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At least 235 records · Page 13Linked to original sources

USGS2013

Vascular flora of saline lakes in the southern high plains of Texas and eastern New Mexico

Saline lakes and freshwater playas form the principal surface hydrological feature of the High Plains of the Southern Great Plains. Saline lakes number less than 50 and historically functioned as discharge wetlands with relatively consistent water availability due to the presence of one or more springs. Currently, less than ten saline lakes contain functional springs. A survey of vascular plants at six saline lakes in the Southern High Plains of northwest Texas and one in eastern New Mexico during May and September 2009 resulted in a checklist of 49 species representing 16 families and 40 genera. The four families with the most species were Asteraceae (12), Amaranthaceae (8), Cyperaceae (5), and Poaceae (12). Non-native species (Bromus catharticus, Poa compressa, Polypogon monspeliensis, Sonchus oleraceus, Kochia scoparia, and Tamarix ramosissima) accounted for 10% of the total species recorded. Whereas nearly 350 species of vascular plants have been identified in playas in the Southern High Plains, saline lakes contain a fraction of this species richness. The Southern High Plains saline lake flora is regionally unique, containing taxa not found in playas, with species composition that is more similar to temperate desert wetlands of the Intermountain Region and Gulf Coastal Plain of North America.

New Mexico, Texas↗

USGS2014

Modeling erosion of ice-rich permafrost bluffs along the Alaskan Beaufort Sea coast

The Arctic climate is changing, inducing accelerating retreat of ice-rich permafrost coastal bluﬀs. Along Alaska’s Beaufort Sea coast, erosion rates have increased roughly threefold from 6.8 to 19 m yr −1 since 1955 while the sea ice-free season has increased roughly twofold from 45 to 100 days since 1979. We develop a numerical model of bluﬀ retreat to assess the relative roles of the length of sea ice-free season, sea level, water temperature, nearshore waveﬁeld, and permafrost temperature in controlling erosion rates in this setting. The model captures the processes of erosion observed in short-term monitoring experiments along the Beaufort Sea coast, including evolution of melt notches, topple of ice wedge-bounded blocks, and degradation of these blocks. Model results agree with time-lapse imagery of bluﬀ evolution and time series of ocean-based instrumentation. Erosion is highly episodic with 40% of erosion is accomplished during less than 5% of the sea ice-free season. Among the formulations of the submarine erosion rate we assessed, we advocate those that employ both water temperature and nearshore waveﬁeld. As high water levels are a prerequisite for erosion, any future changes that increase the frequency with which water levels exceed the base of the bluﬀs will increase rates of coastal erosion. The certain increases in sea level and potential changes in storminess will both contribute to this eﬀect. As water temperature also inﬂuences erosion rates, any further expansion of the sea ice-free season into the midsummer period of greatest insolation is likely to result in an additional increase in coastal retreat rates.

Alaska↗

USGS2016

Probabilistic assessment of erosion and flooding risk in the northern Gulf of Mexico

We assess erosion and flooding risk in the northern Gulf of Mexico by identifying interdependencies among oceanographic drivers and probabilistically modeling the resulting potential for coastal change. Wave and water level observations are used to determine relationships between six hydrodynamic parameters that influence total water level and therefore erosion and flooding, through consideration of a wide range of univariate distribution functions and multivariate elliptical copulas. Using these relationships, we explore how different our interpretation of the present-day erosion/flooding risk could be if we had seen more or fewer extreme realizations of individual and combinations of parameters in the past by simulating 10,000 physically and statistically consistent sea-storm time series. We find that seasonal total water levels associated with the 100 year return period could be up to 3 m higher in summer and 0.6 m higher in winter relative to our best estimate based on the observational records. Impact hours of collision and overwash—where total water levels exceed the dune toe or dune crest elevations—could be on average 70% (collision) and 100% (overwash) larger than inferred from the observations. Our model accounts for non-stationarity in a straightforward, non-parametric way that can be applied (with little adjustments) to many other coastlines. The probabilistic model presented here, which accounts for observational uncertainty, can be applied to other coastlines where short record lengths limit the ability to identify the full range of possible wave and water level conditions that coastal mangers and planners must consider to develop sustainable management strategies.

