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At least 1,657 records · Page 92Linked to original sources
USGS1992

Utility of radiocarbon-dated stratigraphy in determining late Holocene earthquake recurrence intervals, upper Cook Inlet region, Alaska

During the great 1964 earthquake, parts of coastal southern Alaska subsided tectonically as much as 2 m, and this led to burial of high-intertidal organic-rich marshes by low-intertidal and tidal silt. In the tectonically active part of upper Cook Inlet, the presence of stratigraphic sections containing numerous prehistoric interbedded layers of peat and silt suggests that such stratigraphy resulted when marshes and forests were similarly inundated and buried by intertidal and tidal sediment as a result of great, prehistoric earthquakes. This study tests the feasibility of using buried, radiocarbon-dated, late Holocene peat layers that are exposed in the intertidal zone of upper Cook Inlet to determine earthquake recurrence intervals, because estimates of the recurrence intervals of past earthquakes are needed for evaluation of the potential for future earthquakes. In a reconnaissance study of interbedded peat and silt, 65 conventional radiocarbon dates from peat and other organic material in 25 measured sections in the intertidal zone and one drillhole were used. Radiocarbon ages from the tops of peat beds cluster weakly but may indicate that regional subsidence events recurred at irregular intervals between about 200 to 800 radiocarbon yr within the past 3,200 radiocarbon yr. Conversion to calibrated ages does not alter this range substantially but may extend both ends of the age range. Coeval and correlative stratigraphy and radiocarbon data in the buried peat layers of upper Cook Inlet strongly suggest sudden, subsidence-induced layering. Because of problems associated with conventional radiocarbon dating, the complex stratigraphy of the study area, the tectonic setting, and regional changes in sea level, conclusions from the study do not permit precise identification of the timing and recurrence of paleoseismic events.

Alaska↗
USGS2007

Beach morphology monitoring in the Columbia River Littoral Cell: 1997-2005

This report describes methods used, data collected, and results of the Beach Morphology Monitoring Program in the Columbia River Littoral Cell (CRLC) from 1997 to 2005. A collaborative group primarily consisting of the US Geological Survey and the Washington State Department of Ecology performed this work. Beach Monitoring efforts consisted of collecting topographic and bathymetric horizontal and vertical position data using a Real Time Kinematic Differential Global Positioning System (RTK-DGPS). Sediment size distribution data was also collected as part of this effort. The monitoring program was designed to: 1) quantify the short- to medium-term (seasonal to interannual) beach change rates and morphological variability along the CRLC and assess the processes responsible for these changes; 2) collect beach state data (i.e., grain size, beach slope, and dune/sandbar height/position) to enhance the conceptual understanding of CRLC functioning and refine predictions of future coastal change and hazards; 3) compare and contrast the scales of environmental forcing and beach morphodynamics in the CRLC to other coastlines of the world; and 4) provide beach change data in a useful format to land use managers.

Oregon, Washington↗
USGS2017

Basal debris entrainment and transport in glaciers of southwestern Bylot Island, Canadian Arctic

Glaciers on southwestern Bylot Island in the Canadian Arctic flow from an alpine setting in high-grade crystalline Archean terrane, on to coastal lowlands underlain by clastic sedimentary strata of Cretaceous to Tertiary age. We have used the contrasting mineralogy of the substrate as a tool to study subglacial entrainment and transport of debris in two large piedmont glaciers on Bylot Island. High chlorite/ and mica-illite/smectite ratios indicate that most basal debris is derived from crystalline rocks underlying the upper reaches of the glaciers. The subglacial accretion of Cretaceous-Tertiary sediments appears restricted to the lowermost part of the basal zone and is most noticeable near the glaciers' termini. Ice associated with discrete silty-sandy debris layers is characterized by an isotopic signature indicative of refreezing of meltwater at the glacier sole. The compositional, textural and isotopic characteristics of basal sediment and ice lead us to conclude that subglacial entrainment through basal ice accretion occurs in both the upper and marginal parts of the glaciers.

