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173 páginas El 19 de febrero de 1600 d. C. el volcán Huaynaputina (Moquegua) situado en el sur del Perú, presentó una gran erupción de tipo pliniana, la cual es considerada la erupción histórica más voluminosa de Sudamérica (Thouret et al., 1999, 2002; Adams et al., 2001), que generó uno de los más importantes impactos climáticos globales (en términos de reducción de temperatura promedio) en los últimos 1500 años (Stoffel et al., 2015). El estratovolcán Huaynaputina es parte de una agrupación de domos, construido sobre un volcán compuesto, constituido de flujos de lavas y depósitos piroclásticos emplazados durante el Pleistoceno y Holoceno. La erupción de 1600 d. C. destruyó los domos de lava y depósitos piroclásticos preexistentes que afloran en el borde del anfiteatro del volcán, cubriendo con depósitos piroclásticos los sectores proximales y distales del Huaynaputina. Thouret et al. (2002) reconocieron cinco fases eruptivas y cinco unidades tefroestratigráficas en los depósitos de la erupción: 1) un depósito de caída de tefra pliniana; 2) una secuencia de capas de cenizas interpretadas como caídas de cenizas de tipo vulcaniano; 3) una secuencia de depósitos de ignimbritas no soldadas correspondientes a una fase de flujos y oleadas piroclásticas; 4) un depósito de caída de ceniza rica en cristales (hasta 80 % de cristales libres); 5) un depósito de flujo de cenizas de pequeño volumen. Recientes estudios tefroestratigráficos permitieron realizar un recálculo de los parámetros de la erupción del volcán Huaynaputina del año 1600 d. C. Este recálculo se realizó en base a más de 670 puntos de control, donde se incluyeron 42 nuevas secciones efectuadas entre los años 2015 y 2018, ubicadas en las zonas proximal y medial del volcán. Las medidas de espesor, compiladas en una base SIG, permitieron elaborar un nuevo mapa de isópacas. Este mapa muestra que las tefras fueron dispersadas a más de 400 km, con ejes de dispersión en dirección O-NO y O para las isópacas distales, y un tercer eje en dirección O-SO para las isópacas proximales a mediales (Japura, 2018). La estimación del volumen erupcionado fue basada en modelos Power Law, Weibull, Pyle; se han adaptado los modelos de Bonadonna y Houghton (2005), Burden et al. (2011), Bonadonna & Costa (2012) para integrar la isópaca más distal posible. Se calculó un volumen de tefra actual de 8.00 a 9.93 km3 (Thouret et al., 2002ª; Japura, 2018). Recientemente, en base a modelos estadísticos, utilizando la base de datos indicada anteriormente, se ha realizado una nueva estimación del volumen de los depósitos de caída pliniana, los cuales arrojaron valores entre 13 y 14 km3, que es casi el doble de estimaciones de estudios anteriores (Prival et al., 2020). Estos datos de volúmenes obtenidos radican en que valores más bajos corresponden a medidas de espesores que no consideraron los depósitos de tefra por debajo de la isópaca de 1 cm (Prival et al., 2020). Adams et al. (2001) calcularon una altura de columna de 34 – 45 km en base a los espesores y a las medidas de clastos del depósito de caída pliniana. Con los mapas de isopletas (pómez y líticos) y utilizando el modelo de Carey y Sparks (1986), se estimó una altura de columna eruptiva entre 35 ± 2 km, con una velocidad de viento entre 10 a 30 m/s, un valor similar a las estimaciones preexistentes (Thouret et al., 2002; Japura, 2018). Prival et al. (2020) calcularon una columna eruptiva entre 26 a 31 km, considerando la cuenta de advección de viento en el penacho (Biass et al., 2015; Rossi et al., 2019). Los últimos estudios indican que la altura ha sido recalculada a 32.2 ± 2.5 km. Estudios realizados por Thouret et al. (2002) muestran una tasa de descarga volumétrica eruptiva en el rango de 5.4-6.6X104 a 1X105 m3/s, una tasa de descarga de masa (MER) de 1.3-1.6X108 kg/s. Actualmente, en base a la altura, se calculó la tasa de descarga volumétrica de 1.01x105 a 1.57x105 m3/s y un MER entre 2.20 x108 a 4x108 kg/s. Prival et al. (2020) obtuvieron valores entre 1.4x108 y 3.2x108 kg/s. Las tasas de descarga en combinación con las estimaciones de volumen nos permiten obtener duraciones de la erupción que oscilan entre 5 y 19 h (Prival et