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USGS2014

Coastal tectonics on the eastern margin of the Pacific Rim: Late Quaternary sea-level history and uplift rates, Channel Islands National Park, California, USA

The Pacific Rim is a region where tectonic processes play a significant role in coastal landscape evolution. Coastal California, on the eastern margin of the Pacific Rm, is very active tectonically and geomorphic expressions of this include uplifted marine terraces. There have been, however, conflicting estimates of the rate of late Quaternary uplift of marine terraces in coastal California, particularly for the orthern Channel Islands. In the present study, the terraces on San Miguel Island and Santa Rosa Island were mapped and new age estimates were generated using uranium-series dating of fossil corals and amino acid geochronology of fossil mollusks. Results indicate that the 2nd terrace on both islands is ~120 ka and the 1st terrace on Santa Rosa Island is ~80 ka. These ages correspond to two global high-sea stands of the Last Interglacial complex, marine isotope stages (MIS) 5.5 and 51, respectively. The age estimates indicate that San Miguel Island and Santa Rosa Island have been tectonically uplifted at rates of 0.12e0.20 m/ka in the late Quaternary, similar to uplift rates inferred from previous studies on neighboring San Cruz Island. The newly estimated uplift rates for the northern Channel Islands are, however, an order of magnitude lower than a recent study that generated uplift rates from an offshore terrace dating to the Last Glacial period. The differences between the estimated uplift rates in the present study and the offshore study are explained by the magnitude of glacial isostatic adjustment (GIA) effects that were not known at the time of the earlier study. Set in the larger context of northeastern Pacific Rim tectonics, Channel Islands uplift rates are higher than those coastal localities on the margin of the East Pacific Rise spreading center, but slightly lower than those of most localities adjacent to the Cascadia subduction zone. The uplift rates reported here for the northern Channel Islands are similar to those reported for most other localities where strike-slip tectonics are dominant, but lower than localities where restraining bends (such as the Big Bend of the San Andreas Fault) result in crustal shortening.

California↗

USGS2023

Multiscale assessment of shoreline evolution in the US Pacific Northwest via a process-based model

Prediction of shoreline evolution in coastal environments is critical to aid adaptation strategy planning for coastal communities. To perform reliable predictions, process-based shoreline change models have recently gained popularity in many applications. The study region here, Tillamook County, Oregon, on the US Pacific Northwest coast, has recently been experiencing elevated shoreline erosion rates. The inherent uncertainties driving coastal change, e.g., sea-level rise and changing patterns of storminess, emphasize the need for robust shoreline evolution predictions in this region. To this end, we applied CoSMoS-COAST, an ensemble data-assimilated shoreline model that simulates short- and long-term shoreline change processes. We calibrated and validated the model using the hindcasted wave time series and observed shoreline positions and found a strong correlation between the number of observed shoreline positions and the model’s hindcasting skill. Moreover, results revealed an alongshore close-to-uniform shoreline change rate in the past several years, mainly driven by short-term, wave-driven processes. So far CoSMoS-COAST has performed satisfactorily with the spatially sparse supply of quality historical shoreline positions in our application. Moreover, this model resolves various components (e.g., short- and long-term processes) in the shoreline change sufficiently. This study represents a starting point in the long-term projection of shoreline evolution throughout the entire PNW (Oregon and Washington) coastline since Tillamook County features the majority of the coastal settings present in other coastal regions in the PNW.

Oregon↗

USGS1992

Evidence from Cd/Ca ratios in foraminifera for greater upwelling off California 4,000 years ago

UPWELLING of nutrient-rich Pacific deep water along the North American west coast is ultimately driven by the temperature difference between air masses over land and over the ocean. The intensity of upwelling, and biological production in the region, could therefore be affected by anthropogenic climate change. Examination of the geological record is one way to study the link between climate and upwelling. Because Pacific deep water is enriched in cadmium, dissolved cadmium concentrations in coastal water off central California reflect the intensity of upwelling. By demonstrating that the Cd/Ca ratio in the shell of a benthic foraminifer, Elphidiella hannai, is proportional to the Cd concentration in coastal water, we show here that foraminiferal Cd/Ca ratios can be used to detect past changes in mean upwelling intensity. Examination of a sediment core from the mouth of San Francisco Bay reveals that foraminiferal Cd/Ca decreased by about 30% from 4,000 years ago to the present, probably because of a reduction in coastal upwelling. This observation is consistent with predictions of atmospheric general circulation models that northwesterly winds, which drive upwelling, became weaker over this period as summer insolation of the Northern Hemisphere decreased.

