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At least 469 records · Page 26Linked to original sources

USGS2006

Geologic impacts of the 2004 Indian ocean tsunami on Indonesia, Sri Lanka, and the Maldives

The December 26, 2004 Indian Ocean tsunami was generated by a large submarine earthquake (magnitude ???9.1) with an epicenter located under the seafloor in the eastern Indian Ocean near northern Sumatra, Indonesia. The resulting tsunami was measured globally and had significant geologic impacts throughout the Indian Ocean basin. Observations of tsunami impacts, such as morphologic change, sedimentary deposits, and water-level measurements, are used to reconstruct tsunamogenic processes. Data from Sumatra, Sri Lanka, and the Maldives provide a synoptic view of tsunami characteristics from a wide range of coastal environments both near- and far-field from the tsunami origin. Impacts to the coast as a result of the tsunami varied depending upon the height of the wave at impact, orientation of the coast with regard to direction of wave approach, and local topography, bathymetry, geology, and vegetation cover. Tsunami deposits were observed in all the countries visited and can be generally characterized as relatively thin sheets (<80 cm), mostly of sand. ?? 2006 Gebru??der Borntraeger.

Conference Paper↗

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↗

USGS2018

Paleocene–Eocene Thermal Maximum prolonged by fossil carbon oxidation

A hallmark of the rapid and massive release of carbon during the Palaeocene–Eocene Thermal Maximum is the global negative carbon isotope excursion. The delayed recovery of the carbon isotope excursion, however, indicates that CO 2 inputs continued well after the initial rapid onset, although there is no consensus about the source of this secondary carbon. Here we suggest this secondary input might have derived partly from the oxidation of remobilized sedimentary fossil carbon. We measured the biomarker indicators of thermal maturation in shelf records from the US Mid-Atlantic coast, constructed biomarker mixing models to constrain the amount of fossil carbon in US Mid-Atlantic and Tanzania coastal records, estimated the fossil carbon accumulation rate in coastal sediments and determined the range of global CO 2 release from fossil carbon reservoirs. This work provides evidence for an order of magnitude increase in fossil carbon delivery to the oceans that began ~10–20 kyr after the event onset and demonstrates that the oxidation of remobilized fossil carbon released between 10 2 and 10 4 PgC as CO 2 during the body of the Palaeocene–Eocene Thermal Maximum. The estimated mass is sufficient to have sustained the elevated atmospheric CO 2 levels required by the prolonged global carbon isotope excursion. Even after considering uncertainties in the sedimentation rates, these results indicate that the enhanced erosion, mobilization and oxidation of ancient sedimentary carbon contributed to the delayed recovery of the climate system for many thousands of years.

Nature Geoscience↗

USGS2011

Sea-floor geology and topography offshore in Eastern Long Island Sound

A gridded multibeam bathymetric dataset covers approximately 133.7 square kilometers of sea floor offshore in eastern Long Island Sound. Although originally collected for charting purposes during National Oceanic and Atmospheric Administration hydrographic survey H11997, these acoustic data, and the sea-floor sampling and photography stations subsequently occupied to verify them during USGS cruise 2010-015-FA, are part of an expanding series of studies that provide a fundamental framework for research and resource management (for example, cables, pipelines, and dredging) activities in this major East Coast estuary. Results show the composition and terrain of the seabed and provide information on sediment transport and benthic habitat. Bedrock outcrops, erosional outliers, lag deposits of boulders, scour depressions, and extensive gravel pavements are common in the eastern part of the study area. These features, which result from the near-constant exposure to strong tidal currents, indicate sedimentary environments dominated by processes associated with erosion. Large fields of transverse and barchanoid sand waves in the western part of the study area reflect slightly lower energy levels and sedimentary environments where processes associated with coarse bedload transport prevail.

