techniques to map the surficial and shallow subsurface expression of these processes in two areas roughly 15 by 25 km in size. High-resolution multi-channel seismic-reflection data were collected simultaneously with the sidescan imagery to provide a link to the deeper subsurface. Additional multi-channel and Huntec seismic data were collected along regional lines between the detailed study areas to tie these studies to other areas of known hydrates and to wells where shallow overpressured sands have been drilled. The detailed studies attempted to map entire geological systems in this upper slope environment to provide a broader perspective than can be seen from studying a single lease block. One study area focused on two adjacent salt withdrawal basins to assess the processes that are shaping the flanks of the basins, the processes affecting sedimentation in the basin floors, and to compare the deeper structures and surficial processes between the basins. The second study area focused on three salt domes, the processes associated with them, and how they affect the shallow subsurface stratigraphy. Initial observations suggest that most of the surface and shallow subsurface geohazards are associated with the flanks of salt structures. Here active salt movement generates faults along which hydrocarbons can escape to the seafloor, and tectonic oversteepenning generates slope failures.

In 1999, the USGS, in partnership with the South Carolina Sea Grant Consortium, began a study to investigate processes affecting shoreline change along the northern coast of South Carolina, focusing on the Grand Strand region. Previous work along the U.S. Atlantic coast shows that the structure and composition of older geologic strata located seaward of the coast heavily influences the coastal behavior of areas with limited sediment supply, such as the Grand Strand. By defining this geologic framework and identifying the transport pathways and sinks of sediment, geoscientists are developing conceptual models of the present-day physical processes shaping the South Carolina coast. The primary objectives of this research effort are: 1) to provide a regional synthesis of the shallow geologic framework underlying the coastal upland, shoreface and inner continental shelf, and define its role in coastal evolution and modern beach behavior; 2) to identify and model the physical processes affecting coastal ocean circulation and sediment transport, and to define their role in shaping the modern shoreline; and 3) to identify sediment sources and transport pathways; leading to construction of a regional sediment budget.

Lake Mead is a large interstate reservoir located in the Mojave Desert of southeastern Nevada and northwestern Arizona. It was impounded in 1935 by the construction of Hoover Dam and is one of a series of multi-purpose reservoirs on the Colorado River. The lake extends 183 km from the mouth of the Grand Canyon to Black Canyon, the site of Hoover Dam, and provides water for residential, commercial, industrial, recreational, and other non-agricultural users in communities across the southwestern United States. Extensive research has been conducted on Lake Mead, but a majority of the studies have involved determining levels of anthropogenic contaminants such as synthetic organic compounds, heavy metals and dissolved ions, furans/dioxins, and nutrient loading in lake water, sediment, and biota (Preissler, et al., 1998; Bevans et al, 1996; Bevans et al., 1998; Covay and Leiker, 1998; LaBounty and Horn, 1997; Paulson, 1981). By contrast, little work has focused on the sediments in the lake and the processes of deposition (Gould, 1951). To address these questions, sidescan-sonar imagery and high-resolution seismic-reflection profiles were collected throughout Lake Mead by the USGS in cooperation with researchers from University of Nevada Las Vegas (UNLV). These data allow a detailed mapping of the surficial geology and the distribution and thickness of sediment that has accumulated in the lake since the completion of Hoover Dam. Results indicate that the accumulation of post-impoundment sediment is primarily restricted to former river and stream beds that are now submerged below the lake while the margins of the lake appear to be devoid of post-impoundment sediment. The sediment cover along the original Colorado River bed is continuous and is typically greater than 10 m thick through much of its length. Sediment thickness in some areas exceeds 35 m while the smaller tributary valleys typically are filled with less than 4 m of sediment. Away from the river beds that are now covered with post-impoundment sediment, pre-impoundment alluvial deposits and rock outcrops are still exposed on the lake floor.

Lake Mead is a large interstate reservoir located in the Mojave Desert of southeastern Nevada and northwestern Arizona. It was impounded in 1935 by the construction of Hoover Dam and is one of a series of multi-purpose reservoirs on the Colorado River. The lake extends 183 km from the mouth of the Grand Canyon to Black Canyon, the site of Hoover Dam, and provides water for residential, commercial, industrial, recreational, and other non-agricultural users in communities across the southwestern United States. Extensive research has been conducted on Lake Mead, but a majority of the studies have involved determining levels of anthropogenic contaminants such as synthetic organic compounds, heavy metals and dissolved ions, furans/dioxins, and nutrient loading in lake water, sediment, and biota (Preissler, et al., 1998; Bevans et al, 1996; Bevans et al., 1998; Covay and Leiker, 1998; LaBounty and Horn, 1997; Paulson, 1981). By contrast, little work has focused on the sediments in the lake and the processes of deposition (Gould, 1951). To address these questions, sidescan-sonar imagery and high-resolution seismic-reflection profiles were collected throughout Lake Mead by the USGS in cooperation with researchers from University of Nevada Las Vegas (UNLV). These data allow a detailed mapping of the surficial geology and the distribution and thickness of sediment that has accumulated in the lake since the completion of Hoover Dam. Results indicate that the accumulation of post-impoundment sediment is primarily restricted to former river and stream beds that are now submerged below the lake while the margins of the lake appear to be devoid of post-impoundment sediment. The sediment cover along the original Colorado River bed is continuous and is typically greater than 10 m thick through much of its length. Sediment thickness in some areas exceeds 35 m while the smaller tributary valleys typically are filled with less than 4 m of sediment. Away from the river beds that are now covered with post-impoundment sediment, pre-impoundment alluvial deposits and rock outcrops are still exposed on the lake floor.