Dissertations / Theses on the topic 'Quantitative Geomorphology'

Craters formed by impact and volcanic processes are among the most fundamental planetary landforms. This study examines the morphology of diverse craterforms on Io, the Moon, Mars, and Earth using quantitative, outline-based shape analysis and multivariate statistical methods to evaluate the differences between different types of. Ultimately, this should help establish relationships between the form and origin of craterforms. Developed in the field of geometric morphometrics by paleontological and biological sciences communities, these methods were used for the analysis of the shapes of crater outlines. The shapes of terrestrial ash-flow calderas, terrestrial basaltic shield calderas, martian calderas, Ionian paterae, and lunar impact craters were quantified and compared. Specifically, we used circularity, ellipticity, elliptic Fourier analysis (EFA), Zahn and Roskies (Z-R) shape function, and diameter. Quantitative shape descriptors obtained from EFA yield coefficients from decomposition of the Fourier series that separates the vertical and horizontal components among the outline points for each shape. The shape descriptors extracted from Z-R analysis represent the angular deviation of the shapes from a circle. These quantities were subjected to multivariate statistical analysis including principal component analysis (PCA) and discriminant analysis, to examine maximum differences between each a priori established group. Univariate analyses of morphological quantities including diameter, circularity, and ellipticity, as well as multivariate analyses of elliptic Fourier coefficients and Z-R shape function angular quantities show that ash-flow calderas and paterae on Io, as well as basaltic shield calderas and martian calderas, are most similar in shape. Other classes of craters are also shown to be statistically distinct from one another. Multivariate statistical models provide successful classification of different types of craters. Three classification models were built with overall successful classification rates ranging from 90% to 75%, each conveying different shape information. The EFA model including coefficients from the 2nd to 10th harmonic was the most successful supervised model with the highest overall classification rate and most successful predictive group membership assignments for the population of examined craterforms. Multivariate statistical methods and classification models can be effective tools for analyzing landforms on planetary surfaces and geologic morphology. With larger data sets used to enhance supervision of the model, more successful classification by the supervised model could likely reveal clues to the formation and variables involved in the genesis of landforms.

Um momento chave para o entendimento da evolução da linhagem filogenética da Geomorfologia é o pós-Segunda Guerra Mundial, quando profundas transformações sociais, econômicas e culturais, contribuem para uma nova fase do pensamento científico, mais objetivo e pragmático, e é nesse momento em que a Geomorfologia americana passa por uma quebra de seu paradigma. A construção do conhecimento sobre os processos naturais é antiga e passa por uma série de evoluções ao longo da história, merecendo destaque o estabelecimento dos estudos a partir da revolução científica do século XVII, quando a Geologia começa a ser organizada como um corpo de conhecimento bem definido, e dentro dele, a Geomorfologia aparece como uma importante base de estudos sobre a evolução do relevo. A segunda metade do século XIX é dominada pela influencia de William Moris Davis, que através de seus estudos estabeleceu um modelo de evolução do relevo, denominado de Ciclo Geográfico, dominado por fases de acordo com o grau de transformação provocada pelos rios. Essa teoria, calcada em uma abordagem histórica e geológica, acaba sendo largamente utilizada nos Estados Unidos, Europa Ocidental (exceto Alemanha) e países de língua inglesa em geral. Porém em 1945 é publicado um artigo seminal de Robert E. Horton, que é considerado o ponto de mudança e quebra do paradigma davisiano, ao servir de base para uma série de grupos que desenvolvem uma leitura da Geomorfologia muito mais voltada para a análise de processos, com bases na engenharia e na física, sendo que esse novo enfoque costuma receber o nome de Geomorfologia quantitativa. Dois grupos se destacam nessa transformação, um organizado por Arthur N Strahler, da Universidade de Columbia; e outro constituído por pesquisadores da USGS, unidos pela figura de Luna Leopold. Durante a década de 50 e 60 esses grupos publicaram uma série de artigos e livros que acabam por influenciar os estudos da Geomorfologia fluvial até os dias atuais, buscando a construção de um novo paradigma pós-davisiano, baseado na utilização da linguagem matemática e na formulação de leis, numa clara inspiração nos preceitos do positivismo lógico, inaugurando assim uma nova fase na Geomorfologia, que ainda mantem algumas características estabelecidas nesse período.
A key point for understanding the evolution of phylogenetic lineage of Geomorphology is the post-World War II, when profound social, economic and cultural transformations, contribute to a new phase of scientific thought, more objective and pragmatic, and that is when the American geomorphology involves a breach of its paradigm. The construction of knowledge about natural processes is old and undergoes a series of changes throughout history, with emphasis the establishment of studies from the scientific revolution of the seventeenth century, when the geology begins to be organized as a body of knowledge well defined, and within it, geomorphology appears as an important foundation for studies on the evolution of relief. The second half of the nineteenth century is marked by the influence of William Moris Davis, who through their studies established a model for the evolution of relief, named Geographic cycle, dominated by stages according to the degree of transformation caused by rivers. This theory, based on a historical and geological approach ends up being widely used in the United States, Western Europe (excluding Germany) and English-speaking countries in general. But in 1945 is published a seminal article by Robert E. Horton, who is considered the turning point and breaks of the davisian paradigm, to serve as the basis for a number of groups who develop a reading of Geomorphology much more focused on process analysis with bases in engineering and physics, and this new approach is usually given the name of \"quantitative geomorphology. Two groups stand out in this transformation, one organized by Arthur N Strahler, Columbia University; and another consisting of researchers from the USGS, united by the figure of Luna Leopold. During the 50s and 60s these groups published a series of articles and books that end up influencing the study of fluvial geomorphology to the present day, seeking the construction of a new post-davisian paradigm, based on the use of mathematical language and formulation of laws, a clear inspiration in the precepts of logical positivism, thus inaugurating a new phase in Geomorphology, which still maintains some characteristics established in this period.

