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At least 613 records · Page 34Linked to original sources
USGS2018

Ceres internal structure from geophysical constraints

Thermal evolution modeling has yielded a variety of interior structures for Ceres, ranging from a modestly differentiated interior to more advanced evolution with a dry silicate core, a hydrated silicate mantle, and a volatile‐rich crust. Here we compute the mass and hydrostatic flattening from more than one hundred billion three‐layer density models for Ceres and describe the characteristics of the population of density structures that are consistent with the Dawn observations. We show that the mass and hydrostatic flattening constraints from Ceres indicate the presence of a high‐density core with greater than a 1σ probability, but provide little constraint on the density, allowing for core compositions that range from hydrous and/or anhydrous silicates to a mixture of metal and silicates. The crustal densities are consistent with surface observations of salts, water ice, carbonates, and ammoniated clays, which indicate hydrothermal alteration, partial fractionation, and the possible settling of heavy sulfide and metallic particles, which provide a potential process for increasing mass with depth.

Meteoritics and Planetary Science↗
USGS2001

Geophysics: Silent slip on the Cascadia subduction interface

G eodetic satellites of the Global Positioning System (GPS) now permit continuous recording of surface motions around earthquake faults and volcanoes with millimeter precision. Data from distinct points on Earth's surface can be combined to infer the locations of the sources of deformation at depth in the crust. These data are radically altering our understanding of earthquake processes, justifying ambitious new sensor arrays to image active deformation sources in Earth's crust. In recent years, large continuous GPS arrays have been deployed in Japan and southern California, and smaller networks have been installed in other seismically active regions. On page 1525 of this issue ( 1 ), Dragert et al. provide a glimpse of the kinds of insights we can expect from these arrays.

Cascadia subduction zone↗
USGS1966

Airborne geophysical study in the Pensacola Mountains of Antarctica

A seismic reflection, gravity, and aeromagnetic reconnaissance was made in the Pensacola Mountains, Antarctica, during the 1965-66 austral summer. Prominent ice streams located between the Neptune and Patuxent Ranges and east of the Forrestal Range overlie channels in the rock surface 2000 meters below sea level which are probably of glacial origin. Seismic reflections show that the Filchner Ice Shelf is 1270 meters thick near its southern margin. Along the boundary between West and East Antarctica, Bouguer anomalies decrease from +60 milligals in West Antarctica to -80 milligals in East Antarctica. An abrupt change in crustal structure across this boundary is required to explain the 2 milligals per kilometer gradient. This may indicate a fault extending through the crust into the mantle. Aeromagnetic profiles delineate anomalies up to 1800 γ associated with the basic stratiform intrusion which comprises the Dufek and Forrestal ranges. A probable minimum area of 9500 square kilometers is calculated for the intrusive body on the basis of the magnetic anomalies, making it one of the largest bodies of its type. The extension of this magnetic anomaly across a fault forming the north border of the Pensacola Mountains probably precludes transcurrent movement.

Science↗
USGS1993

Geophysical investigations of the tectonic boundary between East and West Antarctica

The Transantarctic Mountains (TAM), which separate the West Antarctic rift system from the stable shield of East Antarctica, are the largest mountains developed adjacent to a rift. The cause of uplift of mountains bordering rifts is poorly understood. One notion based on observations of troughs next to many uplifted blocks is that isostatic rebound produces a coeval uplift and subsidence. The results of an over-snow seismic experiment in Antarctica do not show evidence for a trough next to the TAM but indicate the extension of rifted mantle lithosphere under the TAM. Furthermore, stretching preceded the initiation of uplift, which suggests thermal buoyancy as the cause for uplift.