al., 2020). Este rango de valores es consistente con las 12 a 19 h estimadas a partir del análisis de las crónicas españolas (Thouret et al., 2002 en base a datos históricos interpretados por Jara et al., 2000). Estos datos nos permitieron definir el índice de magnitud de 5.8 e índice de intensidad de 11, obteniendo un Índice de Explosividad Volcánica (IEV) de 6. La densidad de la pómez se encuentra entre 0.6 y 0.7 g/cm3 para los sectores proximales, 0.8 g/cm3 para los sectores mediales y 0.9 g/cm3 para los distales. Los valores de densidad varían con un incremento horizontalmente por cada sección (ultra proximal, proximal, medial) de manera proporcional a la distancia dispersada con respecto al cráter (Cueva, 2018). La densidad aparente seca de cada subunidad del depósito de caída pliniana ha sido medida en 32 sitios, donde se tienen resultados de 0.62 g/cm3 para depósitos proximales y 0.72 g/cm3 para depósitos distales (Prival et al., 2020). La distribución granulométrica de la caída de lapilli pómez pliniana varía según las zonas de depositación. En la zona proximal y medial, el depósito de caída pliniana presenta una distribución bimodal y unimodal, mientras que en la zona distal presenta una distribución únicamente unimodal. Esto indica que la sedimentación del tamaño de partículas es variable según la distancia al cráter e influenciada por la dirección del viento (sotavento). Se realizó la distribución total de tamaño de grano para inferir el estilo de fragmentación y de erupción, donde casi el 70 % de la masa del depósito se encuentra entre -4.0 y -1.0 phi (φ), con tamaños entre 1.6 cm a 2 mm. Los componentes litológicos de los productos de la erupción han sido estudiados en base a 100 muestras de fracciones de 4, 2, 0.5 y 0.125 mm, donde la mayor parte del depósito está compuesto por material juvenil (91 %), líticos cogenéticos (4 %), líticos no juveniles (3 %) y cristales libres de plagioclasa, biotita, anfíbol y minerales opacos (1 %) para la fracción 0.4 mm. Recientes investigaciones geológicas, geofísicas y tefroestratigráficas nos han permitido identificar y conocer las características de seis de los principales poblados enterrados: Calicanto, Chimpapampa, Cojraque, Estagagache, Moro Moro y San Juan de Dios, ubicados en el flanco suroeste, sureste, sur y noroeste del cráter del volcán Huaynaputina. Se han elaborado los mapas geológicos de Calicanto, Chimpapampa y Estagagache a escalas 1:2000, 1:3000 y 1:2500. Según las columnas estratigráficas levantadas y descripciones de campo, el depósito de caída pliniana presenta espesores entre 1 a 3 m, mientras que los depósitos de flujos piroclásticos llegan hasta 6 m. Todo este material piroclástico habría cubierto los pueblos establecidos en las periferias del volcán. Se utilizaron varios métodos geofísicos para analizar las características de los pueblos sepultados: Georradar GPR, cámaras infrarrojos – térmica IR (Cámara FLIR) y Prospección Magnética GEMSYS GSM19, los que permitieron obtener radargramas y mapas de anomalías magnéticas en zonas donde las estructuras están localizadas a una profundidad entre 0.5 y 2 metros. Con el uso de la Fotogrametría con Drones (Phantom 3 y 4Pro), se obtuvieron Modelos de Elevación Digital (DEM) con alta resolución espacial (1.7 cm/píxel) e imágenes satelitales de alta resolución, que cubrieron un área de hasta 78 ha, los cuales sirvieron como base para la visualización los mapas geológicos y de prospección geofísica. Se han realizado trabajos de educación y difusión durante el periodo 2015-2019, en los dos centros más poblados, Quinistaquillas ubicado a unos 20 km al sur y Omate a unos 15 km al SO del volcán Huaynaputina. Se impartieron capacitaciones, charlas, talleres, encuestas, dirigidas a estudiantes de colegios, universidades, municipalidades y público en general con el objetivo de brindar información acerca del estudio de los volcanes y sensibilizar a la población para el manejo de crisis volcánicas. En base a la caracterización geológica y geofísica de los 6 pueblos sepultados por la erupción, se realizó un mapa geoturístico, donde se proponen 12 geositios ubicados alrededor del volcán Huaynaputina con el propósito de fomentar el turismo geológico y cultural en la zona.

