<p> Cryoconite holes are vertical columns of meltwater within the shallow subsurface of glaciers. In the McMurdo Dry Valleys (MDV) of Antarctica cryoconite holes are a source of meltwater and harbor microbial communities in an otherwise arid environment with low biologic activity. The holes form as sediments on the ice surface, which are darker than the surrounding ice, are preferentially heated by solar radiation. The warm sediments melt the underlying ice and migrate downwards. An ice lid forms, isolating them from the below-freezing atmosphere enabling them to remain thawed. In this study, field observations, laboratory experiments, and numerical modeling are used to characterize the fundamental variables controlling cryoconite hole development. </p><p> Field and laboratory results show that solar radiation drives cryoconite hole melting by controlling the energy available to the cryoconite and to warm the surrounding ice. Holes deepen further in warmer ice. Laboratory results show that at temperatures of &ndash;10 &deg;C at least 405 (W m^&ndash;2) are needed to warm the cryoconite sufficiently to melt surrounding ice. Numerical modeling shows that increased radiation flux into the subsurface and warmer air temperatures cause cryoconite to descend deeper and the meltwater-filled holes to enlarge, while increased surface ablation decreases their average depth. Cryoconite holes thaw sooner and refreeze later when the optical properties of the ice facilitate greater radiation transmission. Cryoconite warms the ice significantly more than ice without cryoconite. Within the melt-filled hole, the heat capacity of the water keeps the surrounding ice warm for several weeks after the cryoconite-free ice has cooled. The cryoconite itself is last to completely freeze.</p><p>

<p> The upper Wilcox group in the Tullos-Urania oilfield has not been imaged with enough resolution for interpretation. Prior seismic data collected in the area was designed for formations much deeper than the Wilcox Group. The purpose of this investigation was to produce an image of the subsurface and identify formations of interest for production of oil and gas by applying different processing methods. With an optimal processing workflow and use of limited well logs, an interpretation of the data was provided to the oil company. </p><p> The advantage of using an accelerated weight-drop source is the shallow horizons, ranging from 1,500 to 3,000 feet in-depth, become distinct with higher resolution. The acquisition achieved a dominant frequency averaging around 45&ndash;65 Hz compared to a nearby pre-existing 3D survey volume with a dominant frequency range of 15&ndash;35 Hz. Refracted waves dominated the unprocessed shot records from this data. Consequently, the field records had a significantly low signal-noise ratio. Therefore, the most critical processing steps focused on signal processing and velocity analysis. Without enough ground roll and noise suppression, the velocity analysis would not have been coherent. Some obstacles faced with processing the data included a sparse horizontal sampling and a lack of velocity logs along the seismic line. </p><p> The results of this study included a set of stacked lines, velocity models, and an optimal processing workflow for future high-frequency shallow seismic exploration surveys in the vicinity of LaSalle, LA. These results have concluded seismic surveying with an accelerated weight-drop source is a cost-effective method to produce a high- resolution cross-section of the high and low-velocity sand and shale channels of the fluvial Wilcox strata of Northern Louisiana. Further research should look to build on these results and gather a 3D survey to image the structure of the Tullos-Urania oilfield and identify hydrocarbons-in-place. </p><p>