Science↗
USGS1960

Geophysical investigation of Mono Basin, California

Gravity and seismic studies in Mono Basin , Mono County, California , completed during the summer of 1957 revealed a large, roughly triangular block that had subsided about 18,000 ± 5000 feet and received an accumulation of about 300 ± 100 cubic miles of light clastic sediments and volcanic material of Cenozoic age. The seemingly near-vertical faults that bound this great block are displaced toward the center of the basin from the surrounding mountain masses, but in general they are parallel to well-defined Basin and Range trends. The gravity minimum anomaly associated with the Mono Basin structure has a residual gravity relief of about 50 mgals, and the lowest gravity readings (on Paoha Island) yield a complete Bouguer gravity value of about - 260 mgals with respect to the International Ellipsoid. The computed depth of subsidence is based on a density of 2.3 gms/ cm 3 for the basin fill and 2.7 gms/cm 3 for the basement rocks. Seismic-refraction profiles at several places in the basin demonstrate that the Cenozoic deposits are thick where the gravity is low and relatively thin where the gravity is higher. Along common seismic and gravity profiles steep seismic dips coincide with steep gravity gradients. Numerous seismic reflections are present within the basin fill. Anomalies on four aeromagnetic profiles are related in part to volcanic material within the Cenozoic section. It is concluded that Mono Basin may be a volcano-tectonic depression caused by subsidence along faults, following extrusion of magma from a magma chamber at depth. Volcanic rocks of Pliocene(?) and Pleistocene ages are exceptionally abundant in this area.

California↗
USGS1971

Petrologic and geophysical nature of serpentinites

Mineralogically, serpentinites consist predominantly of lizardite, clinochrysotile, and antigorite. Recent work has shown that these minerals are not polymorphs. Chrysotile is the only mineral recognized as a synthetic product in experimental studies of the system MgO-SiO 2 -H 2 O. Antigorite seems to be stable at higher temperatures than lizardite or chrysotile. The density of individual serpentine species is dependent on their morphology; the low-density serpentinites (<2.55g/cc) consist predominantly of clino-chrysotile. Seismic velocities and magnetic susceptibilities of serpentinites are related to the degree of serpentinization. The transition of massive serpentinites from ductile to brittle behavior in laboratory experiments at high confining pressures and temperatures above 300°C has been related to dehydration which may provide a mechanism for developing deep-focus earthquakes along Benioff zones. Serpentinite is formed by direct hydration of ultramafic protolith in the crust. The most common ultramafic protoliths are harzburgite, dunite, and Iherzolite. The assemblage generally developed from these is lizardite + chrysotile + brucite + magnetite. In areas of high-grade metamorphism, antigorite is the predominant serpentine mineral. The common, large, alpine-type serpentinized ultramafic masses contain brucite and have MgO/SiO 2 ratios similar to those of their protolith, resulting in volume increase during serpentinization. Metamorphic serpentinites and some highly sheared alpine-type serpentinites have lower MgO/SiO 2 ratios than their protolith, lack brucite, and appear t o have been formed by volume-for-volume replacement with concomitant loss of magnesium or addition of silica. Many large, young masses of peridotite appear to be slabs of oceanic mantle over-thrust onto continental edges. Subsequent sedimentation, serpentinization, and tectonism have greatly modified these original slabs so that their recognition in older orogenic zones is equivocal. The concept of the tectonic evolution of ultramafic rocks from oceanic crust-mantle slabs invading continental margins and being incrementally serpentinized and moved by later tectonic events provides a working hypothesis that allows a better explanation of the many peculiar and varied occurrences of serpentinite. The evidence does not support Hess' suggestion that the third layer of the oceanic crust consists of partly serpentinized mantle peridotite.

Bulletin of the Geological Society of America↗
USGS1973

Trans-Andean geophysical profile, southern Colombia

Negative Bouguer anomalies (−80 mgals) near the Pacific coast of southern Colombia define the position of the Tertiary Bolívar trough. Values increase eastward to a huge positive anomaly (+75 mgals) over Mesozoic “eugeosynclinal” rocks of the western Andes. This anomaly is part of the West Colombian gravity high, which extends from Panamá into western Ecuador and is caused by shallow mafic crust. Bouguer anomalies are strongly negative (−220 mgals) over pre-Mesozoic(?) metamorphic rocks, Mesozoic(?) granitic bodies, and Tertiary to Holocene volcanic rocks of the central Andes between Pasto and Ipiales. The steep gravity gradient between the West Colombian gravity high and the negative anomaly of the central Andes represents the transition between mafic crust to the west and continental crust to the east. This zone parallels the Romeral-Cauca megashear system. East of the Andes, Bouguer anomalies range from −50 to −120 mgals over a Mesozoic-Tertiary basin of the Putumayo district, indicating that the crust there is thinner or denser than it is beneath the central Andes. Models derived from gravity data suggest that the crust is about 45 km thick under the south-central Colombian Andes. If this is correct, the crust must thicken southward along the strike of the Andes, as thicknesses of 70 km have been reported in the Andes of southern Perú, Bolivia, and northern Chile by Lomnitz (1962) and James (1971a). Such differing crustal thicknesses may reflect different intensities of tectonic activity, greater crustal thickness indicating more intense or rapid growth of the volcano-plutonic arc or foreshortening of an existing crustal section.