Open-File Report↗

USGS1984

Paleomagnetic constraints on the interpretation of early Cenozoic Pacific Northwest paleogeography

Widespread Cenozoic clockwise tectonic rotation in the Pacific Northwest is an established fact; however, the geologic reconstructions based on these rotations are the subject of continuing debate. Three basic mechanisms have been proposed to explain the rotations: (1) simple shear rotation of marginal terranes caught in the dextral shear couple between oceanic plates and North America; (2) rotation during oblique microplate collision and accretion to the continental margin; and (3) rotation of continental margin areas during episodes of intracontinental extension. In areas where detailed structure and stratigraphy are available, distributed shear rotations are amplv demonstrated paleomagnetically. However, rotation due to asymmetric interarc extension must be significant, especially for the Oregon Coast Range, in light of recent estimates of large Tertiary extension across the northern Basin and Range. The relative importance of shear versus extension is difficult to determine, but shear could account for nearly onehalf of the observed rotations. Oblique microplate collision has not contributed significantly to the observed Cenozoic rotations because most of the rotation post-dates collision-related deformation in the Oregon and Washington. Coast Range. The resultant continental reconstructions suggest that about 300 km of extension has occurred at 42°N. latitude (southern Oregon border) since early Eocene time. This reconstruction suggests that Cretaceous sedimentary basins east of the Klamath Mountains have undergone significant Tertiary extension (about f<0%) , but little rotation. Upper Cretaceous sedimentary rocks in the Blue Mountains of Oregon near Mitchell are probably rotated at least 15° and perhaps as much as 60°, which allows considerable latitude in the restoration of that part of the basin.

Pacific Section S.E.P.M.↗

USGS1993

The hydrogeology of Kilauea volcano

The hydrogeology of Kilauea volcano and adjacent areas has been studied since the turn of this century. However, most studies to date have focused on the relatively shallow, low-salinity parts of the ground-water system, and the deeper hydrothermal system remains poorly understood. The rift zones of adjacent Mauna Loa volcano bound the regional ground-water flow system that includes Kilauea, and the area bounded by the rift zones of Kilauea and the ocean may comprise a partly isolated subsystem. Rates of ground-water recharge vary greatly over the area and discharge is difficult to measure, because streams are ephemeral and most ground-water discharges diffusely at or below sea level. Hydrothermal systems exist at depth in Kilauea's cast and southwest rift zone, as evidenced by thermal springs at the coast and wells in the lower east-rift zone. Available data suggest that dike-impounded, heated ground water occurs at relatively high elevations in the upper east-and southwest-rift zones of Kilauea, and that permeability at depth in the rift zones (probably < 10-15 m2) is much lower than that of unaltered basalt flows closer to the surface (> 10 10 m2). Substantial variations in permeability and the presence of magmatic heat sources influence the structure of the fresh water-salt water interface, so the Ghyben-Herzberg model will often fail to predict its position. Numerical modeling studies have considered only subsets of the hydrothermal system, because no existing computer code solves the coupled fluid-flow, heat- and solute-transport problem over the temperature and salinity range encountered at Kilauea. ?? 1993.

Geothermics↗

USGS2015

Sediment yields from small, steep coastal watersheds of California

Global inventories of sediment discharge to the ocean highlight the importance of small, steep watersheds (i.e., those having drainage areas less than 100,000 km2 and over 1000 m of relief) that collectively provide a dominant flux of sediment. The smallest of these coastal watersheds (e.g., those that have drainage areas less than 1000 km2) can represent a large portion of the drainage areas of active margin coasts, such as California’s coast, but remain almost universally unmonitored. Here we report on the suspended-sediment discharge of several small coastal watersheds (10-56 km2) of the Santa Ynez Mountains, California, that were found to have ephemeral discharge and suspended-sediment concentrations ranging between 1 and over 200,000 mgL-1. Sediment concentrations were weakly correlated with discharge (r2 = 0.10–0.25), and all types of hysteresis patterns were observed during high flows (clockwise, counterclockwise, no hysteresis, and complex). Sediment discharge varied strongly with time and was measurably elevated in one watershed following a wildfire. Although sediment yields varied by over 100-fold across the watersheds (e.g., 15 – 2100 tkm-2 yr -1during the relatively wet 2005 water year), the majority of sediment discharge (65-80%) occurred during only 1% of the time for all watersheds. Furthermore, sampling of dozens of high flow events provides evidence that sediment yields were generally related to peak discharge yields, although these relationships were not consistent across the watersheds. These results suggest that small watersheds of active margins can provide large fluxes of sediment to the coast, but that the rates and timing of this sediment discharge is more irregular in time – and thus more difficult to characterize – than the better monitored and studied watersheds that are 1000-100,000 km2.