Journal of Geophysical Research C: Oceans↗

USGS2008

Oceanic loading of wildfire-derived organic compounds from a small mountainous river

Small mountainous rivers (SMRs) export substantial amounts of sediment into the world's oceans. The concomitant yield of organic carbon (OC) associated with this class of rivers has also been shown to be significant and compositionally unique. We report here excessively high loadings of polycyclic aromatic hydrocarbons (PAHs), lignin, and levoglucosan, discharged from the Santa Clara River into the Santa Barbara Channel. The abundance of PAHs, levoglucosan, and lignin in Santa Barbara Channel sediments ranged from 201.7 to 1232.3 ng gdw-1, 1.3 to 6.9 ??g gdw-1, and 0.3 to 2.2 mg per 100 mg of the sedimentary OC, respectively. Assuming a constant rate of sediment accumulation, the annual fluxes of PAHs, levoglucosan, and lignin, to the Santa Barbara Channel were respectively, 885.5 ?? 170.2 ng cm-2 a-1, 3.5 ?? 1.9 ??g cm-2 a-1 and 1.4 ?? 0.3 mg per 100 mg OC cm-2 a-1, over ???30 years. The close agreement between PAHs, levoglucosan, and lignin abundance suggests that the depositional flux of these compounds is largely biomass combustion-derived. To that end, use of the Santa Clara River as a model for SMRs suggests this class of rivers may be one of the largest contributors of pyrolyzed carbon to coastal systems and the open ocean. Wildfire associated carbon discharged from other high yield fluvial systems, when considered collectively, may be a significant source of lignin, pyrolytic PAHs, and other pyrogenic compounds to the ocean. Extrapolating these methods over geologic time may offer useful historical information about carbon sequestration and burial in coastal sediments and affect coastal carbon budgets. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗

USGS1996

Cadmium in the California Current system: Tracer of past and present upwelling

Over 100 samples were collected off the west coast of North America during 1991–1993 to determine the relation between wind‐driven upwelling and nearshore concentrations of dissolved silicate (Si), phosphate (P), and cadmium (Cd). Highly enriched in deep water offshore, these constituents are sensitive indicators of upwelling. Coastal water was sampled from the shore in January and June 1992 at 12 sites distributed between 36° and 48°N latitude. In January the composition of nearshore water along this transect was fairly uniform: 5–15 μmol/kg for Si, 0.5 to 1.0 μmol/kg for P, and 0.1–0.3 nmol/kg for Cd. In June, elevated concentrations of Si (30 μmol/kg), P (2.0 μmol/kg), and Cd (0.6 nmol/kg) revealed a region of intense upwelling between 38° and 40°N. The pattern is broadly consistent with meridional gradients in coastal upwelling calculated from the long‐term mean of alongshore winds compiled from ship reports. Nearshore water was also collected biweekly to monthly at two sites 3 km apart near San Francisco Bay (37.5°N) during 1991–1993. The variability seen in the time series suggests that the composition of nearshore water integrates the effect of alongshore winds over timescales of several weeks. Seasonal variations in Si (5–50 μmol/kg), P (0.5–2.5 μmol/kg), and Cd (0.1–0.8 nmol/kg) concentrations were consistent with upwelling during spring and summer. Maximum Si, P, and Cd concentrations reached in May 1991 were consistent with advection to the very nearshore region from a depth of about 300 m relative to a vertical profile at a distance of 200 km from the coast. Nearshore Si, P, and Cd concentrations were reduced relative to 1991 in 1992, and, to a lesser extent, in 1993 due to weaker upwelling linked to the warm phase of the El Niño‐Southern Oscillation. During periods of weaker upwelling or downwelling, variations in P, Si, and Cd concentrations became uncoupled. There is a good correlation between the coastal Cd time series near San Francisco Bay (37.5°N) and a second order polynomial function of the upwelling index of Bakun [1975] at 36°N, filtered with a 30‐day running mean ( r 2 = 0.71, n = 39). The index is a daily estimate of coastal upwelling calculated from 6‐hourly mean atmospheric pressure distributions at 36°N. From this function and a record of daily upwelling indices, we infer a range of annually averaged coastal Cd concentrations of at least 0.3–0.5 nmol/kg since 1967. Cd/Ca ratios in shells of foraminifera from San Francisco Bay suggest that average coastal Cd concentrations 3500–4500 years ago were at the upper end of this range.

