The volcanic area of the Colli Albani, on the outskirts of Rome, which has remained in an absolute state of calm for 36.000 years now - despite myths and legends that have accredited eruptions up to Roman times - is active and new is accumulating several kilometers deep magma, foreshadowing an awakening in thousands of years. This is supported by a study signed by INGV, Sapienza University of Rome, CNR and the University of Madison, published in Geophysical Research Letters
The Colli Albani, the volcanic area on the outskirts of Rome, is beginning to show signs of a future awakening. This was established by a multidisciplinary study Assessing the volcanic hazard for Rome: 40Ar/39Ar and In-SAR constraints on the most recent eruptive activity and present-day uplift at Colli Albani Volcanic District, conducted by a team of researchers from the National Institute of Geophysics and Volcanology (INGV), in collaboration with the Department of Geological Sciences - "Sapienza" University of Rome, the Institute of Environmental Geology and Geoengineering of the National Research Council (IGAG-CNR), and the Geochronology Laboratory of the University of Madison, which has made it possible to reconstruct the history of the eruptions that occurred from 600.000 years ago to today in the volcanic district of the Colli Albani, together with that of the deformations of the earth's crust that have accompanied its evolution over time.
"The surprising result", says Fabrizio Marra, a researcher at INGV, "is that not only is the volcano far from extinct, but it has just started a new cycle of feeding the magma chambers which could take it into the next millennium, from one dormant state to waking state. Hence the need to monitor this volcanic area starting today".
The elements that emerged from the study are many, linked to various geophysical indicators, all converging in indicating that the volcanic area is active and that new magma is accumulating several kilometers deep.
“How long it takes for this magma to find a way up and give rise to an eruption is difficult to establish with precision, what is certain is that the physical times for which this can happen are on the scale of several thousand years. A completely different story compared to Vesuvius, where the eruptions took place in historical times and the return times of volcanic activity are of the order of tens and hundreds of years: in the Colli Albani everything proceeds with times of thousands and tens of thousands of years. Starting with the return times of the eruptions”, continues Marra.
Throughout the entire period of activity, regardless of the size of the individual eruptions, the eruptions at the Colli Albani occurred with very regular cycles of about 40.000 years, separated by periods of almost absolute quiescence.
“Starting from 600 thousand years ago”, explains the INGV researcher, “there have been 11 of these eruptive cycles. The last one, which took place at the Albano crater, began 41.000 years ago and ended around 36.000 years ago. This means that the time elapsed since the last eruption is of the same order as the return times: therefore the volcano must be considered active and ready for a new future awakening”.
The researchers also ascertained that in the most recent period of activity, starting from 100.000 years ago, the return times were slightly shorter and were of the order of 30.000 years. The area in which all the more recent eruptions took place is concentrated in a long sector in a north-south direction and includes the craters of Ariccia (200 years), Nemi (150 years), Valle Marciana (100 years), Albano (two cycles at 69 and 41-36 years), and the volcanic cone of Monte Due Torri (40 years).
“This sector corresponds exactly to an area in which satellite telemetry observations (InSar), made by INGV researchers, have revealed continuous uplift, with rates of 2-3 mm/year, over the last 20 years. This therefore suggests that new magma is accumulating below the area where the most recent eruptions took place, causing the surface to swell. Reevaluation of past crustal tomography studies suggests that this accumulation zone may be between 5 and 10 km deep. Deep enough, therefore, not to cause concern at the moment”, continues Marra.
Finally, the third important element arose from the studies that investigated the causes of the long periods of inactivity that separated the different eruptions.
"Here too it was understood that the cause of this peculiar behavior, different from the other volcanic districts active in the same period of time in central Italy (Vulsini, Vico, Monti Sabatini and Roccamonfina), lies in the particular geodynamic conditions of the Rome area , where predominantly compressive crustal forces have been active, compared to the extensional forces of the surrounding areas, which has the effect of sealing the fractures and faults that constitute the magma ascent routes during eruptions. Thus the magma remains in depth until the progressive accumulation generates pressures such as to overcome the crustal compressive forces. At this point a vertical thrust is exerted which reopens the faults and fractures: that is, the stress field becomes extensional as in the surrounding regions, and a new eruptive cycle begins", adds Marra.
At present the geophysical indicators indicate the existence of an extensional stress field in the Colli Albani and in the Rome area, compatible with an ongoing uplift and favorable to the eventual ascent of magma.
At the same time “no element deriving from the ongoing geochemical and geophysical observations suggests that an eruption could take place either in the short or medium term. Therefore, if a recharge of the magma reservoirs is in progress, this will undoubtedly last thousands of years before it can give rise to an eruption”, concludes Marra.
Extended
The Colli Albani is a dormant volcanic area located only 20 km southeast of Rome and, despite myths and legends that have suggested the occurrence of eruptions in ancient Roman times, it has remained completely quiet during the last 36,000 years; however, a growing body of independent geophysical indicators suggest that a new batch of magma is currently accumulating at several km of depth, and it may give rise to a new eruption in the next 1,000 years.
This is the result of a multi-disciplinary study conducted by a team of researchers of the INGV, in collaboration with the Geology Department of the Sapienza University of Rome, the Institute of Geoengineering and Environmental Geology - CNR, and the Wiscar Laboratory of Madison University . By means of 40Ar/39Ar dating on the volcanic products the researchers have reconstructed the eruptive history of the Colli Albani during the last 600,000 years and have established that eruptive cycles occurred with a fairly regular average recurrence time, and that the time elapsed since the last eruption (36,000 years) overruns the recurrence time of 31,000 years observed in the last 100,000.
This means that the volcanic area is active and "ready" for a new eruption.
Moreover, new satellite (InSar) data covering the years 1993-2010 revealed ongoing inflation with maximum uplift rates of 2-3 mm/yr in the area hosting the craters of most recent volcanic activity, suggesting that the observed uplift might be caused by injection of new magma. Finally, the researchers have found geological evidence for a recent (<2000 years) switch of the local stress-field from a previous compressive state, sealing fractures and faults representing potential pathways for uprising of deep fluids, to an extensional state favorable to magma uprising .
These observations highlight that the Colli Albani volcanic area is slowly waking up, and it may be affected by a new eruption in the next thousands years.
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