Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODP Expedition 340

IODP Expedition 340 successfully drilled a series of sites offshore Montserrat, Martinique and Dominica in the Lesser Antilles from March to April 2012. These are among the few drill sites gathered around volcanic islands, and the first scientific drilling of large and likely tsunamigenic volcanic island-arc landslide deposits. These cores provide evidence and tests of previous hypotheses for the composition and origin of those deposits. Sites U1394, U1399, and U1400 that penetrated landslide deposits recovered exclusively seafloor-sediment, comprising mainly turbidites and hemipelagic deposits, and lacked debris avalanche deposits. This supports the concepts that i/ volcanic debris avalanches tend to stop at the slope break, and ii/ widespread and voluminous failures of pre-existing low-gradient seafloor sediment can be triggered by initial emplacement of material from the volcano. Offshore Martinique (U1399 and 1400), the landslide deposits comprised blocks of parallel strata that were tilted or micro-faulted, sometimes separated by intervals of homogenized sediment (intense shearing), while Site U1394 offshore Montserrat penetrated a flat-lying block of intact strata. The most likely mechanism for generating these large-scale seafloor-sediment failures appears to be propagation of a decollement from proximal areas loaded and incised by a volcanic debris avalanche. These results have implications for the magnitude of tsunami generation. Under some conditions, volcanic island landslide deposits comprised of mainly seafloor sediment will tend to form smaller magnitude tsunamis than equivalent volumes of subaerial block-rich mass flows rapidly entering water. Expedition 340 also successfully drilled sites to access the undisturbed record of eruption fallout layers intercalated with marine sediment which provide an outstanding high-resolution dataset to analyze eruption and landslides cycles, improve understanding of magmatic evolution as well as offshore sedimentation processes. This article is protected by copyright. All rights reserved

Automatic vector signal generator calibration method suitable for multiport large-signal measurements

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Méthode d’étalonnage automatique pour générateurs de signaux vectoriels en configuration multiport

International audienceLes bancs de mesure utilisant plusieurs géné-rateurs de signaux vectoriels se multiplient avec l'appari-tion d'amplificateurs à entrées multiples tels que les Do-herty numériques, les techniques d'outphasing ou l'amplification à injection de modulation (LMBA). Par consé-quent un étalonnage absolu des sources, en amplitude et phase, doit être réalisé. Une méthode d'étalonnage com-plète pour une génération multiport est présentée ici. Elle fait intervenir comme nouveau standard, un dispositif pas-sif multiport préalablement caractérisé en paramètres S. Cette méthode est détaillée analytiquement puis validée expérimentalement. Des mesures étalonnées d'amplifica-teurs de puissance à double entrée sont également présentées

Méthodologie de conception d'un amplificateur Doherty GaN double entrée avec gestion numérique de la combinaison vectorielle de puissance

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Timing, origin and emplacement dynamics of mass flows offshore of SE Montserrat in the last 110 ka: implications for landslide and tsunami hazards, eruption history, and volcanic island evolution

Mass flows on volcanic islands generated by volcanic lava dome collapse and by larger volume flank collapse, can be highly dangerous locally and may generate tsunamis that threaten a wider area. It is therefore important to understand their frequency, emplacement dynamics and relationship to volcanic eruption cycles. The best record of mass flow on volcanic islands may be found offshore, where most material is deposited, and where intervening hemipelagic sediment aids dating. Here we analyse what is arguably the most comprehensive sediment core data set collected offshore from a volcanic island. The cores are located southeast of Montserrat, on which the Soufriere Hills volcano has been erupting since 1995. The cores provide a record of mass flow events during the last 110?ka. Older mass flow deposits differ significantly from those generated by the repeated lava dome collapses observed since 1995. The oldest mass flow deposit originated through collapse of the basaltic South Soufriere Hills at 103-110?ka, some 20-30?ka after eruptions formed this volcanic centre. A ~1.8?km3 blocky debris avalanche deposit that extends from a chute in the island shelf records a particularly deep-seated failure. It likely formed from a collapse of almost equal amounts of volcanic edifice and coeval carbonate shelf, emplacing a mixed bioclastic-andesitic turbidite in a complex series of stages. This study illustrates how volcanic island growth and collapse involved extensive, large-volume submarine mass flows with highly variable composition. Run-out turbidites indicate that mass flows are emplaced either in multiple stages or as single events

