June 17, 2020: The volcano of Stromboli
Explosive volcanic eruptions can be so violent and sudden that they catch most monitoring networks by surprise. These phenomena pose not only a scientific challenge but a serious danger, especially for those volcanoes located in inhabited areas or visited by hordes of tourists.
Take the sudden eruptions of Mount Ontake in Japan in 2014 and White Island in New Zealand in 2019. Despite being constantly monitored, these volcanic eruptions resulted in more than 80 deaths among unsuspecting hikers.
One of the most famous explosive volcanoes in the world is Stromboli, located in the Aeolian Islands, off of Sicily. Its gentle yet spectacular explosions, which launch lava and incandescent fragments to several hundred meters in height, have been occurring at a nearly constant rate every 10-20 minutes for thousands of years.
This ongoing, moderate explosive activity is unique and allows for close observation of an erupting volcano. This is how Stromboli has become an international reference point in the study of explosive dynamics. Many of the technological innovations and methodologies commonly used in volcano observatories today were developed and/or calibrated on Stromboli.
Magmatic systems
Two exceptionally violent explosive events, which happened in July and August 2019, interrupted this moderate activity. They generated eruptive columns which were several kilometers high, as well as fires and tsunami waves, ultimately covering coastal villages with ash and rocks.
These violent explosions involved deep portions of the magmatic system (up to about seven kilometers in depth) and are, therefore, believed to have followed a dynamic process different from the regular activity.
The volcano 'deflates' due to the release of gases and lava fragments into the atmosphere.
The use of highly sensitive sensors capable of measuring angles of a few millionths of a degree has shown that these violent explosions are preceded by a weak but clear ground deformation.
The entire volcano begins to 'inflate' about ten minutes before the explosion, following an exponential trend due to the expansion of gases during the magma ascent in the feeding conduit. Then, during the explosion, the deformation reverses as the volcano 'deflates' due to the release of gases and lava fragments into the atmosphere.
Real-time alert system
The Experimental Geophysics Laboratory (Lgs) at the University of Florence, in collaboration with numerous researchers from other Italian and foreign universities, has analyzed thousands of data points collected over more than 15 years of research. This has allowed for the determination that the volcano deforms in an identical manner following inflation/deflation cycles with each explosion, from the weakest to the most violent.
The more violent the explosion, the greater the amplitude and duration of inflation, but its temporal pattern remains unchanged. This indicates that the explosive process always follows the same dynamics and allows for the distinction of ground deformations preceding eruptions from signals produced by other natural sources (atmospheric pressure, temperature, tides, rainfall, earthquakes, etc.).
This uniqueness of the deformation process has led to the development of the world's first real-time alert system for explosive volcanic eruptions.
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