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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Importance of Concentrated Flow Paths in Agricultural Watersheds of Southern Illinois

Shrestha, Prabisha 01 May 2017 (has links)
Field scale research shows concentrated flow paths (CFPs) are prevalent in agricultural watersheds. They are an important source of soil erosion in cropland and significantly contribute to the transport and delivery of agricultural pollutants such as sediment and nutrients to nearby water resources. High resolution LiDAR data have enabled the investigation of the prevalence of concentrated flow at a large geographic extent. This study focused on identifying CFPs in 389 agricultural fields in Jackson County in southern Illinois and estimating the contribution of the CFPs to drainage of the fields. Addressing the lack of literature on factors influencing CFP characteristics, this study also investigates various topographical and soil factors that influence CFP development. LiDAR derived DEMs with a cell resolution of 3 meters were used to identify areas of flow concentration and delineate a drainage basin of each CFP using the Hydrology tools in the Spatial Analyst toolbox in ArcMap 10.3.1. Information on the topographical and soil characteristics were obtained from the DEMs and SSURGO database using the Soil Data Viewer 6.2 extension for ArcMap. Multiple regression analysis in SAS v. 9.4 was used to identify factors influencing CFP characteristics, while CART analysis in R v. 3.3.1 was conducted to detect linear dependencies among predictor variables. An average of 5 CFPs per agricultural field were observed in the study area with a minimum of 0 and maximum of 17 CFPs, but only two fields had no CFPs indicating a high prevalence of CFPs throughout the study area. The mean percent of field area drained by CFPs was estimated to be 81 percent with minimum of 36 percent and ii maximum of 100 percent. The majority of the fields, 85 percent, had more than 70 percent of their area drained by CFPs. Statistically significant regression equations were found for all CFP characteristics with slope, LS factor, K factor and organic matter as the factors influencing CFP characteristics. However, the factors only explained 2 to 22 percent of variation observed. Both multiple regression and CART analysis indicated slope as the most important influencing factor. Variation in CFP characteristics followed regional trends with higher values in the floodplain region and lower values in the rough hills region suggesting residual variation could be explained by other environmental factors along with topographical and climatological factors which were not included in the study. Results from this study highlight the prevalence of CFPs at a regional scale and their substantial contribution to field drainage identifying a need for research in quantifying the impacts of CFP on soil loss and water quality. This study also reports a need of future research to identify important factors controlling CFP formation and development that could help build empirical and physical models to accurately predict CFP locations and morphology. Such information could be useful in designing and targeting conservation practices that protect both soil health and water quality.
12

Causas e consequências da ocorrência de voçorocas nas estradas AM-330 (Silves) e AM-363 (Itapiranga), Amazonas – Brasil

