207 research outputs found

    Scale‐Dependent Processes and Runout in Bidisperse Granular Flows:Insights From Laboratory Experiments and Implications for Rock/Debris Avalanches

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    The bidispersity observed in the particle‐size distribution of rock avalanches and volcanic debris avalanches (rock/debris avalanches) has been proposed as a factor contributing to their long runout. This has been supported by small‐scale analog experimental studies, which observe that a small proportion of fine particles mixed with coarser particles enhances granular avalanche runout. However, the mechanisms enabling this phenomenon and their resemblance to rock/debris avalanches have not been directly evaluated. Here, binary mixture granular avalanche experiments are employed to constrain the processes and conditions under which bidispersity enhances the runout of granular avalanches in experiments. Structure‐from‐motion photogrammetry is used to measure center of mass displacement and assess energy dissipation. Subsequently, this study evaluates the dynamic scaling and flow regimes in the lab and field to assess whether the runout‐enhancing mechanism is applicable to rock/debris avalanches. In small‐scale experiments, the granular mass propagates under a collisional regime, enabling kinetic sieving and size segregation. Fine particles migrate to the base where they reduce frictional areas between coarse particles and the substrate and encourage rolling. The reduced energy dissipation increases the kinetic energy conversion and avalanche mobility. However, rock/debris avalanches are unlikely to acquire a purely collisional regime; instead, they propagate under a frictional regime. The size segregation which is essential for the process observed at the lab‐scale is prohibited by the frictional regime, as evident by the sedimentology of rock/debris avalanche deposits. The proposal of bidispersity as a runout‐enhancing mechanism overlooks that scale‐dependent behaviors of natural events are often omitted in small‐scale experiments

    Rock Slopes from Mechanics to Decision Making

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    http://lmrwww.epfl.ch/Eurock/Eurock2010/files/papers%20grouped.pdfRock slope instabilities are discussed in the context of decision making for risk assessment and management. Hence, the state of the slope and possible failure mechanism need to be defined first. This is done with geometrical and mechanical models for which recent developments are presented. This leads with appropriate consideration of uncertainties to risk determination and to the description of tools for risk management through active and passive countermeasures, including warning systems. The need for sensitivity analysis is then demonstrated, and final comments address updating through information collection.National Science Foundation (U.S.)MIT-Portugal ProgramPortuguese Science and Technology FoundationNorwegian Geotechnical Institute (International Centre for Geohazards)United States. Dept. of Energ

    Three-Dimensional Magnetotelluric Characterization of the Travale Geothermal Field (Italy) Remote Sens. 2022, 14, 542.

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    The geoelectrical features of the Travale geothermal field (Italy), one of the most productive geothermal fields in the world, have been investigated by means of three-dimensional (3D) magnetotelluric (MT) data inversion. This study presents the first resistivity model of the Travale geothermal field derived from derivative-based 3D MT inversion. We analyzed MT data that have been acquired in Travale over the past decades in order to determine its geoelectrical dimensionality, directionality, and phase tensor properties. We selected data from 51 MT sites for 3D inversion. We carried out a number of 3D MT inversion tests by changing the type of data to be inverted, the inclusion of static-shift correction at some sites where new time-domain electromagnetic soundings (TDEM) were acquired, the grid rotation, as well as the starting model in order to assess the connection between the inversion model and the geology. The final 3D model herein presents deep elongated resistive bodies between the depths of 1.5 and 8 km. They are transverse to the Apennine structures and suggest a correlation with the strike-slip tectonics. Comparison with a seismic velocity model and well log data suggests a highly-fractured volume of rocks with vapor-dominated circulation. The outcome of this study provides new insights into the complex geothermal system of Travale