Nature↗

USGS2025

Assessment of channel morphology, hydraulics, and bedload transport along the Siletz River, western Oregon

Significant Findings Chinook salmon ( Oncorhynchus tshawytscha ) and Pacific lamprey ( Entosphenus tridentatus ) are native, anadromous fish species in the Siletz River Basin, western Oregon, that face many threats to their survival in freshwater and the ocean. The Confederated Tribes of Siletz Indians of Oregon seek to mitigate freshwater threats to Chinook salmon and Pacific lamprey, where possible, with habitat conservation and restoration efforts. This study was conducted to assist the Confederated Tribes of Siletz Indians of Oregon in documenting and understanding the hydrogeomorphic processes shaping present-day habitat conditions and assessing future habitat implications for Chinook salmon and Pacific lamprey along the main-stem Siletz River. As such, this study focused on understanding geomorphic processes and patterns of channel change, including lateral and vertical adjustments in channel position and changes in bed-material sediment (sands, gravels, and cobbles that mantle the channel bed), which collectively determine overall patterns of channel morphology and fluvial habitats. Objective One was to evaluate lateral changes in channel position, vertical changes in bed elevation, and longitudinal patterns in bed-material particle size along the Siletz River using detailed channel maps developed from aerial photographs collected from 1939 to 2016, long-term records of stage and discharge collected by the U.S. Geological Survey (USGS) near the City of Siletz, and sediment particle size data. Objective Two was to assess hydraulic conditions using one- and two-dimensional hydraulic models and transport capacity of bed-material sediment using bedload transport models and sediment particle size data for a range of discharge conditions. Objective Three was to identify potential burrowing habitat for lamprey larvae (PBH) along the Siletz River network and provide insights in local factors influencing PBH along the main-stem Siletz River. The overall findings are synthesized to describe habitat implications for Chinook salmon and Pacific lamprey under present-day and future conditions. Results of Objective One, an evaluation of changes in channel position and bed elevations and longitudinal patterns in bed-material particle size along the Siletz River, include the following From 1939 to 2016, channel planform and the mapped area of gravel bars did not change considerably along the 97.2-kilometers (km) of Siletz River between Elk Creek and Millport Slough, except for in short sections generally less than 1 km long. This inherent lateral channel stability results from the resistant bedrock and terraces that bound most of the channel and limit lateral changes in channel position. Intermittent sections along the study reach where the active channel widened at channel bends displayed noticeable planform changes and increases in mapped bar area. From water year (WY; a 12-month period from October 1 through September 30 and named for the year in which it ends) 1906 to 2021, changes in the stage-discharge relation interpreted as rising and lowering channel bed levels were observed at the USGS streamgage 14305500 (Siletz River at Siletz, OR) in response to floods (such as high flows in February 1996 and January 2002 that exceeded 0.1 and 0.667 annual exceedance probabilities [AEP] events, respectively). However, the rating curve representing the stage-discharge relation did not change in response to high-magnitude floods between 2007 and 2021. Along the approximately 54-km of the Siletz River between Moonshine Park and the Bulls Bag area, surficial particle distributions varied considerably between sampling sites in response to changes in channel width and gradient, sediment inputs from tributaries, and basin geology. Despite this variability, median particle sizes tended to decrease in size in the downstream direction over the 54 km. Results of Objective Two, an evaluation of hydraulic and bedload transport conditions along the Siletz River, include the following The most substantial increases in maximum and mean water velocity and bedload sediment transport capacity occurred at events between the 0.995 and 0.50 AEPs. Events of these magnitudes occur approximately every 1–2 years. Smaller events (0.995 AEP) are generally contained by the banks of the main channel, whereas larger events (0.50 AEP) generally spill over the banks and inundate high-elevation bar and low-elevation floodplain surfaces. Multiple smaller floods within a WY that exceed the 0.995 and 0.50 AEPs (such as in WY 1996) can transport as much or more bed-material sediment than a single, higher magnitude event (such as the maximum event recorded in WY 2000 with an estimated AEP of around 0.002). Bedload transport capacity generally exceeds sediment supply (greater than 2 millimeters [mm]) for most of the study area from Wildcat Creek to the City of Siletz as evidenced by substantial in-channel bedrock. Despite overall conditions of limited sediment supply, transport capacity still varies considerably within and between years with discharge magnitude and spatially in relation to local hydraulics imposed by bedrock, channel morphology, and human infrastructure (such as bridges). Results of Objective Three, an analysis of PBH for lamprey larvae, include the following About 28 percent of the Siletz River network meets the mean annual suspended sediment loads and channel slope criteria for PBH. Along the main-stem Siletz River, in-channel bedrock outcrops and high transport capacity are expected to further constrain PBH. Together, these results suggest that most of the Siletz River between Wildcat Creek and the City of Siletz has had only modest vertical and lateral change between the 1930s and 2010s because of the bedrock in and along the main channel and the river’s relatively high transport capacity relative to bed-material sediment supply. However, localized sections of the Siletz River where the active channel widens, particularly at channel bends, exhibited some change in channel planform and the locations and area of gravel bars. In the future, moderate increases in autumn-winter discharge may not result in substantial changes in coarse gravel bars along the Siletz River but may result in selective transport of finer bed-material sediment (gravel, sands, and silts) that provide spawning habitats for Chinook salmon and Pacific lamprey and burrowing habitats for lamprey larvae. Assuming no substantial changes in bed-material sediment supply, increased bedload transport capacity may cause frequent entrainment of lamprey larvae that are burrowed in coarse sand deposits, suspension and downstream transport of salmon eggs incubating in gravels, and reductions in the areas of spawning gravels for Chinook salmon and Pacific lamprey. Exact implications of current and future discharge conditions for these species along the Siletz River depends on many factors, including sediment supply, local hydraulics, and the timing of flood events relative to fish life stages.

