Dissertations / Theses on the topic 'Department of Geology and Geophysics'

The lateral "corners" where Kamb and Whillans Ice Streams (KIS and WIS) discharge into the Ross Ice Shelf share common geometries and ice mechanical settings. At both corners of the now-stagnant KIS outlet, shear margins of apparently different ages confine regions with a relatively flat, smooth surface expression. These features are called the "Duckfoot" on the northern, right-lateral side and the "Goosefoot" on the other. It has been suggested, on evidence found in ice internal layers, that the flat ice terrains on KIS were afloat in the recent past, at a time when the ice stream grounding line was upstream of its present location. The overdeepening in the bed just upstream of the KIS grounding line supports this view of the past geometry.

The right-lateral margin at the outlet of the currently active WIS, the location of Subglacial Lake Englehardt (SLE), appears to have many similarities with the right lateral margin of KIS, though with a less developed looking inboard margin. This paper presents a mechanical analysis using surface and bed topography and velocity datasets comparing the Duckfoot flat ice terrain with the terrain around Subglacial Lake Englehardt. At both locations mechanical thinning along shear margins and lows in the bed topography redirects basal water routing towards the features. Here, I consider the history of these features and their role in ice stream variability by comparison of the relict and modern features and via numerical modeling of ice shelf grounding and ungrounding in response to variations in ice flow.

We propose two scenarios for the development of flat ice terrains/subglacial lakes at the outlets of ice streams. In the first, development of a lake in the hydraulic potential low along a shear margin forces a margin jump as shearing develops along the inboard shore of the margin lake. This thesis presents evidence for an inboard (relative to the main outboard shear margin) zone of shear along the inboard shoreline of SLE, suggesting that subglacial lakes along shear margins are capable of facilitating shear margin jumps. In the second, grounding line advance around a relative low in the bed, creating adjacent margins along the lakeshores, forms a remnant lake. Discerning which of these scenarios is appropriate at the KIS outlet has implications for understanding the history of the ice stream grounding line.

An ice flow model is used to place these local conditions in a regional context by studying the effect of internal perturbations, such as ice rise stagnation or inward margin jumps, on grounding line position. Bathymetry is important in determining ice stream flow in the ways that might not be otherwise realized in 1-D flow model studies. In the numerical modeling experiments, grounding line advance across the KIS outlet is mediated by the overdeepening in the bed and proceeds not in the direction of ice flow but transverse to flow. This finding adds complexity to both a flowline view of grounding line migration and the theory that grounding lines are unstable in the presence of inward sloping bed topography.

This thesis examines different methods of communicating volcanic hazards to the population of Flagstaff, Arizona using the results of a recent lava flow hazard assessment of the nearby San Francisco Volcanic Field (SFVF). Harburger (2014) determined that given a lava flow originating in the SFVF, there is a statistical probability that it will inundate the city of Flagstaff or even originate from a vent within the city limits. Based on the recurrence rates for the most recent eruptions (3 x 10-4/year), the probability of lava flow inundation in Flagstaff is 1.1 x 10-5 per year.

This study considers the effects of three different communication methods on participants’ perceived risk. The methods were administered through a questionnaire and included a statement of probability of lava flow inundation per year, a statement of probability over a 100 year period, and an interactive lava flow map derived from the results of the lava flow hazard assessment. Each method was followed by questions gauging level of concern. Questionnaires were administered to 213 Flagstaff residents over a two week period in February 2015.

Results showed that levels of concern, rated from 1 (not concerned) to 5 (very concerned), varied based on each method of communication. The method with the greatest effect on perceived risk was the simulated lava flow map, while the first method with a one year odds resulted in a statistically lower mean rating of concern. It is suggested that the best way to change levels of perceived risk when communicating lava flow hazards includes a combination of comprehensible odds and visual aids. Further studies could also include visualization of the entire eruption scenario, including time scales and other volcanic hazards, which may have more effect on concern than a simplified visualization of lava flows.

A 3D seismic volume across the campus of California State University, Long Beach images the Alamitos Heights fault, a splay of the Newport-Inglewood fault zone (NIFZ). The Alamitos Heights fault is a zone that strikes approximately N55°W, dips on average 80°SW, and bounds the northeast extent of the Seal Beach oil field structure. It plays a role in the complex evolution of the Newport-Inglewood fault zone within the Los Angeles sedimentary basin, which is closely related to timing and trapping mechanisms of nearby oil fields. Its origin and development may be related to fault steps or discontinuities along the main NIFZ. Seismic evidence suggests the Alamitos Heights fault may have originated as a transtensional feature during the Miocene before transitioning to its current transpressional stress regime.