Geological Society of America Bulletin↗
USGS2013

Geophysical constraints on Rio Grande rift structure and stratigraphy from magnetotelluric models and borehole resistivity logs, northern New Mexico

Two- and three-dimensional electrical resistivity models derived from the magnetotelluric method were interpreted to provide more accurate hydrogeologic parameters for the Albuquerque and Española Basins. Analysis and interpretation of the resistivity models are aided by regional borehole resistivity data. Examination of the magnetotelluric response of hypothetical stratigraphic cases using resistivity characterizations from the borehole data elucidates two scenarios where the magnetotelluric method provides the strongest constraints. In the first scenario, the magnetotelluric method constrains the thickness of extensive volcanic cover, the underlying thickness of coarser-grained facies of buried Santa Fe Group sediments, and the depth to Precambrian basement or overlying Pennsylvanian limestones. In the second scenario, in the absence of volcanic cover, the magnetotelluric method constrains the thickness of coarser-grained facies of buried Santa Fe Group sediments and the depth to Precambrian basement or overlying Pennsylvanian limestones. Magnetotelluric surveys provide additional constraints on the relative positions of basement rocks and the thicknesses of Paleozoic, Mesozoic, and Tertiary sedimentary rocks in the region of the Albuquerque and Española Basins. The northern extent of a basement high beneath the Cerros del Rio volcanic field is delineated. Our results also reveal that the largest offset of the Hubbell Spring fault zone is located 5 km west of the exposed scarp. By correlating our resistivity models with surface geology and the deeper stratigraphic horizons using deep well log data, we are able to identify which of the resistivity variations in the upper 2 km belong to the upper Santa Fe Group sediment

New Mexico↗
USGS2022

Geophysical extent of the Wyoming Province, western USA: Insights into ancient subduction and craton stability

A new 3-D resistivity model, estimated from inversion of magnetotelluric data, images crustal and upper-mantle structure of the Wyoming Province and adjacent areas. The Archean province is imaged as a coherent resistive domain, in sharp contrast to active tectonic domains of the western U.S. Prominent high-conductivity belts define the northern, eastern, and southern margins of the Wyoming Province and are interpreted as sutures marking the remnants of Paleoproterozoic orogens. The model results suggest the northern boundary of the Wyoming Province is located 150 km south of its traditional placement and adjacent to a composite orogen separating the Wyoming Province and Medicine Hat block. The eastern province boundary is clearly imaged along the Black Hills, whereas the western margin is obscured by Cenozoic extension and magmatism. An internal boundary within the Wyoming Province is interpreted to represent a Neoarchean suture; in stark contrast to Proterozoic sutures, though, it is not marked by a high-conductivity belt. This difference in conductivity is speculated to reflect changes in the subduction process through time. The absence of high-conductivity along Archean sutures appears to be global in nature and related to reduced continental freeboard in the Archean which limited continental weathering and the delivery of carbon-rich sediments to the seafloor. Although the entire Wyoming Province has been proposed to have undergone lithospheric modification that lessened its stability, the resistivity model suggests a thick lithospheric root remains in place except along its western margin. These results suggest that Archean cratons may be more resistant to lithospheric modification by influx of heat and fluids associated with extension and plumes than previously thought, and that metasomatism does not necessarily weaken the lithosphere and set a craton on the path to destruction.

Colorado, Montana, Utah, Wyoming↗
USGS2024

Geophysical constraints on continental rejuvenation in central China: Implications for outward growth of the Tibetan Plateau