Oregon↗

USGS1986

Pb-, Sr- and Nd-Isotopic systematics and chemical characteristics of cenozoic basalts, Eastern China

Forty-eight Paleogene, Neogene and Quaternary basaltic rocks from northeastern and east-central China have been analyzed for major-element composition, selected trace-element contents, and Pb, Sr and Nd isotopic systematics. The study area lies entirely within the marginal Pacific tectonic domain. Proceeding east to west from the continental margin to the interior, the basalts reveal an isotopic transition in mantle source material and/or degree of crustal interaction. In the east, many of the rocks are found to merge both chemically and isotopically with those previously reported from the Japanese and Taiwan island-arc terrains. In the west, clear evidence exists for component(s) of Late Archean continental lithosphere to be present in some samples. A major crustal structure, the Tan-Lu fault, marks the approximate boundary between continental margin and interior isotopic behaviors. Although the isotopic signature of the western basalts has characteristics of lower-crustal contamination, a subcrustal lithosphere, i.e. an attached mantle keel, is probably more likely to be the major contributor of their continental “flavor”. The transition from continental margin to interior is very pronounced for Pb isotopes, although Sr and Nd isotopes also combine to yield correlated patterns that deviate strikingly from the mid-ocean ridge basalt (MORB) and oceanic-island trends. The most distinctive chemical attribute of this continental lithosphere component is its diminished U/Pb as reflected in the Pb isotopic composition when compared to sources of MORB, oceanic-island and island-arc volcanic rocks. Somewhat diminished Sm/Nd and elevated Rb/Sr, especially in comparison to the depleted asthenospheric mantle, are also apparent from the Nd- and Sr-isotopic ratios.