Bylot Island↗
USGS2019

A 50-year Sr/Ca time series from an enclosed, shallow-water Guam coral: In situ monitoring and extraction of a temperature trend, annual cycle, and ENSO and PDO signals

Located on the northern edge of the West Pacific Warm Pool and having a developed economy and modern infrastructure, Guam is well positioned and equipped for obtaining natural records of the west Pacific maritime paleoclimate. This study was a proof of concept to explore whether useful climate proxy records might be obtained from coral at readily accessible, even if geochemically nonoptimal, coastal sites. A 50-year Sr/Ca record (1960–2010) was thus obtained from a shallow-water, near-shore Porites lutea colony at a recreational facility inside Guam's Apra Harbor and compared with local and regional meteorological records, including the El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) indices. The accessibility of the site enabled documentation of relevant environmental variables for 16 months (September 2009–December 2010): seawater δ 18 O, pH, seawater cations, and nitrate. Time series of seawater δ 18 O, pH, and cations show evidence of freshwater input from direct rainfall and stream discharge into the harbor. An anomalously higher mean and variable concentrations of Ba suggest the presence of river-borne, fine-grained terrigenous sediment. Nevertheless, the Sr/Ca time series reproduces a long-term warming trend seen in historical records of local air temperature and regional sea-surface temperature (SST) and closely tracks the ENSO and PDO indices over the entire 50-year record. The consistency of the results with Guam's historical instrumental records, previous coral δ 18 O results from Guam obtained by others, and previous Sr/Ca proxy results for SST in similar environments elsewhere demonstrate that accessible near-shore sites—where environmental conditions can be monitored—can produce useful Sr/Ca records of local and regional climate phenomena.

Journal of Coastal Research↗
USGS2023

2023 Coastal master plan: ICM-wetlands – Submerged aquatic vegetation (SAV) updates

Submerged aquatic vegetation (SAV) provides critical structural habitat for valuable nekton and wildlife species across coastal ecosystems and can buffer the negative effects of land loss. Landscape change and restoration efforts across coastal Louisiana can impact the occurrence, coverage, and species assemblages of SAV, and changes to these foundational species can have cascading impacts across food webs. To support the 2023 Coastal Master Plan efforts, a unique SAV model was developed to assess coverage and occurrence of SAV across aquatic waterbodies in response to environmental variables evaluated. This effort created a spatial model describing the probability of presence of SAV across the study area in response to changing conditions over the modeled time period. To develop the initial coverage data layer, we used remotely sensed Normalized Difference Vegetation Index (NDVI) and modified Normalized Difference Water Index (mNDWI) data from 2015-2018 to identify areas containing variable vegetation and water spectral reflectance. Key environmental variables evaluated included total suspended sediments (TSS), salinity, and physical exposure. Seasonal estimates for TSS and salinity were used, as research indicates that seasonal environmental variability is a significant driver for SAV establishment. Seasonal salinity was derived from Coast-wide Reference Monitoring Station (CRMS) data, and seasonal TSS was estimated from hyperspectral imagery. Estimates of physical exposure have previously been provided by calculating fetch (the distance across water over which waves can propagate), but this proved to be too computationally intensive to be feasible, and we found distance to land to be a reasonable proxy for exposure. To represent geographic conditions and historical factors influences on SAV establishment and occurrence (e.g., variables too numerous and complex to model) we developed a basin variable that served as a proxy for complex historical, or prior, conditions, determined by the forested, fresh, intermediate, brackish, or saline (FFIBS) score. The final model included spring TSS, spring salinity, distance to land, and the basin prior. The model performed well for the area evaluated, correctly classifying SAV (as present or absent) 89% of the time (Kappa = 580). SAV probability of presence responded as expected to change in these environmental variables, with likelihood of occurrence decreasing in response to increasing spring TSS, spring salinity, and distance to land. However, the model was more accurate at predicting absence (true negative = 0.940) than predicting presence (true positive = 0.626), suggesting that the scale of the model may limit the ability to predict presence. Moreover, the simplicity of the model limited the accuracy in highly dynamic environments, for example near the outflow of diversions or areas of significant changes in salinity or TSS. Through incorporating underwater communities like SAV, this master plan provides a holistic view of coastal change and restoration. To create healthy ecological structure and function in wetland habitats, the submergent communities must be considered alongside the emergent habitats. As the benefits of SAV are increasingly recognized, both here in Louisiana and beyond, SAV restoration and the use of SAV communities in assessing and improving ecological condition are becoming more common.