    Slope stability models for rainfall-induced lahars during long-lasting eruptions

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    In this study we analyse the spatial distribution of potential lahar sources during long-lasting eruptions using two slope stability models (SHALSTAB and TRIGRS). The analysis is based on observed deposit grain-size and thickness, rainfall data and slope angle of the lahar events, in the area surrounding the Cordón Caulle volcano, Chile, that occurred during the 2011 eruption. The main phase of the eruption (4–7 June) was characterized by eruptive plumes from 7 to 11 km high which dispersed most of the tephra eastward toward Argentina, with a total estimated volume of about 1 km3. Tephra-fallout blanketed the region from ESE to ENE of the volcano with the thickness of the tephra-fallout layers between approximately 1 m (15 km from vent) and 0.06 m (240 km from the vent). On 10 June 2011, a major lahar occurred close to the Argentina-Chile border that reached the National road 231 (28 km from the vent). Three field campaigns were undertaken to collect samples and data from tephra-fallout deposits and triggering mechanisms in the lahar source area. Model input parameters were obtained from geotechnical tests and field measurements. Several metrics were used for model evaluation and best fit to the data were obtained for simulations considering non-cohesive ash layers for SHALSTAB and a cohesion of 0.5 kPa for TRIGRS. Both models are sensitive to the physical properties of the tephra-fallout deposit and the hydraulic and materiel strength properties of the study area. They both also show good agreement with field data but provide different information: TRIGRS provides an estimate of the timing (based on a storm event) and location of a potentially unstable area, while SHALSTAB simulations result in landslide susceptibility classes based on critical rainfall value. These outcomes provide fundamental insights into lahar triggering during long-lasting volcanic eruptions and are crucial to the compilation of lahar hazard maps and emergency management plans in the South Andes volcanic region

    The propagation and emplacement mechanisms of the Tenteniguada volcanic debris avalanche (Gran Canaria): Field evidence for brittle fault-accommodated spreading

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    The Tenteniguada volcanic debris avalanche deposit is located on the east of the island of Gran Canaria, Spain. Its internal structure is composed of a complex assemblage of extensional features and shearing structures including normal faults, horst and graben, brittle/ductile boudinage and clastic dike injections. Examination of these features in the field and evaluation of their distribution have allowed the generation of a new conceptual model for the transport and emplacement of this debris avalanche, and potentially others. In the majority of the deposit, the degree of disaggregation is low, with large portions of the original edifice preserved, although displaced by brittle deformation. Greater disaggregation is observed deeper and in the more distal section of the deposit. The findings suggest that the propagation of the volcanic debris avalanche was most likely facilitated by the normal fault-accommodated spreading and extension of the mass, with the majority of stress focused in fault zones. The greater disaggregation exhibited in the deeper and the more distal part of the deposit is likely to be due to greater stress accommodation from fault convergence and momentum transfer respectively. The abundance of competent lava lithologies and scarcity of weaker material that could be easily disaggregated is the most likely reason Tenteniguada did not fully evolve from a slide to a granular flow, and therefore generated a deposit which bears resemblance to non-volcanic blockslide deposits. Therefore, lithological properties are potentially a vital factor for the propagation mechanisms, distribution of stress and consequently the evolution of a debris avalanche from the initial collapse to its emplacement. The present study highlights the importance of dedicated field examinations of sedimentological, morphological, and structural features for providing constraints for models of debris avalanche propagation mechanisms and the factors dictating them

    Semences et séquences génétiques en open source ? Expériences récentes et stratégies futures

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    Le concept d'open source appliquĂ© aux semences vĂ©gĂ©tales a un avenir prometteur. Ce concept inverse la logique du systĂšme de propriĂ©tĂ© intellectuelle pour une ressource renouvelable que l'on rend disponible en la sortant du domaine exclusif de la propriĂ©tĂ© intellectuelle. Aujourd'hui, les instruments juridiques font encore dĂ©faut pour Ă©tablir un cadre lĂ©gal complet. Toutefois, le concept d'open source, que l'on pourrait traduire ici par licence libre et ouverte, engendre au fil du temps une masse critique d'utilisateurs et de soutiens qui entraĂźne une lĂ©gitimitĂ© sociale grandissante. À terme, cette lĂ©gitimitĂ© pourrait renforcer le pouvoir juridique. L'extension future Ă  d'autres matĂ©riels dans diffĂ©rents contextes doit ĂȘtre rĂ©flĂ©chie en s'appuyant sur les expĂ©riences actuelles de semences sous licences libres et ouvertes conduites aux États-Unis, en Europe et en Afrique

    Comparative analysis of anti-polyglutamine Fab crystals grown on Earth and in microgravity

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    Huntington's disease is one of nine neurodegenerative diseases caused by a polyglutamine (polyQ)-repeat expansion. An anti-polyQ antigen-binding fragment, MW1 Fab, was crystallized both on Earth and on the International Space Station, a microgravity environment where convection is limited. Once the crystals returned to Earth, the number, size and morphology of all crystals were recorded, and X-ray data were collected from representative crystals. The results generally agreed with previous microgravity crystallization studies. On average, microgravity-grown crystals were 20% larger than control crystals grown on Earth, and microgravity-grown crystals had a slightly improved mosaicity (decreased by 0.03°) and diffraction resolution (decreased by 0.2 Å) compared with control crystals grown on Earth. However, the highest resolution and lowest mosaicity crystals were formed on Earth, and the highest-quality crystal overall was formed on Earth after return from microgravity
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