Chemical Geology↗

USGS2021

The snag’s the limit: Habitat selection modeling for the western purple martin in a managed forest landscape

The western purple martin ( Progne subis arboricola ), an avian insectivore, is a species of conservation concern throughout the Pacific Northwest. Compared to the well-studied eastern subspecies ( Progne subis subis ), little is known of the life history and biology of the western subspecies. Availability of breeding habitat is believed to be a major limiting factor for western purple martins in forested habitat, but fundamental information on their current distribution and selection of nesting habitat is deficient. To fill this gap, we compared habitat characteristics at three spatial scales (snag-level, stand-level [48.6 ha], landscape-level [314 ha]) surrounding nest snags occupied by purple martins in western Oregon to unoccupied sites. We found habitat for nesting purple martins was defined by the presence of moderately decayed snags with nest cavities, located well away from closed-canopy forest in sufficiently large (>15 ha) open areas. Our modeling efforts suggested suitable habitat was rare within the study region because: 1) snags were scarce on private industrial forest lands and 2) large disturbed patches were uncommon on federal lands. We conclude that a disturbance regime characterized by infrequent but major stand-replacing events, such as fire or timber harvest, is likely the key to maintaining breeding habitat for purple martins in upland forests in western Oregon.

Oregon↗

USGS2015

Projection of wave conditions in response to climate change: A community approach to global and regional wave downscaling

Future changes in wind-wave climate have broad implications for coastal geomorphology and management. General circulation models (GCM) are now routinely used for assessing climatological parameters, but generally do not provide parameterizations of ocean wind-waves. To fill this information gap, a growing number of studies use GCM outputs to independently downscale wave conditions to global and regional levels. To consolidate these efforts and provide a robust picture of projected changes, we present strategies from the community-derived multi-model ensemble of wave climate projections (COWCLIP) and an overview of regional contributions. Results and strategies from one contributing regional study concerning changes along the eastern North Pacific coast are presented.

Conference Paper↗

USGS2025

Wetter winters, drier summers: Quantifying the change in hydrological response around the Puget Sound area using the wflow_sbm hydrological model and CMIP6 projections

Climate change is expected to impact hydrological regimes worldwide, including the Pacific Northwest of the United States. This study investigates how climate change will affect river discharge in the Puget Sound region of the State of Washington, with a focus on King and Pierce Counties. We simulated river discharge under historical and future conditions using the physically based, spatially distributed wflow_sbm hydrological model, which was calibrated and validated against U.S. Geological Survey discharge records. Future forcing was based on an ensemble of six high-resolution CMIP6 climate models, which were bias corrected using empirical quantile mapping. The results indicate a decrease in summer discharges (5–10%) and an increase in winter discharges (5–10%) across the study region. The high discharges (90th percentile) are projected to increase in winter, and the low discharges are projected to decrease in summer, due to shifts in precipitation regimes, snowpack hydrology, and evapotranspiration. However, variability between individual CMIP6 models often exceeds the magnitude of ensemble mean changes, underscoring substantial uncertainty in climate projections and the importance of including multiple climate models in climate change analysis. Furthermore, model consensus increased with elevation, which could be the result of the higher elevation areas being driven by less diverse hydrological processes. These findings highlight potential challenges for regional water management, ecosystem health, and flood risk mitigation in the Puget Sound region under future climate conditions.

EarthArXiv↗

USGS1972

Determination of channel capacity of the Mokelumne River downstream from Camanche Dam, San Joaquin and Sacramento Counties, California

