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At least 1,117 records · Page 62Linked to original sources

USGS1965

Structure, Quaternary history, and general geology of the Corral Canyon area, Los Angeles County, California

The Corral Canyon nuclear power plant site consists of about 305 acres near the mouth of Corral Canyon in the central Santa Monica Mountains; it is located on an east-trending segment of the Pacific Coast between Point Dume and Malibu Canyon, about 28 miles due west of Los Angeles. The Santa Monica Mountains are the southwesternmost mainland part of the Transverse Ranges province, the east-trending features of which transect the otherwise relatively uniform northwesterly trend of the geomorphic and geologic features of coastal California. The south margin of the Transverse Ranges is marked by the Santa Monica fault system, which extends eastward near the 34th parallel for at least 145 miles from near Santa Cruz Island to the San Andreas fault zone. In the central Santa Monica Mountains area the Santa Monica fault system includes the Malibu Coast fault and Malibu Coast zone of deformation on the north; from the south it includes an inferred fault--the Anacapa fault--considered to follow an east-trending topographic escarpmemt on the sea floor about 5 miles south of the Malibu Coast fault. The low-lying terrain south of the fault system, including the Los Angeles basin and the largely submerged Continental Borderland offshore, are dominated by northwest-trending structural features. The Malibu Coat zone is a wide, east-trending band of asymmetrically folded, sheared, and faulted bedrock that extends for more than 20 miles along the north margin of the Santa Monica fault system west of Santa Monica. Near the north margin of the Malibu Coast zone the north-dipping, east-trending Malibu Coast fault juxtaposes unlike, in part contemporaneous sedimentary rock sections; it is inferred to be the near-surface expression of a major crustal boundary between completely unrelated basement rocks. Comparison of contemporaneous structural features and stratigraphic sections (Late Cretaceous to middle Miocene sedimentary, rocks and middle Miocene volcanic and intrusive igneous rocks on the north; middle and upper Miocene sedimentary and middle Miocene volcanic rocks on the south) across the fault demonstrates that neither strike slip of less than 25 miles nor high-angle dip slip can account for this juxtaposition. Instead, the Malibu Coast fault is inferred to have been the locus of large-magnitude, north-south oriented, horizontal shortening (north, or upper, block thrust over south block). This movement occurred at or near the northern boundary of the Continental Borderland, the eastern boundary of which is inferred to be the northwest-trending known-active Newport-Inglewood zone of en echelon right lateral strike-slip faults in the western Los Angeles basin. Local structural features and their relation to regional features, such as those in the Malibu Coast zone, form the basis for the interpretation that the Malibu Coast fault has acted chiefly as a thrust fault. Within the Malibu Coast zone, on both sides of the Malibu Coast fault, structural features in rocks that range in age from Late Cretaceous to late Miocene are remarkably uniform in orientation. The predominant trend of bedding, axial surfaces of numerous asymmetric folds, locally pervasive shear surfaces, and faults is approximately east-west and their predominant dip is northward.. The axes of the folds plunge gently east or west. Evidence from faults and shears within the zone indicates that relative movement on most of these was north (upper) over south. Beyond the Malibu Coast zone to the north and south the rocks entirely lack the asymmetric folds, overturned beds, and the locally abundant shears that characterize the rocks within the zone; these rocks were therefore not subjected to the same deforming forces that existed near the Malibu Coast fault. Movement on the Malibu Coast fault and deformation in the Malibu Coast zone occurred chiefly during the interval between late Miocene and late Pleistocene time. The youngest-known faulting in the Malibu Coast zone is late Pl

Open-File Report↗

USGS2007

Coastal systems and low-lying areas

Since the IPCC Third Assessment Report (TAR), our understanding of the implications of climate change for coastal systems and low-lying areas (henceforth referred to as ‘coasts’) has increased substantially and six important policy-relevant messages have emerged. Coasts are experiencing the adverse consequences of hazards related to climate and sea level (very high confidence). Coasts are highly vulnerable to extreme events, such as storms, which impose substantial costs on coastal societies [6.2.1, 6.2.2, 6.5.2]. Annually, about 120 million people are exposed to tropical cyclone hazards, which killed 250,000 people from 1980 to 2000 [6.5.2]. Through the 20th century, global rise of sea level contributed to increased coastal inundation, erosion and ecosystem losses, but with considerable local and regional variation due to other factors [6.2.5, 6.4.1]. Late 20th century effects of rising temperature include loss of sea ice, thawing of permafrost and associated coastal retreat, and more frequent coral bleaching and mortality [6.2.5]. Coasts will be exposed to increasing risks, including coastal erosion, over coming decades due to climate change and sea-level rise (very high confidence). Anticipated climate-related changes include: an accelerated rise in sea level of up to 0.6 m or more by 2100; a further rise in sea surface temperatures by up to 3°C; an intensification of tropical and extra-tropical cyclones; larger extreme waves and storm surges; altered precipitation/run-off; and ocean acidification [6.3.2]. These phenomena will vary considerably at regional and local scales, but the impacts are virtually certain to be overwhelmingly negative [6.4, 6.5.3]. Corals are vulnerable to thermal stress and have low adaptive capacity. Increases in sea surface temperature of about 1 to 3°C are projected to result in more frequent coral bleaching events and widespread mortality, unless there is thermal adaptation or acclimatisation by corals [Box 6.1, 6.4]. Coastal wetland ecosystems, such as saltmarshes and mangroves, are especially threatened where they are sediment starved or constrained on their landward margin [6.4.1]. Degradation of coastal ecosystems, especially wetlands and coral reefs, has serious implications for the well-being of societies dependent on the coastal ecosystems for goods and services [6.4.2, 6.5.3]. ncreased flooding and the degradation of freshwater, fisheries and other resources could impact hundreds of millions of people, and socio-economic costs on coasts will escalate as a result of climate change [6.4.2, 6.5.3]. The impact of climate change on coasts is exacerbated by increasing human-induced pressures (very high confidence). Utilisation of the coast increased dramatically during the 20th century and this trend is virtually certain to continue through the 21st century. Under the SRES scenarios, the coastal population could grow from 1.2 billion people (in 1990) to 1.8 to 5.2 billion people by the 2080s, depending on assumptions about migration [6.3.1]. Increasing numbers of people and assets at risk at the coast are subject to additional stresses due to land-use and hydrological changes in catchments, including dams that reduce sediment supply to the coast [6.3.2]. Populated deltas (especially Asian megadeltas), low-lying coastal urban areas and atolls are key societal hotspots of coastal vulnerability, occurring where the stresses on natural systems coincide with low human adaptive capacity and high exposure [6.4.3]. Regionally, South, South- East and East Asia, Africa and small islands are most vulnerable [6.4.2]. Climate change therefore reinforces the desirability of managing coasts in an integrated manner [6.6.1.3]. Adaptation for the coasts of developing countries will be more challenging than for coasts of developed countries, due to constraints on adaptive capacity (high confidence). While physical exposure can significantly influence vulnerability for both human populations and natural systems, a lack of adaptive capacity is often the most important factor that creates a hotspot of human vulnerability. Adaptive capacity is largely dependent upon development status. Developing nations may have the political or societal will to protect or relocate people who live in low-lying coastal zones, but without the necessary financial and other resources/capacities, their vulnerability is much greater than that of a developed nation in an identical coastal setting. Vulnerability will also vary between developing countries, while developed countries are not insulated from the adverse consequences of extreme events [6.4.3, 6.5.2]. Adaptation costs for vulnerable coasts are much less than the costs of inaction (high confidence). Adaptation costs for climate change are much lower than damage costs without adaptation for most developed coasts, even considering only property losses and human deaths [6.6.2, 6.6.3]. As post-event impacts on coastal businesses, people, housing, public and private social institutions, natural resources, and the environment generally go unrecognised in disaster cost accounting, the full benefits of adaptation are even larger [6.5.2, 6.6.2]. Without adaptation, the high-end sea-level rise scenarios, combined with other climate changes (e.g., increased storm intensity), are as likely as not to render some islands and lowlying areas unviable by 2100, so effective adaptation is urgently required [6.6.3]. The unavoidability of sea-level rise, even in the longer-term, frequently conflicts with present-day human development patterns and trends (high confidence). Sea-level rise has substantial inertia and will continue beyond 2100 for many centuries. Irreversible breakdown of the West Antarctica and/or Greenland ice sheets, if triggered by rising temperatures, would make this long-term rise significantly larger, ultimately questioning the viability of many coastal settlements across the globe. The issue is reinforced by the increasing human use of the coastal zone. Settlement patterns also have substantial inertia, and this issue presents a challenge for long-term coastal spatial planning. Stabilisation of climate could reduce the risks of ice sheet breakdown, and reduce but Chapter 6 Coastal systems and low-lying areas 317 not stop sea-level rise due to thermal expansion [Box 6.6]. Hence, it is now more apparent than it was in the TAR that the most appropriate response to sea-level rise for coastal areas is a combination of adaptation to deal with the inevitable rise, and mitigation to limit the long-term rise to a manageable level [6.6.5, 6.7].