Journal of Geophysical Research C: Oceans↗

USGS2004

Annual layers revealed by GPR in the subsurface of a prograding coastal barrier, southwest Washington, U.S.A

The southwest Washington coastline has experienced extremely high rates of progradation during the late Holocene. Subsurface stratigraphy, preserved because of progradation and interpreted using ground-penetrating radar (GPR), has previously been used successfully to document coastal response to prehistoric storm and earthquake events. New GPR data collected at Ocean Shores, Washington, suggest that the historic stratigraphy of the coastal barrier in this area represents a higher resolution record of coastal behavior than previously thought. GPR records for this location at 200 MHz reveal a series of gently sloping, seaward-dipping reflections with slopes similar to the modern beach and spacings on the order of 20-45 cm. Field evidence and model results suggest that thin (1-10 cm), possibly magnetite-rich, heavy-mineral lags or low-porosity layers left by winter storms and separated by thick (20-40 cm) summer progradational sequences are responsible for generating the GPR reflections. These results indicate that a record of annual progradation is preserved in the subsurface of the prograding barrier and can be quantified using GPR. Such records of annual coastal behavior, where available, will be invaluable in understanding past coastal response to climatic and tectonic forcing.

Washington↗

USGS2025

Vulnerability of gulf ribbed mussels to marsh surface maximum temperatures

Gulf ribbed mussels ( Geukensia granosissima ) act as ecosystem engineers and reside within the marsh platform of saltmarshes across the northern Gulf of Mexico. With climate models projecting increasing temperatures, and more frequent and extreme heat events, these mussels face increasing temperature-related risks. Marsh surface and subsurface (5-cm depth) temperature was measured continuously in the summer of 2022 in south Louisiana Gulf ribbed mussel habitat at nine stations. Marsh surface maximum temperatures were 5°C higher and more variable than recorded water temperatures, exceeding 38°C for periods of up to 3 h which generally coincided with low tides and peak solar radiation. Marsh subsurface temperatures were cooler with a lower mean and maximum temperature compared with the marsh surface, but higher than adjacent water. In two laboratory experiments the acclimated and acute thermal tolerance of wild mussels collected from the saltmarsh where temperatures were recorded, were explored. G. granosissima survived more than 40 days of continuous exposure in the laboratory to mean daily temperature values recorded for the marsh and subsurface microhabitats (28°C–34°C) but their calculated median lethal time (LT 50 ) ranged from 35 to 56 days (36°C), to less than 3 days (40°C). Mussels acclimated to temperatures similar to long-term average water temperatures (28°C–32°C) and then exposed to maximum daily temperatures acutely experienced LT 50 of less than 6 days (38°C), <1 day (40°C), and of less than 5 h (42°C). For G. granosissima both their thermal tolerance and behavioral response likely contribute to their survival in the face of extreme heat events, and their resulting distribution across the marsh surface and subsurface. Overall, results indicate that ribbed mussels in coastal Louisiana may rely on their ability to migrate vertically and bury in the marsh to avoid extreme heat exposure (temperature, duration) that may be lethal. The ability of Gulf ribbed mussels to endure short-term thermal extremes may ultimately determine the mussels' use as a tool in marsh stabilization and coastal restoration.

