Mathieu Gouhier

Tephra sedimentation during the 2010 Eyjafjallajökull eruption (Iceland) from deposit, radar, and satellite observations

The April-May 2010 eruption of Eyjafjallajokull volcano (Iceland) was characterized by a nearly continuous injection of tephra in the atmosphere that affected various economic sectors in Iceland and caused a global-wide interruption of air traffic. Eruptive activity during 4-8 May 2010 was characterized based on short-duration physical parameters in order to capture transient eruptive behavior of a long-lasting eruption (i.e., total grainsize distribution, erupted mass and mass eruption rate averaged over 30-minute activity). Resulting 30-minute total grainsize distribution based on both ground and MSG-SEVIRI satellite measurements is characterized by Mdphi of about 2 phi and a fine-ash content of about 30wt%. Accumulation rate varied by two orders of magnitude with an exponential decay away from the vent, whereas Mdphi shows a linear increase until about 18 km from vent reaching a plateau of about 4.5 phi between 20-56 km. Associated mass eruption rate is in between 0.6-1.2 x 10^5 kg s^-1. In-situ sampling showed how fine ash mainly fell as aggregates of various typologies. About 5 to 9 wt% of the erupted mass remained in the cloud up to 1000 km from the vent, suggesting that nearly half of the ash >7 phi settled as aggregates within the first 60 km. Particle sphericity and shape factor varied between 0.4 and 1 with no clear correlation with size and distance from vent. Our experiments also demonstrate how satellite retrievals and Doppler radar grainsize detection can provide real-time description of the source term but for a limited particle-size range.

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

[1] We present a new method for estimating particle loading parameters (mass, number, volume) of eruptive jets by inversion of echo power data measured using a volcano Doppler radar (VOLDORAD) during typical Strombolian activity from the southeast (SE) crater of Mount Etna on 4 July 2001. Derived parameters such as mass flux, particle kinetic and thermal energy, and particle concentration are also estimated. The inversion algorithm uses the complete Mie (1908) formulation of electromagnetic scattering by spherical particles to generate synthetic backscattered power values. In a first data inversion model (termed the polydisperse model), the particle size distribution (PSD) is characterized by a scaled Weibull function. The mode of the distribution is inferred from particle terminal velocities measured by Doppler radar for each explosion. The distribution shape factor is found to be 2.3 from Chouet et al.’s (1974) data for typical Strombolian activity, corresponding to the lognormal PSDs commonly characteristic of other Strombolian deposits. The polydisperse model inversion converges toward the Weibull scale factor producing the best fit between synthetic and measured backscattered power. A cruder, alternative monodisperse model is evaluated on the basis of a single size distribution assumption, the accuracy of which lies within 25% of that of the polydisperse model. Although less accurate, the monodisperse model, being much faster, may be useful for rapid estimation of physical parameters during real-time volcano monitoring. Results are illustrated for two explosions at Mount Etna with contrasted particle loads. Estimates from the polydisperse model give 58,000 and 206,000 kg as maxima for the total mass of pyroclasts, 26,400 and 73,600 kg s � 1 for mass flux rates, 38 and 135 m 3 (22 and 76 m 3 equivalent magma volume) for the pyroclast volumes, and 0.02–0.4 and 0.06–0.12 kg m � 3 for particle concentrations, respectively. The time-averaged kinetic energy released is found to be equal to 4.2 � 10 7 and 3.9 � 10 8 J, and thermal energy is estimated at 8.4 � 10 10 and 3 � 10 11 J.

Near real-time monitoring of the April–May 2010 Eyjafjallajökull ash cloud: an example of a web-based, satellite data-driven, reporting system

During the 2010 eruption of Eyjafjallajokull volcano (Iceland) we set up a system designed to ingest satellite data and output volcanic ash cloud products. The system (HVOS = HotVolc Observing System) ingested on-reception data provided every 15 minutes by the SEVIRI sensor flown aboard the Meteosat Second Generation (MSG) satellite. Data were automatically processed and posted on the web to provide plume location maps, as well as to extract plume metrics (cloud top height and mass flux), in near-real time. Given the closing speeds for aircraft approaching such hazardous ash clouds, reporting delays for such products have to be minimised.

HOTVOLC: a web-based monitoring system for volcanic hot spots

Abstract Infrared (IR) satellite-based sensors allow the detection and quantification of volcanic hot spots. Sensors flown on geostationary satellites are particularly helpful in the early warning and continuous tracking of effusive activity. Development of operational monitoring and dissemination systems is essential to achieve the real-time ingestion and processing of IR data for a timely response during volcanic crises. HOTVOLC is a web-based satellite-data-driven monitoring system developed at the Observatoire de Physique du Globe de Clermont-Ferrand (Clermont-Ferrand), designed to achieve near-real-time monitoring of volcanic activity using on-site ingestion of geostationary satellite data (e.g. MSG-SEVIRI, MTSAT, GOES-Imager). Here we present the characteristics of the HOTVOLC system for the monitoring of effusive activity. The system comprises two acquisition stations and secure databases (i.e. mirrored archives). The detection of volcanic hot spots uses a contextual algorithm that is based on a modified form of the Normalized Thermal Index (NTI*) and VAST. Raster images and numerical data are available to open-access on a Web-GIS interface. Tests are carried out and presented here, particularly for the 12–13 January 2011 eruption of Mount Etna, to show the capability of the system to provide quantitative information such as lava volume and time-averaged discharge rate. Examples of operational application reveal the ability of the HOTVOLC system to provide timely thermal information about volcanic hot spot activity.

Erratum to: Lava discharge during Etna’s January 2011 fire fountain tracked using MSG-SEVIRI

In the paper by Gouhier, M., Harris, A., Calvari, S., Labazuy, P., Guehenneux, Y., Donnadieu, F., Valade, S, entitled “Lava discharge during Etna’s January 2011 fire fountain tracked using MSG-SEVIRI” (Bull Volcanol (2012) 74:787–793, DOI 10.1007/s00445-011-0572-y), we present data from a Doppler radar (VOLDORAD 2B). This ground-based Lband radar has been monitoring the eruptive activity of the summit craters of Mt. Etna in real-time since July 2009 from a site about 3.5 km SSE of the craters. Examples of applications of this type of radar are reviewed by Donnadieu (2012) and shown on the VOLDORAD website (http://wwwobs. univbpclermont.fr/SO/televolc/voldorad/). Although designed and owned by the Observatoire de Physique du Globe in Clermont-Ferrand (OPGC), France, VOLDORAD 2B is operated jointly with the INGV-Catania (Italy) in the framework of a technical and scientific collaboration agreement between the INGV of Catania, the French CNRS and the OPGC-Universite Blaise Pascal in ClermontFerrand. The system also utilizes a dedicated micropatch antenna designed at the University of Calabria (Boccia et al. 2010) and owned by INGV. The objective of the joint acquisition of the radar data by INGV-Catania and the OPGC is twofold: (1) to mitigate volcanic risks at Etna by better assessing the hazards arising from ash plumes and (2) to allow detailed study of volcanic activity and its environmental impact. In the paper by Gouhier et al. (2012), we failed to highlight this important collaboration between the INGV Catania and the OPGC; a cooperation essential for the past, current and future generation of such valuable data sets. Specifically we wish to acknowledge the roles of Mauro Coltelli, Michele Prestifilippo and Simona Scollo for their important input into this project, and pivotal role in setting up, and maintaining, this collaborative deployment.