This deliverable collects the main results obtained from evaluations of the piloted safety measures selected in earlier phases of the SAFER-LC project. This deliverable reports the descriptions of the piloted measures at railway level crossings, method and data to evaluate the safety effects of the selected measures, as well as the results of evaluations together with their discussion.

International audience; Dike management has become a major concern in France over the last 20 years after several flood disasters caused by dikes failures. The poor condition of more than 60% of the dikes in the country and the increase of flood occurrences/intensities due to global climate change obviously lead to a closer monitoring of the structures and their reinforcement. The most commonly used method for routine and crisis monitoring of dikes is based on visual inspections on the field. It allows the detection of surface indicators (i.e animal burrows, deformations, water seepage, etc.) resulting from internal disorders. However, this method is time-consuming for pluri-kilometric sections of dikes and not safe for the field operators during a flood. The DIDRO (DIke monitoring by DROnes) project develops a solution for high efficiency routine and crisis monitoring of dikes, using a UAV carrying multiple remote sensing sensors and aquatic equipment. Remote sensing sensors include LiDAR, thermal infrared, near-infrared and visible sensors and provide high resolution data of the surface of the dike. Such sensors, never combined on a UAV for this type of survey, allow the detection of a large number of surface indicators of internal and external dike disorders. Aquatic measurements consist 1) in flow velocity estimations using floating targets dropped in the river or in the sea by the UAV and 2) in a system for water turbidity estimation towed by the UAV. This system is particularly useful for the detection of erosion during a flood. Geophysical methods have been thought to be particularly useful to complement the UAV system and include electrical resistivity imagery, self potential and background seismic noise equipment. The UAV is then used to tow or to drop some of the equipments along the dike and to remotely collect data. This can be particularly useful during flooding, when accessing the dike may be dangerous. The switch from one payload configuration to another is made easy by a specific mounting system, adaptable to different types of UAV. This makes the DIDRO solution more easily deployable during flooding events. This presentation focuses on the description of the different payload configurations of DIDRO and on the specifications of the equipment used, and will present some results obtained during tests carried out on several dikes in France.