Book chapter↗

USGS2012

Physical Climate Forces

Key Findings The coasts of the U.S. are home to many large urban centers and important infrastructure such seaports, airports, transportation routes, oil import and refining facilities, power plants, and military bases. All are vulnerable to varying degrees to impacts of global warming such as sea-level rise, storms, and flooding. High Confidence. Physical observations collected over the past several decades from the land, coasts, oceans, and the atmosphere, as well as environmental indicators, show that warming and some related environmental changes are occurring globally at rates greater than can be expected due to natural processes. These climate-related changes are highly varied, but some are likely due in large part to anthropogenically increased atmospheric concentrations of greenhouse gases and altered land surface properties. High Confidence. Findings from many independent scientific studies conclude that these changes are consistent with global warming. The primary changes observed are rising sea level and average global air, land, and ocean temperatures; heightening temperature and precipitation extremes in some regions; and increasing levels of oceans acidification and rates of glacier and ice sheet melt. High Confidence. Most coastal landforms, such as barrier islands, deltas, bays, estuaries, wetlands, coral reefs, are highly dynamic and sensitive to even small changes in physical forces and feedbacks such as warming, storms, ocean circulation, waves and currents, flooding, sediment budgets, and sea-level rise. High Confidence. The effects of sea-level rise on coasts vary considerably from region-to-region and over a range of spatial and temporal scales. Land subsidence in certain locations causes relative sea-level rise to exceed global mean sea-level rise. Land uplift such as that found in Alaska and the Northwestern Pacific coast can reduce effects of global mean rise. The effects will be greatest and most immediate on low-relief, low-elevation parts of the U.S. coast along the Gulf of Mexico, mid-Atlantic states, northern Alaska, Hawaii, and island territories and especially on coasts containing deltas, coastal plains, tidal wetlands, bays, estuaries, and coral reefs. Beaches and wetlands on steep cliff coasts and shores backed with seawalls may be unable to move landward or maintain their landform with sea-level rise. Many areas of the coast are especially vulnerable because of the often detrimental effects of development on natural processes. High Confidence. The gradual inundation from recent sea-level rise is evident in many regions such as the mid-Atlantic and Louisiana where high tides regularly flood roads and areas that were previously dry, and in stands of “ghost forests,” in which trees are killed by intrusion of brackish water. High Confidence. Sea level change and storms are dominant driving forces of coastal change as observed in the geologic record of coastal landforms. Increasingly, sea-level rise will become a hazard for coastal regions because of continued global mean sea-level rise, including possibly accelerated rates of rise that increase risk to coastal regions. As the global climate continues to warm and ice sheets melt, coasts will become more dynamic and coastal cities and low-lying areas will be increasingly exposed to erosion, inundation, and flooding. High Confidence. No coordinated, interagency process exists in the U.S. for identifying agreed upon global mean sea-level rise projections for the purpose of coastal planning, policy, or management, even though this is a critical first step in assessing coastal impacts and vulnerabilities. High Confidence. Global sea level rose at a rate of 1.7 millimeters/year during the 20th century. The rate has increased to over 3 millimeters/year in the past 20 years and scientific studies suggest high confidence (>9 in 10 chance) that global mean sea level will rise 0.2 to 2 meters by the end of this century. Some regions such as Louisiana and the Chesapeake Bay will experience greater relative rise due to factors such as land subsidence, gravitational redistribution of ice-sheet meltwater, ocean circulation changes, and regional ocean thermostatic effects. Other regions undergoing land uplift, such as Alaska, will experience lesser sea-level rise. High Confidence. Variability in the location and time-of-year of storm genesis can influence landfalling storm characteristics, and even small changes can lead to large changes in landfalling location and impact. Although scientists have only low confidence in the sign of projected changes to the coast of storm-related hazards that depend on a combination of factors such as frequency, track, intensity, and storm size, any sea-level rise is virtually certain to exacerbate storm-related hazards. High Confidence. Although sea-level rise and climate change have occurred in the past, the increasing human presence in the coastal zone will make the impacts different for the future. Land use and other human activities often inhibit the natural response of physical processes and adaptation by plants and animals. In some areas, erosion and wetland loss are common because sediment budgets have been reduced, while, in other regions, excess sediment is in-filling harbors, channels, and bays. High Confidence. Observations continue to indicate an ongoing, warming-induced intensification of the hydrologic cycle that will likely result in heavier precipitation events and, combined with sea-level rise and storm surge, an increased flooding severity in some coastal areas, particularly the northeast U.S. Moderate Confidence. Temperature is primarily driving environmental change in the Alaskan coastal zone. Sea ice and permafrost make northern regions particularly susceptible to temperature change. For example, an increase of two degrees Celsius could basically transform much of Alaska from frozen to unfrozen, with extensive implications. Portions of the north and west coast of Alaska are seeing dramatic increases in the rate of coastal erosion and flooding due to sea ice loss and permafrost melting. As a consequence, several coastal communities are planning to relocate to safer locations. Relocation is a difficult decision that is likely to become more common in the future for many coastal regions. High Confidence. Methane is a primary greenhouse gas. Large reserves of methane are bound-up in Alaska’s frozen permafrost. These are susceptible to disturbance and methane release if the Arctic continues to warm. The additional methane released may result in even greater greenhouse warming of the atmosphere. High Confidence.