Silva, Emerson Dias da 21 August 2014 (has links)
Submitted by Geyciane Santos (geyciane_thamires@hotmail.com) on 2015-10-06T13:39:41Z No. of bitstreams: 1 Dissertação - Emerson Dias da Silva.pdf: 7900774 bytes, checksum: d967e7e483fcf3fd65dc3ec5c6ca759a (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-10-06T20:53:12Z (GMT) No. of bitstreams: 1 Dissertação - Emerson Dias da Silva.pdf: 7900774 bytes, checksum: d967e7e483fcf3fd65dc3ec5c6ca759a (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-10-06T20:56:55Z (GMT) No. of bitstreams: 1 Dissertação - Emerson Dias da Silva.pdf: 7900774 bytes, checksum: d967e7e483fcf3fd65dc3ec5c6ca759a (MD5) / Made available in DSpace on 2015-10-06T20:56:55Z (GMT). No. of bitstreams: 1 Dissertação - Emerson Dias da Silva.pdf: 7900774 bytes, checksum: d967e7e483fcf3fd65dc3ec5c6ca759a (MD5) Previous issue date: 2014-08-21 / FAPEAM - Fundação de Amparo à Pesquisa do Estado do Amazonas / This research has as its object of study the process of voçorocamento roads AM - 330 AM and in Silves - 363 in Itapiranga belonging to the Metropolitan Region of Manaus (RMM). Was held in the said survey mapping regarding the environmental impacts of the action of gullies along these pathways. The process observed voçorocamento presented as main impacts the advancement of gullies towards the roads, which also resulted in the silting of canals in the vicinity of roads. The research about the process of voçorocamento has relevance on the various problems caused as a result of its dynamism, since it occurs very frequently in urban areas and highways / roads in the Amazon. The emergence and expansion of gullies are conditioned by natural (erodibility erossividade) and anthropogenic action elements, which led to several changes in the landscape, as well as changes in the dynamics of the incisions. Equipment for data collection were used, as the auger, the rain gauge, GPS, cisalhômetro, the impact penetrometer, the infiltrometer and the phmetrer. These were used for soil samples; measuring the amount of rain; to identify the geographic location of the incisions; to obtain the shear of the soil; measuring the penetration soil; measuring soil infiltration; obtaining the level of acidity of the soil, respectively. Geology, geomorphology, climate, hydrology, soil and vegetation: During the characterization of the study area the main information about the gullies, such as length, width, depth, slope of the land, beyond the physical characteristics were observed. The paper is organized in four chapters divided thus: the first deals with discussions about the definitions of gullies; the second focuses on the natural characteristics of the study area; the third explains the methodology adopted as the equipment used in the field, the scientific approach among others; the fourth and final reports results from the methodology and the answers about the possibilities of the emergence of the incisions and in some cases the expansion or reduction of some features. Both the emergence of the new features in the increase of the size of these, the major factor was changes in storm drainage and hence the runoff and the paving of roads also contributed to the changes in the dynamics of new incisions. / A presente pesquisa teve como objeto de estudo o processo de voçorocamento nas estradas AM – 330 em Silves e AM – 363 em Itapiranga, pertencentes à Região Metropolitana de Manaus (RMM). Realizou-se na referida pesquisa um mapeamento a respeito dos impactos ambientais decorrentes da ação das voçorocas ao longo dessas vias. O processo de voçorocamento observado apresentou como principais impactos o avanço das voçorocas em direção às estradas, que resultou também no assoreamento dos canais nas proximidades das vias. A pesquisa acerca do processo de voçorocamento apresenta relevância diante dos vários problemas causados por consequência de seu dinamismo, pois ocorre com muita frequência em áreas urbanas e em estradas/estradas na Amazônia. O surgimento e a expansão das voçorocas são condicionados por elementos naturais (erodibilidade, erossividade) e pela ação antrópica, os quais provocaram diversas modificações na paisagem, bem como alterações na dinâmica das incisões. Foram utilizados equipamentos para a obtenção dos dados, como: o trado, o pluviômetro, o GPS, o cisalhômetro, o penetrômetro de impacto, o infiltrômetro e o phmetro. Estes foram utilizados para obter as amostras de solo; para medição da quantidade de chuva; para identificar a localização geográfica das incisões; obter o cisalhamento do solo; medir a penetração ao solo; medir a infiltração no solo; obter o nível de acidez do solo, respectivamente. Durante a caracterização da área de estudo foram observadas as principais informações a respeito das voçorocas, como comprimento, largura, profundidade, declividade do terreno, além das características físicas: geologia, geomorfologia, clima, hidrografia, solo e vegetação. O trabalho está organizado em quatro capítulos divididos assim: o primeiro trata das discussões sobre as definições sobre voçorocas; o segundo aborda sobre as características naturais da área de estudo; o terceiro explica sobre a metodologia adotada como os equipamentos utilizados em campo, a abordagem científica seguida entre outros; o quarto e último relata os resultados provenientes da metodologia e as respostas a respeito das possibilidades do surgimento das incisões e em alguns casos a expansão ou diminuição de algumas feições. Tanto no surgimento das novas feições quanto no aumento do tamanho destas, o fator preponderante foi alterações na drenagem pluvial e, consequentemente, no escoamento superficial e a pavimentação das estradas também contribuiu para as mudanças na dinâmica das novas incisões.
13

Mapeamento das áreas de risco a voçorocamento e caracterização geoambiental da rodovia Am-010 Manaus/Itacoatiara - Am