This work have quantitatively determine the catchment variables controlling the sinuosity transition of non-valley constrained DFS channels in Alaska, Himalaya and the Andes. Results from the characterisation of channel sinuosity were used through regression analyses to determine the catchment and channel bed parameters controlling reach sinuosity trend and transition of fluvial channel planforms in order to infer a control on the heterogeneity of DFS in the rock record. The catchment approach used was necessary because the studied fluvial systems are associated with DFS (which are regarded as larger forms of alluvial fans) and catchment based approach have been used to investigate controls on alluvial fan morphology. In addition, catchment based investigations are rare in the analyses of the discriminant functions that are considered as controlling factors on channel sinuosity and planform employed previously in the tributary systems. Two distinct channel types were found through the characterisation of 553 reaches of fluvial channels in 3 different modern continental sedimentary basins; channels with no transition in sinuosity/planform (group 1), and channels with transition in sinuosity/planform (group 2) Among the channel bed and catchment quantitative variables investigated in this work, catchment area is the only parameter that shows a general relationship with the channel distance from the apex to the transition point in channel sinuosity through the overall regression results. The result shows that the bigger the catchment area the longer the transition point which is related to a higher water and sediment discharge. Thus, the point at which the channel sinuosity transition will occur can be predicted from the catchment area through the regression equation [y=0.0017x + 28] of the overall linear regression line, where x is the catchment area and y is the channel distance from the apex to the point of transition in channel sinuosity. As the studied channels are associated with DFS, this relation also reflects the prediction of the transition point in the DFS fluvial styles in the rock record. Overall regression analysis results show statistically poor results for the relationship between catchment elevation, catchment slope, channel bed elevation, channel bed slope and either the channel sinuosity or the sinuosity transition. However, in all the three study areas, the majority of the datasets show a trend with the catchment area/sinuosity transition relationship. Additionally, the study area with mainly the biggest catchments (longer channel sinuosity transition) is associated with the highest catchment slope, lowest channel bed elevation and more anabranching channels. Also, the study area with mainly the smallest catchments (shorter channel sinuosity transition) is associated with lower catchment slope, higher channel bed elevation and fewer anabranching channels. This suggests that the higher water and sediment discharge may be related to the steeper slopes and the anabranching channels may reflect the lower channel bed elevation. However, deviations obeserved in the overall regression result in the three study areas are attributed to the differences in the climatic, geologic and tectonic factors in the 3 settings. Although, the differences in these study areas have been shown, nevertheless the interpretations cannot be substantiated in this work with the available data. Thus, there is need for further research to prove any conclusive relationship between these factors and hence remains an issue of debate. In conclusion, this work shows that catchment area is an important controlling parameter on the transition in channel sinuosity of non-valley constrained DFS channels and consequently reflects a a control on the transition in spatial variations of the associated DFS in the rock record.