This study evaluates the adequacy of a 39-mile reach of the Mokelumne River in San Joaquin and Sacramento Counties, California, to carry planned flood releases between Camanche Reservoir and the Bensons Ferry Bridge near Thornton. The flood releases from Camanche Reservoir are to be restricted, insofar as possible, so that the flows in the Mokelumne River will not exceed 5,000 cfs (cubic feet per second) as measured at the gaging station below Camanche Dam. Areas of inundation and computed floodwater profiles are based on channel conditions in late 1970 and on observed water-surface profiles during flood releases of about 5,000 cfs in January 1969 and January 1970. The inundated area shown on the maps (appendix A) and the water-surface elevations indicated on the cross sections (appendix G) are for the flood releases of those dates. The following conclusions are contingent on there being no levee failures during periods of high flow and no significant channel changes since the flood release of January 1970. 1. High tides in San Francisco Bay and, to a greater degree, flood stages on the Cosumnes River, cause backwater in the study reach. Severe backwater conditions occurring simultaneously with a flow of 5,000 cfs in the Mokelumne River can increase the flood stage 4 to 6 feet at Bensons Ferry Bridge (cross section 1). Backwater effects decrease in an upstream direction and are less than 0.5 foot at cross section 35, a river distance of 8.6 miles upstream from cross section 1, and 1.5 miles downstream from the Peltier Road bridge. 2. In the reach between cross sections 1 and 35, a 5,000 cfs release from Camanche Reservoir with maximum backwater effect (measured at cross section 1 at the mouth of the Cosumnes River) is confined within the natural or leveed banks except on the right bank flood plain between cross sections 12 and 19. 3. Upstream from cross section 35, there is overbank flooding at a flow of 5,000 cfs between cross sections 48 and 51, and 62 and 67.5. An increase in flow from 5,000 to 6,000 cfs will cause flooding between cross sections 43 and 47, 52 and 56, and 73 and 85. 4. A discharge of 5,000 cfs will pass through all bridge openings in the study reach except that of the Western Pacific Railroad Co. bridge at cross section 4. If large amounts of debris lodge on the railroad bridge when backwater from the Cosumnes River occurs, the debris could cause higher stages and flooding along the right bank between cross sections 5 and 12.

California↗

USGS2011

Coastal circulation and water-column properties off Kalaupapa National Historical Park, Molokai, Hawaii, 2008-2010

More than 2.2 million measurements of oceanographic forcing and the resulting water-column properties were made off U.S. National Park Service's Kalaupapa National Historical Park on the north shore of Molokai, Hawaii, between 2008 and 2010 to understand the role of oceanographic processes on the health and sustainability of the area's marine resources. The tides off the Kalaupapa Peninsula are mixed semidiurnal. The wave climate is dominated by two end-members: large northwest Pacific winter swell that directly impacts the study site, and smaller, shorter-period northeast trade-wind waves that have to refract around the peninsula, resulting in a more northerly direction before propagating over the study site. The currents primarily are alongshore and are faster at the surface than close to the seabed; large wave events, however, tend to drive flow in a more cross-shore orientation. The tidal currents flood to the north and ebb to the south. The waters off the peninsula appear to be a mix of cooler, more saline, deeper oceanic waters and shallow, warmer, lower-salinity nearshore waters, with intermittent injections of freshwater, generally during the winters. Overall, the turbidity levels were low, except during large wave events. The low overall turbidity levels and rapid return to pre-event background levels following the cessation of forcing suggest that there is little fine-grained material. Large wave events likely inhibit the settlement of fine-grained sediment at the site. A number of phenomena were observed that indicate the complexity of coastal circulation and water-column properties in the area and may help scientists and resource managers to better understand the implications of the processes on marine ecosystem health.

Hawai'i↗

USGS2017

P- and S-wave velocity models incorporating the Cascadia subduction zone for 3D earthquake ground motion simulations, Version 1.6—Update for Open-File Report 2007–1348

In support of earthquake hazard studies and ground motion simulations in the Pacific Northwest, three-dimensional P- and S-wave velocity ( V P and V S , respectively) models incorporating the Cascadia subduction zone were previously developed for the region encompassed from about 40.2°N. to 50°N. latitude, and from about 122°W. to 129°W. longitude. This report describes updates to the Cascadia velocity property volumes of model version 1.3 (V1.3), herein called model version 1.6 (V1.6). As in model V1.3, the updated V1.6 model volume includes depths from 0 kilometers (mean sea level) to 60 kilometers, and it is intended to be a reference for researchers who have used, or are planning to use, this model in their Earth science investigations. To this end, it is intended that the V P and V S property volumes of model V1.6 will be considered a template for a community velocity model of the Cascadia region as additional results become available. With the recent and ongoing development of the National Crustal Model, we envision any future versions of this model will be directly integrated with that effort.

