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

Did high Neo-Tethys subduction rates contribute to early Cenozoic warming?

International audienceThe 58–51 Ma interval was characterized by a long-term increase of global temperatures (+4 to +6 • C) up to the Early Eocene Climate Optimum (EECO, 52.9– 50.7 Ma), the warmest interval of the Cenozoic. It was recently suggested that sustained high atmospheric pCO 2 , controlling warm early Cenozoic climate, may have been released during Neo-Tethys closure through the subduction of large amounts of pelagic carbonates and their recycling as CO 2 at arc volcanoes. To analyze the impact of Neo-Tethys closure on early Cenozoic warming, we have mod-eled the volume of subducted sediments and the amount of CO 2 emitted along the northern Tethys margin. The impact of calculated CO 2 fluxes on global temperature during the early Cenozoic have then been tested using a climate carbon cycle model (GEOCLIM). We show that CO 2 production may have reached up to 1.55 × 10 18 mol Ma −1 specifically during the EECO, ∼ 4 to 37 % higher that the modern global volcanic CO 2 output, owing to a dramatic India-Asia plate convergence increase. The subduction of thick Greater Indian continental margin carbonate sediments at ∼ 55–50 Ma may also have led to additional CO 2 production of 3.35 × 10 18 mol Ma −1 during the EECO, making a total of 85 % of the global volcanic CO 2 outgassed. However , climate modeling demonstrates that timing of maximum CO 2 release only partially fits with the EECO, and that corresponding maximum pCO 2 values (750 ppm) and surface warming (+2 • C) do not reach values inferred from geo-chemical proxies, a result consistent with conclusions arising from modeling based on other published CO 2 fluxes. These results demonstrate that CO 2 derived from decarbonation of Neo-Tethyan lithosphere may have possibly contributed to, but certainly cannot account alone for early Cenozoic warming. Other commonly cited sources of excess CO 2 such as enhanced igneous province volcanism also appear to be up to 1 order of magnitude below fluxes required by the model to fit with proxy data of pCO 2 and temperature at that time. An alternate explanation may be that CO 2 consumption, a key parameter of the long-term atmospheric pCO 2 balance, may have been lower than suggested by modeling. These results call for a better calibration of early Cenozoic weathering rates

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

Further evidence for superterminal raindrops

A network of optical disdrometers (including laser precipitation monitors and a two‐dimensional video disdrometer) was utilized to determine whether the recent reports of “superterminal” raindrops were spurious results of drop breakup occurring on instrumentation. Results unequivocally show that superterminal raindrops at small (less than 1 mm) sizes are ubiquitous, are measurable over an extended area, and appear in every rain event investigated. No evidence was found to suggest that superterminal drops are the result of drop breakup due to impact with the measurement instrument; thus, if the superterminal drops are the result of drop fragmentation, this fragmentation happens in the ambient atmosphere during all rain events measured in this study. The ubiquity of superterminal drops at small drop sizes raises natural questions regarding rain accumulation estimations, estimates of drop size distributions, and erosion characterization

Investigating ocean deoxygenation during the PETM through the Cr isotopic signature of foraminifera

Over the past several decades, oxygen minimum zones have rapidly expanded due to rising temperatures raising concerns about the impacts of future climate change. One way to better understand the drivers behind this expansion is to evaluate the links between climate and seawater deoxygenation in the past especially in times of geologically abrupt climate change such as the Palaeocene-Eocene Thermal Maximum (PETM), a well characterised period of rapid warming ~56 million years ago. We have developed and applied the novel redox proxies of foraminiferal Cr isotopes(δ53Cr) and Ce anomalies (Ce/Ce*) to assess changes in paleo-redox conditions arising from changes in oxygen availability. Both δ53Cr and Cr concentrations decrease notably over the PETM at intermediate to upper abyssal water depths,indicative of widespread reductions in dissolved oxygen concentrations. An apparent correlation between the sizes of δ53Cr and benthic δ18O excursions during the PETM suggests temperature is one of the main controlling factors of deoxygenation in the open ocean. ODP Sites 1210 in the Pacific and 1263 in the Southeast Atlantic suggest that deoxygenation is associated with warming and circulation changes, as supported by Ce/Ce* data. Our geochemical data are supported by simulations from an intermediate complexity climate model (cGENIE), which show that during the PETM anoxia was mostly restricted to the Tethys Sea, while hypoxia was more widespread as a result of increasing atmospheric CO2 (from 1 to 6 times pre-industrial values)

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

Improvement of ash plume monitoring, modeling and hazard assessment in the MED-SUV project