Dans les chaînes de montagnes, les séismes de magnitudes intermédiaires à fortes (Mw>6) déclenchent systématiquement un grand nombre de glissements de terrain responsables de l'introduction de volumes massifs de sédiments dans le réseau fluviatile. L'évacuation progressive de ces sédiments hors de la zone épicentrale affecte la dynamique des rivières et provoque des aléas hydro-sédimentaires dans les plaines alluviales (avulsion des rivières, crues...). La quantification des transferts sédimentaires est essentielle pour mieux comprendre l'évolution des paysages à court et moyen terme (de l'heure au siècle) et permettre une gestion efficace des risques dans les zones d'accumulation. Cependant, les flux de sédiments grossiers étant difficiles à mesurer, les facteurs contrôlant l'évacuation des glissements de terrain restent à ce jour mal compris. Cette thèse a donc porté sur l'étude, via la modélisation, des paramètres influençant la mobilisation des glissements de terrain, la préservation de la capacité de transport la transition entre gorge et plaine alluviale et la dynamique court terme des cônes alluviaux soumis à de forts apports sédimentaires. Les approches développées sont appliquées au contexte de la côte Ouest de la Nouvelle Zélande où la probabilité d'occurrence d'un séisme de magnitude 8 est de 50% dans les 50 ans à venir. Cette problématique à été abordée analytiquement et via une approche numérique avec le modèle 2D d'évolution des paysages et des rivières, Eros. Avec l'approche analytique, nous démontrons que la conservation de la capacité de transport long terme à la transition entre gorges et plaines alluviales est généralement réalisée par le passage à un système en tresse. Nous identifions aussi la variabilité des débits comme facteur dominant de la capacité de transport long terme comparé à l'effet de la végétation riparienne. Avec l'approche numérique, nous utilisons Eros qui est composé 1. d'un modèle hydrodynamique 2D, 2. d'un modèle de transport/dépôt de sédiments et 3. de modèles gérant les flux latéraux d'érosion et de dépôt. La combinaison de ces éléments permet l'émergence de diverses géométries de rivières alluviales (droites/sinueuses ou en tresses) en fonction des forçages externes qu'elles subissent (débit d'eau, flux sédimentaires). L'application d'Eros à des cas naturels a nécessité la validation et la calibration de ses paramètres principaux à l'aide: 1. de solutions analytiques et 2. de la reproduction morphodynamique de systèmes naturels, tel que l'évolution de la rivière Poerua en Nouvelle Zélande suite au glissement de terrain du Mont Adams. Dans la partie aval du bassin, les simulations numériques démontrent les capacités du modèle 1) à prédire efficacement l'évolution de plaines alluviales soumises à plusieurs scénario d'apports sédimentaires massifs et 2) à générer des cartes de risques probabilistes. Dans la partie amont du bassin, les résultats mettent en évidence le rôle clef de la réduction dynamique de largeur des rivières par rapport à la largeur de la gorge fluviatile, sur l'accélération de l'évacuation des sédiments issus des glissements de terrain. Une loi unique caractérisant les temps d'export d'une distribution de glissements de terrain peut être définie en fonction du rapport entre volume de sédiment et capacité de transport initiale de la rivière, permettant ainsi d'estimer leur temps de résidence moyen à 5-30 ans pour un scénario de séisme de Mw=8 beaucoup plus faibles que ceux estimés précédemment (~100 ans). L'approche numérique développée dans ce travail suggère que l'étude de la réponse des chaînes de montagnes à un forçage sismique fort ne peut être effectuée efficacement qu'avec un modèle 2D capable de prendre en compte les non-linéarités entre écoulements des rivières, leurs géométries et le transport sédimentaire. Les résultats obtenus permettent une meilleure caractérisation de la dynamique des paysages à l'échelle du cycle sismique et des aléas à court terme
In mountainous areas, intermediate to large earthquakes (Mw > 6) systematically trigger a large number of landslides supplying the fluvial network with massive volumes of sediment. The progressive evacuation of the sediment out of the epicentral area alters river dynamics and may cause hydro-sedimentary hazards in alluvial plains (river avulsion, inundations, bank erosion, ...). The quantification of sediment transfers is critical to better understand landscape evolution on short timescales (i.e. hours to centuries) and improve hazard management in deposition areas. However, the factors controlling the coarse sediment transfers are still poorly known due to a lack of field measurements and adequate numerical models. The aim of this work is thus to study, via numerical modeling, the parameters influencing landslides evacuation, the transport capacity variations at the gorge/alluvial plain transition and the short-term dynamics and hazards of alluvial fans. This work is set up in the context of the West Coast of New Zealand (NZ) which presents a 50% probability to experience a magnitude 8 earthquake in the next 50 years. This problematic has been addressed analytically and via a numerical approach. Using the analytical approach, we demonstrate that the conservation of long-term transport capacity at the bedrock gorge and alluvial plain transition usually implies the channel narrowing in the alluvial part that is generally realized by a transition to a braided system. We identify discharge variability as the dominant factor of alluvial river long term transport capacity compared to riparian vegetation. To explore the role of channel self-organization on coarse sediment transport, we use Eros, a 2D morphodynamic model able to simulate landscape evolution improved by a new 2D hydrodynamic model. Combined with a sediment transport/deposition model and lateral fluxes modeling (bank erosion and transverse deposition), Eros allows for the emergence of diverse alluvial river regimes and geometries (e.g. straight/sinuous and braided channels) as a function of the external forcing experienced by the river (water and sediment fluxes). The application of Eros on natural cases has required the validation and calibration of its principal parameters using analytical solutions and the morphodynamic reproduction of natural systems such as the evolution of the Poerua river in New Zealand following the Mount Adams landslide. In the downstream part of the catchment, the ensemble numerical simulations demonstrate Eros abilities to 1) efficiently predict the morphodynamic evolution of alluvial fans submitted to different scenarios of large sediment supplies and 2) generate probabilistic risk maps. In the upstream part, the results highlight the dominant role of dynamic river narrowing reducing export times of landslide-derived sediments. We define a new law characterizing export times as a function of landslide volume and pre-landslide transport capacity that predicts mean residence times for a M8 earthquake in a mountain range of 5-30 yr, much lower than previous estimations of ~ 100 yr. The numerical approach developed in this work suggests that the study of mountain ranges response to severe landslide disruption can only be addressed with a 2D model able to account for the non-linearities between river flow, channel geometry and sediment transport. The results allow for a better characterization of landscape dynamics at the scale of a seismic cycle and hydro-sedimentary hazards in the short term

The study area extends from west of the Great Divide to the Broken Hill and Tibooburra regions of far western New South Wales, encompassing several important mining districts that not only include the famous Broken Hill lodes (Pb-Zn-Ag), but also Parkes (Cu-Au), Peak Hill (Au), Cobar (Cu-Au-Zn) and White Cliffs (opal). The area is generally semi-arid to arid undulating to flat terrain covered by sparse vegetation. ¶ During the Cretaceous, an extensive sea retreated across vast plains, with rivers draining from the south and east. After the uplift of the Great Divide associated with opening of the Tasman Sea in the Late Cretaceous, drainage swung to the west, cutting across the Darling River Lineament. The Murray-Darling Basin depression developed as a depocentre during the Paleogene. Climates also underwent dramatic change during the Cenozoic, from warm-humid to cooler, more seasonal climates, to the arid conditions prevalent today. Up until now, there has been very little temporal constraint on the development of this landscape over this time period. This study seeks to address the timing of various weathering and landscape evolution events in northwestern New South Wales. ¶ The application of various regolith dating methods was undertaken. Palaeomagnetic dating, clay δ18O dating, (U+Th)/He and U-Pb dating were all investigated. Palaeomagnetic and clay dating methods have been well established in Australian regolith studies for the last 30 years. More recently, (U+Th)/He dating has been successfully trialled both overseas and in Australia. U-Pb dating of regolith materials has not been undertaken. Each method dates different regolith forming processes and materials. Palaeomagnetic and clay dating were both successfully carried out for sites across northwestern New South Wales, providing a multi-technique approach to resolving the timing of weathering events. Although (U+Th)/He dating was unsuccessful, there is scope for further refinement of the technique, and its application to regolith dating. U-Pb dating was also unsuccessfully applied to late-stage anatase, which is a cement in many Australian silcretes. ¶ Results from this study indicate that the landscape evolution and weathering history of northwestern New South Wales dates back at least 60 million years, probably 100 million years, and perhaps even as far back as 180 million years. The results imply that northwestern New South Wales was continuously sub-aerially exposed for the last 100 Ma, indicating that marine sedimentation in the Murray-Darling and Eromanga-Surat Basins was separated by this exposed region. The ages also provide further evidence for episodic deep chemical weathering under certain climatic conditions across the region, and add to the data from across Australia for similar events. In particular, the palaeomagnetic ages, which cluster at ~60 ± 10 Ma and 15 ± 10 Ma, are recorded in other palaeomagnetic dating studies of Australian regolith. The clay ages are more continuous across the field area, but show older clays in the Eromanga Basin sediments at White Cliffs and Lightning Ridge, Eocene clays in the Cobar region, and Oligocene – Miocene clays in the Broken Hill region, indicating progressively younger clay formation from east to west across northwestern New South Wales, in broad agreement with previously published clay weathering ages from around Australia. ¶ These weathering ages can be reconciled with reconstructions of Australian climates from previously published work, which show a cooling trend over the last 40 Ma, following an extended period of high mean annual temperatures in the Paleocene and Eocene. In conjunction with this cooling, total precipitation decreased, and rainfall became more seasonal. The weathering ages fall within periods of wetness (clay formation), the onset of seasonal climate (clay formation and palaeomagnetic weathering ages) and the initiation of aridity in the late Miocene (palaeomagnetic weathering ages). ¶ This study provides initial weathering ages for northwestern New South Wales, and, a broad geochronology for the development of the landscape of the region. Building on the results of this study, there is much scope for further geochronological work in the region.