Roatán Island is the largest of the Bay Islands of Honduras. These islands form an emergent crest off the Caribbean coast of Honduras called the Bonacca Ridge. The Bartlett Trough to the north and subsequent Bonacca Ridge were likely formed due to the transform fault system of the Motagua-Swan Islands Fault System. This fault system forms the tectonic plate boundary between the North American and Caribbean plates. Although the timing and kinematics are poorly constrained, the Bay Islands and the Bonacca Ridge were likely uplifted due to transpression along this left-lateral strike-slip system. With limited regional exposures along the adjacent tectonic boundary, this study aimed to present a structural interpretation for Roatán. This new interpretation is further explained through regional considerations for a suggested geologic history of the northwestern Caribbean.

In order to better constrain the kinematics of uplift and exhumation of Roatán Island, structural, gravity, and magnetic surveys were conducted. Principal attention was directed to the structural relationship between the geologic units and their relationship to one another through deformation. Resulting geologic cross-sections from this study present the metamorphic basement exposed throughout the island to be in a normal structural order consisting of biotite schist and gneiss, with overlying units of chlorite schist, carbonate, and conglomerate. These units have relatively concordant strike and dip measurements, consistent with resultant magnetic survey readings. Additionally, large and irregular bodies of amphibolite and serpentinite throughout the island are interpreted to have been emplaced as mafic and ultra-mafic intrusions in weakness zones along Early Paleogene transform system fault planes.

The interpretation and suggested geologic history from this study demonstrate the importance of transpressive tectonics both local to Roatán and regionally throughout geologic history. Consideration of this interpretation will help to further constrain regional studies over the northwestern Caribbean.

The depositional environment of the middle to late Eocene Oberlin sand of Northwest Oberlin Field and Pilgrim Church Field in central Allen Parish, Louisiana, was investigated. The depositional environment of the Oberlin sand has been interpreted from observations of spontaneous potential log signatures, conventional core reports, paleontological reports, shape of isochore maps, coherency extraction attribute, amplitude extraction attribute, and multiple seismic and subsurface cross sections. Focus is centered on the juxtaposition of component sand bodies and their proximity to the interdistributary and prodelta environments. Sand bodies include distributary channels, distributary mouth bars, crevasse subdeltas and shelfal bars and are interpreted to be the products of lower deltaic and shelf processes. The results of this study are based on seismic analysis, display techniques and subsurface maps calibrated to well logs, models, and recognition criteria of modern and ancient depositional environments previously described in the regional literature. The integration of all available data provides an objective and systematic approach detailing the origin, lateral extent, geometry and architecture of the Oberlin sand in the lower deltaic plain and shelf environments. The results of this study may be applicable to similar age sands on trend with the study area. Understanding of sand component types of the lower deltaic and shelf environments is vital to exploration success and development optimization of hydrocarbon bearing reservoirs.

Possible sea-floor spreading anomalies are indentified in marine magnetic surveys conducted in the eastern Gulf of Mexico. A symmetric pattern of lineated anomalies can be correlated with the geomagnetic time scale using previously proposed opening histories for the Gulf of Mexico basin. Lineated magnetic anomalies are characterized by amplitudes of up to 30 nT and wavelengths of 45-55 km, and are correlatable across 12 different ship tracks spanning a combined distance of 6,712 km. The magnetic lineations are orientated in a NW-SE direction with 3 distinct positive lineations on either side of the inferred spreading ridge anomalies. The magnetic anomalies were forward modeled with a 2 km thick magnetic crust composed of vertically bounded blocks of normal and reverse polarity at a model source depth of 10 km. Remnant magnetization intensity and inclination are 1.6 A m^-1 and 0.2° respectively, chosen to best fit the magnetic observed amplitudes and, for inclination, in accord with the nearly equatorial position of the Gulf of Mexico during Jurassic seafloor spreading. The current magnetic field is modeled with declination and inclination of and 0.65° and 20° respectively. Using a full seafloor spreading rate of 1.7 cm/yr, the anomalies correlate with magnetic chrons M21 to M10. The inferred spreading direction is consistent with previous suggestions of a North-East to South-West direction of sea-floor spreading off the west coast of Florida beginning 149 Ma (M21) and ending 134 Ma (M10). The opening direction is also consistent with the counter-clockwise rotation of Yucatan proposed in past models.