Oregon, Vancouver, Washington↗

USGS2021

Egg retention of high-latitude sockeye salmon (Oncorhynchus nerka) in the Pilgrim River, Alaska, during the Pacific marine heatwave of 2014–2016

Ocean and freshwater conditions can influence spawning success of Pacific salmon ( Oncorhynchus spp.) by governing the energy content of fish at the start of and during the spawning migration. Ocean conditions determine the energy stores of fish at the freshwater entry, while freshwater conditions determine how quickly stored energy is depleted as individuals migrate to spawning grounds in natal rivers and lakes. We assessed the occurrence of sockeye salmon ( Oncorhynchus nerka ) egg retention (failure to deposit eggs) in a high-latitude (~ 65°N) watershed that has a large, inter-annual variation in the number of returning adults. We also explored relationships between ocean and freshwater conditions with egg retention of female sockeye salmon. The proportion of females with egg retention (> 50 eggs) varied by threefold (12 to 36%) across years (2013 to 2020) and was related to ocean conditions represented by the North Pacific Index (NPI). Egg retention was more common in years with low NPI values (a stronger Aleutian Low) in association with the Pacific marine heatwave of 2014–2016 that disrupted food webs. This initial study contains the first empirical data observing the influence of ocean conditions on egg retention for any Pacific salmon population. The lack of any relationship between egg retention and freshwater temperatures was consistent with water temperatures primarily occurring below thresholds associated with heat stress related mortality (< 18 °C). Understanding the amount of egg retention and how environmental drivers influence egg retention within Pacific salmon populations provides insights for managers assessing the number of successful spawners and helps refine escapement-based management efforts.

Alaska↗

USGS2025

A soil velocity model for improved ground motion simulations in the U. S. Pacific Northwest

Near-surface seismic velocity structure may significantly impact the intensity, duration, and frequency content of ground shaking during an earthquake. In this study, we compile 649 shear wave velocity (Vs) profiles throughout the U.S. Pacific Northwest and southern British Columbia (PNW) and use these measured profiles to develop a representative soil velocity model for four major Holocene soil provinces: Puget Lowlands, Willamette Valley, fill and alluvium, and `other' soils. The resulting soil velocity model shows good agreement to measured data for a wide range of site conditions, with variability between different geologic domains reflecting fundamental differences in depositional environments. We then show that using this regional soil velocity model in simulations of the 2001 M6.8 Nisqually, Washington earthquake improves the fit to observed high-frequency (≥ 0.5 Hz) ground motions in the Puget Sound region compared to simulations that do not incorporate shallow (≤ 200 m) seismic velocity structure. Overall, this work shows that incorporating localized soil velocity profiles into seismic velocity models is important for accurately estimating high-frequency ground motion and regional seismic hazard in earthquake simulations. Future earthquake simulations and hazard studies in the PNW could incorporate these soil velocity profiles to capture the region's distinct site response characteristics.

Washington↗

USGS2010

Two major Cenozoic episodes of phosphogenesis recorded in equatorial Pacific seamount deposits