Our understanding of tephra depositional processes is significantly improved by high-resolution ground-penetrating radar (GPR) data collected at Cerro Negro volcano, Nicaragua. The data reveal three depositional regimes: (1) a near-vent region on the cone itself, where 10 GPR radargrams collected on the western flank show quantifiable differences between facies formed from low energy normal Strombolian and higher energy violent Strombolian processes, indicating imaging of scoria cone deposits may be useful in distinguishing eruptive style in older cones where the proximal to distal tephra blanket has eroded away; (2) a proximal zone in which horizons identified in crosswind profiles collected at distances of 700 and 1,000 m from the vent exhibit Gaussian distributions with a high degree of statistical confidence, with tephra thickness decreasing exponentially downwind from the cone base (350 m) to ~ 1,200 m from the vent, and where particles fall from a height of less than ~2 km; and (3) a medial zone, in which particles fall from ~4 to 7 km and the deposit is thicker than expected based on thinning trends observed in the proximal zone of the deposit, indicating a transition from sedimentation dominated by fallout from plume margins to that dominated by fallout from the buoyant eruption cloud. Horizons identified in a crosswind profile at 1600 m from vent exhibit Gaussian distributions, again with high degrees of statistical confidence. True diffusion coefficients are calculated from Gaussian fits of crosswind profiles and do not show any statistical variation between zones (2) and (3). Data display thinning trends that agree with the morphology predicted by the advection-diffusion equation to a high degree of statistical confidence, validating the use of this class of models in tephra forecasting. One such model, the Tephra2 model, is reformulated for student use. A strategy is presented for utilizing this research-caliber model to introduce university undergraduates to key concepts in model literacy, encouraging students to develop a deeper understanding of the applicability and limitations of hazard models generally. For this purpose, the Tephra2 numerical model is implemented on the VHub.org website, a venture in cyberinfrastructure that brings together volcanological models and educational materials, and provides students with the ability to explore and execute sophisticated numerical models like Tephra2.