Continental rejuvenation results from the tectonic reactivation of crustal structures and lithospheric reworking by mantle flow. Geochemical observations and field mapping have traditionally provided the primary evidence for the secular evolution of crustal composition and tectonic processes during continental rejuvenation. Nonetheless, the impact of continental rejuvenation on the observed present-day strain rate and orogenic-scale lithospheric structure has not been well constrained. The pre-existing E-W–trending Central China Orogenic Belt has been overprinted by the N-S–trending Central Longitudinal Seismic Belt and constitutes the intracontinental West Qinling Syntaxis in central China, where the tectonic setting changes eastward from contraction to extension. Combining updated global positioning system data and high-resolution crustal seismic tomography, we reveal a modern continental rejuvenation process within the West Qinling Syntaxis in central China. The northward extrusion of the Tibetan Plateau's weak lithospheric layer (middle-lower crust and lithospheric mantle) of southwestern China relative to the rigid Sichuan Basin/Ordos Block of the eastern West Qinling Syntaxis results in regional dextral shearing that shapes the Central Longitudinal Seismic Belt and defines the eastern Tibetan Plateau margin. The pre-existing E-W–trending Central China Orogenic Belt has been preserved above the brittle-ductile transition zone, and the northward movement of the deep lithospheric layer drives the deformation of the upper crust in the West Qinling Syntaxis. Our results, along with previous studies, suggest the presence of an intracontinental lithospheric interchange structure in central China. The continental rejuvenation of the West Qinling Syntaxis results from a combination of fault reactivation in the upper crust (Stage I, Eocene–Oligocene) and reworking of the deep lithosphere (Stage II, middle–late Miocene) related to the plateau-wide shift in stress accommodation ultimately driven by the redistribution of mass outward from the central Tibetan Plateau. At present, the transition zone between the high- and low-velocity anomalies along the Central Longitudinal Seismic Belt not only shapes the landscape boundary but controls the size and recurrence interval of earthquakes within the West Qinling Syntaxis in central China.

GSA Bulletin↗
USGS2020

Three-dimensional shape and structure of the Susitna basin, south-central Alaska, from geophysical data

We use gravity, magnetic, seismic reflection, well, and outcrop data to determine the three-dimensional shape and structural features of south-central Alaska’s Susitna basin. This basin is located within the Aleutian-Alaskan convergent margin region and is expected to show effects of regional subduction zone processes. Aeromagnetic data, when filtered to highlight anomalies associated with sources within the upper few kilometers, show numerous linear northeast-trending highs and some linear north-trending highs. Comparisons to seismic reflection and well data show that these highs correspond to areas where late Paleocene to early Eocene volcanic layers have been locally uplifted due to folding and/or faulting. The combined magnetic and seismic reflection data suggest that the linear highs represent northeast-trending folds and north-striking faults. Several lines of evidence suggest that the northeast-trending folds formed during the middle Eocene to early Miocene and may have continued to be active in the Pliocene. The north-striking faults, which in some areas appear to cut the northeast-trending folds, show evidence of Neogene and probable modern movement. Gravity data facilitate estimates of the shape and depth of the basin. This was accomplished by separating the observed gravity anomaly into two components—one representing low-density sedimentary fill within the basin and one representing density heterogeneities within the underlying crystalline basement. We then used the basin anomaly, seismic reflection data, and well data to estimate the depth of the basin. Together, the magnetic, gravity, and reflection seismic analyses reveal an asymmetric basin comprising sedimentary rock over 4 km thick with steep, fault-bounded sides to the southwest, west, and north and a mostly gentle rise toward the east. Relations to the broader tectonic regime are suggested by fold axis orientations within the Susitna basin and neighboring Cook Inlet basin, which are roughly parallel to the easternmost part of the Alaska-Aleutian trench and associated Wadati-Benioff zone as it trends from northeast to north-northeast to northeast. An alignment between forearc basin folds and the subduction zone trench has been observed at other convergent margins, attributed to strain partitioning generated by regional rheologic variations that are associated with the subducting plate and arc magmatism. The asymmetric shape of the basin, especially its gentle rise to the east, may reflect uplift associated with flat-slab subduction of the Yakutat microplate, consistent with previous work that suggested Yakutat influence on the nearby Talkeetna Mountains and western Alaska Range. Yakutat subduction may also have contributed to Neogene and later reverse slip along north-striking faults within the Susitna basin.

Alaska↗
USGS2022

Insights into the geometry and evolution of the southern San Andreas Fault from geophysical data, southern California

Two new joint gravity-magnetic models in northern Coachella Valley provide additional evidence for a steep northeast dip of the Mission Creek strand of the southern San Andreas fault (southern California, USA). Gravity modeling indicates a steep northeast dip of the Banning fault in the upper 1–2 km in northern Coachella Valley. The Mission Creek strand and its continuation to the southeast (Coachella segment) coincide with the northeastern margin of a Cenozoic basin and are marked by prominent gravity and magnetic gradients that are consistent with these strands of the San Andreas fault having accommodated >160 km of right-lateral and 1–5 km of vertical displacement. These anomalies are best fit by a moderate to steep northeast dip. Such a geometry is further supported by seismicity, reflectivity, geodesy, and boundary-element modeling. We explore the possibility that these fault strands forming the margin of Coachella Valley were originally near vertical and have rotated into their present orientation by underplating of a localized high-velocity, lower-crustal prong within the Peninsular Ranges batholith. Reconstructions of San Andreas fault offset suggest that this crystalline body was translated into the San Gorgonio Pass area at the time of major fault reorganization at 1.1–1.3 Ma.