Louisiana↗

USGS2019

Sea level rise in the Samoan Islands escalated by viscoelastic relaxation after the 2009 Samoa‐Tonga earthquake

The Samoan islands are an archipelago hosting a quarter million people mostly residing in three major islands, Savai'i and Upolu (Samoa), and Tutuila (American Samoa). The islands have experienced sea level rise by 2–3 mm/year during the last half century. The rate, however, has dramatically increased following the M w 8.1 Samoa‐Tonga earthquake doublet (megathrust + normal faulting) in September 2009. Since the earthquake, we found large‐scale gravity increase (0.5 μ Gal/year) around the islands and ongoing subsidence (8–16 mm/year) of the islands from our analysis of Gravity Recovery And Climate Experiment gravity and GPS displacement data. The postseismic horizontal displacement is faster in Samoa, while the postseismic subsidence rate is considerably larger in American Samoa. The analysis of local tide gauge records and satellite altimeter data also identified that the relative sea level rise becomes faster by 7–9 mm/year in American Samoa than Samoa. A simple viscoelastic model with a Maxwell viscosity of 2–3 × 10 18 Pa s for the asthenosphere explained postseismic deformation at nearby GPS sites as well as Gravity Recovery And Climate Experiment gravity change. It is found that the constructive interference of viscoelastic relaxation from both megathrust and normal faulting has intensified the postseismic subsidence at American Samoa, causing ~5 times faster sea level rise than the global average. Our model indicates that this trend is likely to continue for decades and result in sea level rise of 30–40 cm, which is independent of and in addition to anticipated climate‐related sea level rise. It will worsen coastal flooding on the islands leading to regular nuisance flooding.

Journal of Geophysical Research↗

USGS2018

Mechanisms of wave‐driven water level variability on reef‐fringed coastlines

Wave‐driven water level variability (and runup at the shoreline) is a significant cause of coastal flooding induced by storms. Wave runup is challenging to predict, particularly along tropical coral reef‐fringed coastlines due to the steep bathymetric profiles and large bottom roughness generated by reef organisms, which can violate assumptions in conventional models applied to open sandy coastlines. To investigate the mechanisms of wave‐driven water level variability on a reef‐fringed coastline, we performed a set of laboratory flume experiments on an along‐shore uniform bathymetric profile with and without bottom roughness. Wave setup and waves at frequencies lower than the incident sea‐swell forcing (infragravity waves) were found to be the dominant components of runup. These infragravity waves were positively correlated with offshore wave groups, signifying they were generated in the surf zone by the oscillation of the breakpoint. On the reef flat and at the shoreline, the low‐frequency waves formed a standing wave pattern with energy concentrated at the natural frequencies of the reef flat, indicating resonant amplification. Roughness elements used in the flume to mimic large reef bottom roughness reduced low frequency motions on the reef flat and reduced wave run up by 30% on average, compared to the runs over a smooth bed. These results provide insight into sea‐swell and infragravity wave transformation and wave setup dynamics on steep‐sloped coastlines, and the effect that future losses of reef bottom roughness may have on coastal flooding along reef‐fringed coasts.

Journal of Geophysical Research C: Oceans↗

USGS2011

Status and distribution of the Kittlitz's murrelet Brachyramphus brevirostris in Kenai Fjords, Alaska

The Kittlitz's Murrelet Brachyramphus brevirostris is a candidate species for listing under the US Endangered Species Act because of its apparent declines within core population areas of coastal Alaska. During the summers of 2006-2008, we conducted surveys in marine waters adjacent to Kenai Fjords National Park, Alaska, to estimate the current population size of Kittlitz's and Marbled murrelets B. marmoratus and examine seasonal variability in distribution within coastal fjords. We also evaluated historical data to estimate trend. Based on an average of point estimates, we find the recent population (95% CI) of Kittlitz's Murrelet to be 716 (353-1080) individuals, that of Marbled Murrelet to be 6690 (5427-7953) individuals, and all Brachyramphus murrelets combined to number 8186 (6978-9393) birds. Within-season density estimates showed Kittlitz's Murrelets generally increased between June and July, but dispersed rapidly by August, while Marbled Murrelets generally increased throughout the summer. Trends in Kittlitz's and Marbled murrelet populations were difficult to assess with confidence. Methods for counting or sampling murrelets varied in early decades of study, while in later years there is uncertainty due to highly variable counts among years, which may be due in part to timing of surveys relative to the spring bloom in coastal waters of the Gulf of Alaska.

