Applied a modern multidisciplinary approach to understand the origin of the New Southeast Crater of Etna. This was announced by a study by INGV and Roma Tre University, recently published in Frontiers in Earth Science
Why do volcanoes change? What makes them so "unstable" at the summit vents? A team of researchers from the National Institute of Geophysics and Volcanology (INGV) and the Roma Tre University answers these questions, retracing the history of the recently formed New South-East Crater of Etna.
I study (http://journal.frontiersin.org/article/10.3389/feart.2016.00067/full) was published in the journal Frontiers in Earth Science.
Volcanoes usually erupt from their tops, from one or more summit craters. An activity that generally occurs in a "persistent" way, almost continuously over time, and uses the vents already present on the top of the volcano. Precisely for this reason, it is very rare to observe the birth of a new permanent summit crater and, even more exceptional, as in this case, to see a new vent replace the previous vents.
"Etna is one of the few volcanoes in the world where it has been possible to capture and monitor the birth of a new summit eruptive vent, which occurred in the last decade", says Marco Neri, coordinator of the work and first researcher at the Etna Observatory of INGV (INGV-OE). "Actually, new summit vents had also opened in the last century, but only now, for the first time, have we managed to apply a modern multidisciplinary approach to monitor the birth of the new crater".
The New Southeast Crater was formed at the eastern base of the "older" Southeast Crater, along a NW-SE (Northwest Southeast) oriented fracture, repeatedly "injected" by magma in the last decade (Figure 1).
“Growing rapidly on the edge of the Valle del Bove, close to a sheer wall about a thousand meters high, the new eruptive cone is intrinsically unstable and potentially subject to landslides. Also for this reason, therefore, it is necessary to monitor the morpho-structural evolution of this new crater with extreme attention”, continues Neri.
Land and aerial surveys, together with satellite thermal data and ground deformation data with high precision GPS (Global Positioning System), have made it possible to define the volcanological and structural variations associated with the formation of this new summit crater.
“The causes of this epochal event in the recent history of Etna”, adds the researcher, “have been identified in the complex instability which characterizes, in particular, the north-eastern flank of the volcano. In fact, Etna undergoes cyclically over time phenomena of inflation (swelling), followed by deflation (deflating) which generally last from a few months to a few years. Recently, during periods of inflation, the north-eastern flank of Etna has been deformed, following semi-circular "translation" trajectories: the summit portion has moved towards the north-east, the intermediate part towards the east and finally the distal, near the Ionian Sea, is shifted towards the South-East (observe the purple arrows in Figure 2). The shift towards the North-East of the summit part of the volcano has favored the opening of numerous eruptive fissures oriented in the NW-SE direction (North-West South-East) and the consequent birth of the New South-East Crater”. Volcanoes that have shown major structural changes in recent decades, such as Mount St. Helens (Washington, USA) and Bezymianny (Kam?atka, Russia), have not had their summit craters moved.
“It is over longer periods of time (hundreds or thousands of years) that a volcanic edifice can change the configuration of its eruptive vents, as revealed by geological data. A very important event in the history of a volcano, as it testifies to the geometric variation of the conduits that transfer magma towards the surface, and when this happens it always has important repercussions on volcanic hazards", continues Valerio Acocella, researcher at the Roma Tre University and co-author of the work. The example of the New Southeast Crater shows how an active volcano, characterized by a continuous instability of its flanks, is strongly conditioned to change the position of the magma rising conduits, and this can happen in a relatively short time. "The case of Etna is, therefore, an exceptional example for better understanding the eruptive dynamics of active volcanoes, especially if subject to gravitational sliding and deformation of the sides of the apparatuses", concludes Marco Neri.
Abstract:
Mature volcanoes usually erupt from a persistent summit crater. Permanent shifts in vent location are expected to occur after significant structural variations and are seldom documented. Here, we provide such an example that recently occurred at Etna. Eruptive activity at Mount Etna during 2007 focused at the Southeast Crater (SEC), the youngest (formed in 1971) and most active of the four summit craters, and consisted of six paroxysmal episodes. The related erupted volumes, determined by field-based measurements and radiant heat flux curves measured by satellite, totaled 8.67 × 106 m3. The first four episodes occurred, between late-March and early-May, from the summit of the SEC and short fissures on its flanks. The last two episodes occurred, in September and November, from a new vent (“pit crater” or “proto-NSEC”) at the SE base of the SEC cone; this marked the definitive demise of the old SEC and the shift to the new vent. The latter, fed by NW-SE striking dikes propagating from the SEC conduit, formed since early 2011 an independent cone (the New Southeast Crater, or “NSEC”) at the base of the SEC. Detailed geodetic reconstruction and structural field observations allow defining the surface deformation pattern of Mount Etna in the last decade. These suggest that the NSEC developed under the NE–SW trending tensile stresses on the volcano summit promoted by accelerated instability of the NE flank of the volcano during inflation periods. The development of the NSEC is not only important from a structural point of view, as its formation may also lead to an increase in volcanic hazard. The case of the NSEC at Etna here reported shows how flank instability may control the distribution and impact of volcanism, including the prolonged shift of the summit vent activity in a mature volcano.
Rome, 21 July 2016
Images:
Figure 1 – Aerial view from the south of the summit crater area of Etna. In the foreground, the New Southeast Crater (NSEC) recently grown on the eastern base of the older Southeast Crater (SEC). Top left, the craters Voragine (VOR) and Bocca Nuova (BN). Photo by Marco Neri.
Figure 2 – North-eastern portion of Etna represented by a digital terrain model in gray tones. The purple arrows indicate the deformation trajectories of the northern sector of the volcano, which draw a sort of "semi-vortex", or a semi-circular path, moving from the summit area towards the area next to the Ionian coast. The length of the purple arrows is proportional to the amount of displacement. The black lines indicate the location of major faults. The red lines correspond to eruptive fissures. The figure is extracted from: Acocella et al., (2016), doi: 10.3389/feart.2016.00067.
Figure 3 – November 15, 2011: the New Southeast Crater erupts loudly, producing yet another "lava fountain". The new summit crater grows on the eastern flank of the "old" one, which remains inactive, visible in the photograph on the left. Photo by Marco Neri.
Figure 4 – The New Southeast Crater produces yet another paroxysmal eruption on the morning of March 4, 2012. A dense column of gas and volcanic ash rises for a few kilometers above the summit of the volcano, and is then dispersed by the north- East. Photo by Marco Neri.
Figure 5 - In the foreground, the New Southeast Crater, which shows a semicircular vent on its summit, which grew on the eastern flank of the "old" one. Immediately behind these two craters is the Central Crater, characterized by abundant gaseous emissions. Photo by Marco Neri.
