High rates of soil loss and high sediment loads in rivers necessitate efficient monitoring and quantification methodologies so that effective land management strategies can be designed. Constructing a sediment budget is a useful approach to address these issues. Quantifying a sediment budget using classical field-based techniques, however, is labour intensive and expensive for poorly gauged, large drainage basins. The availability of global environmental datasets in combination with GIS techniques provides an opportunity for studying large basins. Following this approach, a framework is presented for constructing sediment budgets for large, data-sparse drainage basins, which is applied to the mountainous upper Indus River basin in northern Pakistan. The methodological framework consists of five steps: (1) analyzing hydro-climatological data for dividing the drainage basin into characteristic regions, and calculating sediment yields; (2) investigation of major controls on sediment yields; (3) identification and mapping of sediment source areas by spatially distributed modelling of erosional processes; (4) spatially distributed modelling of sediment yields; and (5) carrying out the sediment budget balance calculation at the basin outlet. Further analysis carried out on the Indus data has enabled a better understanding of sediment dynamics in the basin.<p> Analysis of the available hydro-climatological data indicates that the basin can be subdivided into three characteristic regions based on whether runoff production and subsequent sediment generation is controlled by temperature (Region 1, upper, glacierized sub-basins), precipitation caused by the monsoon and western disturbances (Region 3, lower sub-basins), or a combination of the two (Region 2, middle reach sub-basins). It is also demonstrated that contrary to the conventional model, the specific sediment yield increases markedly with drainage area along the Indus River. An investigation of major controls on specific sediment yield in the basin indicates that percent snow/ice cover is a major land cover control for specific sediment yield. Spatially distributed erosion modelling predictions indicate that 87% of the annual gross erosion takes place in the three summer months with greatest erosion potential concentrated in sub-basins with high relief and a substantial proportion of glacierized area. Lower erosion rates can be explained by the arid climate and low relief on the Tibetan Plateau, and by the dense vegetation and lower relief in the lower monsoon sub-region. The model predicts an average annual erosion rate of 3.2 mm/a or 868 Mt/a. Spatially distributed sediment yield predictions made with coupled models of erosion and sediment delivery indicate that the Indus sub-basins generally show an increase of sediment delivery ratio with basin area. The predicted annual basin sediment yield is 244 Mt/a and the overall sediment delivery ratio in the basin is calculated as 0.28. The long-term mean annual sediment budget, based on mass balance, is characterized by a gross erosion of 762.9, 96.7 and 8.4 Mt, and a gross storage of 551.4, 66.1, and 6.5 Mt in the upper, middle, and lower regions of the basin, respectively. The sediment budget indicates that the major sources of eroded sediment are located in the Karakoram, in particular in the Hunza basin. Substantial sediment storage occurs on the relatively flat Tibetan Plateau and the Indus River valley reach between Partab Bridge and Shatial. The presented framework for sediment budget construction requires relatively few data, mostly derived from global datasets. It therefore can be utilized for other ungauged or poorly gauged drainage basins of the world.

abstract: The Himalayan orogenic system is one of the youngest and most spectacular examples of a continent-continent collision on earth. Although the collision zone has been the subject of extensive research, fundamental questions remain concerning the architecture and evolution of the orogen. Of particular interest are the structures surrounding the 5 km high Tibetan Plateau, as these features record both the collisional and post-collisional evolution of the orogen. In this study we examine structures along the southwestern margin of the Tibetan Plateau, including the Karakoram (KFS) and Longmu Co (LCF) faults, and the Ladakh, Pangong and Karakoram Ranges. New low-temperature thermochronology data collected from across the Ladakh, Pangong and Karakoram Ranges improved the spatial resolution of exhumation patterns adjacent to the edge of the plateau. These data show a southwest to northeast decrease in cooling ages, which is the trailing end of a wave of decreased exhumation related to changes in the overall amount of north-south shortening accommodated across the region. We also posit that north-south shortening is responsible for the orientation of the LCF in India. Previously, the southern end of the LCF was unmapped. We used ASTER remotely sensed images to create a comprehensive lithologic map of the region, which allowed us to map the LCF into India. This mapping shows that this fault has been rotated into parallelism with the Karakoram fault system as a result of N-S shortening and dextral shear on the KFS. Additionally, the orientation and sense of motion along these two systems implies that they are acting as a conjugate fault pair, allowing the eastward extrusion of the Tibet. Finally, we identify and quantify late Quaternary slip on the Tangtse strand of the KFS, which was previously believed to be inactive. Our study found that this fault strand accommodated ca. 6 mm/yr of slip over the last ca. 33-6 ka. Additionally, we speculate that slip is temporally partitioned between the two fault strands, implying that this part of the fault system is more complex than previously believed. / Dissertation/Thesis / Ph.D. Geological Sciences 2014