A quantification of the role that barrier island overwash plays in the evolution of Onslow Beach, a barrier island located on Marine Corps Base Camp Lejeune, North Carolina, is presented. Ground-penetrating radar (GPR) and sediment vibracores provide an estimate of the relevant-sand prism above a silty/peat contact underlying the island. The average thickness from the surface, as determined from lidar, to this geologically-defined base, is less than 1 m and equates a total volume of approximately 1.8 ± 1.1 × 106 m3 over the 4.8 km stretch of Onslow Beach from 1 km north of the New River Inlet to Riseley Pier (~ 2 km2). Approximately 39% of the relevant-sand prism (680 ± 215 x 103 m3) is contained within the area of the island currently exhibiting signs of overwash events (i.e., the active overwash complex). Based upon the average cumulative thickness of distinct washover facies within 12 sediment cores (52 cm) and the surface area of the active overwash region, it is estimated that the volume sedimentologically distinct washover deposits equals 199 ± 88 × 103 m3 (approximately 29% of the active overwash complex or 11% of the entire relevant-sand prism). A time series of aerial imagery from 1938 to 2008 details the spatial and temporal trends in migration of both the wet/dry line (a shoreline proxy) and the vegetation line (indicating the landward extent of overwash). Long-term shoreline erosion rates in excess of 3 m/yr occurred over the southern portion of Onslow Beach while the northern portion experienced up to 1.7 m/yr of accretion within the same 80-year time span. Between 1938 and 2008, the vegetation line moved an average of 85 m landward over the length of the entire island and over 450 m in overwash sites at the southern end of the island where shoreline erosion rates are highest. A comparison with long-term shoreline change rates suggests that a simple linear relationship between spatial and temporal variability in shoreline behavior and volume of the relevant-sand prism does not exist. Trends based upon the past 80 years suggest that a positive correlation exists between storm frequency and overwash extent. Furthermore, the region experiencing the highest rates of shoreline erosion and the highest occurrence of overwash does not coincide with the area regularly subject to military training activities. These data suggest that natural forcings (sea level, wind and wave energy, geology, etc.) exert first-order control on the evolution of this barrier island. The ability to quantify and evaluate the relative importance of such forces is paramount to understanding how, and over what timescales, the nearshore environment responds to changes in external forcings (e.g., sea-level rise, storms, etc.) and, in turn, is fundamental to the development of reliable forecasts of shoreline trends and storm susceptibility models.

Elevated water levels and large waves during storms cause beach erosion, overwash, and coastal flooding, particularly along barrier island coastlines. While predictions of storm tracks have greatly improved over the last decade, predictions of maximum water levels and variations in the extent of damage along a coastline need improvement. In particular, physics based models still cannot explain why some regions along a relatively straight coastline may experience significant erosion and overwash during a storm, while nearby locations remain seemingly unchanged. Correct predictions of both the timing of erosion and variations in the magnitude of erosion along the coast will be useful to both emergency managers and homeowners preparing for an approaching storm. Unfortunately, research on the impact of a storm to the beach has mainly been derived from "pre" and "post" storm surveys of beach topography and nearshore bathymetry during calm conditions. This has created a lack of data during storms from which to ground-truth model predictions and test hypotheses that explain variations in erosion along a coastline. We have developed Coastal Lidar and Radar Imaging System (CLARIS), a mobile system that combines a terrestrial scanning laser and an X-band marine radar system using precise motion and location information. CLARIS can operate during storms, measuring beach topography, nearshore bathymetry (from radar-derived wave speed measurements), surf-zone wave parameters, and maximum water levels remotely. In this dissertation, we present details on the development, design, and testing of CLARIS and then use CLARIS to observe a 10 km section of coastline in Kitty Hawk and Kill Devil Hills on the Outer Banks of North Carolina every 12 hours during a Nor'Easter (peak wave height in 8 m of water depth = 3.4 m). High decadal rates of shoreline change as well as heightened erosion during storms have previously been documented to occur within the field site. In addition, complex bathymetric features that traverse the surf-zone into the nearshore are present along the southern six kilometers of the field site. In addition to the CLARIS observations, we model wave propagation over the complex nearshore bathymetry for the same storm event. Data reveal that the complex nearshore bathymetry is mirrored by kilometer scale undulations in the shoreline, and that both morphologies persist during storms, contrary to common observations of shoreline and surf-zone linearization by large storm waves. We hypothesize that wave refraction over the complex nearshore bathymetry forces flow patterns which may enhance or stabilize the shoreline and surf-zone morphology during storms. In addition, our semi-daily surveys of the beach indicate that spatial and temporal patterns of erosion are strongly correlated to the steepness of the waves. Along more than half the study site, fifty percent or more of the erosion that occurred during the first 12 hours of the storm was recovered within 24 hours of the peak of the storm as waves remained large (>2.5 m), but transitioned to long period swell. In addition, spatial variations in the amount of beach volume change during the building portion of the storm were strongly correlated with observed wave dissipation within the inner surf zone, as opposed to predicted inundation elevations or alongshore variations in wave height.