Louisiana↗
USGS1996

Denitrification and nitrogen transport in a coastal aquifer receiving wastewater discharge

Denitrification and nitrogen transport were quantified in a sandy glacial aquifer receiving wastewater from a septage-treatment facility on Cape Cod, MA. The resulting groundwater plume contained high concentrations of NO3- (32 mg of NL-1), total dissolved nitrogen (40.5 mg of N L-1), and dissolved organic carbon (1.9 mg of C L-1) and developed a central anoxic zone after 17 months of effluent discharge. Denitrifying activity was measured using four approaches throughout the major biogeochemical zones of the plume. Three approaches that maintained the structure of aquifer materials yielded comparable rates: acetylene block in intact sediment cores, 9.6 ng of N cm-3 d-1 (n = 61); in situ N2 production, 3.0 ng of N cm-3 d-1 (n = 11); and in situ NO3- depletion, 7.1 ng of N cm-3 d-1 (n = 3). In contrast, the mixing of aquifer materials using a standard slurry method yielded rates that were more than 15-fold higher (150 ng of N cm-3 d-1, n = 16) than other methods. Concentrations and ??15N of groundwater and effluent N2, NO3-, and NH4+ were consistent with the lower rates of denitrification determined by the intact-core or in situ methods. These methods and a plumewide survey of excess N2 indicate that 2-9% of the total mass of fixed nitrogen recharged to the anoxic zone of the plume was denitrified during the 34-month study period. Denitrification was limited by organic carbon (not NO3-) concentrations, as evidenced by a nitrate and carbon addition experiment, the correlation of denitrifying activity with in situ concentrations of dissolved organic carbon, and the assessments of available organic carbon in plume sediments. Carbon limitation is consistent with the observed conservative transport of 85-96% of the nitrate in the anoxic zone. Although denitrifying activity removed a significant amount (46250 kg) of fixed nitrogen during transport, the effects of aquifer denitrification on the nitrogen load to receiving ecosystems are likely to be small (<10%).

Environmental Science & Technology↗
USGS2023

A 1300-year microfaunal record from the Beaufort Sea shelf indicates exceptional climate-related environmental changes over the last two centuries

The environments of Arctic Ocean nearshore areas experience high intra- and inter-annual variability, making it difficult to evaluate the impact of anthropogenic warming. However, a sediment record from the southern Canadian Beaufort Sea allowed us to reconstruct the impacts of climate and environmental changes over the last 1300 years along the northern Yukon coast, Canada. The coring site (PG2303; 69.513°N, 138.895°W; water depth 32 m) is located in the Herschel Basin, where high sedimentation rates (0.1–0.5 cm a −1 ) allowed analyses at sub-centennial to decadal resolutions. Benthic foraminiferal, ostracod, and tintinnid assemblages, as well as the stable isotope composition of the foraminifera Elphidium clavatum and Cassidulina reniforme were used as paleoclimatic and ecological indicators, while the age model was based on the combined radiometric data of 14 C, 210 Pb and 137 Cs . From ca 700 to 1050 CE, our data suggest penetration of offshore shelf-break waters inferred by the dominance of C. reniforme followed by the relatively abundant Triloculina trihedra in the foraminiferal assemblages as both species are associated with stable saline conditions. Afterwards, the occurrence of ostracods Kotoracythere arctoborealis and Normanicythere leioderma suggests influx of Pacific-sourced waters until ca. 1150 CE. From ∼1150–1650 CE, persistent frigid waters, limited sediment supply, and low abundances of microfossils suggest cold conditions with pervasive annual sea-ice cover that may have restricted upwelling of oceanic waters. After ∼1800 CE, the co-occurrence of Tintinnopsis fimbriata and bacterial/complex organic carbon feeder foraminifera ( Quinqueloculina stalkeri , Textularia earlandi and Stetsonia horvathi ), suggest an increased influence of freshwater rich in particulate organic matter, which may be related to the spreading of the Mackenzie River plume and/or increased coastal permafrost erosion during longer ice-free seasons. Based on these proxy data, the shift at ∼1800 CE marks the onset of regional warming, which further intensified after ∼1955 CE, likely in response to the anthropogenic forcing.

Alaska, Yukon↗
USGS1998

Response of a small Oregon estuary to coseismic subsidence and postseismic uplift in the past 300 years

The Sixes River estuary, south coastal Oregon, sits above the locked portion of the Cascadia subduction zone, which intermittently releases in subduction-zone earthquakes. One such Cascadia earthquake ∼300 years ago caused subsidence and a tsunami at the Sixes estuary. The subsidence raised the river's base level, resulting in an ∼3 km upstream shift of the head of tide of the estuary. At the upper end of the expanded estuary, more than 4 m of overbank sediment was deposited in the first decades or century after subsidence. Subsequent incision through the overbank deposits accompanied the gradual emergence of the estuary, and attendant downstream shift of the head of tide, as relative sea level fell in response to interseismic uplift.