Seamount phosphorites have been recognized since the 1950s, but this is the first study to provide an in depth exploration of the origin and history of these widespread deposits. Representative samples from equatorial Pacific Cretaceous seamounts were analyzed for chemical, mineralogical, and stable isotope compositions. The phosphorites occur in a wide variety of forms, but most commonly carbonate fluorapatite (CFA) replaced middle Eocene and older carbonate sediment in a deep water environment (>1000 m). Element ratios distinguish seamount phosphorites from continental margin, plateau, and insular phosphorites. Uranium and thorium contents are low and total rare earth element (REE) contents are generally high. REE ratios and shale-normalized patterns demonstrate that the REEs and host CFA were derived from seawater. Strontium isotopic compositions compared with inferred Cenozoic seawater curves define two major episodes of Cenozoic phosphatization: Late Eocene/early Oligocene (39–34 Ma) and late Oligocene/early Miocene (27–21 Ma); three minor events are also indicated. The major episodes occurred at times of climate transition, the first from a nonglacial to glacial earth and the second from a predominantly glacial to warm earth. The paleoceanographic conditions that existed at those times initiated and sustained development of phosphorite by accumulation of dissolved phosphorus in the deep sea during relatively stable climatic conditions when oceanic circulation was sluggish. Fluctuations in climate, sealevel, and upwelling that accompanied the climate transitions may have driven cycles of enrichment and depletion of the deep-sea phosphorus reservoir. As temperature gradients in the oceans increased, Antarctic glaciation expanded and oceanic circulation and upwelling intensified. Expansion and intensification of the oxygen minimum zone may have increased the capacity for midwater storage of phosphorus supplied by dynamic upwelling around seamounts; however, the bottom waters never became anoxic during the phosphogenic episodes. Fluctuations in the CCD and lysocline, CO 2 fluxes, and changes in bottom water circulation and temperatures may have bathed the seamount carbonates in more corrosive waters which, coupled with increased supplies of dissolved phosphorus, promoted replacement processes. The late Eocene/early Oligocene phosphogenic episode recorded in seamount deposits is not matched by large phosphorite deposits in the geologic record, whereas the late Oligocene/early Miocene episode and middle Miocene event are matched by large deposits distributed globally. The seamount phosphorites are exposed at the surface of the seamounts and have been for most of the Neogene and Oligocene. The phosphorites do not show signs of etching that would indicate substantial undersaturation of seawater phosphate with respect to CFA. Mass balance calculations indicate that about 5.4–19 × 10 12 g of P 2 O 5 are locked up in equatorial Pacific seamount phosphorites. That amount is equivalent to about 2-7 years of the present annual input from rivers.

Paleoceanography and Paleoclimatology↗

USGS1988

Erosion and slope instability on Horizon Guyot, Mid-Pacific Mountains

Seismic-reflection profiles, sediment cores, and current velocities were assessed to study the impact of erosion and sediment redistribution on the pelagic sediment cap of Horizon Guyot, a flat-topped submarine volcanic ridge in the Mid-Pacific Mountains. These processes seem to concentrate their effect around the rim of the sediment cap. Sediment slumping occurs on the northwest perimeter of the guyot's sediment cap. Slope stability analysis suggests that if overconsolidation on Horizon Guyot is the result of current reworking or if local undercutting by bottom currents steepens the sea floor declivity, the sediment cap may be unstable during infrequent earthquake loading, transporting sediment from the guyot summit to the abyssal sea floor. ?? 1988 Springer-Verlag New York Inc.

Geo-Marine Letters↗

USGS2011

Comparative health assessment of western Pacific leatherback turtles (Dermochelys coriacea) foraging off the coast of California, 2005-2007

Leatherback turtles ( Dermochelys coriacea ) are critically endangered, primarily threatened by the overharvesting of eggs, fisheries entanglement, and coastal development. The Pacific leatherback population has experienced a catastrophic decline over the past two decades. Leatherbacks foraging off the coast of California are part of a distinct Western Pacific breeding stock that nests on beaches in Indonesia, Papua New Guinea, and the Solomon Islands. Although it has been proposed that the rapid decline of Pacific leatherback turtles is due to increased adult mortality, little is known about the health of this population. Health assessments in leatherbacks have examined females on nesting beaches, which provides valuable biological information, but might have limited applicability to the population as a whole. During September 2005 and 2007, we conducted physical examinations on 19 foraging Pacific leatherback turtles and measured normal physiologic parameters, baseline hematologic and plasma biochemistry values, and exposure to heavy metals (cadmium, lead, and mercury), organochlorine contaminants, and domoic acid. We compared hematologic values of foraging Pacific leatherbacks with their nesting counterparts in Papua New Guinea ( n =11) and with other nesting populations in the Eastern Pacific in Costa Rica ( n =8) and in the Atlantic in St. Croix ( n =12). This study provides the most comprehensive assessment to date of the health status of leatherbacks in the Pacific. We found significant differences in blood values between foraging and nesting leatherbacks, which suggests that health assessment studies conducted only on nesting females might not accurately represent the whole population. The establishment of baseline physiologic data and blood values for healthy foraging leatherback turtles, including males, provides valuable data for long-term health monitoring and comparative studies of this endangered population.