Marine Ornithology: Journal of Seabird Research an↗

USGS2012

Utilizing multichannel electrical resistivity methods to examine the dynamics of the fresh water–seawater interface in two Hawaiian groundwater systems

Multichannel electrical resistivity (ER) measurements were conducted at two contrasting coastal sites in Hawaii to obtain new information on the spatial scales and dynamics of the fresh water–seawater interface and rates of coastal groundwater exchange. At Kiholo Bay (located on the dry, Kona side of the Big Island) and at a site in Maunalua Bay (Oahu), there is an evidence for abundant submarine groundwater discharge (SGD). However, the hydrologic and geologic controls on coastal groundwater discharge are likely to be different at these two sites. While at Kiholo Bay SGD is predominantly through lava tubes, at the Maunalua Bay site exchange occurs mostly through nearshore submarine springs. In order to calculate SGD fluxes, it is important to understand the spatial and temporal scales of coastal groundwater exchange. From ER time series data, subsurface salinity distributions were calculated using site-specific formation factors. A salinity mass balance box model was then used to calculate rates of point source (i.e., spatially discreet) and total fresh water discharge. From these data, mean SGD rates were calculated for Kiholo Bay (&sim;9,200 m 3 /d) and for the Maunalua Bay site (&sim;5,900 m 3 /d). While such results are on the same order of magnitude to geochemical tracer-derived SGD rates, the ER SGD rates provide enhanced details of coastal groundwater exchange that can enable a more cohesive whole watershed perspective.

Hawai'i↗

USGS2024

Predicting characteristic length scales of barrier island segmentation in microtidal environments

Segmented barrier islands can be found in regions with small tidal ranges. In contrast to tidally dominated barriers, where inlet dynamics are thought to control island length scales, the controls on barrier island length scales in wave-dominated environments have not been quantified. These microtidal barriers typically have a curved shoreline, suggesting the influence of wave-driven alongshore sediment transport. Microtidal barriers are also typically hydrodynamically isolated from one another, as weak tidal flows limit interactions between adjoining barriers. To better understand the controls on and scales of barrier segmentation in the relative absence of tides, here we develop a theoretical framework to estimate the alongshore length scales at which a barrier will either breach or heal following a disturbance in the barrier morphology. The non-dimensional framework compares the timescales of overwash (advective) and alongshore sediment transport (diffusive) processes along barrier island chains. We then apply this framework to modern barrier islands in the microtidal Gulf of Mexico using wave hindcast data and the lengths, widths, heights, and lagoon depths measured from remotely sensed geospatial data and topobathymetric data. We find that most of these barriers are currently longer than their critical length scale, often as a result of coastal restoration efforts. Our critical length scale analysis suggests that most of the Gulf of Mexico barriers are vulnerable to segmentation despite coastal restoration efforts intended to protect fisheries and the mainland coasts.

Florida, Louisiana, Mississippi↗

USGS2000

Time-averaged fluxes of lead and fallout radionuclides to sediments in Florida Bay