Os fatores condicionantes antrópicos e morfométricos são determinantes na formação do escoamento pluvial, do manejo do solo e na concentração de fluxos e detritos. No município de São Pedro (SP) é notória a ocorrência desses processos, sendo classificado, segundo o mapa de erosão do Estado de São Paulo como de alta suscetibilidade. Desta forma, a bacia do córrego Espraiado, localizada neste município, foi selecionada com objetivo de analisar a gênese e a distribuição das feições erosivas a partir da influência dos parâmetros morfométricos (curvatura, declividade e hipsometria) e antrópicos numa escala evolutiva (1962, 1972, 2000 e 2006) e também numa análise integrada e quantitativa (feições erosivas, uso do solo e parâmetros morfométricos), por meio do cálculo dos seguintes índices: Concentração de Erosão (CE) e Potencial de Erosão (PE). O primeiro índice é a razão entre o número de células em cada classe afetadas pela erosão e o número total de células na bacia, enquanto o segundo índice é a razão entre o número de células em cada classe afetadas pela erosão e o número total de células na mesma classe. Nos mapas das feições erosivas, observou-se que a partir do cenário de 1962 até 2006 a área total das feições erosivas registrou uma redução, no qual a cabeceira das drenagens revelou o setor com maior ocorrência e concentração de feições. O mapa do uso do solo revelou que o aumento do percentual de mata, da área urbana consolidada e da silvicultura, e a redução do solo exposto e da pastagem tiveram um papel determinante para a diminuição das feições erosivas, embora a classe de área urbana consolidada tenha influenciado diretamente para o surgimento de novas feições e a evolução de outras. A análise integrada mostrou que a curvatura côncava, a declividade entre 20 e 40% e as classes de solo exposto e de pastagens foram as mais suscetíveis e que estão presente principalmente nas áreas das cabeceiras de drenagens, setor que está associado a solos pouco espesso. Os índices também indicaram que mesmo as áreas com a presença de curvatura convexa ou retilínea e declividades entre 0 e 15% com baixos índices de PE mas com alterações antrópicas significativas, obtiveram aumento do potencial de ocorrência de feições erosivas, assim como, as classes de uso com baixo índice de PE quando associados aos parâmetros morfométricos de alto índice, propiciaram aumento da formação de feições erosivas.
The anthropic and morphometric factors are significant in the formation of runoff, soil management and concentration flows and debris. In the São Pedro city (SP) is recognized to exist of these processes, being classified, according to the erosion map of São Paulo state as high susceptibility. Thus, the Espraiado basin, located in this city, was selected to analyze the genesis and distribution of erosional features by the influence of morphometric parameters (curvature, slope and elevation) and anthropic in the evolutionary scale (1962, 1972, 2000 and 2006) and also an integrated and quantitative analysis (erosional features, land use and morphometric parameters), by calculating the following index: Erosion Concentration (EC) and Erosion Potential (EP). The first index is the ratio of the number of cells in each class affected by the erosion areas to the total number of cells in the basin, while the second index is the ratio of the number of cells in each class affected by the areas of erosion to the total number of cells in the same class. In the erosional features maps, we observed from 1962 to 2006 scenario, that the total area of erosional features decrease, in which the head drainages revealed the sector with the highest occurrence and concentration of features. The land use map showed that the increase of the percentages of the forest, of the urban area consolidated and the forestry, and the reduction of exposed soil and pasture were the role played on the reducing the erosive features, although the class of urban area consolidated was directly influenced in the new features and developments of the others. The integrated analysis showed that the concave curvature, the slope between 20 and 40% and the classes of exposed soil and pasture were the most susceptible and are primarily in the headwaters, a sector that is associated with very thick soils. These areas of high concentration runoff flow and debris, with fragile lithology and have a PE high, is related to the presence of curvature concave, in profile and plant, and concentrated flows, as well as high slope that increases the erosive power of the flow, factors that are associated with the erosion formation. The index also indicated that even the areas with the presence of convex or straight curvatures, slopes between 0 and 15%, with low PE but with significant anthropogenic changes, obtained an increase of the potential occurrence of erosional features, as well as classes use with low PE when associated with morphometric parameters of high, caused an increase of erosional features.

Le sujet de ce travail est une analyse géomorphologique et tectonique pluri-échelle de la Provence, où des séismes historiques d'intensités majeures (VIII voire IX) ont été répertoriés durant les derniers siècles (par exemple à Lambesc, 1909). Si l'intensité des séismes historiques est relativement élevée en Provence, la région ne subit qu'une faible microsismicité, d'où la nécessité d'une approche tectonique, géomorphologique et paléosismologique pour y étudier les déformations récentes. Afin d'appréhender la morphogénèse grande longueur d'onde en Provence, nous avons évalué les taux de dénudation des massifs carbonatés de la région grâce à des mesures de concentrations en isotopes cosmogéniques 36Cl. Nous obtenons des taux de dénudation comparables entre les différents sites (de l'ordre de 20 à 60 mm/ka) et comparables aux études précédentes dans ce type de contextes, sauf pour le Grand Luberon et la montagne de Lure, qui s'érodent plus rapidement (jusqu'à 140 mm/ka). Cette approche a été appliquée à plus petite échelle sur le Petit Luberon, où nous comparons la dénudation de la surface sommitale à la dénudation moyennée sur plusieurs bassins versants de ses flancs sud et nord.Enfin, nous avons implémenté une approche pluri-disciplinaire à une échelle locale, associant cartographie haute-résolution, mesures de résistivités électriques, paléosismologie, granulométrie et datations afin d'obtenir une meilleure compréhension du comportement Quaternaire et Holocène d'un segment de faille localisé à Vinon-sur-Verdon. Notre analyse confirme de la déformation dans les 200 derniers milliers d'années sur ce contact mais démontre l'absence de déformation depuis 16000 ans
This manuscript deals with a multi-scale geomorphological and tectonic analysis of Provence, a region where large scale historical earthquakes (intensities of VIII or even IX) have been recorded during the last centuries (e.g. in Lambesc, 1909). If the intensity of historical earthquakes is relatively high in Provence, the region undergoes a weak microseismicity, hence the need for a tectonic, geomorphologic and paleoseismologic approach to understand the recent deformations.In order to evaluate the large-scale morphogenesis in Provence, we evaluated the denudation rates of the carbonate ranges of the region by measuring 36Cl cosmogenic isotope concentrations. We obtain comparable denudation rates between different sites (in the order of 20-60 mm/ka) and comparable to previous studies in this type of contexts (e.g. Ryb et al., 2014a, b), except for the Grand Luberon and the Lure mountain, which erode more quickly (up to 140 mm/ka). This approach was applied on a smaller scale by focusing on the Petit Luberon, where we compare the denudation of the summit surface to the denudation averaged over several watersheds on its southern and northern flanks.Finally, we implemented a multi-disciplinary approach on a local scale, associating high-resolution mapping, electrical resistivity measurements, paleoseismology, granulometry, 14C and OSL dating, in order to obtain a better understanding of Quaternary and Holocene behavior of a fault segment located in Vinon-sur-Verdon. Our analysis confirms that deformation occurred in the last 200 thousand years on this contact but demonstrates the absence of deformation in the last 16000 years