Previous work conducted by Kushiyama (2010) identified a relative gravity profile with an abnormal anomaly across a normal fault. The relative gravity should have decreased when crossing from the upthrown side to the downthrown side. Additional relative gravity data were collected and incorporated with the existing data to create an improved gravity anomaly map. The map shows that the gravity generally increases from the southwest to the northeast in the study area. In two areas where profiles cross the fault at nearly a perpendicular angle, the fault is clearly visible and interpretable from the gravity data. However, along Chris Road, that is not the case. This is most likely caused by an underlying salt ridge (Varvaro, 1958). The mobilization of this salt upwards through more dense strata might be the cause of the low gravity effect of the upthrown side of the fault along Chris Road.

The seismic attribute High-Frequency Absorption (HFA) is a method of evaluating the absorptive properties of rocks as nonstationary wavelets pass through the substrate. This technique is used today as a direct hydrocarbon indicator, where it should be used as a diagnostic tool in conjunction with several other geophysical and geological processes for the delineation of hydrocarbon reservoirs. Understanding the absorptive properties of target reservoirs and correlating their geophysical aspects to geologic properties, courtesy of well logs, may allow us to interpret patterns between hydrocarbon saturation and HFA on local reservoir scales. The ability to estimate hydrocarbon saturation can significantly affect the risk evaluations of potential prospects and further increase our rate of success when wildcatting or developing fields. Analysis shows that in this particular project, proper data, such as neutron-density logs, are seldom run in the wells of this area, thus making estimation of water/hydrocarbons very difficult and very inaccurate. Other complications include the resolution of seismic data compared to well log data. Due to these obstacles, high-resolution correlations of HFA to hydrocarbon saturation proved to be unsuccessful. However, association of proven vs. false prospects showed very high correlations to HFA signatures.

This study examines the relationship of the Palos Verdes Fault Zone (PVFZ), an important fault zone in the Inner Borderland (IB), to the Palos Verdes Anticlinorium, Wilmington Graben, and other structures through detailed mapping of the fault zone constructed from high resolution 2D and 3D seismic reflection data and well logs. The data reveal a Mohnian-Delmontian trough, controlled by rifting and predating Palos Verdes Anticlinorium uplift, along the western PVFZ boundary. Sediment growth in the trough, the bulk of which occurred during the Mohnian, locally persisted into the Repettian. The western PVFZ boundary fault then transitioned to a transpressional regime beginning during the Repettian, inverting trough sediments. Typical of transpressional restraining bends along strike-slip faulting, varying degrees of inversion occur along the fault, with moderate inversion occurring on the central shelf with areas of little to no inversion to the north and south, all bounded by extreme inversion in the Palos Verdes Peninsula to the north and Lasuen Knoll to the south.

The present location and geometry of the PVFZ with its various restraining and releasing bends, is potentially a product of the early rifting episode, which is related to other sub-parallel major IB rifts, such as San Pedro Basin, San Diego Trough, and Los Angeles Basin. At roughly 65 km long, 1-7 km wide, and 1-1.5 km deep, the PVFZ trough is much narrower than the other IB basins, except the San Diego Trough.

The Taranaki Basin is the only known producing basin within New Zealand. Since the drilling of the first well in 1865, the Taranaki basin has remained relatively underexplored. The Arawa-1 well was drilled in 1992 using 2D seismic lines as a control. New Zealand has started an exploration initiative by publicly releasing all geological and geophysical information gathered on and offshore New Zealand. The gathered information includes the Parihaka 3D survey, which directly overlaps with the Arawa-1 well and original 2D lines. This study focused on the Miocene-Pliocene Mangaa Formation, which exhibited reservoir quality within the Arawa-1 well. Seismic attributes have been used to locate an area of interest within the Mangaa Formation. A Coherence attribute was useful for identifying geomorphological features as well as faults. An average energy volume was used to emphasize brighter amplitudes from background signatures and to define lateral boundaries of the reservoir. Upon mapping an area of interest within the Mangaa Formation, the amplitude anomalies were conformable to structural highs. Results were compared to an analog well, Karewa-1, where amplitude anomalies were relatively identical. Amplitude versus offset analysis was conducted for the amplitude anomaly within the Mangaa Formation and found a class 4 anomaly. The interpreter performed fluid replacement modeling with the assumption of 100% gas, derived from the analog, Karewa-1. The interpreter compared the resulting model to the observed trends inside and outside of the amplitude anomaly. The gas model signature resembled that of the amplitudes inside of the amplitude anomaly, and the amplitude signature of the original water saturation resembled that of the amplitudes outside of the anomaly. The results allow the interpreter to use the correlation of amplitude signatures and fluids in place to assist in de-risking prospect potential.