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23018号 / 理博第4695号 / 新制||理||1673(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 河上 哲生, 教授 田上 高広, 教授 下林 典正 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

The Himalayan region is experiencing population growth and a process of rapid urbanization. At the same time the existing government structure is struggling to provide basic services to the burgeoning urban population and does not have the financial or human resources to address urban risk. This dissertation explores how this problem can be addressed by urban risk governance rather than ‘all-of-society’ engagement. The rapidly urbanizing town of Almora in the Uttarakhand Himalayas is selected as a case study. Primary sources of data are government documents pertaining to land-use planning and building regulation, 150 household surveys as well as 24 key informant interviews. The dissertation identifies gaps in the existing government framework of land use and building regulation while arguing for the adoption of the concept of urban risk governance. However, various challenges to achieving a working model are revealed when risk governance is contextualized in the case of Almora. These are related to the local level developmental process, formal and informal actors as well as local risk knowledge. Such challenges must be resolved in order to successfully implement urban risk governance.

Himalayan glaciers are key components of earth's cryosphere, acting as hydrological reservoirs vital to many human and natural systems. Most Himalayan glaciers are shrinking in response to changing climate, which will potentially impact water resources, natural hazards, sea level rise, and many other aspects. However, there is much uncertainty regarding the state of these glaciers, as direct field data are difficult to obtain. Accordingly, long-timespan remote sensing techniques are needed to measure changing glaciers, which have memory and often respond to climate on decadal timescales. This study uses declassified historical imagery from the Hexagon spy satellite database to fulfill this requirement. A new highly-automated, computer-vision based solution is used to extract historical terrain models from Hexagon imagery, which are used as a baseline to compute geomorphic change for glaciers in the Kingdom of Bhutan and Tibet Autonomous Region of the eastern Himalayas. In addition to glaciers, the new method is used to quantify changes resulting from the Thistle Creek Landslide (surface elevation changes resulting from the landslide show an average elevation decrease of 14.4 ± 4.3 meters in the source area, an increase of 17.6 ± 4.7 meters in the deposition area, and a decrease of 30.2 ± 5.1 meters resulting from a new roadcut) and Mount St. Helens eruption in western North America (results show an estimated 2.48 ± 0.03 km3 of material was excavated during the eruption-triggered debris slide). These additional results illustrate the applicability of Hexagon imagery to a variety of landscape processes. Regarding the primary application in the Himalayas, all studied glaciers show significant ice loss. Futhermore, the multi-decadal timespan reveals important aspects of glacier dynamics not detectable with temporally shorter datasets. Some glaciers exhibit inverted mass-balance gradients due to variations in debris-cover, while enhanced ice losses are prominent on glacier toes terminating in moraine-dammed proglacial lakes, resulting from calving caused by thermal undercutting. Remarkably, debris-covered glaciers show significant thinning despite insulating effects of the debris, likely due to poorly-understood ice cliff and melt pond mechanisms. The mean annual geodetic mass balance of 22 studied glaciers over a 32-year period is estimated to be -0.16 ± 0.03 m yr-1 water equivalent. Thus, these glaciers are not in equilibrium with current climate, and appear to be losing significant amounts of ice regardless of debris-cover.

No description available.

The Himalayan orogen provides an incredible natural laboratory to test models for continent-continent collision. The highest peaks of the Himalayas are composed of the Greater Himalayan Sequence (GHS), which is bound by a north-dipping low angle detachment fault above (South Tibetan detachment; STD) and by a thrust fault below (Main Central thrust; MCT). Assuming simultaneous movement on these features, the GHS can be modeled as a southward extruding wedge or channel. Channel flow models describe the coupling between mid-crustal flow, driven by gradients in lithostatic pressure between the Tibetan Plateau and the Indian plate, and focused denudation on the range front. Although the general geometry and shear sense criteria for these bounding shear zones has been documented, prior to this investigation, relatively few attempts had been made to quantify the spatial and temporal variation in flow path history for rocks from an exhumed section of the proposed mid-crustal channel. Results from this investigation demonstrate that mid-crustal flow at high deformation temperatures was distributed throughout the proposed channel. As these rocks began to exhume to shallower crustal conditions and therefore lower temperatures, deformation began to become partitioned away from the core of the channel and into the bounding shear zones. Based on these results a new method (Rigid Grain Net) to measure the relative contributions of pure and simple shear (vorticity) is proposed. Detailed thermobarometric analysis was conducted on rocks from the highest structural level in the Khumbu region, Nepal to construct pressure-temperature-time-deformation paths during the tectonic evolution of the GHS between ~32-16 Ma. Another aspect of the project suggests that the most active feature of the region is the N-S trending Ama Drime Massif (ADM). By combining new structural interpretation with existing remote sensing data this investigation proposes that the ADM is being exhumed during extension that is coupled with denudation in the trans-Himalayan Arun River gorge. Together these data provide important insights into the dynamic links between regional-scale climate and crustal-scale tectonics. / Ph. D.