Geology↗
USGS2006

Geomorphic effects of large debris flows and flash floods, northern Venezuela, 1999

A rare, high-magnitude storm in northern Venezuela in December 1999 triggered debris flows and flash floods, and caused one of the worst natural disasters in the recorded history of the Americas. Some 15,000 people were killed. The debris flows and floods inundated coastal communities on alluvial fans at the mouths of a coastal mountain drainage network and destroyed property estimated at more than $2 billion. Landslides were abundant and widespread on steep slopes within areas underlain by schist and gneiss from near the coast to slightly over the crest of the mountain range. Some hillsides were entirely denuded by single or coalescing failures, which formed massive debris flows in river channels flowing out onto densely populated alluvial fans at the coast. The massive amount of sediment derived from 24 watersheds along 50 km of the coast during the storm and deposited on alluvial fans and beaches has been estimated at 15 to 20 million m3. Sediment yield for the 1999 storm from the approximately 200 km2 drainage area of watersheds upstream of the alluvial fans was as much as 100,000 m3/km2. Rapid economic development in this dynamic geomorphic environment close to the capital city of Caracas, in combination with a severe rain storm, resulted in the death of approximately 5% of the population (300,000 total prior to the storm) in the northern Venezuelan state of Vargas. ?? 2006 Gebru??der Borntraeger.

Zeitschrift fur Geomorphologie, Supplementband↗
USGS1997

Bathymetric comparisons adjacent to the Louisiana barrier islands: Processes of large-scale change

This paper summarizes the results of a comparative bathymetric study encompassing 150 km of the Louisiana barrier-island coast. Bathymetric data surrounding the islands and extending to 12 m water depth were processed from three survey periods: the 1880s, the 1930s, and the 1980s. Digital comparisons between surveys show large-scale, coherent patterns of sea-floor erosion and accretion related to the rapid erosion and disintegration of the islands. Analysis of the sea-floor data reveals two primary processes driving this change: massive longshore transport, in the littoral zone and at shoreface depths; and increased sediment storage in ebb-tidal deltas. Relative sea-level rise, although extraordinarily high in the study area, is shown to be an indirect factor in causing the area's rapid shoreline retreat rates.

Louisiana↗
USGS2023

A numerical investigation of the mechanisms controlling salt intrusion in the Delaware Bay Estuary

Salinity intrusion in coastal systems is mainly controlled by freshwater inflows. However, extreme events like drought, low-pressure storms, and longer-term sea level rise can exacerbate the landward salt migration and threaten economic infrastructure and ecological health. Along the eastern seaboard of the United States, approximately 13 million people rely on the water resources of the Delaware River basin. Salinity intrusion is actively managed through river discharge targets to suppress the propagation of the salt front (∼0.52 daily averaged psu line). The purpose of this study is to examine the mechanisms controlling the location of the salt front in the Delaware Bay estuary using a calibrated three-dimensional hydrodynamic model, the Coupled Ocean Atmosphere Wave and Sediment Transport modeling system. This study explored how river discharge, tidal motions, interactions with bathymetric and topographic features, and meteorological events affected the location of the salt front. The model was forced with tides, subtidal water levels, bulk atmospheric conditions, and waves. Compared with the observationally derived location of the salt front line, the model captured the major dynamics throughout the year and performed particularly well during times of low discharge, when salinity intruded up estuary at a constant rate of 0.4 km /day . The daily average salt front moved almost 16 km (10 mi) within a neap-spring tidal cycle, and low-pressure storm systems were found to move the daily averaged salt front by 13–16 km in one event.