Analysis of the anisotropy of magnetic susceptibility (AMS) is an easy, non-destructive method to determine the preferred orientations of minerals in rocks and rock analogs. The orientations of the principal susceptibility axes (K_max≥K_int≥K_min) of the AMS ellipsoid are generally parallel to the principal axes of the strain ellipsoid (X≥Y≥Z). The orientations of the AMS axes as well as the magnitudes change in response to strain, though a generally accepted correlation between the magnitudes of the principal axes of AMS and strain has not yet been established. A successful correlation of the magnitudes of the principal susceptibility axes of AMS and strain would allow an easy and non-destructive method of quantitative strain analysis. This would also allow quantitative strain analyses of rocks where traditional methods using strain markers fail. In this study, the quantitative aspect of the relationship between strain and AMS is investigated experimentally using artificial mineral mixtures with a sedimentary initial magnetic fabric in an attempt to correlate strain to AMS. Mineral mixtures of magnetite, biotite, and specular hematite with a matrix of Art Time Dough^® (similar to Playdoh^®) were mixed separately. To create a random magnetic fabric, the samples were kneaded by hand for approximately 15 minutes. The samples were then strained to 70% strain in one direction to create a sedimentary initial magnetic fabric. The orientation of this strain became the Z axis of the strain ellipsoid. The samples were then strained perpendicular to this axis incrementally from 0% to 40% strain in 5% increments, with the AMS measured at each interval. The orientation of this strain became the Y axis of the strain ellipsoid. The data from these experiments resulted in the quantitative correlation of strain and AMS for the magnetite mineral mixtures. The biotite and specular hematite mixtures contain enough magnetite inclusions and magnetite conversion respectively to dominate the AMS. This creates a more complex relationship that is not easily correlated quantitatively to strain. The experiments demonstrate that a strong qualitative relationship exists between both the orientations and the magnitudes of the axes of the strain and AMS ellipsoids.

Among the most important properties controlling the production from conventional oil and gas reservoirs is the distribution of porosity and permeability within the producing geologic formation. The geometry of the pore space within these reservoirs, and the permeability associated with this pore space geometry, impacts not only where production can occur and at what flow rates but can also have significant influence on many other rock properties. Zones of high matrix porosity can result in an isotropic response for certain reservoir properties whereas aligned porosity/permeability, such as open, natural fracture trends, have been shown to result in reservoirs being anisotropic in many properties.

The ability to identify zones within a subsurface reservoir where porosity/permeability is significantly higher and to characterize them according to their geometries would be of great significance when planning where new boreholes, particularly horizontal boreholes, should be drilled. The detection and characterization of these high porosity/permeability zones using their isotropic and anisotropic responses may be possible through the analysis of azimuthal (also referred to as azimuth-limited) 3D seismic volumes.

During this study the porosity/permeability systems of a carbonate, pinnacle reef within the northern Michigan Basin undergoing enhanced oil recovery were investigated using selected seismic attributes extracted from azimuthal 3D seismic volumes. Based on the response of these seismic attributes an interpretation of the geometry of the porosity/permeability system within the reef was made. This interpretation was supported by well data that had been obtained during the primary production phase of the field. Additionally, 4D seismic data, obtained as part of the CO₂ based EOR project, supported reservoir simulation results that were based on the porosity/permeability interpretation.

Located in LaSalle Parish, Louisiana, the area of interest for this study encompasses portions of the Tullos-Urania and Olla oil fields, with their hydrocarbon accumulation stemming from the Wilcox Group. The overall objective of this study is threefold; first, generate structure maps of the strata within this area of investigation and identify the productive formations. Second, utilize seismic modeling from local wells defining the most accurate resistivity-to-sonic transform. The last goal is to generate an accurate seismic-to-well tie employing the most accurate sonic log generated at the wells bounding the high-resolution shallow imaging seismic data. This study must use resistivity data to model sonic logs for the bounding wells which have no sonic logs available. The modeled sonic logs are then used to create time- depth relationships between the acquired seismic data and the wells bounding the seismic line. To use resistivity logs to model a sonic log, this study will compare three equations (Faust, 1953; Kim, 1964; Smiths, 1968) to determine their relative accuracies for a one-step resistivity-to-sonic transform. Accuracy is measured by the absolute average deviation of the modelled sonic data from the measured sonic data from wells within the study area, but distant from the seismic line, which have recorded sonic logs. The results of this study indicate that the one-step resistivity-to- sonic equation proposed by Faust (1953) generates the least amount of error when applied to the short resistivity curve. Throughout the modeled logs, the Faust (1953) equation generates an absolute average deviation of 6.0% for the short resistivity curves while Kim’s (1964) and Smiths (1968) equations produce 9.7% and 12.8% absolute average deviation. By understanding the variability of these models, future studies can ascertain the best fit model for further investigation of shallow hydrocarbon bearing formations within, or similar to, the Paleocene-Eocene aged strata in Central Louisiana.