Recent, unmixed sediments from mud banks of central Florida Bay were dated using 210 Pb/ 226 Ra, and chronologies were verified by comparing sediment lead temporal records with Pb/Ca ratios in annual layers of coral ( Montastrea annularis ) located on the ocean side of the Florida Keys. Dates of sediment lead peaks (1978±2) accord with prior observations of a 6 year lag between the occurrence of maximum atmospheric lead in 1972 and peak coral lead in 1978. Smaller lags of 1–2 years occur between the maximum atmospheric radionuclide fallout and peaks in sediment temporal records of 137 Cs and Pu. Such lags are consequences of system time averaging (STA) in which atmospherically delivered particle-associated constituents accumulate and mix in a (sedimentary?) reservoir before transferring to permanent sediments and coral. STA model calculations, using time-dependent atmospheric inputs, produced optimized profiles in excellent accord with measured sediment 137 Cs, Pu, lead, and coral lead distributions. Derived residence times of these particle tracers (16±1, 15.7±0.7, 19±3, and 16±2 years, respectively) are comparable despite differences in sampling locations, in accumulating media, and in element loading histories and geochemical properties. For a 16 year weighted mean residence time, STA generates the observed 6 year lead peak lag. Evidently, significant levels of nondegradable, particle-associated contaminants can persist in Florida Bay for many decades following elimination of external inputs. Present results, in combination with STA model analysis of previously reported radionuclide profiles, suggest that decade-scale time averaging may occur widely in recent coastal marine sedimentary environments.

Florida↗

USGS2006

Submarine geology of Hana Ridge and Haleakala Volcano's northeast flank, Maui

We present a morphostructural analysis of the submarine portions of Haleakala Volcano and environs, based upon a 4-year program of geophysical surveys and submersible explorations of the underwater flanks of Hawaiian volcanoes that was conducted by numerous academic and governmental research organizations in Japan and the U.S. and funded primarily by the Japan Agency for Marine–Earth Science and Technology. A resulting reconnaissance geologic map features the 135-km-long Hana Ridge, the 3000 km 2 Hana slump on the volcano's northeast flank, and island-surrounding terraces that are the submerged parts of volcanic shields. Hana Ridge below 2000 m water depth exhibits the lobate morphology typical of the subaqueously erupted parts of Hawaiian rift zones, with some important distinctions: namely, subparallel crestlines, which we propose result from the down-rift migration of offsets in the dike intrusion zone, and an amphitheater at its distal toe, where a submarine landslide has embayed the ridge tip. Deformation of Haleakala's northeast flank is limited to that part identified as the Hana slump, which lies downslope from the volcano's submerged shield, indicating that flank mobility is also limited in plan, inconsistent with hypothesized volcanic spreading driven by rift-zone dilation. The leading edge of the slump has transverse basins and ridges that resemble the thrust ramps of accretionary prisms, and we present a model to describe the slump's development that emphasizes the role of coastally generated fragmental basalt on gravitational instability of Haleakala's northeast flank and that may be broadly applicable to other ocean-island slumps.

Hawai'i↗

USGS2015

Using a Bayesian network to predict barrier island geomorphologic characteristics

Quantifying geomorphic variability of coastal environments is important for understanding and describing the vulnerability of coastal topography, infrastructure, and ecosystems to future storms and sea level rise. Here we use a Bayesian network (BN) to test the importance of multiple interactions between barrier island geomorphic variables. This approach models complex interactions and handles uncertainty, which is intrinsic to future sea level rise, storminess, or anthropogenic processes (e.g., beach nourishment and other forms of coastal management). The BN was developed and tested at Assateague Island, Maryland/Virginia, USA, a barrier island with sufficient geomorphic and temporal variability to evaluate our approach. We tested the ability to predict dune height, beach width, and beach height variables using inputs that included longer-term, larger-scale, or external variables (historical shoreline change rates, distances to inlets, barrier width, mean barrier elevation, and anthropogenic modification). Data sets from three different years spanning nearly a decade sampled substantial temporal variability and serve as a proxy for analysis of future conditions. We show that distinct geomorphic conditions are associated with different long-term shoreline change rates and that the most skillful predictions of dune height, beach width, and beach height depend on including multiple input variables simultaneously. The predictive relationships are robust to variations in the amount of input data and to variations in model complexity. The resulting model can be used to evaluate scenarios related to coastal management plans and/or future scenarios where shoreline change rates may differ from those observed historically.