Book chapter↗

USGS2015

California State Waters Map Series — Offshore of Pacifica, California

In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow (to about 100 m) subsurface geology. The Offshore of Pacifica map area is located in northern California, on the Pacific coast of the San Francisco Peninsula about 10 kilometers south of the Golden Gate. The map area extends from Daly City, through Pacifica, to the small coastal community of Montara. Much of the coastal zone is managed by either the State of California or local governments, including Thornton Beach State Park, Mussel Rock Park, Pacifica State Beach, Gray Whale Cove State Beach, and Montara State Beach. The major structure in the transform boundary between the Pacific and North American tectonic plates, the northwest-striking San Andreas Fault, cuts through the map area, crossing the shoreline near Mussel Rock before continuing offshore. The epicenter of the great 1906 California earthquake is located on the offshore part of the San Andreas Fault Zone a few kilometers north of the map area. The map area is located at the northwest end of the Santa Cruz Mountains, much of which has been uplifted in the last 400,000 years. Southwest of the San Andreas Fault Zone, this uplift has resulted in a highly variable coastal morphology characterized by long, narrow beaches bounded by steep cliffs or marine terraces, small pocket beaches surrounded by rocky promontories, and steep, narrow coastal watersheds. Geologic units mapped along the coast include sedimentary, volcanic, and metamorphic rocks of the Franciscan Complex; Cretaceous granitic rocks; Tertiary sedimentary rocks; and Quaternary coastal marine terraces, deep-seated and shallow landslides, and beach and sand dune deposits, all of which contribute sediment to the coastal zone. In contrast to the more rural coastal zone to the south, the highly urbanized coastal zone north of Mussel Rock and the San Andreas Fault Zone is characterized by a narrow beach bounded by steep, 50- to 120-m-high cliffs made up of sand, silt, and clay of the Pliocene and Pleistocene Merced Formation, the source of numerous landslides. Two large landslides along “Northridge bluff” in 2003 and 2007 had estimated volumes of 305,800 to 382,300 m 3 and 120,800 m 3 , respectively. Coastal landslides also are an issue to the south between Mussel Rock and Mori Point, even as bluffs diminish in height and pocket beaches transition to a more continuous strand bounded by Quaternary-age dunes and low-lying marine terraces. Mori Point, a coastal promontory in Pacifica underlain by rocks of the Franciscan Complex, rises abruptly to a height of 90 m from the shoreline. Pocket beaches characterize the shoreline from Mori Point south to Shelter Cove, the largest of which, Pacifica State Beach, is at the mouth of San Pedro Creek. The coastal zone south of Pacifica, which stretches from Shelter Cove to Montara and includes Point San Pedro and Devils Slide, lies at the northwest end of San Pedro Mountain (underlain largely by early Tertiary sedimentary rocks) and Montara Mountain (underlain by Cretaceous granitic rocks). Elevations at Montara Mountain exceed 500 m just 4 km from the shoreline, and steep cliffs along the coast are as high as 275 m. This rugged terrain results in numerous rocky promontories, small pocket beaches, and large coastal landslides. Slope failures along Devils Slide are notorious for closing California Highway 1, creating such a large and persistent problem that the California Department of Transportation has bypassed this coastal section by tunneling through San Pedro Mountain; the tunnel was completed and the new section of highway opened in 2013. Coastal relief diminishes at Montara in the southernmost part of the map area, where the shoreline is bounded by 10- to 20-m-high marine terraces. Throughout the year, this part of the coast is exposed to the north Pacific swell, the southern swell, northwest wind waves, and local wind waves. The north Pacific swell dominates in winter months, having wave heights that range from 2 to 10 m at offshore buoys and wave periods that range from 10 to 25 s. During summer months, the largest waves come from the southern swell, generated by storms in the south Pacific and offshore of Central America. Characteristically, these swells have smaller wave heights (0.3–3 m) but similarly long wave periods (10–25 s). Local wind waves are most common from October to April, whereas northwest wind waves affect the coast throughout the year. These two wind-wave regimes typically have wave heights of 1 to 4 m and short wave periods (3–10 s). Unlike many other parts of the California coast where sediment is supplied primarily from river and (or) stream runoff, sediment supply to the offshore along this part of northern California is a complex mixture of (1) sand transported from the coast north of the Golden Gate, (2) sediment transported to the coast through the San Francisco Bay via the Golden Gate and then dispersed over the adjacent ebb-tide delta, and (3) varying volumes of sediment eroded from adjacent steep coastal bluffs caused by wave-induced landslides and other erosional events. Additionally, since the 1980s, coastal erosion south of the Golden Gate has increased substantially between Ocean Beach (on the west coast of San Francisco, about 5 km north of the map area) and Point San Pedro. The combined sediment load is transported southward along the coast by the generally north-to-south alongshore current, which develops in response to the energetic winter-wave climate associated with the north Pacific swell. Overall, beaches in the map area have a long-term erosional trend, except near Mussel Rock where a long-term accretionary trend may reflect increased sediment supply from landslides. Beach-front riprap armoring and retaining walls are used locally to protect the shoreline from seasonal storm waves, most notably between Mussel Rock and Mori Point. The continental shelf in the map area is about 40 km wide, with water depths at the shelf break that range from about 80 to 120 m. Within California’s State Waters, the midshelf to inner shelf areas are characterized by a relatively flat, shallow (water depths of as much as 44 m) seafloor that dips gently (about 0.2° to 0.3°) westward. The seafloor is composed primarily of unconsolidated Holocene sediment (marine deposits), as well as some nearshore bedrock outcrops that consist primarily of rocks of the Tertiary Purisima Formation and also Cretaceous plutonic rocks (granite or granodiorite).

California↗

USGS2012

Geophysical constraints on Washington convergent margin structure

Gravity and magnetic maps of western Washington reveal the lateral structure and fabric of the Washington Coast Range, Puget Basin, and southern Washington Cascade Range. The magnetic and gravity maps show large amplitude positive anomalies associated with the shallow but largely buried section of Washington Coast Range mafic rocks which are separated by negative anomalies over deep sedimentary basins. The positive anomalies indicate that the Coast Range mafic basement extends farther east than previously thought, at least as far east as the longitude of Seattle. Linear and steep gravity and magnetic gradients indicate many unmapped, often buried faults in the Washington Coast Range Province. Magnetic highs are also associated with mapped batholiths in the Cascade arc. Several magnetic highs observed east of the Coast Range rocks and west of these batholiths may be associated with buried Tertiary plutons or ophiolites. Two-dimensional gravity and magnetic modeling constrained with geological and other geophysical data indicate that the Coast Range Province rocks are about 1 km thick at the coast, thickening to as much as 30 km near their postulated eastern edge. A maximum boundary on the average density of the upper 15–20 km of the rocks that compose the Coast Range Province of 2920 kg/m 3 was established by the modeling, suggesting a composition largely of basalt and gabbro with little interbedded sediments. Under these rocks may be mantle or a subduction complex composed of dense mafic, ultramafic, and sedimentary rocks like that proposed to underlie Vancouver Island. Previous gravity models of the Washington margin include lower densities for the proposed subduction complex than for Vancouver Island, suggesting a lower component of mafic and ultramafic rocks than the rocks underlying Vancouver Island. However, my Washington model requires that the proposed subduction complex be more dense than the trench sediments and, therefore, that material denser than sediments be incorporated within it. The absence of continental mantle and the modeled wedge shape of the Coast Range Province upper crust suggest that erosion of the bottom of the overriding plate by subduction processes may have occurred.

Washington↗

USGS2021

Retreat, detour or advance? Understanding the movements of birds confronting the Gulf of Mexico

During migration, birds must locate stopover habitats that provide sufficient resources to rest and refuel while en route to the breeding or non-breeding area. Long-distance migrants invariably encounter inhospitable geographic features, the edges of which are often characterized by habitat limited in food and safety. In response, they often depart in directions inconsistent with reaching their destination, presumably searching for better habitat. We used automated radio telemetry to track 442 individuals of five species to investigate the behavior of migratory birds as they departed edge habitat along the northern Gulf of Mexico coast during autumn from 2008 to 2014. Most migrants (75%) retreated inland or detoured around rather than advanced across the Gulf, but this depended on bird species and fat-based energy stores. Most individuals in lean condition or of smaller bodied species tended to retreat or detour, rather than advance, when departing from the coast. Twenty-one percent of all birds that departed the coast in 2013–2014 were redetected over 45 km inland, providing a unique opportunity to compare stopover duration, departure times and travel speeds between migrants that retreat away from the coast and those that continue to advance toward their destination. Individuals that retreated the coast and were redetected inland spent ~1 day on the coast before retreating inland, where they spent 11 days before resuming migration. Further when those same individuals retreated from the coast, they departed around evening civil twilight, whereas those that advanced from inland habitats departed after evening civil twilight. Travel speeds were slower for individuals retreating inland compared to those advancing towards the coast from inland habitats. The differences between retreating and advancing individuals suggest how an individual's drive to feed or fly influences behavior. Our study illustrates how the sum of individual decisions can shape habitat use, landscape-scale movements and migration strategies.