L'évolution à long terme des reliefs continentaux résulte de couplages complexes entre processus d'érosion et mouvements tectoniques qui tendent à s'équilibrer pour atteindre éventuellement un état stationnaire. La partie érosion de ces couplages est gouvernée par l'interaction entre des processus élémentaires de versant et de rivière, étroitement couplés, qui contrôlent l'organisation spatiale du réseau de drainage. Ces processus sont caractérisés par des vitesses d'érosion et de transport lentes sur les versants et très rapides dans les rivières, et dépendent souvent non-linéairement de la pente topographique et du flux d'eau. Il en résulte une dynamique complexe à l'échelle locale dont les conséquences à l'échelle continentale sur la vitesse et les volumes de matière transportés ne sont pas encore comprises. L'objectif de cette thèse a été de comprendre et modéliser cette dynamique à l'échelle des temps géologiques, dans le cadre de perturbations tectoniques simples, et pour des conditions climatiques constantes. Nous utilisons un modèle numérique permettant de simuler l'action de différents processus d'érosion de versant et de transport fluvial. Les solutions hors équilibre prédites par ce modèle ne pouvant être validées analytiquement ou à partir de données naturelles, une approche expérimentale inédite a été développée. Elle permet d'étudier précisément l'évolution d'une topographie soumise à l'action simultanée d'une surrection simple et de processus d'érosion et de transport par ruissellement. Au cours d'une expérience, la surface s'auto-organise d'abord en une série de bassins versants de géométrie similaire aux systèmes naturels, puis l'altitude moyenne du système s'approche quasi-exponentiellement d'une valeur constante, traduisant un état d'équilibre macroscopique. L'analyse couplée des expériences et des simulations numériques montre que cette dynamique dépend fortement de la présence de zones de drainages internes non connectées aux conditions limites du système, du degré de non-linéarité entre érosion et pente topographique et de l'existence d'un seuil d'érosion. A partir de l'analyse de systèmes naturels, via le formalisme de la relation pente-aire drainée, nous mettons en évidence l'existence d'un tel seuil dans les systèmes naturels. Pour ce faire nous avons développé un nouveau critère morphologique permettant de caractériser l'état dynamique des reliefs naturels. L'hypothèse d'équilibre dynamique entre érosion et tectonique, nécessaire à l'interprétation correcte des relations entre formes topographiques et processus d'érosion, peut être ainsi (in)validée. Ces résultats suggèrent que le seuil d'érosion habituellement négligé dans le calibrage des lois d'érosion élémentaires doit être explicitement pris en compte pour prédire correctement les formes topographiques naturelles, la dynamique de la croissance des réseaux de drainage et les relations à l'échelle continentale entre taux de dénudation et paramètres topographiques.

On-going population growth and urbanization increasingly force people to occupy environments where natural processes intensely affect the landscape, by way of potentially hazardous natural events. Tectonic plate boundaries, active volcanic regions and rapidly uplifting mountain ranges are prominent examples of geomorphically hazardous areas which today accommodate some of the world’s largest cities. These areas are often affected by more than one hazard such as volcanic eruptions, earthquakes, landslides, tsunamis, floods, storms and wildfires, which frequently interact with each other increasing the total impact on communities. Despite progress in natural hazards research over the last two decades, the increasing losses from natural disasters highlight the limitations of existing methodologies to effectively mitigate the adverse effects of natural hazards. A major limitation is the lack of effective hazard and risk assessments incorporating hazard interactions and cascade effects. Most commonly, the assessment of risks related to different hazards is carried out through independent analyses, adopting different procedures and time-space resolutions. Such approaches make the comparison of risks from different hazard sources extremely difficult, and the implicit assumption of independence of the risk sources leads to neglect of possible interactions among hazard processes. As a result the full hazard potential is likely to be underestimated and lead to inadequate mitigation measures or land-use planning. Therefore there is a pressing need to improve hazard and risk assessments and mitigation strategies especially in highly dynamic environments affected by multiple hazards. A prominent example of such an environment is the western Southern Alps of New Zealand. The region is located along an actively deforming plate boundary and is subject to high rates of uplift, erosion and orographically-enhanced precipitation that drive a range of interrelated geomorphic processes and consequent hazards. Furthermore, the region is an increasingly popular tourist destination with growing visitor numbers and the prospect for future development, significantly increasing societal vulnerability and the likelihood of serious impacts from potential hazards. Therefore the mountainous landscape of the western Southern Alps is an ideal area for studying the interaction between a range of interrelated geomorphic hazards and human activity. In an effort to address these issues this research has developed an approach for the analysis of geomorphic hazards in highly dynamic environments with particular focus on tectonically-active mountains using the western Southern Alps as a study area. The approach aims to provide a framework comprising the stages required to perform multi-hazard and risk analyses and inform land-use planning. This aim was approached through four main objectives integrating quantitative geomorphology, hazard assessments and GIS. The first objective was to identify the dominant geomorphic processes, their spatial distribution and interrelationships and explore their implications in hazard assessment and modelling. This was achieved through regional geomorphic analysis focusing on catchment morphometry and the structure of the drainage networks. This analysis revealed the strong influence and interactions between frequent landslides / debris-flows, glaciers, orographic precipitation and spatially-variable uplift rates on the landscape evolution of the western Southern Alps, which supports the need for hazard assessment approaches incorporating the interrelationships between different processes and accounting for potential event cascades. The second and third objectives were to assess the regional susceptibility to rainfall-generated shallow landslides and river floods respectively, as these phenomena are most often responsible for extensive damage to property and infrastructure, injury, and loss of lives in mountainous environments. To achieve these objectives a series of GIS-based models was developed, applied and evaluated in the western Southern Alps. Evaluation results based on historical records indicated that the susceptibility assessment of shallow landslides and river floods using the proposed GIS-based models is feasible. The output from the landslide model delineates the regional spatial variation of shallow landslide susceptibility and potential runout zones while the results from the flood modelling illustrate the hydrologic response of major ungauged catchments in the study area and identify flood-prone areas. Both outputs provide critical insights for land-use planning. Finally, a multi-hazard analysis approach was developed by combining the findings from the previous objectives based on the concepts of interaction and emergent properties (cascade effects) inherent in complex systems. The integrated analysis of shallow landslides, river floods and expected ground shaking from a M8 plate-boundary fault (Alpine fault) earthquake revealed the areas with the highest and lowest total susceptibilities. Areas characterized by the highest total susceptibility require to be prioritized in terms of hazard mitigation, and areas with very low total susceptibility may be suitable locations for future development. This doctoral research project contributes to the field of hazard research, and particularly to geomorphic hazard analyses in highly dynamic environments such as tectonically active mountains, aiming to inform land-use planning in the context of sustainable hazard mitigation.

