Identification, prediction and mitigation of sinkhole hazards in evaporite karst areas

Abstract Sinkholes usually have a higher probability of occurrence and a greater genetic diversity in evaporite terrains than in carbonate karst areas. This is because evaporites have a higher solubility, and commonly a lower mechanical strength. Subsidence damage resulting from evaporite dissolution generates substantial losses throughout the world, but the causes are only well-understood in a few areas. To deal with these hazards, a phased approach is needed for sinkhole identification, investigation, prediction, and mitigation. Identification techniques include field surveys, and geomorphological mapping combined with accounts from local people and historical sources. Detailed sinkhole maps can be constructed from sequential historical maps, recent topographical maps and digital elevation models (DEMs) complemented with building-damage surveying, remote sensing, and high-resolution geodetic surveys. On a more detailed level, information from exposed paleosubsidence features (paleokarst), speleological explorations, geophysical investigations, trenching, dating techniques, and boreholes, may help to recognize dissolution and subsidence features. Information on the hydrogeological pathways including caves, springs and swallow holes, are particularly important especially when corroborated by tracer tests. These diverse data sources make a valuable database - the karst inventory. From this dataset, sinkhole susceptibility zonations (relative probability) may be produced based on the spatial and temporal distribution of the features and good knowledge of the local geology. Sinkhole distribution can be investigated by spatial distribution analysis techniques including studies of preferential elongation, alignment and nearest neighbor analysis. More objective susceptibility models may be obtained by analyzing the statistical relationships between the known sinkholes and the conditioning factors, such as weather conditions. Chronological information on sinkhole formation is required to estimate the probability of occurrence of sinkholes (number of sinkholes/km² year). Such spatial and temporal predictions, derived from limited records and based on the assumption that past sinkhole activity may be extrapolated to the future, are non-corroborated hypotheses. Validation methods allow us to assess the predictive capability of the susceptibility maps and to transform them into probability maps. Avoiding the most hazardous areas by preventive planning is the safest strategy for development in sinkhole-prone areas. Corrective measures could be to reduce the dissolution activity and subsidence processes, but these are difficult. A more practical solution for safe development is to reduce the vulnerability of the structures by using subsidence-proof designs

Rhythmic dynamics and synchronization via dimensionality reduction : application to human gait

Reliable characterization of locomotor dynamics of human walking is vital to understanding the neuromuscular control of human locomotion and disease diagnosis. However, the inherent oscillation and ubiquity of noise in such non-strictly periodic signals pose great challenges to current methodologies. To this end, we exploit the state-of-the-art technology in pattern recognition and, specifically, dimensionality reduction techniques, and propose to reconstruct and characterize the dynamics accurately on the cycle scale of the signal. This is achieved by deriving a low-dimensional representation of the cycles through global optimization, which effectively preserves the topology of the cycles that are embedded in a high-dimensional Euclidian space. Our approach demonstrates a clear advantage in capturing the intrinsic dynamics and probing the subtle synchronization patterns from uni/bivariate oscillatory signals over traditional methods. Application to human gait data for healthy subjects and diabetics reveals a significant difference in the dynamics of ankle movements and ankle-knee coordination, but not in knee movements. These results indicate that the impaired sensory feedback from the feet due to diabetes does not influence the knee movement in general, and that normal human walking is not critically dependent on the feedback from the peripheral nervous system

Stratigraphic interpretation of Well-Log data of the Athabasca Oil Sands of Alberta Canada through Pattern recognition and Artificial Intelligence

Dissertation submitted in partial fulfillment of the requirements for the Degree of Master of Science in Geospatial Technologies.Automatic Stratigraphic Interpretation of Oil Sand wells from well logs datasets typically involve recognizing the patterns of the well logs. This is done through classification of the well log response into relatively homogenous subgroups based on eletrofacies and lithofacies. The electrofacies based classification involves identifying clusters in the well log response that reflect ‘similar’ minerals and lithofacies within the logged interval. The identification of lithofacies relies on core data analysis which can be expensive and time consuming as against the electrofacies which are straight forward and inexpensive. To date, challenges of interpreting as well as correlating well log data has been on the increase especially when it involves numerous wellbore that manual analysis is almost impossible. This thesis investigates the possibilities for an automatic stratigraphic interpretation of an Oil Sand through statistical pattern recognition and rule-based (Artificial Intelligence) method. The idea involves seeking high density clusters in the multivariate space log data, in order to define classes of similar log responses. A hierarchical clustering algorithm was implemented in each of the wellbores and these clusters and classifies the wells in four classes that represent the lithologic information of the wells. These classes known as electrofacies are calibrated using a developed decision rules which identify four lithology -Sand, Sand-shale, Shale-sand and Shale in the gamma ray log data. These form the basis of correlation to generate a subsurface model