Alabama↗

USGS1970

Aeromagnetic and gravity investigations of the Coastal Area and Continental Shelf of Liberia, West Africa, and their relation to continental drift

An aeromagnetic survey has shown the existence of several basins in which magnetic basement depths are greater than 5 km on the continental shelf off Liberia. Magnetic diabase of 176 to 192 m.y. (Jurassic) in age intruding the Paleozoic (?) rocks and overlain by younger rocks onshore requires the distinction between “magnetic basement” and “basement.” Several lines of evidence suggest that the Paleozoic(?) rocks are less than 1 km thick; this implies that the diabase does not introduce a large error in depth-to-basement estimates. The dikes or their extrusive equivalents are traceable, on the basis of the magnetic data, beneath the younger sedimentary rock in the basins to the edge of the continental slope. The magnetic data also delineate a second zone of diabase dikes 90 km inland, parallel to the coast, which cross the entire country. The intrusion of the younger dikes probably coincides with rifting at the beginning of the separation of Africa and South America, and the associated magnetic anomaly zones appear to be parallel with and continuous into the anomaly bands in the Atlantic. A major northeast-trending break in the magnetic fabric intersects the coast near 9° W. and is associated with Eburnean age rocks (about 2000 m.y.) to the southeast as contrasted with Liberian-age rocks (about 2700 m.y.) to the northwest. Change in magnetic fabric direction inland from northeast to northwest in the coastal area allows recognition of a boundary between the Liberian-age rocks inland and Pan-African-age (about 550 m.y.) rocks in the coastal area northwest of about 9° 20'W. Sets of north-northwest-and west-northwest—trending faults of 1 to 2 km vertical displacement cut the Cretaceous sedimentary rocks onshore and can be traced into the offshore basins. Vertical displacements of several kilometers in the magnetic basement underlying the continental shelf suggest a pattern of block faulting all along the coast and continental shelf. Negative Bouguer anomalies exist over two Cretaceous basins in the coastal area; a negative Bouguer anomaly exists over one of the basins southwest of Monrovia, as shown by a marine traverse, suggesting that Cretaceous or younger sedimentary rocks fill these basins also. A 50 to 60 mgal positive Bouguer anomaly area exists along the coast from Sierra Leone to Ivory Coast. This anomaly correlates with mafic granulites in the Monrovia region, where the gradient is too steep to be entirely due to crustal thickening at the continental margin and may be related to tectonic activity associated with the basins. The only major break in this positive anomaly above basement rocks along the entire coast of Liberia is over granite gneiss adjacent to (and presumably underlying) the only onshore basins on the Liberian coast. Three seismic reflection profiles support the interpretation of a substantial section of sedimentary rock offshore. A suggested sequence of events indicates tectonic activity in the periods about 2700, about 2000, and about 550 m.y. B.P.; uplift and exposure of deep crustal rocks; deposition of Paleozoic sediments; intrusion of diabase dikes in inland zones; intrusion of 176 to 192 m.y.-old dikes and sills accompanying separation of Africa and South and North America; block faulting along coast and continental shelf, and active sea-floor spreading; filling of basins in Cretaceous and Tertiary(?) time; basaltic extrusion on spreading sea floor and sedimentation on continental shelf and slope.

West Africa↗

USGS1983

Intrusive rocks and plutonic belts of southeastern Alaska, U.S.A

About 30 percent of the 175,000-km 2 area of southeastern Alaska is underlain by intrusive igneous rocks. Compilation of available information on the distribution, composition, and ages of these rocks indicates the presence of six major and six minor plutonic belts. From west to east, the major belts are: the Fairweather-Baranof belt of early to mid-Tertiary granodiorite; the Muir-Chichagof belt of mid-Cretaceous tonalite and granodiorite; the Admiralty-Revillagigedo belt of porphyritic granodiorite, quartz diorite, and diorite of probable Cretaceous age; the Klukwan-Duke belt of concentrically zoned or Alaskan-type ultramafic-mafic plutons of mid-Cretaceous age within the Admiralty-Revillagigedo belt; the Coast Plutonic Complex sill belt of tonalite of unknown, but perhaps mid-Cretaceous, age; and the Coast Plutonic Complex belt I of early to mid-Tertiary granodiorite and quartz monzonite. The minor belts are distributed as follows: the Glacier Bay belt of Cretaceous and(or) Tertiary granodiorite, tonalite, and quartz diorite lies within the Fair-weather-Baranof belt; layered gabbro complexes of inferred mid-Tertiary age lie within and are probably related to the Fairweather-Baranof belt; the Chilkat-Chichagof belt of Jurassic granodiorite and tonalite lies within the Muir-Chichagof belt; the Sitkoh Bay alkaline, the Kendrick Bay pyroxenite to quartz monzonite, and the Annette and Cape Fox trondhjemite plutons, all interpreted to be of Ordovician(?) age, together form the crude southern southeastern Alaska belt within the Muir-Chichagof belt; the Kuiu-Etolin mid-Tertiary belt of volcanic and plutonic rocks extends from the Muir-Chichagof belt eastward into the Admiralty-Revillagigedo belt; and the Behm Canal belt of mid- to late Tertiary granite lies within and next to Coast Plutonic Complex belt II. In addition, scattered mafic-ultramafic bodies occur within the Fairweather-Baranof, Muir-Chichagof, and Coast Plutonic Complex belts I and II. Palinspastic reconstruction of 200 km of right-lateral movement on the Chatham Strait fault does not significantly change the pattern of the major belts but does bring parts of the minor mid-Tertiary and Ordovician(?) belts closer together. The major belts are related to the stratigraphic-tectonic terranes of Berg, Jones, and Coney (1978) as follows: the Fairweather-Baranof belt is largely in the Chugach, Wrangell (Wrangellia), and Alexander terranes; the Muir-Chichagof belt is in the Alexander and Wrangell terranes; the Admiralty-Revillagigedo belt is in the Gravina and Taku terranes; the Klukwan-Duke belt is in the Gravina, Taku, and Alexander terranes; the Coast Plutonic Complex sill belt is probably between the Taku and Tracy Arm terranes; and the Coast Plutonic Complex belts I and II are in the Tracy Arm and Stikine terranes. Significant metallic-mineral deposits are spatially related to certain of these belts, and some deposits may be genetically related. Gold, copper, and molybdenum occurrences may be related to granodiorites of the Fairweather-Baranof belt. Magmatic copper-nickel deposits occur in the layered gabbro within that belt. The Juneau gold belt, which contains gold, silver, copper, lead, and zinc occurrences, parallels and lies close to the Coast Plutonic Complex sill belt; iron deposits occur in the Klukwan-Duke belt; and porphyry molybdenum deposits occur in the Behm Canal belt. The Muir-Chichagof belt of mid-Cretaceous age and the Admiralty-Revillagigedo belt of probable Cretaceous age are currently interpreted as possible magmatic arcs associated with subduction events. In general, the other belts of intrusive rocks are spatially related to structural discontinuities, but genetic relations, if any, are not yet known. The Coast Plutonic Complex sill belt is probably related to a post-Triassic, pre-early Tertiary suture zone that nearly corresponds to the boundary between the Tracy Arm and Taku terranes. The boundary between the Admiralty-Revillagigedo and Muir-Chichagof belts coincides nearly with the Seymour Canal-Clarence Strait lineament and also is probably a major post-Triassic suture.