California↗

USGS2021

Historic population estimates for bottlenose dolphins (Tursiops truncatus) in Aragua, Venezuela indicate monitoring need

This study reports historic capture-mark-recapture survival and abundance estimates of common bottlenose dolphins ( Tursiops truncatus ) based on photo-identification surveys of coastal Venezuela (along the Aragua coast between Turiamo Bay and Puerto Colombia). We used the most recent data available: dolphins identified by unique dorsal fin marks during wet and dry season surveys conducted from 2004 to 2008. Dolphin encounter histories were analyzed in the Closed Capture Robust Design framework, with the top model including random movement, constant survival, and capture-recapture probabilities that varied by secondary periods. Survival of marked adults was estimated at 0.99 (95% CI = 0.97 to 1.00). Population estimates for all adults (marked and unmarked) averaged 31 animals (SD = 13.8), and for all dolphins (all adults and calves), 41 animals (SD = 17.2). Coastal bottlenose dolphins face numerous threats, including ship strikes, oil spills, conflict with recreational and industrial fisheries, other negative human interactions, biotoxins, chemicals, noise, freshwater discharge, and coastal development. Further, small populations are, in general, at increased risk due to reduced resiliency and recovery potential when exposed to such threats and to expected environmental and demographic stochasticity. These historic estimates of abundance and survival are critical for establishing a reference state and indicate a need for ongoing monitoring of the small dolphin population while the Aragua coast is still, as of yet, relatively little impacted by humans. Should coastal development increase (as is the global trend) and/or environmental catastrophes (e.g., harmful algal blooms, hurricanes, and oil spills) occur, these historic estimates will be essential for assessing impacts and guiding management and conservation interventions. Our results show year-round dolphin presence and highlight the Venezuelan coastal–oceanic landscape as an area of both future research and conservation importance.

Aragua↗

USGS2025

The 3D Elevation Program—Supporting the economy of Massachusetts

Introduction Massachusetts extends from the mountains of the Appalachian system in the west of the State to the sandy beaches and rocky shorelines of the Atlantic coast in the east. Inland topographic data support a wide range of important activities, including geologic mapping, transportation planning, forest and wildlife management, quantifying ecological services, water supply protection, commonwealth-wide infrastructure planning, local site planning, and flood-plain management. Nearshore bathymetry can be used to support coastal portions of the Commonwealth by addressing the combined threats of ocean warming, strong storm surge, and rising sea levels. The maintenance and (or) expansion of Massachusetts ports (for instance, Boston, New Bedford) and Cape Cod sediment management depends upon the accurate mapping of bathymetry and the frequent influx of sediment and redeposition. Critical applications that address the broad range of requirements depend on light detection and ranging (lidar) data that provide a highly detailed three-dimensional (3D) model of the Earth’s surface and aboveground features. The 3D Elevation Program (3DEP) is managed by the U.S. Geological Survey (USGS) in partnership with Federal, State, Tribal, U.S. territorial, and local agencies to acquire consistent lidar coverage at quality level 2 or better to meet the many needs of the Nation and Massachusetts. The status of available and in-progress 3DEP baseline lidar data in Massachusetts is shown in figure 1. 3DEP baseline lidar data include quality level 2 or better, 1-meter or better digital elevation models, and lidar point clouds, and must meet the Lidar Base Specification version 1.2 ( https://www.usgs.gov/3dep/lidarspec ) or newer requirements. The National Enhanced Elevation Assessment identified user requirements and conservatively estimated that availability of lidar data would result in at least $1.23 million in new benefits annually to Massachusetts. The top 10 Massachusetts business uses for 3D elevation data, which are based on the estimated annual conservative benefits of 3DEP, are shown in table 2.