Dirane, Anne Carolina Marinho 22 February 2016 (has links)
Submitted by Izabel Monteiro (izabel_22@hotmail.com) on 2016-06-13T15:32:39Z No. of bitstreams: 1 Dissertação- Anne Carolina Marinho Dirane.pdf: 21327336 bytes, checksum: ac3d7b64e5658201097449f7f2e49fdf (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2016-06-13T15:36:25Z (GMT) No. of bitstreams: 1 Dissertação- Anne Carolina Marinho Dirane.pdf: 21327336 bytes, checksum: ac3d7b64e5658201097449f7f2e49fdf (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2016-06-13T15:39:30Z (GMT) No. of bitstreams: 1 Dissertação- Anne Carolina Marinho Dirane.pdf: 21327336 bytes, checksum: ac3d7b64e5658201097449f7f2e49fdf (MD5) / Made available in DSpace on 2016-06-13T15:39:30Z (GMT). No. of bitstreams: 1 Dissertação- Anne Carolina Marinho Dirane.pdf: 21327336 bytes, checksum: ac3d7b64e5658201097449f7f2e49fdf (MD5) Previous issue date: 2016-02-22 / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / The erosion process comprehension is essential to prevent and conservation of the soil, in this matter the present study has main objective of mapping the Gully–type erosion incisions and the geo-environmental characterization of the Road- AM-010, which connect Manus to the municipalities of Rio Preto da Eva and Itacoatiara. Having the following specifics objectives: Map and quantify of the gullies during the course of the road AM-010; identify the morphology and morphometry (width, length and depth) of the gullies and erosion features, evolution and growth rate, emphasizing the slope characteristics; identify the capacity of infiltrations and the soil resistance to penetration; describe the geo environmental aspects through the road. The methodological procedures were divided in: bibliography review, fieldwork and data analyze. To characterize the slopes, were observed shape, gradient and orientation. The techniques consisted in observations in loco, notes at cadastral file, use of compass, measuring tape and sketching. It was use parameters to estimate the size and risk scale. The infiltrometer was used to measure the infiltration rate and penetromter the measure the soil resistance to penetration. The results show the mapping of 15 gullies though the road AM-010, showing that the gully located at the km 135 has the greatest length (227,5 m), the greatest width is located at the km 104 (24 m) and greatest depth (9 m) at the km 125. The incision that showed the higest infiltration rate is located at the km 137 (15) and the lowest rate was gullies no5 (km 116), regarding the soil resistance the incision that showed the most compacted surface was the incision no5 (km 116), when associated to results of the infiltration test indicate a compacted surface, allowing the runoff. The occurrence of the incisions is connected to the infrastructure construction (paving and pluvial drainage), as well to the geomorphology. The sections that have concentration of gullies as sections that do not obey the local geomorphology. / A compreensão do processo erosivo é fundamental para a prevenção e conservação do solo, nesse sentido o presente trabalho tem como objetivo principal o mapeamento das incisões erosivas do tipo voçoroca e caracterização geoambiental na rodovia AM-010, que liga Manaus aos municípios de Rio Preto da Eva e Itacoatiara. Tendo comoobjetivos específicos foram o mapeamento e quantificação das voçorocas ao longo da rodovia AM-010; identificação da morfologia e morfometria (largura, comprimento e profundidade) das voçorocas e feições erosivas, evolução e taxa de crescimento, destacando as características das vertentes; identificação da capacidade de infiltração e resistência do solo à penetração; descrição dos aspectos geoambientais ao longo da rodovia. Os procedimentos metodológicos foram divididos em: revisão bibliográfica, pesquisa de campo e análise dos dados. Para caracterização das vertentes, foram observadas: forma, declividade e orientação. As técnicas consistiram em observações diretas em campo, anotações em ficha cadastral, utilização de bussola, trena e croqui. Foram utilizados parâmetros para mensurar o tamanho e a escala de risco. O infiltrômetro foi utilizado para medir a taxa de infiltração e o penetrômetro de impacto para medir a resistência do solo a penetração. Os resultados mostram o mapeamento de 15 voçorocas ao longo da rodovia AM-010, mostrando que a voçoroca localizada no km 135 é a que possui o maior comprimento (227,5 m), a voçoroca com maior largura situa-se no km 104 (24 m) e a com maior profundidade (9 m) no km 125. A incisão que apresentou a maior taxa de infiltração foi a voçoroca do km 137 (15) e a com menor taxa a voçoroca 5 (km 116), quanto a resistência do solo a penetração a incisão que apresentou a superfície mais compactada foi a incisão 5 (km 116), que associada ao teste de infiltração denunciam uma superfície bastante compactada, favorecendo o escoamento superficial concentrado. A ocorrência das incisões está ligadas às obras de infraestrutura ao longo da rodovia (pavimentação e drenagem pluvial), bem como a geomorfologia, os trechos em que há concentração de voçorocas são os trechos da estrada que não obedecem a geomorfologia do local.
14

Dynamique des versants en contexte périglaciaire: apports de la modélisation physique.