Alaska↗

USGS2012

Statewide summary for Texas

The Texas coast (Figure 1) consists of complex and diverse ecosystems with a varying precipitation gradient. The northernmost portion of the coast, extending from Sabine Lake to Galveston Bay, is composed of salt, brackish, intermediate, and fresh marshes, with humid flatwoods inland (Moulton and others, 1997). Coastal prairies are found across the entire coast. From Galveston Bay to Corpus Christi Bay, rivers feed into large bays and estuarine ecosystems. Barrier islands and peninsulas exist along the coast from Galveston Bay to the Mexican border. The southernmost portion of the coast is composed of wind-tidal flats and the hypersaline Laguna Madre. The Laguna Madre lacks rivers and has little rainfall and restricted inlet access to the Gulf. Semiarid rangeland and irrigated agricultural land can be found inland. Approximately 6 million people live in Texas’ coastal counties (U.S. Census Bureau, 2010; Texas GLO, 2013). Seventy percent of the state’s industry and commerce occurs within 160.9 km (100 miles) of the coast (Moulton and others, 1997). Texas ports support 1.4 million jobs and generate $6.5 billion in tax revenues (Texas GLO, 2013). Chemical and petroleum production and marine commerce thrive on the Texas coast. Agriculture, grazing, commercial and recreational fishing, and recreation and tourism are strong industries along the coast and in adjacent areas; oil and gas production, agriculture, and tourism are the state’s three largest industries.

Texas↗

USGS1979

Surface faults in the gulf coastal plain between Victoria and Beaumont, Texas

Displacement of the land surface by faulting is widespread in the Houston-Galveston region, an area which has undergone moderate to severe land subsidence associated with fluid withdrawal (principally water, and to a lesser extent, oil and gas). A causative link between subsidence and fluid extraction has been convincingly reported in the published literature. However, the degree to which fluid withdrawal affects fault movement in the Texas Gulf Coast, and the mechanism(s) by which this occurs are as yet unclear. Faults that offset the ground surface are not confined to the large (>6000-km 2 ) subsidence “bowl” centered on Houston, but rather are common and characteristic features of Gulf Coast geology. Current observations and conclusions concerning surface faults mapped in a 35,000-km 2 area between Victoria and Beaumont, Texas (which area includes the Houston subsidence bowl) may be summarized as follows: (1) Hundreds of faults cutting the Pleistocene and Holocene sediments exposed in the coastal plain have been mapped. Many faults lie well outside the Houston-Galveston region; of these, more than 10% are active, as shown by such features as displaced, fractured, and patched road surfaces, structural failure of buildings astride faults, and deformed railroad tracks. (2) Complex patterns of surface faults are common above salt domes. Both radial patterns (for example, in High Island, Blue Ridge, Clam Lake, and Clinton domes) and crestal grabens (for example, in the South Houston and Friendswood-Webster domes) have been recognized. Elongate grabens connecting several known and suspected salt domes, such as the fault zone connecting Mykawa, Friendswood-Webster, and Clear Lake domes, suggest fault development above rising salt ridges. (3) Surface faults associated with salt domes tend to be short (<5 km in length), numerous, curved in map view, and of diverse trend. Intersecting faults are common. In contrast, surface faults in areas unaffected by salt diapirism are frequently mappable for appreciable distances (>10 km), occur singly or in simple grabens, have gently sinuous traces, and tend to lie roughly parallel to the ENE-NE “coastwise” trend common to regional growth faults identified in subsurface Tertiary sediments. (4) Evidence to support the thesis that surface scarps are the shallow expression of faults extending downward into the Tertiary section is mostly indirect, but nonetheless reasonably convincing. Certainly the patterns of crestal grabens and radiating faults mapped on the surface above salt domes are more than happenstance; analogous fault patterns have been documented around these structures at depth. Similarly, some of the long surface faults not associated with salt domes seem to have subsurface counterparts among known regional growth faults documented through well logs and seismic data. Correlations between surface scarps and faults offsetting subsurface data are not conclusive because of the large vertical distances (1900- 3800 m) involved in making the most of the inferred connections. Nevertheless, the large number of successful correlations - in trend, movement sense, and position - suggests that many surface scarps represent merely the most recent displacements on faults formed during the Tertiary. (5) Upstream-facing fault scarps in this region of low relief can be significant impediments to streams. Locally, both abandoned, mud-filled Pleistocene distributary channels and, more commonly, Holocene drainage lines still occupied by perennial streams reflect the influence of faulting on their development. Some bend sharply near faults and have tended to flow along or pond against the base of scarps; others meander within topographically expressed grabens. Such evidence for Quaternary displacement of the ground surface is widespread in the Texas Gulf coast. In the general, however, streams in areas now offset by faulting show no disruption of their courses where they cross fault scarps. Such scarps are probably very young, and where they can be demonstrated to partly or wholly predate fluid withdrawal, very recent natural fault activity is indicated. (6) Early aerial photographs (1930) of the entire region and topographic maps (1915-16 surveys) of Harris County (Houston and vicinity) show that many faults had already displaced the land surface at a time when appreciable pressure declines in subjacent strata were localized to relatively few areas of large-scale pumping. Prehistoric faulting of the land surface, as noted above, appears to have affected much of the Texas Gulf Coast. (7) A relation between groundwater extraction and current motion on active faults is suspected because of the increased incidence of ground failure in the Houston-Galveston subsidence bowl. This argument is weakened somewhat by recognition of numerous surface faults, some of them active today, far beyond the periphery of the strongly subsiding area. Moreover, tilt beam records from two monitored faults in northwest Houston and accounts of fault damage from local residents demonstrate a complex, episodic nature of fault creep which can only partially be correlated with groundwater production. Nevertheless, although specific mechanisms are in doubt, the extraction of groundwater from shallow (<800-m) sands is probably a major factor in contributing to current displacement of the ground surface in the Houston-Galveston region. Within this large area, the number of faults recognizable from aerial photographs has increased at least tenfold between 1930 and 1970. Elsewhere in the Texas Gulf Coast only a moderate increase has been noted, some of which is possibly attributable to oil and gas production. Surface fault density in the Houston-Galveston region is far greater than in any other area of the Texas Gulf Coast investigated to date. A plausible explanation for these differences is that large overdrafts of groundwater over an extended period of time in the Houston-Galveston region have stimulated fault activity there. Throughout the Texas Gulf Coast, however, a natural contribution to fault motion remains a distinct possibility.