Nous evaluons ici la part respective du climat et de la tectonique dans la morphogenese des versants du fosse rhenan. Une approche structurale de surface et de subsurface permet de mieux contraindre la geometrie des deformations synrifts. De strasbourg jusqu'au s du fosse, le bassin est structure sur sa bordure occidentale par un detachement crustal au pendage superficiel superieur a 60\. Les deformations syntectoniques s. S. (priabonien) sont rapides (3 ma) et correspondent au decollement et au drapage de la couverture sedimentaire prerift. Les deformations posterieures (rupelien) correspondent a des reequilibrages intrasedimentaires d'origine gravitaire qui n'impliquent pas le jeu des failles de socle. Un analogue physique base sur la reponse flexurale a un chargement d'une plaque mince reposant sur un fluide incompressible permet d'expliquer la geometrie des massifs bordiers. L'implementation de ce modele suggere que le relief actuel des epaulements resulte principalement de l'etirement oligocene. Un controle rheologique lie a la structuration de la lithosphere permet au s de la zone de cisaillement hercynienne de lalaye-lubine une reponse flexurale viscoelastique d'ou des sommets plus eleves, alors que la reponse demeure elastique plus au n. Les caracteristiques morphologiques de plus courte longueur d'onde resultent de la structuration tectonique du bassin. L'utilisation d'un analogue diffusif a permis de dater au travers de sa forme un escarpement de terrasse rhenane quaternaire au s du fosse rhenan (depression de sierentz). Une des approches possibles s'interesse a la distribution des pentes sur un profil topographique transversal. Si le processus d'evolution est diffusif, cette distribution correspond a une gaussienne dont l'ecart type renvoie l'age de l'escarpement. Nous montrons que l'age obtenu necessite pourtant une correction quand la diffusivite des materiaux est faible. Elle permet par contre d'identifier une eventuelle reactivation de l'escarpement (reincision, glissement). La mise en oeuvre de cette approche a permis d'estimer le taux d'incision verticale et de discriminer un signal de courte longueur d'onde d'origine tectonique. Le taux d'incision verticale moyen et de soulevement tectonique local avoisineraient respectivement 0,4 et 0,2 mm/a entre 30 et 15 ka.

L'objectif de ce travail de recherche est de (1) définir l'évolution du rivage et de la bathymétrie sur le long terme (siècle) sur différents types de plages de Méditerranée française (plages de poche de Provence, plages ouvertes du Golfe du Lion), (2) définir l'impact de l'élévation du niveau marin moyen, (3) déterminer l'impact des tempêtes. Ce travail se base sur un suivi topographique et bathymétrique important et sur une analyse par emboîtement d'échelles spatiales et temporelles qui s'inscrit dans une démarche de géomorphologie littorale quantitative. L'approche croisée de terrain et de modélisation (simulation des transports sédimentaires selon différents types de conditions d'agitation) permet d'adopter également une approche prospective nécessaire à la gestion de ce type de milieu. Les résultats indiquent que les plages de poche de Provence conservent un volume constant alors qu'elles ont perdu en moyenne ½ de leur surface en un siècle essentiellement du fait de la montée de la mer. Si la montée de la mer se poursuit, les plages de poche semblent menacées de disparition d'ici 2100. En Camargue, l'élévation du niveau marin joue un rôle minime dans les mouvements sédimentaires observés, car ils sont liés principalement liés à la houle. Enfin, l'analyse des tempêtes dans le Languedoc-Roussillon montre qu'elles peuvent être érosives ou constructives car leur impact morphologique dépend principalement du budget sédimentaire de l'avant côte plutôt que des caractéristiques hydrodynamiques des houles. A partir de ces constats, il s'agit de s'interroger sur la pertinence de concepts d'évolution de l'avant côte utilisés dans les études des dynamiques sédimentaires littorales.