Védie, Emeric 29 February 2008 (has links) (PDF)
La modélisation physique en enceinte de gel est utilisée pour analyser les impacts du réchauffement climatique sur l'évolution des paysages en contexte périglaciaire. Les données expérimentales nous montrent (i) l'importance des conditions de saturation de la couche active dans le déclenchement des mécanismes lents et rapides des sols et (ii) l'impact des perturbations des régimes thermiques et hydriques du sol qui modifient à la fois les taux d'érosion et la dynamique des versants périglaciaires. - Lors de précipitations modérées, cryoexpulsion, cryoreptation/gélifluxion et glissements gravitaires sont autant de processus intervenant dans la modification de la morphologie du versant (érosion régressive). - Lors de précipitations intenses, les processus d'érosion rapide type coulées de débris deviennent prédominants, accélérant la dégradation du versant. Ils s'initient systématiquement (i) au niveau des pentes les plus fortes et (ii) en présence d'un pergélisol qui limite l'infiltration de l'eau en profondeur et joue le rôle de plan de glissement. Les taux d'érosion les plus forts sont enregistrés au cours des précipitations les plus intenses. Ces résultats devraient (i) constituer une aide précieuse pour établir une méthodologie de mesure in situ des systèmes périglaciaires et (ii) améliorer la connaissance sur l'évolution morphologique des versants, lorsque le réchauffement climatique augmente à la fois la profondeur du toit du pergélisol et la quantité d'eau apportée aux versants lors des dégels de printemps. Le travail doit désormais se focaliser sur le contrôle exercé par la dynamique de saturation du sol sur les processus d'érosion de versant.
15

Evoluation géomorphologique des ravins de l'Artois et du Pays de Thelle (Bassin parisien) / Geomorphological evolution of the ravines of Artois and the Pays de Thelle (Paris basin)

Bochi, Lara 03 December 2014 (has links)
En raison de son importance comme source de sédiments et de sa capacité à modifier l'eau et la connectivité des sédiments lors de pluies intenses, en particulier dans les terres cultivées, le ravinement a besoin d'être mieux compris afin de pouvoir le gérer et atténuer ses effets. Le Pays de Thelle et l'Artois sont les deux régions du Bassin parisien qui concentrent le plus grand nombre de ravins, or les études sur les processus de ravinement ainsi que les tentatives de modélisation restent rares. En utilisant l'analyse morphométrique et l'étude des dépôts conservés à l'aval des incisions, la recherche vise à déterminer quelles sont les variables du système contrôlant de telles incisions, et à reconstituer les étapes de la morphogenèse de ces incisions et les risques qu'elles représentent aujourd'hui. Les ravins se développent là où l'aire drainée et la pente sont suffisantes pour que l'écoulement concentré puisse éroder, on les trouve souvent au niveau de rupture de pente. La mesure des volumes érodés et accumulés montre que l'érosion l'emporte largement sur le dépôt.Les ravins ont enregistré plusieurs phases d'incision dont l'importance s'explique par la conjonction de précipitations exceptionnelles, de fortes pressions anthropiques (défrichements et mise en culture) et de phénomènes tectoniques (soulèvement lent des axes anticlinaux du Bray et de l'Artois). Ces ravins sont des formes fluviatiles, mais la néotectonique joue un rôle essentiel dans le Pays de Thelle, alors qu'en Artois ce sont plutôt les phénomènes karstiques qui l'emportent. Le boisement récent des ravins freine l'incision, mais n'empêche pas l'érosion régressive de faire reculer les têtes de ravins et les risques d'inondations et de coulées boueuses menacent toujours les villages situés à l'aval immédiat de ces ravins / Because of its importance as a source of sediment and its capacity to change the water and the connectivity of sediments during intense rainfall, particularly in the cultivated lands, the gullies have need to be better understood for being able to manage them and mitigate its effects. The Pays de Thelle and Artois are the two regions of the Parisian Basin in which the largest number of ravines is concentrated ; however the studies about the processes of gullies and the attempts of modeling remain rare. Using the morphometric analysis and the study of the preserved deposits in the downstream of the incisions, the research aims to determine which are the variables of the controlling system such incisions, and to reconstruct the morphogenesis stages of these incisions and the risks they represent today. Ravines are occurring where the area draining and the slope are sufficient to make concentrated flow that can erode, they are often found at the level of slope's breakdown. The measurement of the volumes which have been eroded and accumulated shows that the erosion wins largely on the depot. The ravines have recorded several phases of incision in which the importance is explained by the conjunction of exceptional rainfall, strong anthropogenic pressures (land clearing and cultivation) and tectonic phenomena (uprising slow anticlinal axes of Bray and Artois). These ravines are fluvial forms, but the Neotectonic plays an essential role in the Pays de Thelle, whereas it is rather the karst phenomena which prevail in Artois. The recent afforestation of ravines slows the incision, but does not prevent the regressive erosion to roll back the heads of gullies and the risks of floods and mudslides muddy still threaten the villages located immediately downstream of these ravines
16