Texas↗

USGS2015

California State Waters Map Series — Offshore of Bodega Head, California

Introduction In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow subsurface geology. The Offshore of Bodega Head map area is located in northern California, about 70 km north of San Francisco and about 80 km south of Point Arena. The onshore part of the map area is largely undeveloped, used primarily for recreation, farms and ranches, and a few wineries. The small town of Bodega Bay, located on the east side of Bodega Harbor, is the largest cultural center. Bodega Harbor is an important commercial fishing base and, in season, an active sport fishing and recreation harbor. Much of the coastline from Bodega Head north to about 6 km north of the Russian River is part of Sonoma Coast State Park. The Offshore of Bodega Head map area includes two California Marine Protected Areas, the Bodega Head State Marine Reserve and the northern part of the Bodega Head State Marine Conservation Area. Additionally, the inland parts of two large estuaries in the map area, Estero Americano and Estero de San Antonio, have been designated as State Marine Recreational Management Areas. The map area is cut by the northwest-striking San Andreas Fault, the right-lateral transform boundary between the North American and Pacific plates. This fault juxtaposes rocks of the Jurassic and Cretaceous Franciscan Complex on the northeast with Cretaceous granitic rocks on the southwest, and it has an estimated slip rate of about 17 to 25 mm/yr in this area. The devastating great 1906 California earthquake (M7.8) is thought to have nucleated on the San Andreas Fault offshore of San Francisco, about 80 km south of Bodega Head, with the rupture extending northward through the Offshore of Bodega Head map area and an additional 220 km to the south flank of Cape Mendocino. North of the mouth of Salmon Creek, the coast and shoreline are rugged and scenic, characterized by flights of uplifted marine terraces, rocky promontories, nearshore sea stacks, kelp-rich coves, and both pocket beaches and longer beach strands, the latter of which include Wrights Beach and Portuguese Beach. The coast has lower relief between the mouth of Salmon Creek and Mussel Point, where South Salmon Creek Beach is backed by a large (about 4 km 2 ) complex of coastal sand dunes. The enormous volume of sand on the beach and in the dune field is derived by southward littoral drift from the Russian River, Salmon Creek, and smaller coastal watersheds. The sediment is trapped by protruding bedrock at Mussel Point, which represents the south end of the Russian River littoral cell. Bodega Head is underlain by Cretaceous granitic rocks, and its shoreline is variously characterized by relatively low-lying terraces, steep and high bluffs, and a few pocket beaches. East of Bodega Head, Doran Beach (part of Doran Regional Park) is a 1.7-km-long sand spit that forms the north boundary of Bodega Bay and the south boundary of Bodega Harbor. The coast south of Doran Beach on the east flank of Bodega Bay is composed of rocky bluffs, hummocky marine terraces, and a few small pocket beaches. The bluffs are underlain by sheared rocks of the Franciscan Complex and are highly susceptible to landslides. This section of coast includes two prominent watersheds, Estero Americano and Estero de San Antonio, which drain westward into Bodega Bay. The offshore part of the Offshore of Bodega Head map area is characterized by an extensive, rugged and rocky shelf underlain by Cretaceous granitic rocks. This rocky terrain, centered offshore of Bodega Head, extends northwestward for about 15 km, from the south edge of the map area (where it forms the west boundary of Bodega Bay) to the northern-central part of the map area offshore of the mouth of Salmon Creek. This rocky seafloor reaches water depths of 40 to 80 m and is overlain by young sediment. Circulation over the shelf and seafloor in the map area (and in the broader central California region) is dominated by the southward-flowing California Current, the eastern boundary current of the North Pacific Gyre. Associated upwelling brings cool, nutrient-rich waters to the surface, resulting in high biological productivity. Persistent northwest winds are sometimes weak or absent during the fall and winter, causing the California Current to move farther offshore so that the shelf is affected by the Davidson Current, a weaker northward-flowing countercurrent. As a result, net flow over the continental shelf is commonly southeastward during the spring and summer and northwestward during the fall and winter. Throughout the year, this part of the northern California coast is exposed to four wave climate regimes: the north Pacific swell, the southern swell, northwest wind waves, and local wind waves. The north Pacific swell dominates in winter months (typically November through March). During summer months, the largest waves come from the southern swell, generated by storms in the south Pacific and offshore of Central America. Northwest wind waves affect the coast throughout the year, whereas local wind waves are most common from October to April. Potential marine benthic habitats in the Offshore of Bodega Head map area include unconsolidated continental-shelf sediments, mixed continental-shelf substrate, and hard continental-shelf substrate. Rocky-shelf outcrops and rubble are considered to be promising potential habitats for rockfish and lingcod, both of which are recreationally and commercially important species.

California↗

USGS2014

A global assessment of the conservation status of the American Oystercatcher Haematopus palliatus

The American Oystercatcher Haematopus palliatus is the most widely distributed of the four oystercatcher species in the Western Hemisphere. Its range covers almost the entire Atlantic Coast from northeastern United States to southern Argentina; on the Pacific Coast it is found from northern Mexico to central Chile. This assessment covers the entire range of the species, and is not intended to serve as a substitute or update for conservation plans that cover the U.S. Atlantic and Gulf Coast populations. Readers are advised to refer to those plans, available at www.whsrn.org, for more detailed information about U.S. populations. The subspecific taxonomy of H. palliatus is far from clear, but five races are recognized in this assessment, primarily to facilitate reference to specific populations (Fig. 1). These are nominate H. p. palliatus (coasts of eastern and southern United States; eastern Mexico; Pacific and Caribbean coasts of Central America; the Caribbean; and northern and eastern South America); H. p. frazari (Gulf of California and western Mexico); H. p. pitanay (coast of western South America); H. p. durnfordi (coast of southeast South America) and H. p. galapagensis (Galapagos Islands). The Galapagos race may deserve species status. Based on a review of existing population estimates and an extrapolation of data from quantitative surveys throughout its range, revised estimates are given for the populations of all five subspecies, and a total population of about 43,000 individuals. The nominate race is the most abundant with an estimated population size of about 20,000 individuals, while the least abundant is H. p. galapagensis , with just 300 individuals estimated. Biogeographic population estimates were used to determine 1% threshold levels and identify sites of regional and global conservation importance. A total of 20 sites have been identified for H. p. palliatus , 5 for H. p. frazari , 10 for H. p. pitanay and 10 for H. p. durnfordi . No key sites were identified for H. p. galapagensis as it is found in low density scattered throughout the islands. Of these 45 sites, 14 have counts that surpass the 1% level of the global population, and are thus of global conservation significance for the species. Because the species is a dispersed breeder, the 1% threshold is of limited value in identifying key breeding sites. For the time being, these have been defined as sites holding 20 or more breeding pairs; 17 such sites have been identified, with all but four in the United States. It is hoped that a more rigorous approach for identifying key breeding sites can be developed in the future. As an obligate coastal species, American Oystercatcher is at risk from widespread habitat loss due to coastal development, and recreational activities that lead to nest disturbance and increased predation. This is exacerbated by the species’ low population size and low reproductive success. Climate change also poses a significant future threat, especially with regard to sea-level rise. To address these threats, conservation actions are proposed that focus on increased legal protection for the species and on the conservation of key sites and important habitats. Conservation could include implementing beneficial management practices, such as restoration of nest and roost sites, controlling predation, and reducing disturbance. Education and outreach programs are needed throughout the species’ range, especially for beach users and urban planners. Training programs will be necessary to ensure successful implementation of many of the priority conservation actions. Finally, a key first step in conserving this species across its range is the creation of a H. palliatus Working Group. Modelled after the U.S. American Oystercatcher Working Group this organization could unite researchers, conservationists, and educators from across the hemisphere to foster coordinated research, conservation action, and monitoring as outlined in this assessment.

