A history of deformation within Pietre Cotte rhyolite flow (Vulcano)

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Lava flow mapping and area estimation using radar coherence images

International audienceInterferometric synthetic aperture radar (InSAR), more specifically calculation of coherence images, can be used to infer changes in the ground surface’s geometry. If these changes come from the emplacement of a lava flow, coherence images can then be used to map the flow. For this purpose, we developed an algorithm which separates the lava flow pixels from the others depending on their median shade. After processing the picture, we get a map and a surface for a given date. By doing this for several dates, we thus can follow the time and space evolution of the lava flow. For the August – October 2015 eruption of Piton de la Fournaise, available InSAR data allowed us to map the lava flow at nine different dates between 08/29/15 and 11/01/15. We estimated the flow’s area for each date; at the end of the eruption, the total surface estimation is 4.251 10⁶ ± 4.5 10⁴ m². This work could be pursued to map active parts of the flow and to estimate the volume of emitted products

Insight into the CE 1600 Huaynaputina Plinian tephra, combining the re-analysis of observational datasets with recent methods for tephra dispersal modelling

International audienceIn the Central Andes, large Plinian eruptions (VEI ≥ 6) occur at a relatively high frequency: one every 2000 to 4000 years over the past 50,000 years in southern Peru. This recurring, explosive activity poses a challenge to a region hosting c. three million people. Our objective is to use the 1600 CE Huaynaputina eruption as a reference to better assess the impacts of large events in the region. With VEI 6, this is considered the largest historical eruption in South America. In the framework of the Huayruro project, we have re-examined the Plinian stage of the eruption using recent models to estimate the volume and dispersal of the tephra-fall deposit.We reconsidered the case study in 2015–2017, revising the dataset and applying recent models to unravel to which extent these developments improved tephra studies. These studies have considerably evolved over the past decade. Sampling strategy is now standardized. New tools allow to propagate measurement errors into uncertainty of eruption source parameters. Volume estimation methods have been developed allowing thickness extrapolation to be made beyond the most distal isopach contour, thus better accounting for fine ash dispersed far away from the source. More recent methods consider thickness measurements instead of isopach data, removing the subjectivity inherently associated with hand-drawn contours. Previous studies of the Huaynaputina eruption were done in 1999-2002.The bulk volume of pumice fallout from the Plinian stage is approximately 14–15 km3, almost twice as the previous estimate (7–8 km3 within the 1 cm isopach). The revised plume height estimate, 32.2 ± 2.5 km, is consistent with past studies. As a result, the Huaynaputina 1600 CE Plinian eruption lies in the upper part of the Plinian field close to the ultra-Plinian transition, making this eruption one of the largest in the past millennium

New insights into eruption source parameters of the 1600 CE Huaynaputina Plinian eruption, Peru

Co-auteur étrangerInternational audienceIn the Central Andes, large Plinian eruptions (Volcanic Explosivity Index ≥ 5) occur at a relatively high frequency, i.e. average of one every 2000 to 4000 years over the past 50,000 years in Peru. Such recurring explosive activity represents a significant challenge for regions typically hosting several million people (e.g. southern Peru, western Bolivia and northern Chile). With VEI 6, the 1600 CE Huaynaputina eruption is considered the largest historical eruption in South America. We have reexamined the first Plinian phase of this eruption in order to better assess critical eruption source parameters (i.e. erupted volume, plume height, mass eruption rate, eruption duration). The revised bulk volume of the tephra-fall deposit associated with the Plinian phase is approximately 13-14 km3 , almost twice the previous estimate (7-8 km3 within the 1 cm isopach) based on methods including power law, Weibull function, and Bayesian linear regression. Tephra was dispersed by strong winds to the WNW as far as 400 km on Peruvian territory and then in the Pacific Ocean. Seven villages were buried, killing ~1500 people. The revised plume height estimate, 32.2 ± 2.5 km, is consistent with the early estimations. As a result, the Huaynaputina 1600 CE first eruption phase lies in the upper part of the Plinian field close to the ultra-Plinian transition, making this event one of the largest in the past millennium which coincides with results from recent studies on palaeoclimatic impacts

Unravelling the emplacement dynamics of silicic lava flows: the case of the Grande Cascade trachyte flow (Monts Dore, France)

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Emplacement dynamics of a crystal-rich, highly viscous trachytic flow of the Sancy stratovolcano, France

Emplacement dynamics of highly viscous, silicic lava flows remain poorly constrained due to a lack of consideration of crystal-rich cases. Emplacement models mostly apply to glassy or microlitic, vesiculated rhyolitic flows. However, crystalline, vesicle-free silicic lava can flow differently. We studied the Grande Cascade unit, which is a vesicle-free, phenocryst-rich, trachytic flow in the Monts Dore massif, France. Field work was carried out to define internal structures, and oriented samples were collected for chemical, petrological, and anisotropy of magnetic susceptibility analyses, allowing us to estimate emplacement temperature and viscosity. These data allow us to define a new silicic lava flow subtype that is low in temperature (800−900 °C), high in silica content (up to 66.8 wt%), high in viscosity (109−1011 Pa s), rich in phenocrysts (∼35%), and lacks vesicles. Brittle deformation of the lava occurs upon extrusion, generating a cataclasite basal layer and thin (3-m-thick) shear zone that accommodates all of the stress, allowing most of the flow’s volume to slide over its base as a 40-m-thick plug in which there is no deformation. Blocks are rare, of a single size (10 ± 1 cm), and result from localized break-up of the basal shear zone. Emplacement dynamics are different from those of glassy, pumiceous lava flows. They are closer to glacier dynamics, where most of the volume slides over a thin basal shear zone and till is generated there by abrasion and milling of the underlying layer. For the Grande Cascade lava flow, abrasion means that the flow lacks its classical blocky crust and instead the flow base is marked by a layer rich in fine-grained material. The structures and emplacement dynamics of this crystal-rich flow are consistent with ideal, gravity-driven shear flow. We thus argue for a global reassessment of silicic-rich lava emplacement based on crystal content and using a multidisciplinary approach focused on well-exposed examples in the rock record