An investigation of rainfall characteristics, erosivity and soil erosion on Round Island, Mauritius

Calvert, Darren Rhett 02 1900 (has links)
Round Island is a small (208 ha) islet of volcanic origin located 22.5 km north east of mainland Mauritius and has been classified as a nature reserve since 1957. Two sites were chosen for the installation of environmental monitoring equipment. A series of Gerlach troughs were installed to capture surface sediment transported by runoff, which were used to document sediment yields and determine the particle size distribution. Overall, rainfall and erosivity on Round Island is far less, when compared to mainland Mauritius. However, erosivity from Round Island (2,314.76 MJ.mm.ha-1.h-1.yr-1) is slightly above the global average of 2,190 MJ.mm.ha-1.h-1.yr-1. In terms of sediment transport, the annual sediment movement rates for Round Island were established during this study (0.1248 t.ha-1.yr-1) and were found to be considerably lower than Mauritius (10 t.ha-1.yr-1), as well as other tropical island such as Kauai (0.86 t.ha-1.yr-1) and O’ahu (0.6 t.ha-1.yr-1). Thus, although the estimated rates of soil erosion are very low for humid tropical regions, these rates only reflect the contemporary environmental conditions and cognisance of the landscape history should be incorporated into assessments of soil erosion / Geography / M. Sc. (Geography)
17

Les activités climatiques saisonnières sur Mars et leurs impacts sur la morphologie / Seasonal climatic activities on Mars and their morphological impact