International audience; Dike management has become a major concern in France over the last 20 years, after several major flood disasters caused by river and sea dikes failures. These events, the poor state of more than 60% of the dikes in the country, and the ever-growing threat of floods occurrence increase due to global climate change, have only made obvious the need for dikes reinforcement and for their tighter surveillance. Today, the most commonly used method for both routine and crisis monitoring of dikes is based on visual inspections by field operators. It allows precise detection of most of the surface indicators (i.e animal burrows, structural deformations, topographic anomalies, water seepage, etc.) resulting from disorders affecting these structures. However, this method is time consuming when long sections of dikes are inspected and is not entirely safe for the field operators during a flood. The DIDRO (DIke monitoring by DROnes) project aims at developing a solution for high efficiency routine and crisis monitoring of dikes using a UAV system carrying multiple remote sensing sensors and aquatic measurements equipment. Remote sensing sensors include LiDAR, thermal infrared, near-infrared and visible image sensors, and provide very high resolution data of the surface of the dike. Such very high resolution sensors, which have never been combined so far on a UAV for this type of survey, allow precise detection of a large number of surface indicators of internal and external dike disorders. They can be implemented for both routine and crisis monitoring. Aquatic measurements consist in flow velocity estimations using floating targets dropped in the river or in the sea by the UAV and in a system for water turbidity estimation towed by the UAV. This system is particularly useful for the detection of signs of dike materials erosion during a flood. Also, geophysical methods having proved efficient at providing information on the internal state of dikes, it has been considered very useful to integrate geophysical equipment to the UAV system. Geophysical measurements are conducted using electrical resistivity tomography, self potential and background seismic noise equipment. The UAV is then used to tow or to drop the equipment along the dike and to remotely collect data generated by devices manually positioned. This can be particularly useful during flooding, when accessing the dike may be dangerous. The switch from one payload configuration to another is made easy by a specific mounting system, adaptable to different types of UAV. This makes the DIDRO solution more easily deployable during flooding events. This presentation will focus on the description of the different payload configurations of DIDRO and on the specifications of the equipment used, and will present some results obtained during tests carried out on several dikes in France.

International audience; We report on successful geophysical observations above a buried Gallo-Roman theatre in Normandy, France. The main objective of this study was to complete the previous archaeological surveys in order to localize the structure and precise its depth. The 100 m diameter theatre, lying between 50 cm and 3 m depth, was investigated using 1) a new multichannel Ground Penetrating Radar (GPR); 2) a 2D Electric Resistivity Tomography (ERT) and 3) geotechnical soundings. The multichannel GPR (IDS Stream X) is composed of 7 antennas working at a frequency of 200 MHz and with a spacing of 12 cm. Therefore, such system is well adapted to large-scale high-resolution surveys. In our case, the GPR was able to investigate the entire zone (1600 m2) in few hours. This survey led to the characterization of the subsurface up to 3 m depth. To complete the information obtained with the GPR, seven ERT profiles were acquired longitudinally and transversally to the structure. A Terrameter LS imaging system (ABEM) was used with a dipole-dipole configuration; as such protocol is sensitive to vertical structures. Three profiles are 32 m with a spacing of 1 m between electrodes, 2 profiles are 16 m with a 0.5 m spacing between electrodes, 1 profile is 19.20 m with a spacing of 0.6 m between electrodes and 1 profile is 64 m with a spacing of 1 m between electrodes. Such approach allowed to inverse the electric data up to a depth in the range 4-10 m. An excellent correlation is obtained between both methods, allowing us to propose a precise 3D visualisation of the Gallo-Roman theatre, in agreement with a partial model obtained from the previous archaeological surveys. Moreover, this study led to the discovery of other structures (confirmed by geotechnical soundings) and thus to complete the current archaeological model of the site. The Multichannel GPR clearly offers new potentials for the large-scale imaging of the subsurface. Combined with other geophysical and archaeological methods, it is a powerful tool for future 3D characterization of buried structures within the soil.

