Academic literature on the topic 'Geology. Remote sensing'

This study aims at a description and statistical analysis of tectonic and magmatic fractures in the Western Volcanic Zone (WVZ) on Iceland. Two fracture populations are studied with respect to their distance to the Hengill volcano: The southern area is between 0-10 kilometers from the volcano and the northern area is between 16-25 kilometers from the volcano. The description and analysis of fractures is carried out separately for the two areas as well as for the two areas together to test different mapping procedures, statistical methods and the influence of the volcano on the properties of the fractures. There are various reasons for considering this an important study: Firstly, this is not an extensively researched field and there are many unanswered methodological questions on how to map and describe the fractures. In this study, problems such as how maps are stitched and georeferenced, how fractures are divided into segments and mapped in respect to topography, are discussed. The potential errors caused by these methodological problems are concluded to be large enough to significantly affect statistical tests analyzing fracture populations. In the analysis part, the properties of the fracture populations are studied using Kolmogorov Smirnov and χ 2 goodness-of-fit tests, scatter-plots, simple count and ratios among other methods. It was found that the fracture populations follow distributions that are not easily defined, but that they are of the same and quantifiable type. With more data their common distribution could therefore be modeled, and the factor by which the Hengill volcano affects the strike of fractures per distance unit from the volcano could be calculated. It was also found that magmatic fractures are formed in a similar, but not necessarily the same stress-field as tectonic fractures. Therefore change in magma pressure might change the local stress regime around magmatic fractures, affecting their strike.

Anticosti Island, located in the Gulf of St. Lawrence in eastern Canada, is one of the few places in the world where the Ordovician/Silurian boundary is well preserved and exposed. Its relatively undeformed shallow-water carbonate sequence of approximately 900 m in thickness is rich in fossils and is known to contain traces of hydrocarbons. The island has been for decades the subject of several geological studies, but its stratigraphic succession was never successfully mapped precisely because of its dense forest cover present over almost 95% of its vast territory. This study provides new mapping tools and techniques to support the geological representation of the island stratigraphic succession. Airborne SAR (Synthetic Aperture Radar) data acquired with the active radar system onboard of the former CCRS (Canada Centre for Remote Sensing) Convair-580 aircraft, in single and fully polarimetric modes and with different viewing geometry, were qualitatively and quantitatively evaluated by means of image interpretation and polarimetric analysis for their mapping potential over the densely forested study area. The airborne SAR data, supported with ancillary geoscience data sets and derivative topographic related products, have resulted in the availability of valuable and accurate terrain information such as topographic variations associated with the gently inclined recessive and resistant strata of the island succession. It also provided with information on the polarimetric scattering mechanism of the vegetation cover overlying the surface deposits and bedrock geology, suggesting a possible preferential distribution. With almost 50% of the Canadian territory covered by forest, radar remote sensing, as demonstrated by this study, is a cost-effective tool to produce more accurate regional structural and geological map in areas where traditional mapping campaigns failed due to the presence of an extensive vegetation cover.

This study focuses on the applications of remote sensing techniques and digital analysis to characterizing of tectonic features of the Rincon Mountains metamorphic core complex. Data included Landsat Thematic Mapper (TM) images, digital elevation models (DEM), and digital orthophoto quadrangle quads (DOQQ). The main findings in this study are two nearly orthogonal systems of structures that have never been reported in the Rincon Mountains. The first system, a penetrative faulting system of the footwall rocks, trends N10-30°W. Similar structures identified in other metamorphic core complexes. The second system trends N60-70°E, and has only been alluded indirectly in the literature of metamorphic core complexes. The structures pervade mylonites in Tanque Verde Mountain, Mica Mountain, and the Rincon Peak area. As measured on the imagery, spacing between the N10-30°W lineaments ranges from ∼0.5 to 2 km, and from 0.25 to 1 km for the N60-70°E system. Field inspection reveals that the N10-30°W trending system, are high-angle normal faults dipping mainly to the west. One of the main faults, named here the Cabeza de Vaca fault, has a polished, planar, striated and grooved surface with slickenlines indicating pure normal dip-slip movement (N10°W, 83°SW; slickensides rake 85°SW). The Cabeza de Vaca fault is the eastern boundary of a 2 km-wide graben, with displacement as great as 400 meters. The N10-30°W faults are syn- to post-mylonitic, high-angle normal faults that formed during isostatic uplift of the Rincon core complex during mid-Tertiary time. This interpretation is based on previous works, which report similar fault patterns in other metamorphic core complexes. Faults trending N20-30°W, shape the east flank of Mica Mountain. These faults, on the back dipping mylonitic zone, dip east and may represent late-stage antithetic shear zones. The Cabeza de Vaca fault and the back dipping antithetic faults accommodate as much as 65% of the extension due to doming of the core complex. The N60-70°E structures, not verified as a fault system, are a joint system pervading the footwall rocks of the metamorphic core complex. This system is less systematic. Spacing varies from 0.25 to 1 km. Both systems control the drainage of the mountains.