This work investigates the lithospheric structure beneath the Mesozoic (~140 – ~110 Ma) Chilwa Alkaline Province (CAP) in southern Malawi and northeastern Mozambique using aeromagnetic and satellite gravity data (the World Gravity Model 2012 (WGM 2012). The CAP is a granite, syenite, nepheline syenite, and basanite province with minor intrusions of carbonatite bodies. It intrudes the Precambrian terranes of the Southern Irumide belt and the Unango complex. It is located on the northeastern margin of the Mesozoic Shire graben and on the southeastern edge of the Cenozoic Malawi rift, which is considered the southernmost segment of the Western Branch of the East African Rift System (EARS). Some of the CAP’s intrusive bodies are clearly offset by the border normal faults of the Malawi rift. Previous petrographic, geochemical and isotopic studies have suggested that the CAP is underlain by a thinned sub-continental lithospheric mantle (SCLM) possibly due to the Mesozoic Karoo rifting event. Hence, mantle magmatic source has been favored as an origin for the CAP. However, melting of a thickened continental crust cannot be ruled out for the origin of the CAP as has been suggested for several other alkaline intrusions. In this study: (1) Edge enhancement of the aeromagnetic data showed the CAP to be defined by circular and overlapping magnetic anomalies typical of hypabyssal nested igneous ring complexes. (2) Three-dimensional (3D) Voxi modeling and magnetic susceptibility analysis of the aeromagnetic data covering selected CAP’s intrusive bodies showed that these were emplaced at an average depth of ~ 4 km. (3) Upward continuation of the WGM 2012 Bouguer gravity anomalies suggested that the CAP was sourced from possibly deeper magma chambers now preserved as broad batholiths at ~4 km to~6 km depth. (4) Two-dimensional (2D) radially-averaged power spectral analysis of the WGM 2012 Bouguer gravity anomalies showed that the CAP is underlain by a thick crust (possibly due to mafic magmatic under-platting) where the Moho can be as deep as ~45 km. It also showed that the CAP is underlain by a relatively thin SCLM (possibly due to Mesozoic Karoo rift-related lithospheric stretching) where the asthenosphere-lithosphere boundary (LAB) can be as shallow as ~110 km. This work suggests that thinning of the SCLM might have allowed for the ascendance and decompression melting of the asthenosphere but also provided heat source (through mafic magmatic under-platting) to partially melt the lower crust to form the CAP from a mixed magma source and through caldera collapse mechanism. This model can be tested by additional geochemical and isotopic studies. This work highlights the importance of potential field data for imaging complex continental lithospheric structure. Understanding the lithospheric structure beneath the CAP is helpful in guiding future mineral exploration efforts because igneous ring complexes are important sites for the formation of economic mineralization zones.