International audience; Subsurface airflow in the unsaturated zone of the soil has been extensively investigated in a variety of disciplines such as mining, nuclear waste or agriculture science. In volcanology, the recent discovery of subsurface airflow close to the terminal cone of Piton de La Fournaise volcano (La Réunion Island, France) provides for the first time insights into the convective behavior of air within the unsaturated layer [1]. The characteristics of the aerothermal system, its occurrence in other volcanoes, its ability to transport heat during quiescent periods and the perturbation of this system before eruptions are the key questions we want to address following this discovery. In this study, we present observations of subsurface convective airflow within opened fractures located at the summit of Miyakejima and Piton de la Fournaise volcanoes from anemometric and temperature data. Two anemometers and thermocouples were placed at the surface and at the center of the fracture at two-meter depth during a diurnal cycle. Six thermocouples also measured the temperature at 1 meter-depth, on a profile set perpendicularly to the fracture. Finally, a thermal camera was used to make punctual measurements of the surface temperature of the fracture. At Miyakejima, two surveys were realized in winter 2010 and summer 2011. During the winter, mild air exit was detected from the fracture with a central vertical velocity of 20 to 50 cm/s. The temperature of the site was constant during the diurnal cycle (~ 22°C), leading to a maximum temperature contrast of 15°C between the fracture and the atmosphere just before sunrise. During summer, a different hydrodynamic behavior was observed: Air inflow was detected during the whole diurnal cycle with a mean velocity of 20 cm/s. The temperature of the fracture followed the temperature of the atmosphere at 2 meters-depth. In the case of Piton de la Fournaise volcano, the same convective behavior was observed at two different fractures during winter 2008 and summer 2010. Moreover, the velocities and temperature contrast between the fracture and the atmosphere were close to the ones recorded at Miyakejima. Finally, the temperature profiles realized across the fractures and confirmed by the infrared thermography data allowed us to define the convective patterns. This study represents the first detection and characterization of air convection at a seasonal scale within fractures on volcanoes. It constitutes a preliminary step to further investigations dedicated to the understanding of the perturbation of such systems before eruptions. [1] Antoine R., Baratoux D., Rabinowicz M., Fontaine F.J., Bachèlery P., Staudacher T., Saracco G., Finizola A., Thermal infrared images analysis of a quiescent cone on Piton de La Fournaise volcano: Evidence for convective air flow within an unconsolidated soil, Journal of Volcanology and Geothermal Research, Volume 183, Issues 3-4, 2009, Pages 228-244.

International audience; The mechanism of convection and electric phenomena around an isolated heat source in a fluid saturated porous media is of interest in geothermal processes and volcanology. Laboratory and numerical experiments of transient convective flows and induced electric potentials in a porous layer with a local bottom heat source are reported. Laboratory characterization of fluid flow in porous media has a severe limitation by non-transparent nature of the media comparing to the case for a single fluid. In this study as for the temperature characterization, we utilized gridded thermocouples for multiple temperature measurement. As for the flow characterization, we set multiple electrodes to measure flow-induced potential. Axisymetric laminar plumes were experimentally generated by a small electric heater in a tank filled with water-saturated glass beads. We determined the spread of the plume with horizontally-gridded thermocouples, while vertical sets were used to characterize the time evolution of the plume ascent. Vertically-aligned electrodes along the central line exhibit large positive increase associated with plume ascent. The magnitude is consistent with the temperature increase and applied power. To understand the development of the plume, 2D-3D numerical simulations have been performed for the same situations of laboratory experiments. The flow pattern is investigated for Rayleigh numbers up to 8000. Plumes ascent in two different regimes. For Ra1200, the velocity increases owing to the development of the thermal boundary layer, remains nearly constant during the rise, before decreasing at the top of the tank. Finally, the electric potentials induced by the development of the plume are analyzed. It is shown that the signal initially decreases when the plume is detaching itself from the bottom, but largely increases during the ascension of the water, which is systematically observed in experimental results. We consider flow-induced potential as a good experimental probe for fluid flow characterization in porous media. This study is the first step to further experimental and numerical works on convective cells generation and induced electric potentials in a stratified porous medium.