Out in the Open: A Geoarchaeological Approach to Open-Air Surface Archaeology in the Semi-Arid Interior of South Africa’s Western Cape

Southern African research into the behavioural evolution of Late Pleistocene human adaptability, flexibility, and innovation is typically pursued through the lens of rock shelter deposits. However, rock shelters only cover a very small, geographically specific area of the subcontinent, distorting our understanding of change in human-environment interaction and demography. While still under-represented and under-explored in regional syntheses, more studies are looking to open-air archaeology to fill this geographic void in Late Pleistocene research. These studies either pursue a landscape approach that prioritises spatial coverage, or site-bound excavation to maximise temporal control. However, few investigate the depositional and erosional phenomena involved in the formation of surface archaeology and its surrounding landscape. To rectify this disparity, this thesis explores the complex spatio-temporal relationship between surface archaeology and the formation history of Uitspankraal (UPK) 7 by combining multiple interdisciplinary methods from the Earth and archaeological sciences: randomised surface survey and sampling, geomorphometry, geophysical survey, granulometry, XRD analysis, OSL dating, artefact mapping, and assemblage composition and artefact condition analysis. UPK7 is located in the semi-arid Doring River valley and yields surface archaeology that implies occupation from the Still Bay to the Historic period. Results show that it is an eroding series of source-bordering dunes draped across a palaeoterrace and a hillslope of bedrock and colluvium. UPK7 formed through rapid but pulsed sediment accumulation over at least the last 80 ka, with periods of surface deflation and exposure that facilitated artefact redistribution. Despite the abundance of Late Pleistocene archaeology at UPK7, erosion currently outpaces deposition and deposit stabilisation. Erosion has accelerated in at least the last 5,000 years and especially within the last 300 years, suggesting feedback between Holocene aridification, an increase in oscillations between wet-dry conditions, and an increase in human-ungulate activity in the study area. Together these conditions have differentially erased younger deposits, exposing the consolidated Late Pleistocene sediment and the more ancient material it preserves. The visibility, spatio-temporal distribution, and preservation of UPK7’s surface artefacts reflect the locality’s topography, the timing of their discard and the duration and process of sediment accumulation and erosion. The spatial patterning and diversity of time-diagnostic and non-diagnostic artefacts is shown to correspond with the depositional age of their underlying substrate in areas where topographic conditions minimize or reduce the impact of surface runoff, but where sediment deflation persists. When artefacts are assessed at the scale of the archaeological epoch the spatial distribution of Middle Stone Age artefacts shows a significant association with the oldest deposit, Lower Red. The spatial distribution of Later Stone Age artefacts is significantly associated with Upper Yellow sediment, as opposed to the older Lower Red substrate and the younger Indurated Sand. The findings presented in this thesis caution against forming behavioural interpretations from spatial patterns in surface material without examining their post-depositional history and without forming an understanding of the coevolution of archaeological and landscape formation. This study underscores the need for incorporating a geoarchaeological approach into Late Pleistocene open-air research to improve southern Africa’s landscape-scale insight into greater Africa’s human behavioural evolution

SAND DEPOSIT MAPPING AND AEOLIAN MORPHOLOGIES AS CLUES FOR IDENTIFYING ORIGINS OF DARK SAND IN AEOLIS DORSA, MARS

Dark sand deposits occur at all latitudes on the Martian surface. Sand sources in some regions have been inferred via paleo-wind indicator analyses, sand and source mineralogy comparisons, and climate modeling. However, all known sources are sedimentary, leaving outstanding the question of primary igneous origin(s) of these dark sand deposits. One hypothesis addressing this question is that volcaniclastic deposits are a primary origin of Martian sand. Terrestrial analogs of volcaniclastic units sourcing sand support this hypothesis. However, sand generation has yet to be observed or inferred from any such Martian deposit. This thesis tests this hypothesis via a case study in Aeolis Dorsa, Mars, a locality where sand overlies bedrock consisting of a hypothesized volcaniclastic deposit, the Medusae Fossae Formation (MFF). In addition to the MFF, additional potential external sand sources exist: Elysium Mons, the Cerberus Plains lavas, and the Southern Highlands.To identify likely sand source(s) in Aeolis Dorsa, sand deposits were mapped to address geospatial sand distribution, scour mark orientations were mapped and analyzed to reveal dominant paleo-wind directions, and instances of apparent erosion of bedrock to dark sediment were recorded. Hierarchical clustering analysis of sand distribution revealed preferential sand deposition on the peripheries of the MFF and in the southern depression (where bedrock may be remnant southern highlands material). Hierarchical cluster analysis of scour mark distribution revealed spatial groups of scour marks with consistent paleo-wind directions within groups. Such paleo-wind directions provide no evidence for long-distance sand transport from potential external source regions, but instead provide support for paleo-winds controlled by local topography. Apparent erosion of bedrock to dark sediments occurs in both the MFF (in ~20 localities) and in the southern depression (in over 100 localities), suggesting that both the MFF and bedrock in the southern depression have the potential to generate dark sand. The implication that the MFF has the potential to produce dark sand raises two important possibilities: first, that elsewhere along the Martian equator the MFF may have produced dark sand, and second, that other friable layered deposits (of which the MFF is one) may also serve as sources of Martian sand