Delaware, New Jersey, Pennsylvania↗
USGS2018

Quaternary sea-level history and the origin of the northernmost coastal aeolianites in the Americas: Channel Islands National Park, California, USA

Along most of the Pacific Coast of North America, sand dunes are dominantly silicate-rich. On the California Channel Islands, however, dunes are carbonate-rich, due to high productivity offshore and a lack of dilution by silicate minerals. Older sands on the Channel Islands contain enough carbonate to be cemented into aeolianite. Several generations of carbonate aeolianites are present on the California Channel Islands and represent the northernmost Quaternary coastal aeolianites on the Pacific Coast of North America. The oldest aeolianites on the islands may date to the early Pleistocene and thus far have only been found on Santa Cruz Island. Aeolianites with well-developed soils are found on both San Miguel Island and Santa Rosa Island and likely date to the middle Pleistocene. The youngest and best-dated aeolianites are located on San Miguel Island and Santa Rosa Island. These sediments were deposited during the late Pleistocene following the emergence of marine terraces that date to the last interglacial complex (~ 120,000 yr to ~ 80,000 yr). Based on radiocarbon and luminescence dating, the ages of these units correspond in time with marine isotope stages [MIS] 4, 3, and 2. Sea level was significantly lower than present during all three time periods. Reconstruction of insular paleogeography indicates that large areas to the north and northwest of the islands would have been exposed at these times, providing a ready source of carbonate-rich skeletal sands. These findings differ from a previously held concept that carbonate aeolianites are dominantly an interglacial phenomenon forming during high stands of sea. In contrast, our results are consistent with the findings of other investigators of the past decade who have reported evidence of glacial-age and interstadial-age aeolianites on coastlines of Australia and South Africa. They are also consistent with observations made by Darwin regarding the origin of aeolianites on the island of St. Helena, in the South Atlantic Ocean, more than a century and a half ago.

California↗
USGS2005

Carbon, nitrogen, and phosphorus accumulation in floodplains of Atlantic Coastal Plain rivers, USA

Net nutrient accumulation rates were measured in riverine floodplains of the Atlantic Coastal Plain in Virginia, Maryland, and Delaware, USA. The floodplains were located in watersheds with different land use and included two sites on the Chickahominy River (urban), one site on the Mattaponi River (forested), and five sites on the Pocomoke River (agricultural). The Pocomoke River floodplains lie along reaches with natural hydrogeomorphology and on reaches with restricted flooding due to channelization and levees. A network of feldspar clay marker horizons was placed on the sediment surface of each floodplain site 3–6 years prior to sampling. Sediment cores were collected from the material deposited over the feldspar clay pads. This overlying sediment was separated from the clay layer and then dried, weighed, and analyzed for its total carbon (C), nitrogen (N), and phosphorus (P) content. Mean C accumulation rates ranged from 61 to 212 g·m −2 ·yr −1 , N accumulation rates ranged from 3.5 to 13.4 g·m −2 ·yr −1 , and P accumulation rates ranged from 0.2 to 4.1 g·m −2 ·yr −1 among the eight floodplains. Patterns of intersite variation in mineral sediment and P accumulation rates were similar to each other, as was variation in organic sediment and C and N accumulation rates. The greatest sediment and C, N, and P accumulation rates were observed on Chickahominy River floodplains downstream from the growing metropolitan area of Richmond, Virginia. Nutrient accumulation rates were lowest on Pocomoke River floodplains that have been hydraulically disconnected from the main channel by channelization and levees. Sediment P concentrations and P accumulation rates were much greater on the hydraulically connected floodplain immediately downstream of the limit of channelization and dense chicken agriculture of the upper Pocomoke River watershed. These findings indicate that (1) watershed land use has a large effect on sediment and nutrient retention in floodplains, and (2) limiting the hydraulic connectivity between river channels and floodplains minimizes material retention by floodplains in fluvial hydroscapes.

Delaware, Maryland, Virginia↗
USGS2002

Trends in late Maastrichtian calcareous nannofossil distribution patterns, Western North Atlantic margin