<p> A detailed structural map of the central uplift of Martin Crater in western Thaumasia Planum, Mars, reveals highly folded and fractured geology throughout the 15-km diameter uplift. The stratigraphy in the central uplift of the crater has been rotated to near vertical dip and imaged by high-definition cameras aboard the Mars Reconnaissance Orbiter (MRO). These unique factors allow individual geologic beds in Martin Crater to be studied and located across the length of the uplift. </p><p> Bedding in Martin Crater primarily strikes SSE-NNW and dips near vertically. Many units are separated by a highly complex series of linear faults, creating megablocks of uplifted material. Faulting is dominantly left-slip in surface expression and strikes SW-NE, roughly perpendicular to bedding, and major fold axes plunge toward the SW. Coupled with infrared imagery of the ejecta blanket, which shows an &ldquo;exclusion zone&rdquo; northeast of the crater, these structural indicators provide strong support for a low-angle impactor (approximately 10&ndash;20&deg;) originating from the northeast. </p><p> Acoustic fluidization is the prevailing theoretical model put forth to explain complex crater uplift. The theory predicts that uplifted megablocks in craters are small, discrete, separated and highly randomized in orientation. However, megablocks in Martin Crater are tightly interlocked and often continuous in lithology across several kilometers. Thus, the model of acoustic fluidization, as it is currently formulated, does not appear to be supported by the structural evidence found in Martin Crater.</p><p>

<p> This study investigates the potential for hydrothermal alteration and circulation in lava domes using combined analytical, remote sensing and numerical modeling approaches. This has been accomplished in three parts: <i>1) </i> A comprehensive field, geochemical and remote sensing investigation was undertaken of the hydrothermal system in the Santiaguito lava dome complex in Guatemala. The Santiaguito domes were found to contain mainly hydrous silica alteration, which is unlikely to weaken dome rock, but the summit of Santa Maria was found to contain pervasive argillic alteration (clay minerals), which do pose more of a collapse-related hazard. These results were confirmed by hot spring geochemistry which indicated that water in the domes was responsible for some rock dissolution but had a residence time too short to allow for secondary mineralization. <i>2)</i> A finite element numerical modeling approach was developed which was designed to simulate the percolation of meteoric water in two dome geometries (crater-confined and 'perched'), and the results were compared to the surface expression of hydrothermal systems on existing lava domes. In both cases, we concluded that simulated domes which lacked a high-temperature (magmatic) heat source could not develop a convecting hydrothermal system and were dominated by gravitational water flow. In these low-temperature simulations, warm springs (warmer high fluid fluxes) were produced at the base of the dome talus and cool springs were dispersed lower down the slope/substrate; fumaroles (high vapor fluxes) were confined to the dome summits. Comparison with existing dome cross sections indicates that the simulations were accurate in predicting fumarole locations and somewhat accurate at predicting spring locations, suggesting that springs may be subject to permeability contrasts created by more complicated structural features than were simulated in this study. <i>3)</i> The results of the numerical modeling were used to calculate alteration potential in the simulated domes, indicating the most likely areas where alteration processes might either reduce the strength of a dome or reduce permeability that could contribute to internal pressurization. Rock alteration potential in low-temperature lava domes was found to be controlled by material permeability and the presence or absence of a sustained heat source driving hydrothermal circulation. High RAI values were preserved longer in low-permeability domes, but were more strongly developed in domes with higher permeabilities. Potential for mineral dissolution was highest at the base of the dome core, while the potential for mineral precipitation is highest at the dome core-talus interface. If precipitated minerals are impermeable, the dome core/talus interface would be a likely location for accumulation of gases and initiation of gas-pressurization-related collapse; if alteration is depositing weak (i.e. clay) minerals in this area, the dome core/talus interface might be a candidate for collapses occurring as the result of alteration processes. </p><p> The results of this study are all geared toward answering two broad questions: <i> Where are hydrothermal alteration processes likely to occur or be focused within lava domes?</i> and <i>What effect could these processes have on dome stability?</i> In the specific case of the Santiaguito dome complex, the combination of a quickly-recharged, low-temperature hydrothermal system in the inactive domes actually indicated a low possibility of collapse related to alteration minerals. This result was reinforced by the results of the numerical modeling, which indicated that domes are unlikely to develop sustained hydrothermal convection without the presence of a significant (magmatic) heat source and&mdash;in the case of Santiaguito&mdash;are likely to produce more hydrous silica alteration minerals when they also lack a source of acidic gases. Models of alteration potential do detail, however, that both shallow and deep dome collapses are still a possibility with a low-temperature hydrothermal system, given either a) a source of acidic gases to drive the formation of clay minerals (which are most likely to be deposited at the core/talus interface of a dome, or b) enough deposition of silica minerals in pore spaces to lower permeability in dome rock and promote internal gas pressurization. The results of this study are not limited to lava domes, as the volcanic edifices on which they rest are composed of the same materials that comprise lava domes and are therefore susceptible to the same hydrothermal processes. Further simulations of both lava domes and their associated edifices, including mineral species models, could help constrain under what conditions a lava dome or volcano is likely to develop areas of weak mineral precipitates (such as clay minerals) which could provide sites for collapse, or develop an impermeable cap of silicate minerals which could trap rising vapor and contribute to the pressurization of the edifice in question (which can in turn lead to collapse).</p>

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.