International Wader Studies↗

USGS2006

Projecting future sea level

California’s coastal observations and global model projections indicate that California’s open coast and estuaries will experience increasing sea levels over the next century. Sea level rise has affected much of the coast of California, including the Southern California coast, the Central California open coast, and the San Francisco Bay and upper estuary. These trends, quantified from a small set of California tide gages, have ranged from 10–20 centimeters (cm) (3.9–7.9 inches) per century, quite similar to that estimated for global mean sea level. So far, there is little evidence that the rate of rise has accelerated, and the rate of rise at California tide gages has actually flattened since 1980, but projections suggest substantial sea level rise may occur over the next century. Climate change simulations project a substantial rate of global sea level rise over the next century due to thermal expansion as the oceans warm and runoff from melting land-based snow and ice accelerates. Sea level rise projected from the models increases with the amount of warming. Relative to sea levels in 2000, by the 2070–2099 period, sea level rise projections range from 11–54 cm (4.3–21 in) for simulations following the lower (B1) greenhouse gas (GHG) emissions scenario, from 14–61 cm (5.5–24 in) for the middle-upper (A2) emission scenario, and from 17–72 cm (6.7–28 in) for the highest (A1fi) scenario. In addition to relatively steady secular trends, sea levels along the California coast undergo shorter period variability above or below predicted tide levels and changes associated with long-term trends. These variations are caused by weather events and by seasonal to decadal climate fluctuations over the Pacific Ocean that in turn affect the Pacific coast. Highest coastal sea levels have occurred when winter storms and Pacific climate disturbances, such as El Niño, have coincided with high astronomical tides. This study considers a range of projected future global sea level rises in examining possible impacts at California coastal and estuarine stations. Two climate models and three scenarios considered in this scenarios study provide a set of possible future weather and short-period climate fluctuations, and a range of potential long-term sea level rise values. A range of mean sea level rise was considered in combination with weather and El Niño fluctuations extracted from two global climate models and two GHG emissions scenarios. The mean sea level rise values, determined from a survey of several climate models, range from approximately 10–80 cm (3.9–31 in) between 2000 and 2100. The middle to higher end of this range would substantially exceed the historical rate of sea level rise of 15–20 cm (5.9–7.9 in)per century observed at San Francisco and San Diego during the last 100 years. Gradual sea level rise progressively worsens the impacts of high tides and the surge and waves associated with storms. The potential for impacts of future sea level rise was assessed from the occurrence of hourly sea level extremes. The occurrence of extreme events follows a sharply escalating pattern as the magnitude of future sea level rise increases. The confluence of Low barometric pressures from storms and the presence large waves at the same time substantially increases the likelihood of high, damaging sea levels along the California coast. Similarly, astronomical tides and disturbances in sea level that are caused by weather and climate fluctuations are x transmitted into the San Francisco Bay and Delta, and on into the lower reaches of the Sacramento River. In addition to elevating Bay and Delta sea levels directly through inverse barometer and wind effects, storms may generate heavy precipitation and high fresh water runoff and cause floods in the Sacramento/San Joaquin Delta, increasing the potential for inundation of levees and other structures. There may also be increased risk of levee failure due to the hydraulics and geometry of these structures. Rising sea levels from climate change will increase the frequency and duration of extreme high water levels, causing historical coastal and San Francisco Bay/Delta structure design criteria to be exceeded.

California↗

USGS2025

Estimated average annualized tsunami losses for the United States

Tsunami hazards are substantial threats to coastal communities across the United States (U.S.) and its territories. U.S. states and territories collaborate through the National Tsunami Hazard Mitigation Program (NTHMP) to develop their own tsunami-hazard information for outreach and evacuation planning. An effort to curate this tsunami-hazard information to support comprehensive risk analysis at the national level has not yet been completed. In support of this effort, the Federal Emergency Management Agency (FEMA) collaborated with the NTHMP, the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey (USGS) starting in 2023. This collaboration included the collection and analysis of existing tsunami hazard data and methods in the U.S. Tsunami subject matter experts identified and selected scientifically defensible methods for estimating the risks to buildings and populations in coastal communities. These efforts may support decision making regarding resilience policies, priorities, strategies and funding levels. Tsunamis can be triggered by earthquakes, subaerial or submarine landslides, volcanic eruptions, glacial calving, near-earth objects, weather or other events. These events can cause severe destruction, injuries, and loss of life due to powerful currents and flooding. Tsunamis pose a substantial threat to the western United States and all U.S. territories, as described below. ■ Hawaii is threatened by distant tsunamis due to its central location in the Pacific Ocean basin and has a history of local events. ■ Alaska, particularly the Aleutian Islands, faces local tsunami threats due to proximity to the Alaska-Aleutian Subduction Zone, as well as distant tsunamis from around the Pacific Ocean basin. ■ The western coast of the U.S. is threatened by distant tsunamis from around the Pacific Ocean basin and local source tsunamis from earthquakes generated within the Cascadia Subduction Zone in the Pacific Northwest. ■ American Samoa faces local tsunami threats from earthquakes generated in the nearby Tonga Trench, as well as distant tsunami threats. ■ Guam and the Commonwealth of the Northern Mariana Islands are threatened by local tsunamis from the nearby Mariana Subduction Zone, as well as distant sources from around the Pacific Ocean Basin. ■ Puerto Rico and the United States Virgin Islands are threatened by multiple local and distant tsunami sources, such as the Puerto Rico Trench (PRT), given their location in the complex seismic region of the Caribbean Sea. Several historical events stand out because of their catastrophic impacts. ■ In the Pacific Northwest, the 1700 Cascadia earthquake caused a tsunami that affected coastal Native American communities, though the extent of the damage is not fully documented (Ludwin, et al., 2005). ■ In Puerto Rico, the 1918 earthquake triggered a tsunami that caused $77 million in damage in 2022 dollars and 116 fatalities, primarily along the western coast (Coffman et al., 1982). ■ The 1946 Aleutian Islands earthquake triggered a massive tsunami that devastated Hilo, Hawaii, killing 158 people and resulting in approximately $375 million in damage (adjusted to 2022 dollars) (Fisher et al., 2023). ■ The 1964 Alaska earthquake (M 9.2) generated tsunamis that caused severe destruction in some communities across Alaska, Oregon, and California. This disaster led to a total of 124 fatalities and approximately $2.9 billion in property damage (adjusted to 2022 dollars) (Brocher et al., 2014) (Alaska Science Center, 2024). ■ In American Samoa, a tsunami generated by the 2009 Samoa earthquake (Mw 8.1) caused widespread devastation, resulting in 34 confirmed fatalities (Apatu et al., 2013) and economic losses exceeding $160 million (adjusted to 2022 dollars) (DHS, 2011). More recent events, including the 2010 Chile earthquake, the 2011 Japan earthquake, and the 2022 Tonga volcanic eruption, resulted in millions of dollars in damage to numerous ports and harbors in the U.S. South Pacific territories, Hawaii, and along the west coast of the U.S. (Lynett, et al., 2022) (Wilson, et al., 2013). Since these events, the expansion of the built environment in lowlying areas along the coast has increased the exposure of buildings and people, thereby further escalating community risk from tsunamis. This report provides a comprehensive national assessment of earthquake-generated tsunami risk. It does not include impacts from tsunamis generated by landslides, volcanic eruptions, glacial calving, near-earth objects, weather, or other events. This study is based on the best available hazard data from the U.S. Pacific Coast (California, Oregon and Washington), Alaska, Hawaii, U.S. Pacific Territories (American Samoa, Guam and Commonwealth of the Northern Mariana Islands) and Caribbean Territories (Puerto Rico and United States Virgin Islands). Tsunami risks associated with states along the East Coast, Gulf Coast, and Great Lakes are not included in this study because Hazus 6.1 software (FEMA 2024a) does not currently include the ability to analyze tsunami risk in those states. Once modeling capabilities and tsunami hazard data become available for additional states, FEMA may incorporate these data into future editions of this study.

