C. Del Negro

The initial phases of the 2008–2009 Mount Etna eruption: A multidisciplinary approach for hazard assessment

Accepted for publication in Journal of Geophysical Research. Copyright (2010) American Geophysical Union

A year of lava fountaining at Etna: Volumes from SEVIRI

[1]xa0We present a new method that uses cooling curves, apparent in high temporal resolution thermal data acquired by geostationary sensors, to estimate erupted volumes and mean output rates during short lava fountaining events. The 15 minute temporal resolution of the data allows phases of waxing and peak activity to be identified during short (150-to-810 minute-long) events. Cooling curves, which decay over 8-to-21 hour-periods following the fountaining event, can also be identified. Application to 19 fountaining events recorded at Etna by MSGs SEVIRI sensor between 10 January 2011 and 9 January 2012, yields a total erupted dense rock lava volume of ∼28xa0×xa0106xa0m3, with a maximum intensity of 227xa0m3xa0s−1being obtained for the 12 August 2011 event. The time-averaged output over the year was 0.9xa0m3xa0s−1, this being the same as the rate that has characterized Etnas effusive activity for the last 40xa0years.

Near‐real‐time forecasting of lava flow hazards during the 12–13 January 2011 Etna eruption

We are grateful to EUMETSAT for SEVIRI ndata, to NASA for MODIS data, and toNOAAfor AVHRR data. The authors nthank one anonymous reviewer and V. Acocella for their helpful and constructive ncomments. This study was performed with the financial support nfrom the V3‐LAVA project (INGV‐DPC 2007‐2009 contract).

Spatial vent opening probability map of Etna volcano (Sicily, Italy)

We produce a spatial probability map of vent opening (susceptibility map) at Etna, using a statistical analysis of structural features of flank eruptions of the last 2xa0ky. We exploit a detailed knowledge of the volcano structures, including the modalities of shallow magma transfer deriving from dike and dike-fed fissure eruptions analysis on historical eruptions. Assuming the location of future vents will have the same causal factors as the past eruptions, we converted the geological and structural data in distinct and weighted probability density functions, which were included in a non-homogeneous Poisson process to obtain the susceptibility map. The highest probability of new eruptive vents opening falls within a N-S aligned area passing through the Summit Craters down to about 2,000xa0mu2009a.s.l. on the southern flank. Other zones of high probability follow the North-East, East-North-East, West, and South Rifts, the latter reaching low altitudes (∼400xa0m). Less susceptible areas are found around the faults cutting the upper portions of Etna, including the western portion of the Pernicana fault and the northern extent of the Ragalna fault. This structural-based susceptibility map is a crucial step in forecasting lava flow hazards at Etna, providing a support tool for decision makers.

Dynamics of a lava fountain revealed by geophysical, geochemical and thermal satellite measurements: The case of the 10 April 2011 Mt Etna eruption

[1]xa0Geophysical (tilt, seismic tremor and gravity signals), geochemical (crater SO2flux) and infrared satellite measurements are presented and discussed to track the temporal evolution of the lava fountain episode occurring at Mt Etna volcano on 10 April 2011. The multi-disciplinary approach provides insight into a gas-rich magma source trapped in a shallow storage zone inside the volcano edifice. This generated the fast ascending gas-magma dispersed flow feeding the lava fountain and causing the depressurization of a deeper magma storage. Satellite thermal data allowed estimation of the amount of erupted lava, which, summed to the tephra volume, yielded a total volume of erupted products of about 1 × 106 m3. Thanks to the daylight occurrence of this eruptive episode, the SO2 emission rate was also estimated, showing a degassing cycle reaching a peak of 15,000 Mg d−1 with a mean daily value of ∼5,700 Mg d−1. The SO2 data from the previous fountain episode on 17–18 February to 10 April 2011, yielded a cumulative degassed magma volume of about ∼10.5 × 106 m3, indicating a ratio of roughly 10:1 between degassed and erupted volumes. This volumetric balance, differently from those previously estimated during different styles of volcanic activities with long-term (years) recharging periods and middle-term (weeks to months) effusive eruptions, points toward the predominant role played by the gas phase in generating and driving this lava fountain episode.

