Magma expansion and fragmentation in a propagating dyke     

Benoit Taisne  Claude Jaupart 《Earth and Planetary Science Letters》2011,301(1-2):146-152

The influence of magma expansion due to volatile exsolution and gas dilation on dyke propagation is studied using a new numerical code. Many natural magmas contain sufficient amounts of volatiles for fragmentation to occur well below Earth's surface. Magma fragmentation has been studied for volcanic flows through open conduits but it should also occur within dykes that rise towards Earth's surface. The characteristics of volatile-rich magma flow within a hydraulic fracture are studied numerically. The mixture of melt and gas is treated as a compressible viscous fluid below the fragmentation level and as a gas phase carrying melt droplets above it. The numerical code solves for elastic deformation of host rocks, the flow of the magmatic mixture and fracturing at the dyke tip. With volatile-free magma, a dyke fed at a constant rate in a uniform medium adopts a constant shape and width and rises at a constant velocity. With volatiles involved, magma expands and hence the volume flux of magma increases. With no fragmentation, this enhanced flux leads to acceleration and thinning of the dyke. Simple scaling laws allow accurate predictions of dyke width and ascent rate for a wide range of conditions. With fragmentation, dyke behaviour is markedly different. Due to the sharp drop of head loss that occurs in gas-rich fragmented material, large internal overpressures develop below the dyke tip and induce swelling of the nose region, leading to deceleration of the dyke. These results are applied to the two-month long period of volcanic unrest that preceded the May 1980 eruption of Mount St Helens. An initial phase of rapid earthquake migration from the 7–8 km deep reservoir to shallow levels was followed by very slow progression of magma within the edifice. Such behaviour can be accounted for by magma fragmentation at the top of a dyke.  相似文献   

Reionization and the Cosmic Dawn with the Square Kilometre Array     

Garrelt Mellema  Léon V. E. Koopmans  Filipe A. Abdalla  Gianni Bernardi  Benedetta Ciardi  Soobash Daiboo  A. G. de Bruyn  Kanan K. Datta  Heino Falcke  Andrea Ferrara  Ilian T. Iliev  Fabio Iocco  Vibor Jelić  Hannes Jensen  Ronniy Joseph  Panos Labroupoulos  Avery Meiksin  Andrei Mesinger  André R. Offringa  V. N. Pandey  Jonathan R. Pritchard  Mario G. Santos  Dominik J. Schwarz  Benoit Semelin  Harish Vedantham  Sarod Yatawatta  Saleem Zaroubi 《Experimental Astronomy》2013,36(1-2):235-318

The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21 cm line from the earliest phases of star and galaxy formation in the Universe. This 21 cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope.  相似文献   

A stepwise screening system to select storm-sensitive stalagmites: Taking a targeted approach to speleothem sampling methodology     

Amy Benoit Frappier   《Quaternary International》2008,187(1):25

A stepwise stalagmite sample screening process was applied in order to select a stalagmite as a sensitive recorder of recent tropical cyclone rainfall events near Belize. Field and laboratory criteria were combined in series, to screen out candidate stalagmites whose characteristics indicated lower sensitivity to stormwater infiltration. The approach described here was designed to increase the likelihood that selected stalagmites would increase the signal:noise ratio of the target phenomenon in the resulting proxy records. This four-stage method for sample selection may be an important methodological consideration for researchers attempting to use speleothems for stable isotope paleotempestology. Hallmarks of this approach include: (1) establishing a priori scientific targets, (2) applying sample criteria in the form of contra-indicators, and (3) organizing the sample screening protocol into a series of practical stages. The overall approach to stalagmite selection presented here supports cave conservation, and can be adapted readily by others in support of different scientific goals. It is hoped that other investigators will also publish field and laboratory sample selection schemes, as increased transparency will provide new information invaluable to replication efforts and to advancing the field of speleothem paleo-environmental studies.  相似文献   

Regional VS30 model for the St. Lawrence Lowlands,Eastern Canada     

Miroslav Nastev  Michel Parent  Nicolas Benoit  Martin Ross  Danielle Howlett 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2016,10(3):200-212

Shear-wave velocity of the top 30?m, V_S30, is commonly used for prediction of the seismic site response. This paper presents development, validation and uncertainty assessment of a regional V_S30 model based on a combination of simplified 3D geology and statistically representative velocity values. Results identify soft marine sediments in deep sedimentary basins as zones most susceptible to seismic shaking. Compared to the available urban-scale seismic zonation studies, the regional model showed a success rate of roughly 64% in predicting local site category. The standard deviation was in average 30% of the expected V_S30 value.  相似文献   

Putting the principles of the Sustainable Livelihoods Approach into fisheries development policy and practice   总被引：1，自引：1，他引：1  

Edward H. Allison  Benoit Horemans   《Marine Policy》2006,30(6):757-766

The Sustainable Livelihoods Approach (SLA) combines a conceptual framework with a set of operational principles to provide guidance on policy formulation and development practice. The SLA has been widely used in coastal and fisheries development research and has informed the design of development programmes but experience of operationalising it remains largely undocumented. In the Sustainable Fisheries Livelihoods Programme, which involves 25 West African countries, the SLA has helped to align fisheries policy with wider poverty reduction initiatives and to identify means of contributing to poverty reduction that do not directly increase pressure on fully or over-exploited fish resources.  相似文献   

From model-based prescriptive advice to indicator-based interactive advice     

Trenkel  Verena M.; Rochet  Marie-Joelle; Mesnil  Benoit 《ICES Journal of Marine Science》2007,64(4):768-774

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Closure of a hyperextended system in an orogenic lithospheric pop‐up,Western Pyrenees: The role of mantle buttressing and rift structural inheritance     

Nicolas Saspiturry  Ccile Allanic  Philippe Razin  Benoit Issautier  Thierry Baudin  Eric Lasseur  Olivier Serrano  Sophie Leleu 《地学学报》2020,32(4):253-260

The Early Cretaceous hyperextended Mauléon rift is localized in the north‐western Pyrenean orogen. We infer the Tertiary evolution of the Mauléon basin through the restoration of a 153‐km‐long crustal‐scale balanced cross‐section of the Pyrenean belt, which documents at least 67 km (31%) of orogenic shortening in the Western Pyrenees. Initial shortening, accommodated through inversion of inherited crustal structures, led to formation of a pop‐up structure, in which the opposite edges underwent similar shortening with different tectonic reactivation styles, localized versus. distributed. Underthrusting of the Iberian margin accommodated further convergence, forming the Axial Zone antiformal stack of crustal nappes within a lithospheric pop‐up. Thin‐skinned and thick‐skinned structures propagated outward from the heart of this pop‐up, a block of strong mantle acting as a buttress inhibiting complete inversion of the Mauléon rift basin.  相似文献   

Trend detection in hydrological series: when series are negatively correlated     

Christine Rivard  Harold Vigneault 《水文研究》2009,23(19):2737-2743

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