High temporal and spatial resolution UV camera measurements at Stromboli: insights on passive SO2 gas emission, Strombolian eruptions, and puffing.

Stromboli is one of the most active volcanoes on Earth, and one of the few where passive degassing persistently coexists with the (non-passive) release of over-pressurized gas pockets during both explosions and gas puffing activity. These transient gas bursting-puffing phenomena are difficult to study by conventional spectroscopic scanning techniques (e.g., DOAS), since these have far too low temporal resolution. Here, we take advantage of the high spatial and time resolution (0.6-1 Hz) of the recently developed UV camera technique to obtain a simultaneous characterisation of all the different forms of SO2 release at Stromboli (including passive degassing, Strombolian eruptions and puffing)…

Changes in SO2 flux degassing regime prior to the 2014 Stromboli eruption

Volcanic eruptions are often accompanied by release of huge amounts of magmatic SO2. Capturing sizeable precursory SO2 flux variations prior to eruption has revealed far more challenging, instead, in spite of the recent progresses in instrumental gas monitoring. Here, we report on the SO2 fluxes variations we detected at Stromboli volcano prior to the effusive eruption started on the 6th August 2014. The SO2 fluxes were regularly quantified at high-rate (0.5 Hz) using two fully autonomous permanent SO2 camera devices installed - within the framework the ERC-FP7 project "Bridge"- at two sites located at 0.5 km (Roccette) and 1.75 km (Sciara del Fuoco rim) distance from the crater terrace. Th…

Conduit dynamics and post explosion degassing on Stromboli: A combined UV camera and numerical modeling treatment

Recent gas flux measurements have shown that Strombolian explosions are often followed by periods of elevated flux, or “gas codas,” with durations of order a minute. Here we present UV camera data from 200 events recorded at Stromboli volcano to constrain the nature of these codas for the first time, providing estimates for combined explosion plus coda SO2 masses of ≈18–225 kg. Numerical simulations of gas slug ascent show that substantial proportions of the initial gas mass can be distributed into a train of “daughter bubbles” released from the base of the slug, which we suggest, generate the codas, on bursting at the surface. This process could also cause transitioning of slugs into cap b…

BLAST WAVES AT YASUR VOLCANO

Infrasonic and seismic waveforms were collected during violent strombolian activity at Yasur Volcano (Vanuatu). Averaging similar to 3000 seismic events showed stable waveforms, evidencing a low-frequency (0.1-0.3Hz) signal preceding similar to 5-6s the explosion. Infrasonic waveforms were mostly asymmetric with a sharp compressive (5-106Pa) onset, followed by a small long-lasting rarefaction phase. Regardless of the pressure amplitude, the ratio between the positive and negative phases was constant. These waveform characteristics closely resembled blast waves. Infrared imagery showed an apparent cold spherical front similar to 20 m thick, which moved between 342 and 405m/s before the explo…

High-Frame Rate Thermal Imagery of Strombolian Explosions: Implications for Explosive and Infrasonic Source Dynamics

First gas flux measurements of conduit permeability decrease prior to Strombolian eruption at Stromboli volcano (Italy)

Strombolian eruptions can be described in terms of growth, coalescence, and rise of a gas pocket (aka slug) bursting at the surface of a vent. This model overlooks that the transition to explosive regimes is mostly controlled by the permeability in the upper part of a volcanic conduit. We report here on the first gas flux measurements of Strombolian explosions from a vent that exhibited a significant decrease of passive degassing tens of second prior to the onset of the explosion. This particular explosive activity took place during the July 2014 lava overflows, when the magma level inside the conduit rose up to the crater terrace. The amount of gas that accumulated before the eruption is i…

Enhanced volcanic hot-spot detection using MODIS IR data: results from the MIROVA system

We describe a new volcanic hotspot detection system, named Middle InfraRed Observation of Volcanic Activity (MIROVA), based on the analysis of infrared data acquired by the Moderate Resolution Imaging Spectroradiometer sensor (MODIS). MIROVA uses the middle infrared radiation (MIR), measured by MODIS, in order to detect and measure the heat radiation deriving from volcanic activity. The algorithm combines spectral and spatial principles, allowing the detection of heat sources from 1 megawatt (MW) to more than 10 gigawatt (GW). This provides a unique opportunity to: (i) recognize small-scale variations in thermal output that may precede the onset of effusive activity; (ii) track the advance …

Gravity waves from an extratropical cyclone hitting Iceland