From source to surface: dynamics of Etna’s lava fountains investigated by continuous strain, magnetic, ground and satellite thermal data

We investigated the eruptive episodes that occurred at Etna volcano on 15 November 2011 and 18 March 2012 using different types of data. We present novel data from two recently installed strainmeters that recorded unique signals during the lava fountain phases of these events. The strainmeter data, integrated with those recorded by the magnetic network, and with satellite and ground thermal data, allowed us to follow the path of a gas-rich magma batch from the source inside the volcano to the surface and atmosphere. The amplitude ratio of the volumetric strain changes constrained the storage depth of the magma feeding the lava fountains above 1.5xa0km below sea level. Magnetic data revealed an attempted shallow lateral intrusion, whereas ground and satellite thermal data furnished a quantification of the total erupted volumes of ∼2.2u2009×u2009106u2009m3 for the 15 November event and ∼3.0u2009×u2009106u2009m3 for the 18 March event. Despite different durations of the explosive and effusive phases of the two lava fountain events, the total erupted volume was quite similar, suggesting the emptying of a shallow storage system displaying a steady behaviour.

Thermal insights into the dynamics of Nyiragongo lava lake from ground and satellite measurements

This study was funded by Zanskar Producciones, Cabildo Insular de nTenerife, and the Instituto Volcanologico de Canarias. We are grateful to nEUMETSAT for providing us SEVIRI data and to NASA for the Landsat n7 image. Letizia Spampinato thanks Dr S. Giammanco for funding her nresearch activity on the VIGOR project.

Combining relative and absolute gravity measurements to enhance volcano monitoring

To achieve a balance between uncertainty and efficiency in gravity measurements, we have investigated the applicability of combined measurements of absolute and relative gravity as a hybrid method for volcano monitoring. Between 2007 and 2009, three hybrid gravity surveys were conducted at Mt Etna volcano, in June 2007, July 2008, and July 2009. Absolute gravity data were collected with two absolute gravimeters, which represent the state of the art in recent advances in ballistic gravimeter technology: (1) the commercial instrument FG5#238 and (2) the prototype instrument IMGC-02. We carried out several field surveys and confirmed that both the absolute gravimeters can still achieve a 10 μGal or better uncertainty even when they are operated in severe environmental conditions. The use of absolute gravimeters in a field survey of the summit area of Mt Etna is unprecedented. The annual changes of the gravity measured over 2007–2008 and 2008–2009 provide unequivocal evidence that during the 2007–2009 period, two main phenomena of subsurface mass redistribution occurred in distinct sectors of the volcano, accompanying different eruptive episodes. From 2007 to 2008, a gravity change of −60xa0μGal was concentrated around the North-East Rift. This coincided with a zone affected by strong extensional tectonics, and hence might have been related to the opening of new voids. Between 2008 and 2009, a North-South elongate feature with a maximum gravity change of +80xa0μGal was identified in the summit craters area. This is interpreted to indicate recharge of a deep-intermediate magma storage zone, which could have occurred when the 2008–2009 eruption was still ongoing.

Close temporal correspondence between geomagnetic anomalies and earthquakes during the 2002–2003 eruption of Etna volcano

[1] The early stages of the 2002–2003 lateral eruption at Mount Etna were accompanied by slow changes (over some hours) and some rapid step offsets in the local magnetic field. At five monitoring locations, the total magnetic field intensity has been measured using continuously operating Overhauser magnetometers at a sampling rate of 10 s. The very unique aspect of these observations is the close temporal correspondence between magnetic field offsets and earthquakes that occurred in the upper northern flank of the volcano on 27 October 2002 prior to a primary eruption. Rapid coseismic changes of the magnetic field were clearly identified for three of the most energetic earthquakes, which were concentrated along the Northeast Rift at a depth of about 1 km below sea level. Coseismic magnetic signals, with amplitudes from 0.5 to 2.5 nT, have been detected for three of the largest seismic events located roughly midway between the magnetic stations. We quantitatively examine possible geophysical mechanisms, which could cause the magnetic anomalies. The comparison between magnetic data, seismicity and surface phenomena implies that piezomagnetic effects are the primary physical mechanism responsible for the observed magnetic anomalies although the detailed cause of the rapid high stress change required is not clear. The modeling of the observed coseismic magnetic changes in terms of piezomagnetic mechanism provides further evidence of the complex interaction between volcanic and tectonic processes during dike propagation along the Northeast Rift.