The Hueco and Mesilla Bolsons are part of the intramountain basins of the Rio Grande Rift system. These bolsons are the primary source of groundwater for the El Paso-Ciudad Juarez metropolitan area and contain faults that show evidence of repeated earthquakes during the Quaternary. The region is also associated with has low-level (M<4) seismicity. The collection and analysis of precision gravity data, coupled with information from water wells, multichannel analysis of surface waves (MASW) studies and previously published seismic reflection lines, have been used to examine the structure and faulting within these bolson. This study reveals that the Hueco and Mesilla Bolsons are very different structurally. The southern Mesilla Bolson contains about 500 m of sediment. Faults are difficult to trace and have less than 50-100 m of displacement across them. The southernmost bolson contains numerous Tertiary intrusions and the thickness of Cretaceous bedrock appears to decrease from south to north, possibly delineating the edge of Laramide age deformation within the bolson. The northern Hueco Bolson contains 1800 to 2500 m of basin fill. Displacement along the East Franklin Mountains fault (EFMF), a fault with evidence for repeated earthquakes within the past 64,000 years, is about 1500 m, and displacement on intrabasin faults is 200-300 m. Several intrabasin faults appear to control the saline to freshwater contact within the bolson. The EFMF may extend over 30 km south of the end of its mapped trace at the end of the Franklin Mountains and a number of intrabasin faults also extend south into the urbanized regions of the study area. The EFMF and other basin structures appear to be offset or disrupted at the speculated edge of Laramide deformation that lies beneath the bolson. Horizontal Gradient Methods (HGM) were applied to the gravity data and were successful for tracing faults and older Laramide features within the Hueco Bolson beneath the urbanized regions of the cities. HGM were not as successful at tracing faults within the Mesilla Bolson, however they were helpful for tracing the subsurface extent of igneous intrusions including the Mt. Cristo Rey, River, Three Sisters, and the Westerner outcrops. Some of these features appear linked at depth by a series of dikes and faults. MASW data were used to determine the average shear wave velocity in the upper 30m (Vs 30) at ∼70 sites within the Hueco Bolson. These observations were combined with similar data collected previously in Juarez to produce regional velocity and site classification maps. The results show low velocities are found close to the river within fluvial deposits with higher velocities close to the Franklin Mountains where bedrock is close to the surface and higher velocities in upland regions of northeast El Paso were soils appear to be more highly cemented. These data will be used in conjunction with information on bolson geometries to model the expected effects of strong ground motion from earthquakes in the El Paso-Ciudad Juarez region.

The fluvial and deltaic Wilcox Group is a major target for hydrocarbon and coal exploration in northern and central Louisiana. However, the characterization and delineation of fluvial systems is a difficult task due to the variability and complexity of fluvial systems and their internal heterogeneities.

Seismic geomorphology is studied by recognizing paleogeographic features in seismic stratal slices, which are seismic images of paleo-depositional surfaces. Seismic attributes, which are extracted along seismic stratal slices, can reveal information that is not readily apparent in raw seismic data. The existence and distribution of fluvial channels are recognized by the channel geomorphology in seismic attributes displayed on stratal slices. The lithologies in the channels are indicated by those seismic attributes that are directly related to the physical properties of rocks. Selected attributes utilized herein include similarity, spectral decomposition, sweetness, relative acoustic impedance, root mean square (RMS) amplitude, and curvature. Co-rendering and Red/Green/Blue (RGB) display techniques are also included to better illuminate the channel geometry and lithology distribution. Hydrocarbons may exist in the channel sand-bodies, but are not explicitly identified herein. Future drilling plans for oil and gas exploration may benefit from the identification of the channels and the lithologies that fill them.

The purpose of this study was to identify the geologic signature of paleostorm events within the mid-continent region. This research aimed to create a better understanding of the long-term geologic history of major storms and to allow for better-informed projections regarding future return periods for such storms. The study locations were Cheyenne Bottoms Wildlife Refuge, Kansas and Canton Lake, Oklahoma. To determine the geologic signature of major storms, sediment cores were taken at both locations and sampled at high resolution (3 mm) intervals for grain size analysis using a Cilas laser particle size analyzer. Downcore chronology was determined through Pb-210, Cs-137 and C-14 dating methods. Using a recent known major storm occurrence at Canton Lake, the signature created by storms in the geologic record was identified. The resulting signature was then used to identify paleostorms in the longer-term record in the Cheyenne Bottoms core. The results were also used to determine storm/climate cycles in the long-term geologic record, and to calculate true return periods for major storms. A better understanding of true return periods and possible increases in frequency or intensity of large storms is essential in the effort to mitigate future damage to infrastructure and loss of human life

The United States Bureau of Ocean Energy Management (BOEM)’s Sandy Needs Assessment collected geophysical and geotechnical data, related to beach nourishment activities, along the continental shelf south of Long Island between 2015–2017 in an area offshore the Fire Island National Sea Shore, near Watch Hill, NY. This new geological and geophysical data provides evidence of continuous and ongoing sand transport offshore of Fire Island National Sea Shore. New stratigraphic evidence shows the evolution, migration and erosion of shore-oblique sand ridges formed from the reworking of glacial outwash sand consistent with a conceptual process model. Three separate ridge features are related to each other with evidence of direct ridge migration in the region. Outwash fans and deltas likely provided the cores of mesoscale submarine ridges n the study area. Subsequent episodes of ridge erosion remobilized sand to feed the growth of ridges further west. The possibility of natural transport process actively delivering sand to the shore remains, but is not identified, and will require further work before these ridges can be sustainably utilized in nourishment activities.