Cette thèse s'intéresse à la dynamique des prismes orogéniques à travers l'étude du cas Himalayen. J'ai utilisé une approche pluri-disciplinaire combinant modélisation numérique, cartographie de terrain, analyse structurale et microstructurale, thermochronologie Ar-Ar et détermination des pics de température métamorphique par RSCM (Raman Spectroscopy of Carbonaceous Material).La modélisation numérique m'a permis d'apporter des contraintes sur les paramètres contrôlant la géométrie actuelle de la chaine. A la suite de cette étude, je propose que les variations latérales observées le long de la chaîne Himalayenne soient générées par la combinaison de deux mécanismes : 1) l'advection asynchrone d'une rampe crustale sous le Moyen Pays Himalayen le long de différents segments, qui entraine la présence et le déplacement de la transition topographique le long de la chaîne; 2) des variations dans le contraste rhéologique entre le plateau du Tibet et la croûte continentale Indienne, qui controlent la formation des klippes et influence la largeur de la chaîne.Le travail de terrain a permis d'apporter des données sur une zone jusqu'alors peu documentée de l'Ouest Népalais. Les observations réalisées, ainsi que les analyses effectuées sur les échantillons rapportés de cette campagne de terrain, m'ont amené à proposer une nouvelle coupe géologique pour cette zone. L'existence du “lesser Himalayan Duplex”, jusqu'alors utilisé pour expliquer cette zone, est ainsi discuté ainsi que la géométrie et la signification du “Ramgarh Thrust”.Par ailleurs, un code de modélisation numérique a été développé afin d'étudier les mécanismes thermiques ayant lieu dans la croûte continentale en cours de migmatisation. Ce modèle, appliqué au massif métamorphique de El Oro en Equateur, nous a amené à mettre en évidence l'existence de mécanismes de convection crustale, lors de la migmatisation, dans cette région. Cette étude méthodologiquement proche de celle réalisée sur le prisme orogénique himalayen, apporte des contraintes sur la formation et la dynamique des plateaux continentaux. / This PhD focuses on the dynamics of orogenic wedges using the Himalayas as a case study. I used a multi-disciplinary approach combining numerical modeling, field mapping, structural and microstructural analysis, Ar-Ar thermochronology and metamorphic peak temperature estimation by RSCM (Raman Spectroscopy of Carbonaceous Material) to provide geometrical and timing constraints on the development and evolution of an upper-crustal scale nappe system.Numerical modeling provided the intuition on the parameters that control the current geometry of the belt. According to this study, I propose that along-strike variations observed along the Himalayan Belt are generated by two parallel mechanisms: 1) The asynchronous underthrusting of a crustal ramp beneath the Lesser Hiamalaya, responsible for the presence and displacement of the topographic transition observed along the belt; and 2) variations in the rheological contrast between the Tibetan Plateau and the colliding Indian continental crust, controlling the formation of klippes and the range width.The fieldwork campaign allowed us to bring new data on an area so far poorly documented: the far western Nepal. Field observations as well as analyses performed on samples collected during the field campaign led us to propose a new geological cross section for this area. The existence of the lesser Himalayan duplex, used so far to explain the structure of the belt in the Karnali River area (Western Nepal), is discussed as well as the geometry and tectonic significance of the Ragmarh thrust.In a parallel study, a numerical code has been developed in order to study the thermal behavior of a partially melted continental crust. This model, applied to the El Oro massif in Equator, led us to show the likely presence of crustal convection during partial melting for this area, in the Triassic. This study is similar to the one on the Himalayan orogenic wedge from a methodological point of view and brings new constraints on the formation and kinematics of continental plateau.