Massachusetts↗

USGS2012

Monitoring inland storm tide and flooding from Hurricane Irene along the Atlantic Coast of the United States, August 2011

The U.S. Geological Survey (USGS) deployed a temporary monitoring network of water-level sensors at 212 locations along the Atlantic coast from South Carolina to Maine during August 2011 to record the timing, areal extent, and magnitude of inland hurricane storm tide and coastal flooding generated by Hurricane Irene. Water-level sensor locations were selected to augment existing tide-gage networks to ensure adequate monitoring in areas forecasted to have substantial storm tide. As defined by the National Oceanic and Atmospheric Administration (NOAA; 2011a,b), storm tide is the water-level rise generated by a coastal storm as a result of the combination of storm surge and astronomical tide.

Atlantic Coast↗

USGS2013

Sediment transport in the San Francisco Bay Coastal System: An overview

The papers in this special issue feature state-of-the-art approaches to understanding the physical processes related to sediment transport and geomorphology of complex coastal-estuarine systems. Here we focus on the San Francisco Bay Coastal System, extending from the lower San Joaquin-Sacramento Delta, through the Bay, and along the adjacent outer Pacific Coast. San Francisco Bay is an urbanized estuary that is impacted by numerous anthropogenic activities common to many large estuaries, including a mining legacy, channel dredging, aggregate mining, reservoirs, freshwater diversion, watershed modifications, urban run-off, ship traffic, exotic species introductions, land reclamation, and wetland restoration. The Golden Gate strait is the sole inlet connecting the Bay to the Pacific Ocean, and serves as the conduit for a tidal flow of ~ 8 x 109 m 3 /day, in addition to the transport of mud, sand, biogenic material, nutrients, and pollutants. Despite this physical, biological and chemical connection, resource management and prior research have often treated the Delta, Bay and adjacent ocean as separate entities, compartmentalized by artificial geographic or political boundaries. The body of work herein presents a comprehensive analysis of system-wide behavior, extending a rich heritage of sediment transport research that dates back to the groundbreaking hydraulic mining-impact research of G.K. Gilbert in the early 20th century.

California↗

USGS1967

Stratigraphy and paleoenvironment of the phosphatic miocene strata of North Carolina

Foraminifera and Mollusca collected from the phosphatic Pungo River Formation and the overlying Yorktown Formation in eastern North Carolina were analyzed and interpreted for stratigraphic and environmental significance in order to determine optimum depositional sites for primary phosphorite. The Mollusca and benthonic foraminifera of the Pungo River Formation correlate with those of the Calvert Formation of Maryland, and the planktonic foraminifera in both of these formations correlate with the Globigerinatella insueta zone of Trinidad, postulated as late Aquitanian age. The paleoenvironment of the phosphorite deposition, interpreted primarily from the benthonic foraminifera, was of cool-temperate waters, ranging in depth from 100 to 200 m in the phosphatic beds to less than 70 m in the upper calcareous beds where phosphate is scarce. Phosphorite deposition occurred in an oceanic embayment located south of the Fort Monroe high in southern Virginia and north of a positive feature whose axis lies in the vicinity of New Bern, North Carolina . Cool-temperate waters in this area during Pungo River time indicate that circulation patterns of ocean currents and the resultant faunal provinces were not the same as those at present and later in the Miocene . In the Pungo River and its time equivalents of the Atlantic Coastal Plain, the presence of thick diatomaceous clay units, volcanic ash beds, shards, attapulgite clays, and other minerals probably derived from volcanic rocks, suggests a volcanic source somewhere off the coast during the Miocene . The Yorktown unconformably overlies the Pungo River Formation. The unconformity is marked by channels into the Pungo River, filled with phosphatic pebbles, vertebrate bones, and lower York-town molluscs and microfauna. The coarse-grained phosphatic material is derived from the underlying fine-grained primary phosphorite in the Pungo River and is abundant only in the lower part of the Yorktown Formation. Deposition of the lower part of the Yorktown occurred in waters about 100 m deep. The waters gradually became more shallow as deposition of the formation continued until depths of less than 15 m, and probable brackish conditions, were reached as the uppermost part of the formation was deposited. Temperature of the waters, cool-temperate during lower Yorktown deposition, became warm-temperate to subtropical in later Yorktown time. The faunal patterns suggest that circulation patterns reached their present state during late Yorktown time.

