Through the analysis of gravimetric and vertical soil deformation data collected over 10 years, it was possible to identify a deep magmatic source which, by filling and emptying, determines the variations in the volcano's eruptive activity.
Between 2009 and 2011, Etna was affected by an increase in the earth's gravity field and by a lifting of the ground followed, in the period 2011-2014, by a decrease in gravity accompanied by a phenomenon of subsidence, or lowering of the soil. These variations are connected to the movement of magma from and towards a magma source located under the summit area of the volcano.
This is what emerged from the study , conducted by a team of researchers from the National Institute of Geophysics and Volcanology (INGV) and recently published in the journal 'Journal of Geodesy'.
The results, obtained through the analysis of absolute measurements of the acceleration of the Earth's gravity and of the vertical deformation of the ground, concern the time interval between 2009 and 2018, a period characterized by numerous and intense eruptive phases which affected the summit craters of Etna.
Despite the difficult environmental conditions that characterize the summit of the volcano, researchers have periodically installed absolute gravimeters on Etna, generally designed to operate in laboratory conditions. With the collected data they tracked the smallest changes in the gravity field that occurred on time scales of several years.
“Despite the more than twenty-year history of gravity measurements on Etna, a dataset of approximately 10 years of absolute gravity acceleration measurements, carried out on one of the most active volcanoes in the world, is unprecedented and in itself exceptional”, explains Filippo Greco, INGV researcher and co-author of the study. “With our joint analyses, we have identified a magma source located under the summit area of the volcano, at a depth of about 5 km below sea level. Since the volume variation of the source, which emerged from the analysis of the ground deformation data, corresponds to a much lower mass variation than that necessary to explain the observed gravity variations, we hypothesized that this difference is due to the compressibility of the magma in the identified source, made more efficient by the presence of gas".
“Overall, the gravity and ground deformation data revealed that in the period between 2009 and 2011 there was a magmatic recharge cycle of this source, which was followed by a subsequent depletion cycle between 2011 and 2014. XNUMX”, says Alessandro Bonforte, INGV researcher and co-author of the study. “During the recharge phase, only one outgassing occurred from the summit craters of the volcano while, during the emptying phase, the magma fed the exceptional phase of volcanic activity recorded between 2011 and 2014, when there were numerous episodes of lava fountaining”.
“Our work confirms, with very accurate and unique data, the importance of multidisciplinarity in the study of volcanoes. In fact, it is essential to observe the different effects of the same phenomenon, through the integration and comparison of different but complementary measures and data. This allows, in fact, to obtain a more complete view of the dynamics that occur within complex systems such as volcanic ones", concludes Greco.
The obtained results are important in view of the long-term volcanic risk assessment and encourage the execution of absolute measurements of the acceleration of gravity to integrate the monitoring of ground deformation in volcanoes where magmatic cycles can develop on time scales that ranging from months to years.
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ETNA | The deep magma source feeding the volcanic activity between 2011 and 2014 has been located
Through the analysis of gravimetric and vertical ground deformation data collected over 10 years, it was possible to identify a deep magmatic source which, by filling and emptying, determines the variations in the eruptive activity of the volcano.
Between 2009 and 2011, Etna was affected by an increase in the Earth's gravity field and by a lifting of the ground followed, in the period 2011-2014, by a decrease in gravity accompanied by a phenomenon of subsidence, or lowering of the ground. These variations are connected to the movement of magma from and towards a magma source located under the summit area of the volcano.
This is what emerged from the study conducted by a team of researchers from the National Institute of Geophysics and Volcanology (INGV) and recently published on 'Journal of Geodesy'.
The results, obtained through the analysis of absolute measurements of the acceleration of the Earth's gravity and of the vertical deformation of the ground, concern the time interval between 2009 and 2018, a period characterized by numerous and intense eruptive phases which affected Etna's summit craters.
Despite the difficulties due to the environmental conditions that characterize the summit of the volcano, researchers have periodically installed absolute gravimeters on Etna, generally designed to operate in quiet laboratory conditions. With the collected data, they tracked the very small changes in the gravity field that occurred on time scales of several years.
“Although more than twenty-year history of gravity measurements on Etna, a dataset of approximately 10 years of absolute gravity acceleration measurements, carried out on one of the most active volcanoes in the world, is unprecedented and in itself exceptional”, explains Filippo Greco, INGV researcher and co-author of the study. “With our joint analysis we have identified a magma source located under the summit area of the volcano, at a depth of about 5 km below the sea level. Since the volume variation of the source, which emerged from the analysis of the ground deformation data, corresponds to a much lower mass variation than that necessary to explain the observed gravity variations, we assumed that this difference is due to the compressibility of the magma in the identified source, made more efficient by the presence of gas”.
“Overall, the gravity and ground deformation data revealed that in the period between 2009 and 2011 there was a magmatic recharge cycle of this source, which was followed by a subsequent depletion cycle between 2011 and 2014”, says Alessandro Bonforte, INGV researcher and co-author of the study. “During the recharging phase, only outgassing occurred from the summit craters of the volcano; during the emptying phase, this magma fed the exceptional phase of volcanic activity recorded between 2011 and 2014, when numerous episodes of lava fountaining occurred”.
“Our research confirms, with very accurate and unique data, the importance of multidisciplinarity in the study of volcanoes. Indeed, it is essential to observe the different effects of the same phenomenon, through the integration and comparison of different but complementary measures and data. This allows, in fact, to obtain a more complete view of the dynamics that occur within complex systems such as volcanic ones”, concluded Greco.
The obtained results are important in view of the long-term volcanic risk assessment and encourage the execution of absolute measurements of the acceleration of gravity to integrate the monitoring of ground deformation in volcanoes where magmatic cycles can develop on time scales that range from months to years .
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Figure: Scheme of the two phases revealed by the measurements of absolute gravity and soil deformation. The recharge of 2009-2011 and the subsequent outflow of magma towards more superficial levels led to intense eruptive activity in the period 2011-2014.
Figure: Figure: Sketch of the two phases revealed by the absolute gravity and ground deformation measures. The 2009-2011 recharge and the following magma outflowtowards shallower levels leading to the intense eruptive activity during 2011to 2014.