California↗
USGS2023

High-resolution geophysical and geochronological analysis of a relict shoreface deposit offshore central California: Implications for slip rate along the Hosgri fault

The Cross-Hosgri slope is a bathymetric lineament that crosses the main strand of the Hosgri fault offshore Point Estero, central California. Recently collected chirp seismic reflection profiles and sediment cores provide the basis for a reassessment of Cross-Hosgri slope origin and the lateral slip rate of the Hosgri fault based on offset of the lower slope break of the Cross-Hosgri slope. The Cross-Hosgri slope is comprised of two distinct stratigraphic units. The lower unit (unit 1) overlies the post–Last Glacial Maximum transgressive erosion surface and is interpreted as a Younger Dryas (ca. 12.85–11.65 ka) shoreface deposit based on radiocarbon and optically stimulated luminescence (OSL) ages, Bayesian age modeling, seismic facies, sediment texture, sediment infauna, and heavy mineral component. The shoreface was abandoned and partly eroded during rapid sea-level rise from ca. 11.5 to 7 ka. Unit 2 consists of fine sand and silt deposited in a midshelf environment when the rate of sea-level rise slowed between ca. 7 ka and the present. Although unit 2 provides a thin, relatively uniform cover over the lower slope break of the older shoreface, this feature still represents a valuable piercing point, providing a Hosgri fault slip rate of 2.6 ± 0.8 mm/yr. Full-waveform processing of chirp data resulted in significantly higher resolution in coarser-grained strata, which are typically difficult to interpret with more traditional envelope processing. Our novel combination of offshore radiocarbon and OSL dating is the first application to offshore paleoseismic studies, and our results indicate the utility of this approach for future marine neotectonic investigations.

California↗
USGS2023

Integrated geologic and geophysical modeling across the Bartlett Springs fault zone, northern California (USA): Implications for fault creep and regional structure

The rate and location at depth of fault creep are important, but difficult to characterize, parameters needed to assess seismic hazard. Here we take advantage of the magnetic properties of serpentinite, a rock type commonly associated with fault creep, to model its depth extent along the Bartlett Springs fault zone, an important part of the San Andreas fault system north of the San Francisco Bay, California (western United States). We model aeromagnetic and gravity anomalies using geologic constraints along 14 cross sections over a distance of 120 km along the fault zone. Our results predict that the fault zone has more serpentinite at depth than inferred by geologic relationships at the surface. Existing geodetic models are inconsistent and predict different patterns of creep along the fault. Our results favor models with more extensive creep at depth. The source of the serpentinite appears to be ophiolite thrust westward and beneath the Franciscan Complex, an interpretation supported by the presence of antigorite, a high-temperature serpent ine mineral stable at depth, in fault gouge near Lake Pillsbury.

California↗
USGS1990

Geology, geophysics, and geochronology of the Manson impact structure

A problem with the impact hypothesis for the Cretaceous/Tertiary (K/T) mass extinction is the apparent absence of an identifiable impact site. The Manson impact structure is a candidate site because of its size (the largest such structure recognized in the United States); in addition, the largest and most abundant shocked quartz grains at the K/T boundary are found relatively close by, and its age is indistinguishable from that of the K/T boundary. The region of northwest central Iowa that contains the Manson impact structure is covered by Quaternary glacial deposits, which are underlain by Phanerozoic sedimentary rocks (mostly flat-lying carbonates) and Proterozoic red clastic, metamorphic, volcanic, and plutonic rocks. In a circular area about 22 mi (35 km) in diameter around Manson, Iowa, this normal sequence is absent or “disturbed.” Within the structure, three roughly concentric zones of rock associations have been identified: an outer zone of displaced strata, a zone of completely disrupted strata, and a central area in which basement igneous and metamorphic rocks have been uplifted at least 1,220 ft (4,000 m). Gravity, magnetic, and seismic refraction surveys readily identify the central uplift within the structure. Manson is established as an impact structure based on its circular shape, its central uplift, and the presence of shocked quartz within the granitic central uplift. Paleontological evidence, a fission track age, and preliminary 40 Ar/ 39 Ar dating all allowed a K/T boundary age for the Manson structure. Improved 40 Ar/ 39 Ar age spectra may be interpreted in terms of samples that were incompletely degassed during heating due to the Manson impact. An age of 65.7 ± 1.0 Ma was obtained, a value indistinguishable from that of the K/T boundary.

