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.

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.

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.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20681号 / 工博第4378号 / 新制||工||1680(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 角 哲也, 准教授 竹門 康弘, 准教授 Sameh Kantoush / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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.

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.