International audience; Seven deep pit craters (or skyholes) had been recently discovered North of Arsia Mons (7°S, 240°E) or near the volcano (Cushing et al., 1997). The THEMIS instrument onboard Mars Odyssey imaged these pit craters in the visible and infrared channels with the THEMIS-VIS and THEMIS-IR subsystems. We first report on the finding of about 75 new pit craters in the South of Arsia Mons, near the volcano from THEMIS and HRSC images. These pit craters can be detected from nighttime THEMIS images by their thermal signal. They are systematically warmer than the surrounding at night (Cushing et al., 1997). All pit craters are in average 7K warmer than the background. We also discovered collapsed sinuous rilles which present the same thermal pattern. To try to explain this thermal behaviour, thermal, geologic and geometric characteristics of these pit craters and collapsed sinuous rilles were documented in detail. Geologic and geometric effects, by the specific pit craters shape, do not show any influence on this pattern. The temperature difference is always observed wathever the season and is only present on pit craters and some collapsed sinuous rilles. We propose that the heat detected at night results from the advection of the geothermal heat in a subsurface CO2 circulation system, in the porous media of the volcano flank. This circulation system may consist of cold air entering at the base of the volcano flanks, flowing up the slope while being warmed by the martian geothermal flow. The atmospheric air will exit warmer along the flanks of the pit craters and of the collapsed sinuous rilles. Simple subsurface air flow models show similar temperature excess inside the pit craters and collapsed sinuous rilles considering a geothermal flow of 30 mW/m2 along the flanks of Arsia Mons. This might give an indirect measurement of the martian geothermal flow. References : Cusching et al., 2007, THEMIS observes possible cave skylights on Mars Geophysical Research Letters, 34

International audience; The THEMIS instrument onboard Mars Odyssey imaged deep pits, localised North of Arsia Mons, in the visible and infrared channels.We present a detailed thermal study of these pits to evaluate several hypotheses that could explain their thermal behavior.

International audience; A four-year diachronic study was carried out on coastal badlands cliffs ("les falaises des Vaches Noires", Normandy, France) to assess erosion and acretion volumes. Cretaceous to Jurassic facies at cliffs face are exposed to erosion activated by rainfalls on the tableland and tempests and high tidals at the bottom. Consequences have a direct impact both (i) on housing and civil engineering structures and (ii) on Le Havre harbor and the Seine river waterways. More than ten aerial drone surveys were carried out between 2016 and 2019. Recorded images by drone led to accurate Digital Elevation Model (DEM) models by means of photogrammetry. Each DEM georeferenced with differential global positionning system (DGPS) were then compared with each other. Near surface geophysical methods were also performed to understand materials and their properties involved in such processes . Cliff edge retreat can be assessed, while eroded and accumulated volumes are locally calculated. With help of geological study and mainly Electrical Resistivity Imagery, costline retreat and deposits evolution can be explained and evaluated. This study performed at hectometer scale finally allows a wider interpretation of erosion processes at the regional costline scale. The Vaches Noires cliffs are listed Natural zone of ecological interest, fauna and flora belongs to the 26 studied sites of the National Observation Service DYNALIT, labeled by INSU (National Institute of Sciences of the Universe). The presented outcomes stem from the Normandy regional project TéléDeTaC (Télédétection par Drone du Trait de Côte).