Apport des données SAR à la compréhension et à la surveillance des volcans ; exemple du Piton de la Fournaise

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APPORT DES DONNEES SAR A LA COMPREHENSION ET A LA SURVEILLANCE DES VOLCANS : EXEMPLE DU PITON DE LA FOURNAISE

International audienceLast two decades have proven that remote sensing represents a key tool to improve our knowledge of volcanic systems but also to monitor active volcanoes. Based on the specific case of Piton de la Fournaise, Reunion Island, the most active French volcanoes, we here illustrate how Synthetic Aperture Radar (SAR) data, providing information even in cloudy conditions, make it possible to map eruptive deposits, to quantify their volumes but also to estimate the volcanoes topography (with metric precision) as well as surface deformation fields (with a precision reaching a few millimeters).La télédétection s'est révélée au cours des deux dernières décennies comme un outil essentiel à la fois pour améliorer notre connaissance des systèmes volcaniques mais également pour assurer la surveillance des volcans actifs. En utilisant l'exemple du Piton de la Fournaise, le plus actif des volcans français, nous illustrons ici comment les données radar satellitaires (SAR), dont l'utilisation n'est pas empêchée par la présence de nuages, permettent non seulement de cartographier les dépôts éruptifs et d'estimer leur volume mais aussi de mesurer la topographie de l'édifice volcanique (avec une précision métrique) ainsi que ses déformations de surface (avec une précision atteignant quelques millimètres)

Emplacement dynamics of a crystal-rich, highly viscous trachytic flow of the Sancy stratovolcano, France

Emplacement dynamics of highly viscous, silicic lava flows remain poorly constrained due to a lack of consideration of crystal-rich cases. Emplacement models mostly apply to glassy or microlitic, vesiculated rhyolitic flows. However, crystalline, vesicle-free silicic lava can flow differently. We studied the Grande Cascade unit, which is a vesicle-free, phenocryst-rich, trachytic flow in the Monts Dore massif, France. Field work was carried out to define internal structures, and oriented samples were collected for chemical, petrological, and anisotropy of magnetic susceptibility analyses, allowing us to estimate emplacement temperature and viscosity. These data allow us to define a new silicic lava flow subtype that is low in temperature (800−900 °C), high in silica content (up to 66.8 wt%), high in viscosity (109−1011 Pa s), rich in phenocrysts (∼35%), and lacks vesicles. Brittle deformation of the lava occurs upon extrusion, generating a cataclasite basal layer and thin (3-m-thick) shear zone that accommodates all of the stress, allowing most of the flow’s volume to slide over its base as a 40-m-thick plug in which there is no deformation. Blocks are rare, of a single size (10 ± 1 cm), and result from localized break-up of the basal shear zone. Emplacement dynamics are different from those of glassy, pumiceous lava flows. They are closer to glacier dynamics, where most of the volume slides over a thin basal shear zone and till is generated there by abrasion and milling of the underlying layer. For the Grande Cascade lava flow, abrasion means that the flow lacks its classical blocky crust and instead the flow base is marked by a layer rich in fine-grained material. The structures and emplacement dynamics of this crystal-rich flow are consistent with ideal, gravity-driven shear flow. We thus argue for a global reassessment of silicic-rich lava emplacement based on crystal content and using a multidisciplinary approach focused on well-exposed examples in the rock record

Emplacement dynamics of a crystal-rich, highly viscous trachytic flow of the Sancy stratovolcano, France

Emplacement dynamics of highly viscous, silicic lava flows remain poorly constrained due to a lack of consideration of crystal-rich cases. Emplacement models mostly apply to glassy or microlitic, vesiculated rhyolitic flows. However, crystalline, vesicle-free silicic lava can flow differently. We studied the Grande Cascade unit, which is a vesicle-free, phenocryst-rich, trachytic flow in the Monts Dore massif, France. Field work was carried out to define internal structures, and oriented samples were collected for chemical, petrological, and anisotropy of magnetic susceptibility analyses, allowing us to estimate emplacement temperature and viscosity. These data allow us to define a new silicic lava flow subtype that is low in temperature (800−900 °C), high in silica content (up to 66.8 wt%), high in viscosity (109−1011 Pa s), rich in phenocrysts (∼35%), and lacks vesicles. Brittle deformation of the lava occurs upon extrusion, generating a cataclasite basal layer and thin (3-m-thick) shear zone that accommodates all of the stress, allowing most of the flow’s volume to slide over its base as a 40-m-thick plug in which there is no deformation. Blocks are rare, of a single size (10 ± 1 cm), and result from localized break-up of the basal shear zone. Emplacement dynamics are different from those of glassy, pumiceous lava flows. They are closer to glacier dynamics, where most of the volume slides over a thin basal shear zone and till is generated there by abrasion and milling of the underlying layer. For the Grande Cascade lava flow, abrasion means that the flow lacks its classical blocky crust and instead the flow base is marked by a layer rich in fine-grained material. The structures and emplacement dynamics of this crystal-rich flow are consistent with ideal, gravity-driven shear flow. We thus argue for a global reassessment of silicic-rich lava emplacement based on crystal content and using a multidisciplinary approach focused on well-exposed examples in the rock record