The structures along the Atwater Fold belt form important deep-water hydrocarbon traps in the northern Gulf of Mexico. The purpose of this study is to map and quantify the morphology, sedimentology and architecture of Plio-Pleistocene basin floor fan systems outboard of the Poseidon Minibasin, located along the Atwater deep-water fold belt (mid-Miocene to Pliocene), and apply that information to determine the temporal and spatial nature of the fill and its implications as a reservoir analog. The data set includes ~2200 km sq. of 3D seismic data, along with information from several wells. Wireline logs show the Tertiary age deposits outboard of the Sigsbee Escarpment to be several hundred feet thick, sharp-based, dominantly coarse-grained (sandy) but fining up cycles composed of sandy basin floor fans, mass transport complexes and leveed channels developed in a confined setting within deep-water “valleys.” The largest valley formed in five main stages: initiating from narrow channel incision, widening through lateral incision and sidewall slumping, straightening, and finally flooding and infilling. The valley system is ~20,000 feet across and ~ 1,400 feet deep, with what look like well-developed levees ranging from 700 to 1300 feet at their thickest point extending ~19000 feet away from the channel. This system is underlain by a ~700 foot thick mass transport complex and overlain by younger, low sinuosity leveed channel systems. Both of these systems appear to have been sourced by large submarine drainages, originating from a shelf edge sediment source system to feed the rugose slope with deep-water channel pathways uninhibited by salt wall inflation at the time of valley deposition. Major phases of salt thrusting along the southern edge of the Atwater were contemporaneous with the formation of these large, through-going valley system, which appear to be associated with the period of sheet thickening and development of monoclinal basinward dip related to rafted mini-basin docking. Well log signatures show evidence for armored clay drapes along the valley margins as well as a flattening of lateral accretion packages toward the distal end of the system. The flattening of these packages seems to signal proximity to the fan terminus, which would serve as an important indicator of spatial extent of plays in deep-water.
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博士
國立中央大學
地球物理研究所
97
Due to the plate movement is considerably slow, human history record is too short to identify landscape change for such a long time scale. However, tectonic geomorphology indices can display the characteristics of tectonic movement in a long time. Therefore, the purpose of this study is to evaluate the difference of tectonic movement and characteristics of tectonic evolution between east and west sides of the orogeny in Central Taiwan, by applying a quantitative analysis of geomorphic indices coupled with mathematical fitting function, gradient index and slope vs area relationship from stream power model. Both logarithmic and exponential function of mathematical fitting function were used to illustrate the characteristics of river longitudinal profile and the relationship with tectonic movement. Furthermore, normalized gradient index (SL/k) from the river longitudinal profile of main and tributary was used to plot the 2-D profile for illustrating the characteristics of landscape. Additionally, the concavity (θ: represented to the characteristic of landscape) and steepness ( : represented to the degree of rock lift) from the slope vs area relationship of the stream power model were further applied to examine the characteristics of tectonic movement. The results of this study are listed as following: 1. Different results for the mathematical fitting function were found, in which most of logarithmic function were found on the west side, and most of exponential function were found on the east side. Concavity (θ) also showed the asymmetric landscape of the orogeny in Central Taiwan. 2. Normalized gradient index (SL/k) can response the behavior of rock, knickpoint, continuous-gorge, the active of rock movement, as well as the relationship between geometry of the flow path and the active trend of rock movement. 3. Average log(ksn) and the coefficient of determination (R2) of exponential and logarithmic function were similar for both sides of Central Range. Therefore, this study implied that the orogeny of Central Taiwan is in a steady state. 4. According to the quantitative analysis of geomorphic indices coupled with and SL/k, the degrees of tectonic movement trend are Western Foothills Belt > Hsuehshan Range Belt > Eastern Backbone Ridges Belt > Western Backbone Ridges Belt. Furthermore, the average precipitation in the past 50~60 years and the flow versus the normalized steepness (ksn) index exhibit no remarkable relationship. This study suggested that the control factor of stream evolution is tectonic movement, not the resistance of rock stratum nor climate.

The study area extends from west of the Great Divide to the Broken Hill and Tibooburra regions of far western New South Wales, encompassing several important mining districts that not only include the famous Broken Hill lodes (Pb-Zn-Ag), but also Parkes (Cu-Au), Peak Hill (Au), Cobar (Cu-Au-Zn) and White Cliffs (opal). The area is generally semi-arid to arid undulating to flat terrain covered by sparse vegetation. ¶ During the Cretaceous, an extensive sea retreated across vast plains, with rivers draining from the south and east. After the uplift of the Great Divide associated with opening of the Tasman Sea in the Late Cretaceous, drainage swung to the west, cutting across the Darling River Lineament. The Murray-Darling Basin depression developed as a depocentre during the Paleogene. Climates also underwent dramatic change during the Cenozoic, from warm-humid to cooler, more seasonal climates, to the arid conditions prevalent today. Up until now, there has been very little temporal constraint on the development of this landscape over this time period. This study seeks to address the timing of various weathering and landscape evolution events in northwestern New South Wales. ¶ ...

Les mécanismes de transport et d'érosion en domaine fluvial sont les facteurs dominants qui contrôlent la morphologie des continents et des flux sédimentaires. La quantification de ces processus à grande échelle est de ce fait nécessaire à la compréhension des interactions qui existent entre la tectonique et l'évolution des reliefs sur le long terme. La présente étude s'intéresse au développement des profils longitudinaux et des plaines de divagation de rivières situées dans les Alpes du Dauphiné, sur des échelles de temps variables (103-105 ans). Les taux d'incisions et les paléo-profils sont reconstitués grâce à la datation des terrasses fluviatiles par âge d'exposition (10-Be). Les glaciers quaternaires ont soumis ces rivières à des perturbations d'importance variable. L'évolution du profil longitudinal du Drac est contrôlée par des fluctuations de son niveau de base de l'ordre du kilomètre, provoquées par l'obturation de sa vallée par d'importants glaciers. L'évolution post-glaciaire de son profil en long est caractérisée par une érosion régressive extrêmement rapide. La durée totale de la réponse et de la relaxation du système fluvial est de 15-20 ka. Dans le bassin contigu du Buëch, l'influence glaciaire est plus limitée. Les taux d'incision à court terme (103-104 ans) reflètent les effets du forçage climatique. Les taux d'incision à long terme (104-105 ans) sont réguliers (0,8 mm a-1) et proches des taux de dénudation régionaux, suggérant un certain équilibre entre l'incision et la surrection. Une analyse de la morphologie directement produite par les rivières est réalisée à l'aide d'un système d'information géographique sur des rivières situées à proximité des sites de datation. Il apparaît qu'au-delà d'une certaine valeur du rapport entre la puissance érosive des rivières et la résistance du substrat rocheux, le profil longitudinal reste régulièrement concave, les forçages lithologiques et tectoniques se répercutant sur la largeur de la bande de divagation. La complexité de ce signal nécessite néanmoins des étalonnages supplémentaires pour que la surrection puisse être déduite de la seule analyses des formes du relief.