First and last occurrences of several Maastrichtian calcareous nannofossil species are shown to be diachronous across paleodepth and paleoenvironment using the graphic correlation method. Calcareous nannofossil assemblages examined from eleven cores from a deep- to shallow-water transect along the eastern United States Atlantic margin document that the first occurrence of Micula murus (Martini 1961) Bukry 1973 is diachronous, appearing 2.0 million years earlier in open ocean sites than in shallow marine sites. The first occurrence (FO) of Lithraphidites kennethii Perch-Nielsen 1984 is also nonsynchronous, appearing in the deep ocean before its FO in neritic waters. The last occurrence (LO) of L. praequadratus Roth 1978 is diachronous across paleodepth, going locally extinct first in deeper water. The LO of Watznaueria bybelliae Self-Trail 1999 is also diachronous, going locally extinct first in shallow-water settings. Ceratolithoides amplector Burnett 1997, C. pricei Burnett 1997, C. self-trailiae Burnett 1997, C. ultimus Burnett 1997, Cribrocorona gallica (Stradner 1963) Perch-Nielsen 1973. Micula praemurus (Bukry 1973) Stradner and Steinmetz 1984, Pseudomicula quadratus Perch-Nielsen et al. 1978, and Semihololithus spp. are present consistently in common to frequent abundances in ODP holes 1050C and 1052E on the Blake Nose, but they are rare or absent from neritic sections in Coastal Plain cores. It is apparent that these species flourished in an open ocean setting, suggesting that differences in assemblage abundance and diversity between deep ocean and nearshore areas were controlled by paleoceanographic factors. These species are not used for biostratigraphy, but may be useful indicators of open ocean conditions. The line of correlation (LOC) for nine Coastal Plain cores clearly defines the Cretaceous-Tertiary (K/T) boundary unconformity at the top of the Maastrichtian section (Peedee Formation) and the Campanian-Maastrichtian (C/M) unconformity at the base of the Maastrichtian section (Peedee/Donoho Creek formational contact). The K/T boundary unconformity is undulatory in nature; updip Maastrichtian sections have been stripped to a greater depth than the downdip sections. The uppermost Campanian, all of the lowermost Maastrichtian, and the basal upper Maastrichtian sediments are missing from the study area.

Micropaleontology↗
USGS2012

Bathymetry and acoustic backscatter data collected in 2010 from Cat Island, Mississippi

Scientists from the U.S. Geological Survey (USGS), St. Petersburg Coastal and Marine Science Center (SPCMSC), in collaboration with the U.S. Army Corps of Engineers (USACE), conducted geophysical and sedimentological surveys around Cat Island, the westernmost island in the Mississippi-Alabama barrier island chain (fig. 1). The objectives of the study were to understand the geologic evolution of Cat Island relative to other barrier islands in the northern Gulf of Mexico and to identify relationships between the geologic history, present day morphology, and sediment distribution. This report contains data from the bathymetry and side-scan sonar portion of the study collected during two geophysical cruises. Interferometric swath bathymetry and side-scan sonar data were collected aboard the RV G.K. Gilbert September 7-15, 2010. Single-beam bathymetry was collected in shallow water around the island (< 2 meter (m)) from the RV Streeterville from September 28 to October 2, 2010, to cover the data gap between the landward limit of the previous cruise and the shoreline. This report serves as an archive of processed interferometric swath and single-beam bathymetry and side scan sonar data. GIS data products include a 50-m cell size interpolated gridded bathymetry surface, trackline maps, and an acoustic side-scan sonar image. Additional files include error analysis maps, Field Activity Collection System (FACS) logs, and formal Federal Geographic Data Committee (FDGC) metadata.

Alabama;Mississippi↗
USGS2007

High-resolution topographic, bathymetric, and oceanographic data for the Pleasure Point area, Santa Cruz County, California: 2005-2007

The County of Santa Cruz Department of Public Works and the County of Santa Cruz Redevelopment Agency requested the U.S. Geological Survey (USGS) Western Coastal and Marine Geology Team (WCMG) to provide baseline geologic and oceanographic information on the coast and inner shelf at Pleasure Point, Santa Cruz County, California. The rationale for this proposed work is a need to better understand the environmental consequences of a proposed bluff stabilization project on the beach, the nearshore and the surf at Pleasure Point, Santa Cruz County, California. To meet these information needs, the USGS-WCMG Team collected baseline scientific information on the morphology and waves at Pleasure Point. This study provided high-resolution topography of the coastal bluffs and bathymetry of the inner shelf off East Cliff Drive between 32nd Avenue and 41st Avenue. The spatial and temporal variation in waves and their breaking patterns at the study site were documented. Although this project did not actively investigate the impacts of the proposed bluff stabilization project, these data provide the baseline information required for future studies directed toward predicting the impacts of stabilization on the sea cliffs, beach and nearshore sediment profiles, natural rock reef structures, and offshore habitats and resources. They also provide a basis for calculating potential changes to wave transformations into the shore at Pleasure Point.