Pasquon, Kelly 25 January 2018 (has links)
La surface de Mars a longtemps été considérée comme inactive de nos jours. Cependant, de nombreux phénomènes actifs ont été observés ces dernières années comme : des ravines, des tornades de poussières, des écoulements ou des taches sombres. La plupart d’entre eux sont encore inexpliqués et soulèvent de nombreuses questions au regard des conditions de surface existantes actuellement. Afin d’améliorer la compréhension de ces processus et en particulier des ravines, cette thèse a pour but d’en étudier certains par une approche pluridisciplinaire combinant l’analyse de données issues des missions spatiales martiennes et par une approche expérimentale. Les données de télédétection ont permis une analyse morphologique détaillée grâce aux images provenant de la caméra HiRISE (High Resolution Imaging Science Experiment) et de leurs MNT (Modèle Numérique de Terrain). Celles-ci ont été complétées par une analyse de la composition de la surface grâce aux données spectroscopiques CRISM (Compact Reconnaissance Imaging Spectrometer for Mars).Des études expérimentales visant à mieux comprendre l’effet de la pression et des mélanges fluides/grains sur des écoulements martiens ont également été réalisés. Les études morphologiques et compositionnelles réalisées dans l’hémisphère sud de Mars, ont permis d’arriver aux conclusions suivantes : i) Les ravines ont un fonctionnement saisonnier et se différencient entre elles par leur morphologie, leur taille, leur période d’activité, leur orientation et leur pente, ii) Certaines ravines saisonnières sont très récentes : elles se créent et disparaissent actuellement, alors que d’autres fonctionnent depuis une centaine d’années martienne, iii) Le CO₂ semble être le principal agent actif pour leur création, même si l’eau liquide et les saumures ne peuvent être écartées dans certains cas, iv) Les différences d’insolation et l’accumulation de matériel en amont de l’écoulement influencent l’activité des ravines saisonnières. v) Un fluide différent de l’eau peut créer et faire évoluer des sinuosités de nos jours sur Mars. Les expériences réalisées au cours de cette thèse ont montré que : i) Les écoulements d’eau en surface et sub-surface d’un milieu granulaire, vont avoir un impact morphologique plus important à basse pression (~ 7mbar) qu’à pression terrestre (~ 1000 mbar), ii) Il existe des modes de transport des sédiments atypiques à basse pression: un processus de « lévitation » (impliquant des fluides gazeux) et de la saltation. Les morphologies qui en découlent, peu courantes sur Terre, sont susceptibles d’intervenir sur Mars, iii) Des mêmes constituants d’un écoulement peuvent créer des morphologies et des dynamiques réellement différentes. Trois paramètres semblent jouer un rôle important sur la morphologie d’un écoulement : l’épaisseur de sédiment mobilisable, les différences de températures entre la surface et l’écoulement ainsi que la quantité de matériel écoulé. L’analyse dans cette thèse d’un grand nombre d’activités saisonnières ainsi que l’approche pluridisciplinaire utilisée ont permis de mettre en évidence des écoulements actuels reliés avec des processus exotiques. La détermination plus précise des conditions de formation de ces phénomènes actuels ne pourra se faire que grâce à l’acquisition de nouvelles données sur tous ces sites et sur plusieurs saisons. De nouvelles expériences en laboratoire permettant en particulier de mieux comprendre les processus liés au CO₂ sont également nécessaires. / Mars surface has been considered like a currently inactive planet for a long time. Nevertheless, numerous active phenomena have been observed during the last few years such as: gullies, dust devils, dark and bright flows. Most of them are also unexplained and their formation processes are unclear under present Mars conditions. The aim of this PhD is to study some gullies to try to understand their formation processes on Mars at the present time. For this, martian spacecraft data were analyzed and experimental studies were performed. Thanks to HiRISE (High Resolution Imaging Science Experiment) images and HiRISE DTM (Digital Terrain Models), a morphological study was carried out. This study has been completed by a spectroscopic study of the surface thanks to CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) data. Experiments were also performed with a mix of liquid and sand to try to understand the pressure impact on martians flows. Morphological and spectroscopic studies on the southern hemisphere of Mars lead us to conclude that: i) Gullies are seasonal. They have different morphologies, sizes, timing of activities, orientations, and slopes. ii) Gullies are young. They appear and disappear on present-day. Some of them are active since 100 years. iii) CO₂ frost seems to be a good candidate for gullies creation but a participation of liquid water can’t be excluded in some cases. iv) Insolation variations and material accumulations in the upper part of the flow influence the gullies activity. v) Sinuosities can be created by another fluid than liquid water today on Mars. Experiments performed during this PhD demonstrate that: i) Water flow in granular surface and sub-surface triggers higher morphological impact under Martian pressure (~ 7mbar) and Earth pressure (~ 1000 mbar). ii) Exotic sediment transport can be observed at low pressure (~ 7mbar): “levitation” (with gas) and saltation. The morphology and dynamics are influenced by 3 main parameters: the sediment thickness, the temperature variations between the surface and the flow and the amount of flow material. Several seasonal phenomena were analyzed with different approaches. This allowed us to observe and interpret present-day flows and exotic processes. More data and new experiments at low pressure (in particular with CO₂) will help us to better constrain and better understand the formation conditions of current seasonal activities on the Mars surface.
18

Controls on sedimentary processes and 3D stratigraphic architecture of a mid-Miocene to recent, mixed carbonate-siliciclastic continental margin : northwest shelf of Australia