International audience; Rheology of crustal material is a key parameter to understand surface morphology on solid planets. Detections of phyllosilicate-rich units on Mars, made by OMEGA and CRISM instruments, over a major part of the Southern Plains [1] and in some specific regions as ejectas and craters central peaks in the Northern Plains [2], suggest a widespread extend of phyllosicate-rich deposits. Analysis of recent experimental characterization of the rheology of phyllosilicates leads us to propose a link between several types of surface features on Mars and the hydrodynamic instabilities that may develop in such material. More precisely, we propose and argue that the formation of mud volcanoes, giant polygons and chaotic terrains results from the interplay of compaction, hydrothermal convection and plastic convection in thick phyllosilicate-rich units. Indeed, the compaction and hydrothermal convection that may develop in the 4° tilted sedimentary layers in Firsoff crater [3] would lead to the formation of a top light-layered deposit intruded by mud volcanoes. In the same way, compaction coupled with hydrothermal and plastic convection in the 2.5 km thick sediment cover of Utopia [4] and Acidalia Planitiae can explain the formation of the giant polygons and their associated set of mud volcanoes. Besides, strong plastic and hydrothermal convection coupled with compaction acting in the 5 km thick cover of Hydraotes Chaos would explain the formation of (i) the kilometre deep troughs separating the polygonal mesas recorded there, and (ii) the km large pitted mud cones paving these troughs. Finally, we obtain new insights into the sub-surface structure prevailing to the formation of outflow channels. Indeed, we propose the formation of a network of connected deconsolidated clays tubes would provide the necessary hydrological connectivity that eventually led to the major outflow events. [1] e.g. Ehlmann et al., 2013, Spa. Sci. Rev., 174 (1-4); [2] Carter et al., 2010, Science, 328 (5986); [3] Pondrelli et al., Earth and Planet. Sci. Lett., 304 (3-4); [4] Cooke et al., 2011, J. Geophy. Res., 116.

International audience; Thermal infrared data obtained in the [7-14 microns] spectral range are usually used in many Earth Science disciplines. These studies are exclusively based on the analysis of 2D information. In this case, a quantitative analysis of the surface energy budget remains limited, as it may be difficult to estimate the radiative contribution of the topography, the thermal influence of winds on the surface or potential imprints of subsurface flows on the soil without any precise DEM. The draping of a thermal image on a recent DEM is a common method to obtain a 3D thermal map of a surface. However, this method has many disadvantages i) errors can be significant in the orientation process of the thermal images, due to the lack of tie points between the images and the DEM; ii) the use of a recent DEM implies the use of another remote sensing technique to quantify the topography; iii) finally, the characterization of the evolution of a surface requires the simultaneous acquisition of thermal data and topographic information, which may be expensive in most cases. The stereophotogrammetry method allows to reconstitute the relief of an object from photos taken from different positions. Recently, substantial progress have been realized in the generation of high spatial resolution topographic surfaces using stereophotogrammetry. However, the presence of shadows, homogeneous textures and/or weak contrasts in the visible spectrum (e.g., flowing lavas, uniform lithologies) may prevent from the use of such method, because of the difficulties to find tie points on each image. Such situations are more favorable in the thermal infrared spectrum, as any variation in the thermal properties or geometric orientation of the surfaces may induce temperature contrasts that are detectable with a thermal camera. This system, usually functioning with a array sensor (Focal Plane Array) and an optical device, have geometric characteristics that are similar to digital cameras. Thus, it may be possible to extract 3D informations from thermal images taken from different positions. This paper presents the first 3D thermal map of an active volcano (Piton de la Fournaise, La Réunion Island) directly generated from 70 thermal images (so-called "stereothermogrammetric" DEM). The data were obtained above Dolomieu caldera by helicopter just before sunrise, during a clear weather in 2008. They were obtained before the eruptive events occurring within the Dolomieu caldera. We used a 28 mm focal FLIR Thermacam PM695 lent by the Piton de la Fournaise Observatory. The thermal images were acquired automatically every 30 seconds with the helicopter flying around the caldera at low altitude (less than 100 m height above the caldera). This survey led to the acquisition of images with a ground pixel size in the range of 1-3 m. A particular attention has been brought to the obtaining of a high overlap percentage (80 percents) for the localization of the maximum tie points on the image. Finally, the acquisition of 70 images allowed the generation of a 3D thermal model of the caldera containing more than 500000 points. i.e. 1 point each 2 m², considering a surface of 106 m² for the Dolomieu caldera. This model is then compared with a DEM recently obtained with the LIDAR method after the eruptive events occurring within Dolomieu. The comparison of these independent methods leads to the validation of the stereothermogrammetric method. It allows the quantification of the thickness of the lava flows within the Dolomieu collapse in 2008 and 2009, i.e. approximately 80 meters, as estimated by previous studies from field observations.