La sismicité présente le long du méga-chevauchement himalayen, dans la trace du fort séisme de 1505, des variations spatiales qui restaient peu résolues. Nous y avons déployé un réseau sismologique temporaire de 15 stations pour la période 2014-2016, en complément du réseau national. Nous avons effectué une détection automatique Seiscomp3 puis un pointé manuel des séismes enregistrés par le réseau, suivi par une localisation absolue Hypo71 et une relocalisation relative d’essaims HypoDD. Le catalogue résultant compte 2154 évènements dans notre zone d’étude dont les profondeurs (8-16 km) sont bien résolues. La confrontation de la sismicité avec des coupes géologiques équilibrées montre que les séismes se localisent dans le compartiment supérieur à proximité du grand chevauchement himalayen au voisinage de rampes ou contacts suspectés entre écailles de moyen pays. Les variations latérales de structures associées à cette sismicité sont susceptibles de contrôler pour partie les ruptures cosismiques de séismes intermédiaires, qui viennent rompre partiellement le chevauchement, comme l’ont démontré les études du séisme de Mw7.8 de Gorkha-Népal, 2015. La segmentation qui en résulte est une donnée importante dans les études d’aléa sismique. / The seismicity located along the Himalayan mega-thrust, within the trace of the great M8+ 1505AD earthquake, displays striking spatial variations which remained poorly resolved. In order to better constrain and understand these variations, we deployed a 15-stations temporary seismological network for 2 years (2014-2016) as a complement to the national network. We first processed the data with an automatic detection with Seiscomp3, then a manual picking of earthquakes recorded by the network, followed by a Hypo71 absolute localization and HypoDD relative relocation of clustered events. The resulting catalogue contains 2154 local events, shallow to midcrustal (8 - 16 km). The seismicity presented temporal variations suggesting fluid migrations. The confrontation between the seismicity and the geologic balanced cross-sections shows that most eartbquakes happen within the hangingwall of the Main Himalayan Thrust fault nearby ramps or suspected contacts between lesser Himalayan slivers. The lateral variations of some of the structures associated to this seismicity are likely to partially control the extent of the coseismic ruptures during intermediate earthquakes that break partly the locked fault zone, in a similar way as what was reported after the Mw7.8 2015 Gorkha-Nepal earthquake. Better characterizing the segmentation of such faults is an important input for seismic hazard studies.

Au-delà des représentations et des pratiques des alpinistes et trekkeurs, toujours plus nombreux, les conditions du développement et de la pérennisation du système touristique associées à la région népalaise de l’Everest – le Khumbu – semblent de plus en plus reposer sur la valorisation de ressources comme l’eau, l’électricité et l’emplacement foncier. Source de revenus considérables pour les populations locales, et plus particulièrement pour les hébergeurs touristiques, l’accès à ces différentes ressources ne va pourtant pas de soi. Tous les acteurs n’occupent pas les mêmes positions, ni ne possèdent les mêmes moyens pour les valoriser. Cet accès aux ressources, et par extension à de nouvelles positions socio-spatiales, donne lieu à de multiples stratégies fondées sur les capitaux, compétences et intérêts de chacun. Dans cette petite région, néanmoins hautement symbolique, ces stratégies d’accès aboutissent à une lutte des places entre d’une part les membres de la communauté sherpa – qui revendiquent une position d’insiders mais se déploient à l’extérieur du Khumbu par des modes d’habiter très polytopiques –, et d’autre part, de nouvelles populations originaires des basses vallées, en position d’outsiders, qui cherchent à s’y implanter. Dans le contexte d’un espace de plus en plus ouvert sur le monde, en pleine recomposition sociodémographique et culturelle, ce qu’incarne le « Yak Donald’s » – l’un des nombreux nouveaux pubs implantés dans la région –, se pose ainsi la question du partage et de la gouvernance des ressources et des revenus de ce haut-lieu du tourisme. Loin d’être passifs, mais plutôt à l’origine de ces nouvelles dynamiques, cette thèse montre comment les manipulateurs de symboles sherpas contrôlent encore largement le territoire et l’économie du tourisme. / Beyond the representations and practices of mountaineers and trekkers, conditions for the development and functioning of the touristic system linked to the Nepalese Mount Everest area (the Khumbu region) seem to be increasingly based upon resources such as water, electricity and property. With the rise of tourism, these various resources are source of considerable incomes for local populations, especially for lodge owners. However, sharing these resources is not simple. First, the different actors do not occupy the same positions in relation to them. Second, they don’t have the same capacities (i.e., capital and skills) to exploit them. Eventually, they do not have the same interests depending on their social status, so their cooperation is not always guaranteed. In this small but highly symbolic region, local access to resources leads to “locational struggles” (Lussault, 2009). This struggle opposes members of the Sherpa community - who claim to be deeply rooted inhabitants, but whose ways of life are very polytopic – and on the other hand, new populations from the lower valleys, who seek to establish themselves within the Khumbu region. In the context of intense interrelations with the rest of the world, as well as wide socio-demographic and cultural changes, which is embodied in one of the many new pubs established in the region; the "Yak Donald's", this questions the good resources governance of this tourist hub. Far from being passive, but rather very proactive, this thesis shows how the Sherpas still control the territory and its touristic economy.