Sanchez, Carla Maria, 1978- 11 July 2012 (has links)
Determining the relative importance of processes that control the generation and preservation of continental margin stratigraphy is fundamental to deciphering the history of geologic, climatic and oceanographic forcing imprinted on their sedimentary record. The Northern Carnarvon Basin (NCB) of the North West Shelf of Australia has been a site of passive margin sedimentation throughout the Neogene. Cool-water carbonate sedimentation dominated during the early-middle Miocene, quartz-rich siliciclastics prograded over the shelf during the late-middle Miocene, and carbonate sedimentation resumed in the Pliocene. Middle Miocene to Pliocene siliciclastics were deposited as clinoform sets interpreted as delta lobes primarily based on their plan-view morphology and their relief of 40-100 m. Shelf-edge trajectory analysis suggests that part of this stratigraphic succession was built during a long-term, third order, regressive phase, producing shelf-edge deltas, followed by an aggradational episode. These trends appear to correlate with third-order global eustatic cycles. Slope incisions were already conspicuous on the slope before deltas reached the shelf-break. Nevertheless, slope gullies immediately downdip from the shelf-edge deltas are wider and deeper (>1 km wide, ~100 m deep) than coeval incisions that are laterally displaced from the deltaic depocenter (~0.7 km wide, ~25 m deep). This change in gully morphology is likely the result of greater erosion by sediment gravity flows sourced from shelf-edge deltas. Total late-middle to late Miocene margin progradation increased almost three times from 13 km in the southwest to 34 km in the northeast, where shelf-edge deltas were concentrated. Flat-topped carbonate platforms seem to have initiated on subtle antecedent topographic highs resulting from these deltaic lobes. A reduction of siliciclastic supply to the outer paleo-shelf during the Pliocene combined with the onset of a southwestward-flowing, warm-water Leeuwin Current (LC) most likely controlled the initiation of these carbonate platforms. These platforms display marked asymmetry, likely caused by an ancestral LC, which created higher-angle, upcurrent platform margins, and lower-angle, downcurrent clinoforms. The along-strike long-term migration trend of the platforms could be the result of differential subsidence. These platforms constitute the first widespread accumulation of photozoan carbonates in the Northern Carnarvon Basin. They became extinct after the mid-Pleistocene when the LC weakened or became more seasonal. / text
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Remote sensing large-scale surface structures in the Wadden Sea. Application of satellite SAR data (TerraSAR-X) to record spatial distribution and dynamics of habitats and geomorphic structures for monitoring and long-term ecological research

Adolph, Inga Winny 06 April 2021 (has links)
The Wadden Sea off the coast of the southern North Sea is the largest coherent area of tidal flats worldwide. As a highly productive ecosystem it is of global importance, e.g. as nursery for fish and as a feeding and resting area for 10 – 12 million migratory birds following the East Atlantic Flyway. The outstanding ecological significance of this region corresponds to a high level of protection by EU directives and national law and by inscription as UNESCO World Heritage Site, all of which requires regular monitoring and assessment. Apart from the ecological aspects, the Wadden Sea is also of great importance for coastal protection. To survey the extensive, often inaccessible tidal area, remote sensing is essential and while mainly airborne techniques have been carried out for decades, now high-resolution satellite-borne sensors open up new possibilities relevant for monitoring and long-term ecological research. Especially satellite synthetic aperture radar (SAR) sensors offer a high availability of acquisitions as they operate largely independently of daylight and weather. The aim of the studies presented here was to explore the use of data from the TerraSAR-X satellite to record geomorphological structures and habitats for Wadden Sea Monitoring. More than 100 TerraSAR-X acquisitions from 2009 to 2016 were analyzed to distinguish various and variable surface types continuously influenced by tidal dynamics in the main study area, the tidal flats near the island of Norderney. Visual image interpretation supported by extensive in-situ verification proved to be a suitable and unsophisticated approach which is unspecific enough to identify mussel beds, fields of shell-detritus, gully structures, mud fields, and intertidal bedforms in the upper flats of the East Frisian Islands. The method proved to be robust against changes in geometry of acquisition and environmental influences. Several time series of TerraSAR-X data enabled to follow inter-annual and seasonal dynamics as well as event effects (Adolph et al. 2018). The high-frequency TerraSAR-X data revealed novel evidence of an intertidal bedform shift in an easterly direction during the study period. To this aim, an unsupervised ISODATA classification of textural parameters was developed to vectorize and compare the bedforms positions in a GIS (Adolph et al. 2017a). The same intertidal bedform area was chosen as test-site for comparison of different remote sensing methods, namely airborne lidar, satellite-based radar (TerraSAR-X) and electro-optical sensors (RapidEye) (Adolph et al. 2017b). High-resolution SAR data offer a relevant component for Wadden Sea Monitoring and Research, as they provide reliable, regular data with a high repetition rate. In particular, habitats with noticeable surface roughness, specific structures and textures are well reflected. Geomorphic Structures and their dynamics can be observed indirectly via detection of residual water trapped within. A comprehensive concept for Wadden Sea Monitoring however, requires automatized classifications and an integrative, multi-sensor approach (SAR, LIDAR, multi-spectral data, drones) in which different and complementary information, coverage and resolutions (spatial and temporal) contribute to an overall picture. The studies were carried out as part of the joint research project “Scientific monitoring concepts for the German Bight” (WIMO), jointly funded by the Ministry of Environment, Energy and Climate Protection (NMU) and the Ministry of Science and Culture (NMWK) of the Federal State of Lower Saxony. The findings have been published in Geo-Marine Letters 37/2 (2017) and in Remote Sensing 10/7 (2018).

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