Volcanic ash clouds produced by explosive eruptions represent a strong problem for civil aviation, road transportation and other human activities. Since Etna volcano produced in the last 35 years more the 200 explosive eruptions of small and medium size. The INGV, liable for its volcano monitoring, developed since 2006 a specific system for forecasting and monitoring Etna’s volcanic ash plumes in collaboration with several national and international institutions. Between 12 January 2011 and 31 December 2013 Etna produced forty-six basaltic lava fountains. Every paroxysm produced an eruption column ranging from a few up to eleven kilometers of height above sea level. The ash cloud contaminated the controlled airspace (CTR) of Catania and Reggio Calabria airports and caused tephra fallout on eastern Sicily sometime disrupting the operations of these airports. In order to give prompt and detailed warnings to the Aviation and Civil Protection authorities, ash plumes monitoring at Osservatorio Etneo, the INGV department in Catania, is carried out using multispectral (from visible to infrared) satellite and ground-based video-surveillance images; seismic and infrasound signals processed in real-time, a Doppler RADAR (Voldorad IIB) able to detect the eruption column in all weather conditions and a LIDAR (AMPLE) for retrieving backscattering and depolarization values of the ash clouds. Forecasting is performed running tephra dispersal models using weather forecast data, and then plotting results on maps published on a dedicated website. 24/7 Control Room operators were able to timely nform Aviation and Civil Protection operators for an effective aviation safety management. A variety of multidisciplinary activities are planned in the MED-SUV project with reference to volcanic ash observations and studies. These include: 1) physical and analogue laboratory experiments on ash dispersal and aggregation; 2) integration of satellite data (e.g. METEOSAT, MODIS) and ground- based measurements (e.g., RADAR, LIDAR) of Etna’s volcanic plumes to quantify mass eruption rate, grain-size distribution at source, and ash cloud concentration; 3) improvement of tools and automatic procedures for the short-term forecasting of volcanic ash dispersal by adopting a multi-model and multi-scenario approach; 4) development of short-term forecasting tools able to use direct measurements of the plume and ash cloud in almost real time (now-casting); 5) development of long-term probabilistic ash fallout maps at the supersite volcanoes.PublishedVienna, Austria4V. Vulcani e ambienteope

Experimental investigation of the vortical activity in the close wake of a simplified military transport aircraft

This paper focuses on the experimental characterization of the vortex structures that develop in the aft fuselage region and in the wake of a simplified geometry of a military transport aircraft. It comes within the framework of the military applications of airflow influence on airdrop operations. This work relies on particle image velocimetry measurements combined with a vortex-tracking approach. Complex vortex dynamics is revealed, in terms of vortex positions, intensities, sizes, shapes and fluctuation levels, for both closed and opened cargo-door and ramp airdrop configurations

Orbitally forced ice sheet fluctuations during the Marinoan Snowball Earth glaciation

Two global glaciations occurred during the Neoproterozoic. Snowball Earth theory posits that these were terminated after millions of years of frigidity when initial warming from rising atmospheric CO2 concentrations was amplified by the reduction of ice cover and hence a reduction in planetary albedo. This scenario implies that most of the geological record of ice cover was deposited in a brief period of melt-back. However, deposits in low palaeo-latitudes show evidence of glacial–interglacial cycles. Here we analyse the sedimentology and oxygen and sulphur isotopic signatures of Marinoan Snowball glaciation deposits from Svalbard, in the Norwegian High Arctic. The deposits preserve a record of oscillations in glacier extent and hydrologic conditions under uniformly high atmospheric CO2 concentrations. We use simulations from a coupled three-dimensional ice sheet and atmospheric general circulation model to show that such oscillations can be explained by orbital forcing in the late stages of a Snowball glaciation. The simulations suggest that while atmospheric CO2 concentrations were rising, but not yet at the threshold required for complete melt-back, the ice sheets would have been sensitive to orbital forcing. We conclude that a similar dynamic can potentially explain the complex successions observed at other localities

Cenozoic evolution of the steppe-desert biome in Central Asia

The origins and development of the arid and highly seasonal steppe-desert biome in Central Asia, the largest of its kind in the world, remain largely unconstrained by existing records. It is unclear how Cenozoic climatic, geological, and biological forces, acting at diverse spatial and temporal scales, shaped Central Asian ecosystems through time. Our synthesis shows that the Central Asian steppe-desert has existed since at least Eocene times but experienced no less than two regime shifts, one at the Eocene–Oligocene Transition and one in the mid-Miocene. These shifts separated three successive “stable states,” each characterized by unique floral and faunal structures. Past responses to disturbance in the Asian steppe-desert imply that modern ecosystems are unlikely to recover their present structures and diversity if forced into a new regime. This is of concern for Asian steppes today, which are being modified for human use and lost to desertification at unprecedented rates