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This project considers the development of the cultural landscape of Native American chiefdoms in the Yazoo Basin of northwestern Mississippi. Chronicles written by certain members of the Hernando de Soto expedition offer exciting glimpses into the landscape and lifeways of Native American societies in 1541, but they do not shed light on how the landscape of chiefdoms in the Lower Mississippi Valley developed during the period before Spanish contact. This dissertation research focuses on the time period just before Spanish contact, the Mississippi Period (AD 1200-1540), and on Mississippian culture, and it investigates how monuments were built and used in a rapidly changing and dynamic landscape, one in which the meandering and flooding Mississippi river affected the long-term formation of social and political networks. This research relies on environmental, ethnohistoric, and archaeological data to provide a historically contingent description of the processes leading to the development of one of the largest and most important archaeological sites in the region. Sediment cores excavated in mound and off-mound contexts suggest the site was constructed over a crevasse splay, a high-elevation landform. Both coring data and trench excavation demonstrate that Mound D, the largest mound at Carson, was built in four stages and that stages II and III were the largest stages. Excavations on Mound D demonstrate that a moderately large-sized structure was once constructed on the southwest corner of the mound summit and that the structure was used to produce craft goods such as shell beads, shell gorgets, and statuary. Data from mound construction and craft production, as well as ethnohistoric and geomorphic research, are used to describe social organization, hierarchy, and leadership at Carson. / 1 / Jayur Madhusudan Mehta

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains viii, 118 p. : ill. (some col.), maps (some col.). Vita. Includes abstract. Includes bibliographical references (p. 80-88).

Desert pavements consist of a one- to two-layer thick surface armory of stones overlying finer, virtually stone-free material which often adopts the appearance of a meticulously tiled mosaic. They cover half of the arid land surface in North America and are usually concentrated on low-sloping alluvial fans and desert piedmont surfaces. McFadden et al. (1987) suggested the accretionary mantle model of desert pavement formation, following research on pavements atop the Cima volcanic complex in the Mojave Desert. However, the wide-spread applicability of this model to diverse lithologies and geomorphic environments remains to be seen. No research has been conducted on desert pavement at Big Bend National Park (BBNP), Texas, despite the occurrence of well-developed pavements in the park and surrounding regions of the Chihuahuan Desert. This research highlights three diverse desert pavement sites at BBNP through a detailed geomorphic assessment including location of desert pavement distribution, classification into surface mosaic units, examination of sediment and soil characteristics, and determination of lithology of the pavement clasts. At each BBNP study area, values for desert pavement clast size, sorting, and percent ground cover were compared to the parameters set forth in Wood et al. (2002) to classify the desert pavements into surface mosaics based on degree of development. Sediment analysis and soil profile photographs were used to characterize the surface sediments and subsurface soil horizons. To determine geologic origin, dominant lithologies of the pavement clasts were compared to outcrop and bedrock samples and to published geologic maps of BBNP. Desert pavements in this study differ significantly in surface texture, soil characteristics, geologic origin, and degree of development compared to the typical pavements of the Mojave Desert used in much of the fundamental research. Results indicate that the desert pavements at BBNP may not have been derived from bedrock and evolved in-situ, as suggested by the accretionary mantle model. Primarily, a combination of fluvial processes and weathering appears more influential to desert pavements in the semi-arid environment of BBNP. This study presents a new perspective on desert pavement geomorphology in Big Bend National Park and serves as a baseline for continued research.

The aim of this report is to describe the deglaciation in an area on west Greenland in the vicinity of Kangerlussuaq. To do this, the geomorphological landforms were mapped by studying areal photographs and by a two week field study where key areas were examiend. The landforms were transferred to a map using ArcGis and each key area were interpreted.The majority of the geomorphological formations were formed during the last deglaciation and consists of morain ridges, kettle topography in both till and glacifluvium, glacifluvial deltas, two fossil sandurs, and lateral terraces. Based on key areas and an inversion model a geomorphological map was created to illustrate the deglaciation, using the least complex explanation of the genesis of the landforms. The results show that the ice played a major role by damming lakes which enabled formation of many meltwater chanels and delta formations on higher elevations. The morain ridges and lateral terraces showed the extent of the ice margin during the halts in the ice retreat. The deglaciation was dated with help from earlier studies and the conclusion was that the deglaciation started between 7900 and 6700 yr BP. And the area was free from ice 7100-6500 yrs BP.