North Carolina↗

USGS2016

Hydrologic conditions in the South Coast aquifer, Puerto Rico, 2010–15

In 1958, the U.S. Geological Survey began documenting hydrologic conditions, including groundwater levels, groundwater withdrawals for agricultural irrigation and public water supply, and water quality, in the South Coast aquifer, Puerto Rico. This information has improved the understanding of the water resources of the region. The hydrologic data indicate that (1) groundwater levels declined as much as 40 feet in the Salinas area and 11 feet in the Guayama area during 2012–14; (2) groundwater withdrawals for agricultural irrigation increased from 6.0 to 10.5 million gallons per day, or 75 percent, from 2010 to 2012; and (3) total groundwater withdrawals decreased from 29.3 to 23.8 million gallons per day from 2010 to 2014. The quantity and quality of water in the aquifer is primarily affected by variations in aquifer recharge as a result of changing rainfall or modes of irrigation; however, the spatial patterns and magnitude of water withdrawals for all uses have a secondary impact on the quantity and quality of water in the aquifer. National Oceanic and Atmospheric Administration data from climatological stations indicate that the 30-year normal precipitation for the period 1991–2010 in the South Coastal and Southern Slopes climatological regions was about 37.74 and 61.61 inches, respectively; the 30-year moving average precipitation for the period 1985–2014 was 37.94 and 61.80 inches, respectively, for these regions. The mean annual precipitation during 2012–14 was 13 percent below the 30-year moving average for the South Coastal climatological region and 7.7 percent below for the Southern Slopes climatological region. When rainfall is below the 30-year moving average, recharge is diminished and groundwater levels decline. Annual precipitation in the South Coast aquifer, which includes a large part of the South Coastal and Southern Slopes climatological regions, was 39.42, 37.25, and 34.89 inches per year for 2012, 2013, and 2014, respectively. Water level declines reduce the thickness of freshwater in the unconfined parts of the South Coast aquifer. Additionally, the pumping-induced migration of poor-quality water from deep or seaward areas of the aquifer can contribute to reductions in the thickness of freshwater in the aquifer. The reduction in the freshwater saturated thickness of the aquifer in areas near Ponce, Juana Díaz, Salinas, and Guayama is of particular concern because the total saturated thickness of the aquifer is thinner in these areas. Total dissolved solids concentration in groundwater samples indicates a small positive trend in Ponce, Santa Isabel, Salinas, and Guayama. Diminished aquifer recharge during 2012 to 2015 and, to a lesser extent, increased groundwater withdrawals have resulted in a reduction in the freshwater saturated thickness of the aquifer. The reduction in freshwater saturated thickness of the aquifer may affect freshwater resources available for agriculture and public water supply. A prolonged time period with reduced aquifer recharge may have substantial implications for groundwater levels and fresh groundwater availability.

Puerto Rico↗

USGS2019

World’s largest dam removal reverses coastal erosion

Coastal erosion outpaces land generation along many of the world’s deltas and a significant percentage of shorelines, and human-caused alterations to coastal sediment budgets can be important drivers of this erosion. For sediment-starved and erosion-prone coasts, large-scale enhancement of sediment supply may be an important, but poorly understood, management option. Here we provide new topographic measurements that show the patterns and trends of beach accretion following the restoration of sediment supply from a massive dam removal project. River sediment was initially deposited in intertidal-to-subtidal deltaic lobes, and this sediment was reworked by ocean waves into subaerial river mouth bars over time scales of several months. These river mouth bars welded to the shoreline and then initiated waves of sediment accretion along adjacent upcoast and downcoast beaches. Although the downcoast shoreline has a high wave-angle setting, the sedimentation waves straightened the downcoast shoreline rather than forming self-organized quasi-periodic instabilities, which suggests that simple coastal evolution theory did not hold under these conditions. Combined with other mega-nourishment projects, these findings provide new understanding of littoral responses to the restoration of sediment supplies.