California↗
USGS2025

Landsliding follows signatures of wildfire history and vegetative regrowth in a steep coastal shrubland

Five years after the deadly and destructive 9 January 2018 Montecito debris flows (Santa Barbara County, California, USA), an atmospheric river storm on 9 January 2023 triggered widespread landsliding that affected many of the same drainages in the Santa Ynez Mountains. Using high-resolution aerial imagery, we identified >10,000 landslides over an ∼160 km 2 area. Most of the landslides were shallow (<1 m in depth) translational debris slides that initiated on steep (∼40°), south-facing hillslopes, with the highest incidence of landsliding in a sandstone-dominated bedrock unit. The landslides mobilized into debris flows and delivered substantial quantities of sediment downstream, which contributed to costly infrastructure impairments. We detected order-of-magnitude differences in landslide density across the study area that could not be attributed to variations in geomorphology (topographic aspect and slope), geology (bedrock type), or hydrology (seasonal antecedent rainfall, peak hourly storm rainfall intensity, total storm rainfall), which are usually considered relevant factors for shallow landsliding. Rather, we found that vegetation regrowth following wildfire was likely a relevant factor associated with the highly variable landslide densities. Hillslopes with less and different types of vegetation regrowth after fire appear to have been more susceptible to shallow landslides. We identify a possible vegetation control on postfire landsliding, which highlights an opportunity for hypothesis testing using more advanced techniques to track the evolution of vegetation cover and vegetation type in steep shrubland environments following wildfire.

California↗
USGS1975

Metallogenic provinces of the southeastern Pacific region

Metalliferous mineral deposits of the southeastern Pacific region include: (1) hydrothermal, magmatic, and sedimentary deposits of the Andean region, one of the great mineral belts of the world; 2) Scattered hydrothermal mineral occurrences in the Antarctic Peninsula; and 3) metal-enriched pelagic sediments, ferromanganese nodules, and volcanic rocks(?) in the southeast Pacific basin. Andean metalliferous deposits, the chief concern of this report, are for the most part spatially and genetically related to calc-alkaline plutons, sub-volcanic intrusions, and volcanic rocks emplaced during the Andean orogeny of Late Triassic to Quaternary age. These deposits are components of a single metallogenic province superimposed on two or more pre-Andean metallogenic provinces that are indicated by scattered deposits of Paleozoic and Precambrian(?) age. Occurrences in the Antarctic Peninsula are of age and origin similar to the deposits in the Andes and are considered to belong to the Andean province. The Andean metallogenic province may be divided into several subprovinces, each parallel to the Andes and the continental margin and each having a dominant metal or suite of metals. The central Andes of Peru, northern Chile, and Bolivia, which contain the greatest concentration of exploitable deposits and the greatest variety of ore types, have as many as five linear partly overlapping subprovinces. These sub-provinces, from west to east (Pacific coast to the eastern Andean front), are characterized, respectively, by deposits of : 1) iron; 2) copper, with or without associated gold; 3) polymetallic base metals (zinc, lead, copper), generally containing silver; 4) tin; and 5) gold. Iron deposits chiefly are near the coast in central to northern Chile and in southern Peru. The copper and polymetallic provinces are characterized by abundant deposits in the central Andean region but comparatively few scattered deposits in the north (Ecuador, Colombia, and Venezuela) and in southern Chile and Argentina. Scattered gold-rich veins and placers occur along the western Andean front and coastal region, the general area of the copper province, from central Chile to northern Colombia. Similar deposits occur along a discontinuous belt in the eastern Andes from Bolivia to Ecuador and in the central Andes of Colombia. Tin deposits are almost wholly restricted to the eastern Andes of Bolivia. The position and age distribution of plutonic and volcanic rocks and associated metalliferous deposits of the Andes indicate presence of an active subduction zone in this region since at least Late Triassic time. Magmas of the calc-alkaline igneous rocks are believed to have formed chiefly by partial melting of mantle, oceanic sediments, and oceanic crust along the Benioff zone at depths of 100 to 200 km. Plutonic and volcanic rocks show a general though nonuniform progression of decreasing age from west to east. Rocks of Jurassic and Cretaceous age are most abundant near the coast, whereas those of Tertiary and Quaternary age dominate in the Andes. Locally, intrusive rocks and ore deposits of widely different ages are juxtaposed. Metals of the ore deposits associated with the calc-alkaline rocks were supplied by the source rocks in the Benioff zone, some of which probably had been previously enriched in certain metals at the ancestral East Pacific Rise and were mobilized or assimilated from metal-rich zones in the overlying mantle and continental crust by magmas rising from the Benioff zone.

Open-File Report↗