Prevalence of age-related macular degeneration in Nakuru, Kenya: a cross-sectional population-based study.

BACKGROUND: Diseases of the posterior segment of the eye, including age-related macular degeneration (AMD), have recently been recognised as the leading or second leading cause of blindness in several African countries. However, prevalence of AMD alone has not been assessed. We hypothesized that AMD is an important cause of visual impairment among elderly people in Nakuru, Kenya, and therefore sought to assess the prevalence and predictors of AMD in a diverse adult Kenyan population. METHODS AND FINDINGS: In a population-based cross-sectional survey in the Nakuru District of Kenya, 100 clusters of 50 people 50 y of age or older were selected by probability-proportional-to-size sampling between 26 January 2007 and 11 November 2008. Households within clusters were selected through compact segment sampling. All participants underwent a standardised interview and comprehensive eye examination, including dilated slit lamp examination by an ophthalmologist and digital retinal photography. Images were graded for the presence and severity of AMD lesions following a modified version of the International Classification and Grading System for Age-Related Maculopathy. Comparison was made between slit lamp biomicroscopy (SLB) and photographic grading. Of 4,381 participants, fundus photographs were gradable for 3,304 persons (75.4%), and SLB was completed for 4,312 (98%). Early and late AMD prevalence were 11.2% and 1.2%, respectively, among participants graded on images. Prevalence of AMD by SLB was 6.7% and 0.7% for early and late AMD, respectively. SLB underdiagnosed AMD relative to photographic grading by a factor of 1.7. After controlling for age, women had a higher prevalence of early AMD than men (odds ratio 1.5; 95% CI, 1.2-1.9). Overall prevalence rose significantly with each decade of age. We estimate that, in Kenya, 283,900 to 362,800 people 50 y and older have early AMD and 25,200 to 50,500 have late AMD, based on population estimates in 2007. CONCLUSIONS: AMD is an important cause of visual impairment and blindness in Kenya. Greater availability of low vision services and ophthalmologist training in diagnosis and treatment of AMD would be appropriate next steps. Please see later in the article for the Editors' Summary

Assessing Paleoenvironmental and Geomorphic Variability in Relationship to Paleoindian Site Burial; Centennial Valley, Montana

Wave action along the shores of Lima Reservoir in Centennial Valley, Montana is actively eroding the southern margins of three neighboring Paleoindian sites. Despite ostensible similarity among the sites, major site formation differences are apparent in exposed sediments. Shoreline cutbank exposures one-to-five meters high connect the sites and reveal a complicated geomorphic history. Although each site contains artifact evidence of terminal Pleistocene-early Holocene occupations, Paleoindian components at these three localities occur in very different contexts: one is buried, while the other two are apparent surface scatters. This raise the question of why sites of the same age are in both buried and exposed contexts. Moreover, buried sites are more likely to have preserved spatial layout and sites with buried components are more likely to be considered significant under National Register of Historic Places criteria. These factors therefore prompt the management question of where might other buried sites be located in the valley? In order to answer these questions, I used a multi-pronged approach including optically stimulated luminescence dating, sediment grain size analysis, stratigraphic profiling and sediment facies analysis. I accomplished two nested objectives with this research. First, I reconstructed the last 60,000 years of geomorphic events for the area surrounding the three sites in order to determine what conditions resulted in site burial. Second, I used those findings to outline criteria for differentiating occupation-age and pre-occupation-age stratigraphic layers in Centennial Valley. I determined, in part, that cultural-age deposits are present at both high and low elevations and that they may be marked by a specific soil sequence. The oldest packages, far pre-dating potential human occupation, are deep lake and high energy stream sediments that may be recognized by soil color alteration and thick gypsum horizons