Maryland and Virginia↗

USGS2012

Geothermal gradients in the conterminous United States

Geothermal gradients from published temperature/depth measurements in drill holes generally deeper than 600 m are used to construct a temperature gradient map of the conterminous United States. The broadly contoured map displays 284 temperature gradients that are applicable to a depth of 2 km. In terms of the number of contoured areas and the fraction of data points having a value not within a contour interval (outliers), the temperature gradient data and associated deep heat flow data have similar measures of contourability. Areally, most of the United States is contoured from 15° to 35°C/km. The eastern United States is generally cooler (average 25°C/km) than the western United States (average 34°C/km), in accordance with broad heat flow trends. Differences between the temperature gradient and heat flow maps are caused by areal differences in rock thermal conductivities. The effect of conductivity on gradients is particularly apparent in the eastern United States where heat flow is relatively constant over large areas. Gradients are elevated where thick, low-conductivity, sedimentary deposits occur such as in the Atlantic Coastal Plain province and in basins in the Allegheny Plateau and the Great Plains provinces. No clear gradient pattern emerges where both heat flow and conductivity vary widely, such as in the northern Basin and Range and Rocky Mountain provinces. Using the temperature gradients determined in this study and associated heat flow values, derived thermal conductivities are calculated for the depth range of a few hundred meters to 2 km; the average conductivity is 2.5±0.8 W/m °C. Some areas show little variation in derived thermal conductivity, while others show a wide range. The Atlantic Coastal Plain, Appalachian Plateaus, Superior Upland, Gulf Coastal Plain, Columbia Plateaus and Cascade Mountains, and Sierra Nevada provinces have restricted ranges of conductivities, which supports the concept of regional conductivities.

Journal of Geophysical Research Solid Earth↗

USGS1986

Internal-wave currents as a mechanism to account for large sand waves in Navarinsky Canyon head, Bering Sea

Sand waves are found in the heads of four of five large submarine canyons that incise the northern continental margin of the Bering Sea. The sand waves occur in a restricted depth zone of about 175-490 m. Those in Navarinsky Canyon, the area surveyed in most detail, are best developed in water depths of 300-375 m; they average 5 m in height and about 650 m in wavelength, with crests oriented subparallel to isobaths and almost perpendicular to the axes of the two main branches of the canyon. We speculate that internal-wave currents are responsible for the sand waves. Currents generated by internal waves are a particularly attractive mechanism for at least three reasons: 1) the energy of the internal waves could be amplified in the head of Navarinsky Canyon, especially in the area of the sand wave field; 2) upslope boundary-layer intensification of internal-wave currents might be sufficient to move the sediment composing the sand waves; and 3) the wavelengths of higher-frequency internal waves closely match the spacing of the sand waves. Although we based our assumptions on present-day conditions, we do not know if the sand waves are active. Consequently, we do not discount the possibility that the sand waves could have originated in the Pleistocene when Navarinsky Canyon headed in a shallow embayment that was receiving large quantities of sediment discharged by glacial meltwater streams. These conditions probably caused strong vertical density gradients in the coastal waters, which would have been more favorable than those today for the propagation of high-frequency internal waves.

Journal of Sedimentary Research↗

USGS2023

Advances in morphodynamic modeling of coastal barriers: A review

As scientific understanding of barrier morphodynamics has improved, so has the ability to reproduce observed phenomena and predict future barrier states using mathematical models. To use existing models effectively and improve them, it is important to understand the current state of morphodynamic modeling and the progress that has been made in the field. This manuscript offers a review of the literature regarding advancements in morphodynamic modeling of coastal barrier systems and summarizes current modeling abilities and limitations. Broadly, this review covers both event-scale and long-term morphodynamics. Each of these sections begins with an overview of commonly modeled phenomena and processes, followed by a review of modeling developments. After summarizing the advancements toward the stated modeling goals, we identify research gaps and suggestions for future research under the broad categories of improving our abilities to acquire and access data, furthering our scientific understanding of relevant processes, and advancing our modeling frameworks and approaches.

Virginia↗