Washington↗

USGS2012

U.S. Department of the Interior South Central Climate Science Center

On September 14, 2009, the Secretary of the Interior signed a Secretarial Order (No. 3289) entitled, "Addressing the Impacts of Climate Change on America's Water, Land, and Other Natural and Cultural Resources." The Order effectively established the U.S. Department of the Interior (DOI) Climate Science Centers (CSCs) for the purpose of integrating DOI science and management expertise with similar contributions from our partners to provide information to support strategic adaptation and mitigation efforts on public and private lands across the United States and internationally. The South Central Climate Science Center (SC CSC) is supported by a consortium of partners that include The University of Oklahoma, Texas Tech University, Louisiana State University, The Chickasaw Nation, The Choctaw Nation of Oklahoma, Oklahoma State University, and the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory. Additionally, the SC CSC will collaborate with a number of other universities, State and federal agencies, and nongovernmental organizations (NGOs) with interests and expertise in climate science. The primary partners of the SC CSC are the Landscape Conservation Cooperatives (LCCs), which include the Desert, Eastern Tallgrass Prairie and Big Rivers, Great Plains, Gulf Coast Prairie, Gulf Coastal Plains and Ozarks, and Southern Rockies. CSC collaborations are focused on common science priorities that address priority partner needs, eliminate redundancies in science, share scientific information and findings, and expand understanding of climate change impacts in the south-central United States and Mexico.

Arizona;Louisiana;Oklahoma;Texas↗

USGS2021

A climate-mediated shift in the estuarine habitat mosaic limits prey availability and reduces nursery quality for juvenile salmon

The estuarine habitat mosaic supports the reproduction, growth, and survival of resident and migratory fish species by providing a diverse portfolio of unique habitats with varying physical and biological features. Global climate change is expected to result in increasing temperatures, rising sea levels, and changes in riverine hydrology, which will have profound effects on the extent and composition of the estuarine habitat mosaic and its associated nursery quality for juvenile fish. We used a spatially explicit bioenergetics model to assess how different climate change scenarios might affect juvenile salmon growth rate potential relative to present day conditions in the Nisqually River Delta, WA, USA. The model indicated that prey-rich habitats such as emergent salt marshes and eelgrass meadows were most likely to facilitate growth, and that reductions in their areal extent and accessibility could have severe consequences for salmon. For instance, unmitigated sea-level rise halved the predicted extent of low- and high-elevation emergent salt marsh, leading to a 30% reduction in end-of-season weights. Increasing water temperatures compounded these effects during the late spring and summer such that the average daily growth rate of an individual fish decreased by an additional 5–50% when compared to the effects of sea-level rise alone. Lethal temperatures (> 24 °C) were infrequently observed, but they were more likely to occur during summer low tides in the mudflat and eelgrass habitats when accessibility to prey-rich marsh was minimal, thereby limiting foraging capacity and the availability of thermal refugia. Our findings indicate that, barring the enactment of targeted management strategies, rising tidal levels and increasing ocean temperatures may reduce the quality of the estuarine habitat mosaic for out-migrating salmon and other sensitive fish species.

Washington↗

USGS1982

Structure and petroleum potential of the continental margin between Cross Sound and Icy Bay, northern Gulf of Alaska