California↗

USGS2016

Animated tectonic reconstruction of the Lower Colorado River region: Implications for Late Miocene to Present deformation

Although the majority of late Miocene to present Pacific-North America plate boundary strain has been accommodated by faults of the San Andreas and Gulf of California systems, growing evidence of dextral shear east of the San Andreas Fault indicates that a component of plate boundary deformation occurred in the lower Colorado River (LoCR) region. Large-scale tectonic reconstructions across the Gulf of California and Salton Trough (GCAST) region (Fig. 1), a ~500 km-wide zone of deformation that affected the western margin of North America, provide important constraints on the location, timing, style, and magnitude of crustal deformation in the LoCR region (Fig. 2). Characterizing Miocene to present deformation in the LoCR region is important to resolve the presence and kinematics of upper crustal structures that accommodated intracontinental strain and improves our understanding of the processes that promoted localized or diffuse strain during reorganization of the Pacific-North America plate boundary. Map-view translations of crustal blocks influence the relative motions of adjacent blocks, an approach adhered to in global plate-circuit models (Atwater and Stock, 1998; 2013). Thus, a synthesis of the magnitude and timing of horizontal strain across a broad zone of distributed deformation can provide insight into processes of strain partitioning and potential kinematic links between adjacent structural domains. Furthermore, it can help prioritize and guide future work by identifying gaps in our understanding of plate boundary deformation and provide a degree of predictability for palinspastic reconstructions in areas where little information exists. At present, detailed geologic studies of crustal deformation related to the Pacific-North America plate boundary in the LoCR region are limited, leading to considerable uncertainty in the late Cenozoic tectonic evolution of the region. This uncertainty limits our understanding of how plate coupling evolves during the transition from a convergent margin to a transform margin. In this paper, we utilize animated palinspastic fault-based reconstructions to evaluate the tectonic evolution of the LoCR region and to examine potential inconsistencies of the spatio-temporal evolution of the late Cenozoic Pacific-North America plate boundary. Based on revised palinspastic reconstructions and remaining inconsistencies, we hypothesize that (1) late Miocene transtensional faulting related to the Gulf of California shear zone and eastern California shear zone promoted tectonic subsidence in the LoCR region that permitted the subsequent southward lake spillover of the Colorado River and connection with the northern Gulf of California, (2) distributed Pliocene transtensional faulting likely occurred within the southern LoCR region, and is presently unaccounted for in most studies of geologic units related to the Pliocene Colorado River, and (3) the Chocolate Mountains anticlinorium can be reconstructed to a broadly linear, E-W-oriented structure at ca. 11 Ma, consistent with reconstruction of several other strain markers along the southern San Andreas Fault system.

Lower Colorado River↗

USGS2018

Introduction to “Global tsunami science: Past and future, Volume III”

Twenty papers on the study of tsunamis are included in Volume III of the PAGEOPH topical issue “Global Tsunami Science: Past and Future”. Volume I of this topical issue was published as PAGEOPH, vol. 173, No. 12, 2016 and Volume II as PAGEOPH, vol. 174, No. 8, 2017. Two papers in Volume III focus on specific details of the 2009 Samoa and the 1923 northern Kamchatka tsunamis; they are followed by three papers related to tsunami hazard assessment for three different regions of the world oceans: South Africa, Pacific coast of Mexico and the northwestern part of the Indian Ocean. The next six papers are on various aspects of tsunami hydrodynamics and numerical modelling, including tsunami edge waves, resonant behaviour of compressible water layer during tsunamigenic earthquakes, dispersive properties of seismic and volcanically generated tsunami waves, tsunami runup on a vertical wall and influence of earthquake rupture velocity on maximum tsunami runup. Four papers discuss problems of tsunami warning and real-time forecasting for Central America, the Mediterranean coast of France, the coast of Peru, and some general problems regarding the optimum use of the DART buoy network for effective real-time tsunami warning in the Pacific Ocean. Two papers describe historical and paleotsunami studies in the Russian Far East. The final set of three papers importantly investigates tsunamis generated by non-seismic sources: asteroid airburst and meteorological disturbances. Collectively, this volume highlights contemporary trends in global tsunami research, both fundamental and applied toward hazard assessment and mitigation.

Pure and Applied Geophysics↗