L’abbaye Saint-Pierre de Mozac (Puy-de-Dôme) : prospection par géoradar

Implanté à 10 km au nord de Clermont-Ferrand, le site de Mozac abritait au Moyen Âge l’un des plus anciens et des plus importants monastères d’Auvergne. Fondée sous le règne du roi Thierry III (673-691), l’abbaye n’est mentionnée de façon assurée qu’à partir du ixe siècle, puis en 1095 lors de son rattachement à Cluny . Conservant les reliques de saint Austremoine, premier évêque présumé de Clermont, l’abbaye fut plusieurs fois reconstruite. Des études de bâti programmées suivies par le Servi..

The ash mass load of volcanic plumes: retrievals from a new millimeter-wave radar at Stromboli and Sabancaya volcanoes

In the framework of the French Government Laboratory of Excellence ClerVolc initiative, two experiments using a new millimeter-wave radar were carried out to retrieve various physical properties of the ash plumes, especially the mass loading parameters which are critical for the modelling of ash dispersal, as well as to study the internal dynamics of the plumes and their fallout. First measurements at Stromboli in 2015 using a 95 GHz cloud radar prototype with a fixed beam pointing above the crater characterized the distribution of plume internal reflectivities, plume widths and durations at unprecedented space-time resolutions. Combining radar in situ measurements with data modelling from a disdrometer and ash sampling on the ground further allowed the retrieval of ash concentration and gradients inside the plumes, and sometimes proximal fallout. Plume maximum ash concentration range from 1 mg/m3 to about 1 g/m3. Structuration of ash concentration with variations by a factor of 3 was also found to occur inside the falling ash in correlation with variations in the sedimentation rate measured on the ground by the disdrometer. New results from radar measurements inside stronger plumes and fallout at Sabancaya volcano (Peru, May 2018) using volume scans will also be presented

Ash concentration of Sabancaya volcanic plumes retrieved from a 95 GHz radar and a disdrometer

We have carried out an experiment using a 3.2 mm-wavelength scanning Doppler radar and a laser disdrometer to investigate ash plumes of Sabancaya volcano (Peru) in May 2018. Our main objectives were to retrieve the mass loading parameters (concentration, mass flux) which are critical for the modelling of ash dispersal, as well as to study the dimensions and internal dynamics of the eruptive columns, plumes and fallout. The radar and the disdrometer were respectively located at 4.5 km NNE and 4.5 km E from the vent. Multiple radar sounding configurations were tested either in fixed-pointing mode, generally close to the source, or using scans across various regions of the plumes. Particle Size Distribution, shapes and density were characterized from microphysical analyses, sieving and water pycnometry of ash samples collected on the ground. A Parsivel2 disdrometer also recorded the sizes, and settling velocities of fallout, allowing us to estimate sedimentation rates on the ground and to derive an empirical law relating calculated ash concentrations and reflectivities. Comparing the latter with reflectivities measured by the radar at unprecedented space-time resolutions (down to 12.5 m and 0.25 s) allowed us to obtain the internal mass distribution of eruptive columns, plumes, and fallout at various distances from the emission source

Physical impacts of the AD 1600 Huaynaputina VEI 6 eruption on habitat and infrastructure, southern Perù: Geophysical insights from the Huayruro project

The Huayruro project aims at better understanding the physical and socio-economic impacts of the CE 1600 Plinian eruption of Huaynaputina in south Peru (VEI 6, 11-14 km3 ). Despite its global climatic impact, its regional consequences on the Inca population and constructions have been scarcely studied. In particular, the location of ten to fifteen settlements buried by the erupted deposits is not accurately known. Finizola et al. (2018) identified several buried settlements and ruins during several archeological and geophysical surveys during the 2014-2017 period within a 16 km radius of the crater (Coporaque, Calicanto, and Chimpapampa). Extending their work in May 2018, we used ground- penetrating radar at 400 et 200 MHz, magnetic gradiometry, multi-frequency conductivimetry and Structure from Motion (SfM) photogrammetry with multi-view stereo to further explore the sites of Coporaque (12 km WSW of the crater), Estagagache (16 km SSE) and San Juan de Dios (17 km SW), affected by fallout deposits 2.6, 1.5 and 0.4 m thick, respectively. The present study provides spatial constraints for mapping buried house walls, cultivated terraces, rural infrastructure such as grain storage areas, contributing therefore to delineate the extent of the damaged villages. Such geophysical surveys combined with aerial imagery, high-spatial resolution DEMs and tephra studies help to focus on adequate sites for future archeological excavations and assess physical impacts of thick tephras and PDCs deposits on pre-Conquest constructions. The ultimate goal of the Huayruro project is to disseminate volcanic risk knowledge and help create one in situ museum to be built up on the site of Calicanto

The geometry of Strombolian explosions: insights from Doppler radar measurements

International audienc

Ballistics and ash plumes discriminated by Doppler radar

International audienc

Considerations on ejection velocity estimations from infrared radiometer data: A case study at Stromboli volcano

International audienceSynchronous recordings of normal Strombolian explosions with a thermal camera and infrared radiometers provide a unique opportunity to understand signals from less expensive radiometers. Using records from Stromboli volcano, we analyze in particular the limitations of using signals from infrared radiometers alone to quantify the plume ascent kinetics. We conclude that infrared radiometers pointing close to the vent, either single or coupled, are often insufficient for velocity retrieval due to the complex structure and dynamics of the plumes and their evolution with time. In addition to practical implementation difficulties in the field, this is mainly due to the rapid succession and overlapping of thermal components in the radiometer's field of view. Optimized geometries of radiometer fields of view and new retrieval methodologies are proposed to improve velocity estimates from one or coupled radiometers

Mass estimations of ejecta from Strombolian explosions by inversion of Doppler radar measurements

International audienc

Systematic retrieval of ejecta velocities and gas fluxes at Etna volcano using L-Band Doppler radar

International audienc