Iowa↗
USGS2026

Geophysical architecture and geochronology of the Neoarchean Mentor anorthosite intrusive complex, northwestern Minnesota: Largest anorthosite complex of the Superior Province?

The Neoarchean Mentor anorthosite intrusive complex (MAIC) lies within the Wawa subprovince in northwestern Minnesota, in a region where the Wawa, Quetico, and Wabigoon subprovinces are juxtaposed in close proximity. Archean rocks are entirely concealed, and interpretations are developed from aeromagnetic, gravity, and borehole samples. The MAIC includes both anorthosite (dense, weakly magnetized) and oxide-rich gabbro (strongly magnetized) lithologies. Anorthosite is coarse-grained to megacrystic, intensely altered, and locally brecciated. Pervasive epidote alteration enhanced the density of the anorthosite via introduction of higher-density mineral assemblages, explaining why the MAIC produces a significant gravity high. Oxide-rich gabbro forms a border phase of the MAIC and has potential for vanadium, chromium, and titanium mineralization, and produces a strong aeromagnetic high. The MAIC is interpreted to extend over an area of 640 km 2 , making it the largest known anorthosite complex of the Superior Province, as measured by preserved areal extent. Modeling indicates the MAIC extends more than 6 km into the subsurface. A new Pb–Pb zircon age of 2737.2 ± 4.5 Ma is interpretated as the crystallization age of anorthosite within the MAIC, showing that the MAIC formed well before the ca. 2690 Ma Shebandowanian orogeny, and raising new questions about correlations with other parts of the Wawa subprovince. A low-density batholith, here informally called the Fertile batholith, is interpreted to intrude the southern part of the MAIC. A new Pb–Pb zircon age of 2701.1 ± 6 Ma is interpreted as the magmatic age of the Fertile batholith.

Minnesota↗
USGS2023

Fusing geophysical and remotely sensed data for observing overwash occurrence, frequency, and impact

Overwash is an important process that enables a barrier island to migrate landward to adapt to rising sea levels but can also impact vegetated areas and create coastal hazards for populated barrier islands. Our overall objectives were to hindcast overwash events from September 2008 to November 2009 and assess whether overwash impacts could be detected using moderate-resolution imagery (30 m). Estimates of wave and still water levels can be benchmarked against morphological characteristics from elevation datasets to predict overwash events. These observations can be combined with optical remote sensing data used to monitor for changes in vegetation greenness over time to evaluate potential impacts from overwash. This study highlighted how physical-based overwash data can be paired with observations of greenness. The results from our study highlighted that a discernable drop in greenness can be detected for major hurricanes, such as Hurricane Gustav in 2008, with a weaker signal observed for smaller magnitude events in 2009 like Hurricane Ida. Tracking overwash impacts to vegetation can be helpful for observing impacts to vegetation associated with restoration efforts and advancing our understanding of general overwash impacts and recovery.

Conference Paper↗
USGS2015

Integrating geophysical and oceanographic data to assess interannual variability in longshore sediment transport

Despite their utility for prediction of coastal behavior and for coastal management, littoral sediment budgets are difficult to quantify over large regions of coastline and over short time scales. In this study, bathymetric change analysis shows differences in the magnitude and spatial location of erosion and accretion over three years; more net accumulation occurred at the littoral end point of the system in the second year (2012-2013) compared to the first (2011-2012). However, the estimated magnitude of longshore transport based on wave characteristics was lower in the second year than for the first year. Similarly, comparisons of total water levels and island elevation over the study period show increased number of overwash hours in the second year, indicating increased cross-shore sediment losses and presumably less sediment transported alongshore. The storm-mediated degradation of the man-made northern portion of the island resulting in increased sub-aqueous sediment availability may explain the observations.

Conference Paper↗