Alaska, California, Hawaii Oregon, Washington↗

USGS1984

Shoreface translation and the Holocene stratigraphic record: Examples from Nova Scotia, the Mississippi Delta and eastern Australia

Classic descriptive models of barrier sedimentation have been developed with data from the Atlantic and Gulf coasts of the United States. These models are dominated by low to moderate rates of relative sea level (RSL) rise and wave energy. Barriers respond by landward recycling of sediment through the mechanism of shoreface retreat. Sedimentation processes on the central coast of New South Wales (N.S.W.), Australia, consist of rapid RSL rise in early Holocene times followed by a stillstand since 6500 B.P. Wave energy is relatively high year-round and sand sources for barrier formation are only found on the inner shelf. Barrier sedimentation on the central coast of N.S.W. exhibits a thick, composite sequence composed of a basal marine transgressive sand overlain by regressive beach and dune facies. The Louisiana coast surrounding the Mississippi delta is underlain by compacting deltaic muds which generate very rapid rates of RSL rise. The Louisiana coast experiences low wave energy punctuated by high-energy tropical and extra-tropical storm events. Barrier sediments accumulate from the erosion of deltaic headlands and undergo a transformation from subaerial barrier island systems to subaqueous shoals located on the inner shelf. Drumlins experience coastal erosion on the Eastern Shore of Nova Scotia and provide a sediment source for compartmented estuary mouth barriers. An ongoing, moderate rise of RSL results from the passage of a glacial forebulge. Wave energy is intermediate between Louisiana and N.S.W. and displays a seasonal pattern dominated by frequent winter storms. Coastal barrier sedimentation is episodic, consisting of a period of beach ridge progradation followed by barrier destruction and re-establishment further landward. The three contrasting sedimentary sequences found in examples from Louisiana, N.S.W. and Nova Scotia indicate that presently available sedimentation models from locations such as the middle Atlantic or Texas coasts of the United States may only represent well-documented regional case studies. A true generalised coastal sedimentation model is required which can identify the parameters controlling vertical and horizontal translation of the depositional surface and provide relationships between these parameters which quantitatively predict the genesis, distribution and geometry of coastal sedimentary facies.

Marine Geology↗

USGS2009

Coastline degradation as an indicator of global change

Finding a climate change signal on coasts is more problematic than often assumed. Coasts undergo natural dynamics at many scales, with erosion and recovery in response to climate variability such as El Niño, or extreme events such as storms and infrequent tsunamis. Additionally, humans have had enormous impacts on most coasts, overshadowing most changes that one can presently attribute directly to climate change. Each area of coast is experiencing its own pattern of relative sea-level change and climate change, making discrimination of the component of degradation that results from climate change problems. The best examples of a climate influence are related to temperature rise at low and high latitudes, as seen by the impacts on coral reefs and polar coasts, respectively. Observations through the twentieth century demonstrate the importance of understanding the impacts of sea-level rise and climate change in the context of multiple drivers of change; this will remain a challenge under a more rapidly changing climate. Nevertheless, there are emerging signs that climate change provides a global threat—sea ice is retreating, permafrost in coastal areas is widely melting. Reefs are bleaching more often, and the sea is rising—amplifying widespread trends of subsidence and threatening low-lying areas. To enhance the sustainability of coastal systems, management strategies will also need to address this challenge, focusing on the drivers that are dominant at each section of coast. Global warming through the twentieth century has caused a series of changes with important implications for coastal areas. These include rising temperatures, rising sea level, increasing CO2 concentrations with an associated reduction in seawater pH, and more intense precipitation on average.

Book chapter↗

USGS2011

Scenarios for earthquake-generated tsunamis on a complex tectonic area of diffuse deformation and low velocity: The Alboran Sea, Western Mediterranean

The tsunami impact on the Spanish and North African coasts of the Alboran Sea generated by several reliable seismic tsunamigenic sources in this area was modeled. The tectonic setting is complex and a study of the potential sources from geological data is basic to obtain probable source characteristics. The tectonic structures considered in this study as potentially tsunamigenic are: the Alboran Ridge associated structures, the Carboneras Fault Zone and the Yusuf Fault Zone. We characterized 12 probable tsunamigenic seismic sources in the Alboran Basin based on the results of recent oceanographical studies. The strain rate in the area is low and therefore its seismicity is moderate and cannot be used to infer characteristics of the major seismic sources. These sources have been used as input for the numerical simulation of the wave propagation, based on the solution of the nonlinear shallow water equations through a finite-difference technique. We calculated the Maximum Wave Elevations, and Tsunami Travel Times using the numerical simulations. The results are shown as maps and profiles along the Spanish and African coasts. The sources associated with the Alboran Ridge show the maximum potential to generate damaging tsunamis, with maximum wave elevations in front of the coast exceeding 1.5 m. The Carboneras and Yusuf faults are not capable of generating disastrous tsunamis on their own, although their proximity to the coast could trigger landslides and associated sea disturbances. The areas which are more exposed to the impact of tsunamis generated in the Alboran Sea are the Spanish coast between Malaga and Adra, and the African coast between Alhoceima and Melilla.

Marine Geology↗

USGS1999

Occurrence and transport of total mercury and methyl mercury in the Sacramento River Basin, California

Mercury poses a water-quality problem for California's Sacramento River, a large river with a mean annual discharge of over 650 m3/s. This river discharges into the San Francisco Bay, and numerous fish species of the bay and river contain mercury levels high enough to affect human health if consumed. Two possible sources of mercury are the mercury mines in the Coast Ranges and the gold mines in the Sierra Nevada. Mercury was once mined in the Coast Ranges, west of the Sacramento River, and used to process gold in the Sierra Nevada, east of the river. The mineralogy of the Coast Ranges mercury deposits is mainly cinnabar (HgS), but elemental mercury was used to process gold in the Sierra Nevada. Residual mercury from mineral processing in the Sierra Nevada is mainly in elemental form or in association with oxide particles or organic matter and is biologically available. Recent bed-sediment sampling, at sites below large reservoirs, showed elevated levels of total mercury (median concentration 0.28 ??g/g) in every large river (the Feather, Yuba, Bear, and American rivers) draining the Sierra Nevada gold region. Monthly sampling for mercury in unfiltered water shows relatively low concentrations during the nonrainy season in samples collected throughout the Sacramento River Basin, but significantly higher concentrations following storm-water runoff. Measured concentrations, following storm-water runoff, frequently exceeded the state of California standards for the protection of aquatic life. Results from the first year of a 2-year program of sampling for methyl mercury in unfiltered water showed similar median concentrations (0.1 ng/l) at all sampling locations, but with apparent high seasonal concentrations measured during autumn and winter. Methyl mercury concentrations were not significantly higher in rice field runoff water, even though rice production involves the creation of seasonal wetlands: higher rates of methylation are known to occur in stagnant wetland environments that have high dissolved carbon.Mercury poses a water-quality problem for California's Sacramento River, a large river with a mean annual discharge of over 650 m3/s. This river discharges into the San Francisco Bay, and numerous fish species of the bay and river contain mercury levels high enough to affect human health if consumed. Two possible sources of mercury are the mercury mines in the Coast Ranges and the gold mines in the Sierra Nevada. Mercury was once mined in the Coast Ranges, west of the Sacramento River, and used to process gold in the Sierra Nevada east of the river. The mineralogy of the Coast Ranges mercury deposits is mainly cinnabar (HgS), but elemental mercury was used to process gold in the Sierra Nevada. Residual mercury from mineral processing in the Sierra Nevada is mainly in elemental form or in association with oxide particles or organic matter and is biologically available. Recent bed-sediment sampling, at sites below large reservoirs, showed elevated levels of total mercury (median concentration 0.28 ??g/g) in every large river (the Feather, Yuba, Bear, and American rivers) draining the Sierra Nevada gold region. Monthly sampling for mercury in unfiltered water shows relatively low concentrations during the nonrainy season in samples collected throughout the Sacramento River Basin, but significantly higher concentrations following storm-water runoff. Measured concentrations, following storm-water runoff, frequently exceeded the state of California standards for the protection of aquatic life. Results from the first year of a 2-year program of sampling for methyl mercury in unfiltered water showed similar median concentrations (0.1 ng/l) at all sampling locations, but with apparent high seasonal concentrations measured during autumn and winter. Methyl mercury concentrations were not significantly higher in rice field runoff water, even though rice production involves the creation of seasonal wetlands: higher rates of methylation a

Journal of Geochemical Exploration↗