Campagne Seapso 4: Etude morphostructurale de la ride de Valufa dans le bassin de Lau

The Lau Basin lies between the Lau and Tonga ridges and extends over more than 1000 km. Its width decreases from 300 km near 16 degree S to less than 100 km near 24S. It is an actively spreading oceanic back-arc basin created in the Plio-Pleistocene the Tonga Trench. The part of the Valu Fa ridge North of 22 degree S was investigated during the Seapso 4 cruise of R/V Jean Charcot in Jan 1986 and complementary data were obtained during the Papnoum transit (Apr 1987). The techniques used included multibeam bathymetry, single-channel seismic reflection, magnetic and gravity field measurements

Molecular Signatures of Glacial Dissolved Organic Matter From Svalbard and Greenland

Glaciers and ice sheets cover over 10 % of Earth's land surface area and store a globally significant amount of dissolved organic matter (DOM), which is highly bioavailable when exported to proglacial environments. Recent rapid glacier mass loss is hypothesized to have increased fluxes of DOM from these environments, yet the molecular composition of glacially derived DOM has only been studied for a handful of glaciers. We determine DOM composition using ultrahigh resolution mass spectrometry from a diverse suite of Arctic glacial environments, including time series sampling from an ice sheet catchment in Greenland (Russell Glacier) and outflow from valley glaciers in catchments with varying degrees of glacial cover in Svalbard. Samples from the Greenland outflow time series exhibited a higher degree of similarity than glacier outflow between glaciers in Svalbard; however, supraglacial meltwater samples from Greenland and Svalbard were more similar to each other than corresponding glacial outflow. Outflow from Russell Glacier was enriched in polyphenolic formulae, potentially reflecting upstream inputs from plants and soils, or inputs from paleosols overridden by the ice sheet, whereas Svalbard rivers exhibited a high level of molecular richness and dissimilarity between sites. When comparing DOM compositional analyses from other aquatic systems, aliphatic, and peptide-like formulae appear particularly abundant in supraglacial meltwater, suggesting the DOM quickly metabolized in previous incubations of glacial water originates from energy-rich supraglacial sources. Therefore, as glaciers lose mass across the region, higher-quality fuel for microbial degradation will increase heterotrophy in coastal systems with ramifications for carbon cycling

A importância de ser Uros: movimentos indígenas, políticas de identidade e pesquisa genética nos Andes Peruanos

O objetivo deste artigo é explorar as inter-relações entre a pesquisa genética, as lutas políticas de movimentos indígenas e os processos de formação de identidade étnica. Em particular, visa analisar as condições sociais que levaram à colaboração entre os uros, um grupo indígena que habita as ilhas flutuantes do lago Titicaca (Peru), e pesquisadores do projeto Genográfico. Os uros, cujas reivindicações de uma identidade étnica diferenciada eram altamente contestadas no âmbito local, se associaram aos geneticistas com o objetivo de obter um apoio científico para a afirmação dessa identidade e como parte das suas estratégias políticas e demandas territoriais. Assim, esse caso contribui ao maior entendimento da incorporação da pesquisa genética dentro de políticas conceituais travadas em torno das identidades étnicas, bem como da articulação do conhecimento genético com registros preexistentes para definir tais identidadesThe objective of this paper is to explore the interrelations between genetic research with human populations, the political strategies of indigenous movements and processes of identity formation. In particular, it will analyse the social conditions that have resulted in the collaboration between the Uros, an indigenous group living on the floating islands of Lake Titicaca (Peru), and researchers of the Genographic project. The Uros, whose claims to a differentiated ethnic identity were highly contested within the local context, engaged with geneticists with the aim to obtain scientific support for this identity. This was part of their political strategies for their territorial rights. As such, this case offers new insights into the incorporation of genetic research within the conceptual politics waged around ethnic identities, as well as the articulation of genetic knowledge with pre-existing registers to define such identitie