Major structural features of the Yakutat segment, the segment of the continental margin between Cross Sound and Icy Bay, northern Gulf of Alaska, are delineated by multichannel seismic reflection data. A large structural high is centered on Fairweather Ground and lies generally at the edge of the shelf from Cross Sound to west of the Alsek Valley. A basement uplift, the Dangerous River zone, along which the seismic acoustic basement shallows by up to two kilometers, extends north from the western edge of Fairweather Ground towards the mouth of the Dangerous River. The Dangerous River zone separates the Yakutat segment into two distinct subbasins. The eastern subbasin has a maximum sediment thickness of about 4 km, and the axis of the basin is near and parallel to the coast. Strata in this basin are largely of late Cenozoic age (Neogene and Quaternary) and approximately correlate with the onshore Yakataga Formation. The western subbasin has a maximum of at least 9 km of sediment, comprised of a thick (greater than 4.5 km) Paleogene section overlain by late Cenozoic strata. The Paleogene section is truncated along the Dangerous River zone by a combination of erosion, faulting, and onlap onto the acoustic basement. Within the western subbasin, the late Cenozoic basin axis is near and parallel to the coast, but the Paleogene basin axis appears to trend in a northwest direction diagonally across the shelf. Sedimentary strata throughout the Yakutat shelf show regional subsidence and only minor deformation except in the vicinity of the Fairweather Ground structural high, near and along the Dangerous River zone, and at the shoreline near Lituya Bay. Seismic data across the continental slope and adjacent deep ocean show truncation at the continental slope of Paleogene strata, the presence of a thick (to 6 km) undeformed or mildly deformed abyssal sedimentary section at the base of the slope that in part onlaps the slope, and a relatively narrow zone along the slope or at the base of the slope where faulting may have occurred. Observed deformation at the base of the slope is primarily related to the late Cenozoic uplift of Fairweather Ground, and to Quaternary folding perpendicular to the Pacific-North America relative convergence vector. No accretionary section or major deformation is observed along the continental slope. The absence of these features suggests that no major subduction of the Pacific plate beneath the Yakutat margin has occurred during the late Cenozoic. However, transform faulting along the base of the slope has occurred, because probable Oligocene oceanic basement is juxtaposed against Mesozoic and Paleogene sedimentary strata of the Yakutat slope. This juxtaposition most likely occurred during late Oligocene and Miocene time. During much of the late Cenozoic, and especially during Pliocene-Pleistocene time, the Yakutat segment has apparently been moving northward with the Pacific plate. Dredge samples from the continental slope recovered potential hydrocarbon source and reservoir rocks from the Paleogene sedimentary sequence. Most of the organic matter from these samples is immature to marginally mature. Lopatin calculations suggest that rocks beneath the shelf are likely to be thermally mature at a depth of 4 to 5 km and deeper. In general, the strata at these depths are largely of Paleogene age. Thus, the Paleogene strata may have significant resource potential if source and reservoir rocks similar to those dredged at the slope are present below the shelf. The Paleogene strata are contained primarily within the western subbasin; strata in the east subbasin appear to have little resource potential. Structural traps are apparently present in parts of the basin near and along the Dangerous River zone. These traps are in an updip position from potentially mature strata of the western subbasin, and may hold commercial accumulations of hydrocarbons, if sufficient hydrocarbon generation and migration has occurred

Open-File Report↗

USGS2012

Coastal impacts, adaptation, and vulnerabilities: a technical input to the 2013 National Climate Assessment

The coast has long provided communities with a multitude of benefits including an abundance of natural resources that sustain economies, societies, and ecosystems. Coasts provide natural harbors for commerce, trade, and transportation; beaches and shorelines that attract residents and tourists; and wetlands and estuaries that are critical for fisheries and water resources. Coastal ecosystems provide critical functions to cycle and move nutrients, store carbon, detoxify wastes, and purify air and water. These areas also mitigate floods and buffer against coastal storms that bring high winds and salt water inland and erode the shore. Coastal regions are critical in the development, transportation, and processing of oil and natural gas resources and, more recently, are being explored as a source of energy captured from wind and waves. The many benefits and opportunities provided in coastal areas have strengthened our economic reliance on coastal resources. Consequently, the high demands placed on the coastal environment will increase commensurately with human activity. Because 35 U.S. states, commonwealths, and territories have coastlines that border the oceans or Great Lakes, impacts to coastline systems will reverberate through social, economic, and natural systems across the U.S. Impacts on coastal systems are among the most costly and most certain consequences of a warming climate (Nicholls et al., 2007). The warming atmosphere is expected to accelerate sea-level rise as a result of the decline of glaciers and ice sheets and the thermal expansion of sea water. As mean sea level rises, coastal shorelines will retreat and low-lying areas will tend to be inundated more frequently, if not permanently, by the advancing sea. As atmospheric temperature increases and rainfall patterns change, soil moisture and runoff to the coast are likely to be altered. An increase in the intensity of climatic extremes such as storms and heat spells, coupled with other impacts of climate change and the effects of human development, could affect the sustainability of many existing coastal communities and natural resources. This report, one of a series of technical inputs for the third NCA conducted under the auspices of the U.S. Global Change Research Program, examines the known effects and relationships of climate change variables on the coasts of the U.S. It describes the impacts on natural and human systems, including several major sectors of the U.S. economy, and the progress and challenges to planning and implementing adaptation options. Below we present the key findings from each chapter of the report, beginning with the following key findings from Chapter 1: Introduction and Context.

Book↗