Computer simulations of the ascent paths of the magma from the earth's mantle suggest the position of the source which feeds the eruptions of Etna and which, in the past, generated the volcanoes of the Iblei Mountains, now extinct. The study, conducted by researchers from INGV, GFZ Potsdam and the Roma Tre and Catania universities, was published in Earth & Planetary Science Letters, Elsevier BV
It could be the Escarpment of Malta, the source of the magma that feeds the eruptions of Etna and which, in the past, gave life to the volcanoes of the Iblei Mountains, now extinct. This was revealed by the study, Etnean and Hyblean volcanism shifted away from the Malta Escarpment by crustal stresses, conducted by a team of researchers from the National Institute of Geophysics and Volcanology (INGV), German Center for Geosciences (GFZ) of Potsdam, University of Roma Tre and Catania studies.
The research results have been published in Earth & Planetary Science Letters, Elsevier BV ;
“Eruptions and earthquakes are close relatives”, explains Marco Neri, first researcher of the Etna-INGV Observatory. “Like opposite sides of the same coin, both phenomena occur primarily along the edges of the tectonic plates that segment the Earth's surface. However, there are volcanoes that do not follow this rule, because they develop inside the tectonic plates and not on their edges. It is a volcanism that geologists define as "intraplate" type, just like the volcanoes that have been erupting along eastern Sicily for millions of years".
Although from five hundred thousand years to today Etna has been very active, previously and for millions of years it was the Iblei Mountains (a mountainous plateau located in the south-eastern part of Sicily) that dominated the scene, hosting numerous volcanoes distributed from Capo Passero to the plain of Catania and from Syracuse to Grammichele.
But what is the source that feeds the eruptions of Etna? And where do the magmas that gave life to the Hyblean volcanoes come from?
"We have computer simulated the propagation paths of the magma below the Iblei and Etna volcanoes up to the crust-mantle limit, about 30 km deep", continues Neri. “In the calculations we have considered the different tectonic regimes that have alternated in eastern Sicily over the last ten million years. In this area the earth's crust was compressed or dilated with different directions of extension and compression, which in turn favored or opposed the ascent of magmas from the mantle towards the surface. The model has also highlighted the progressive evolution of the faults of the Malta Escarpment, which have deepened over time, increasing the lithostatic load induced by the rock masses in deformation”, adds the OE-INGV researcher.
Scientists have thus discovered that the trajectories followed by magma along its ascent from the earth's mantle towards the surface are not vertical, but variously curved.
"The trajectories of the magma converge, downwards, both for Etna and for the Iblei volcanoes, in the same area, below the so-called Malta Escarpment", says Neri. “It is a tectonic structure that opens the earth's crust in eastern Sicily and allows the magma to rise from the mantle. But the Malta Escarpment is also an imposing system of "seismogenic" faults located just off the eastern coast of Sicily under the Ionian Sea and capable of generating earthquakes. Its faults stretch for over three hundred kilometers producing, in the seabed, an escarpment up to three thousand meters deep".
And it would have been precisely the Malta Escarpment that had generated, on 11 January 1693, in the Val di Noto, the most violent earthquake that has occurred in the last thousand years in Italy: Magnitude Mw7.4, fifty-four thousand victims and a devastating tsunami induced by the shaking of the seabed.
"The study shows that volcanoes and seismogenic faults in eastern Sicily are also the expression of a single volcano-tectonic context that has been active for millions of years and that evolves over time, explaining why the Iblean volcanoes are now extinct, while Etna is still very active . Identifying the area of origin of the magmas also allows us to constrain the geochemical models that investigate why magmas are formed”, concludes Marco Neri.
Abstract
Etnean and Hyblean volcanism shifted away from the Malta Escarpment by crustal stresses
Neri M., Rivalta E., Maccaferri F., Acocella V., Cirrincione R. (2018), Etnean and Hyblean volcanism shifted away from the Malta Escarpment by crustal stresses. Earth and Planetary Science Letters Volume 486, Pages 15–22,
A fraction of the volcanic activity occurs intraplate, challenging our models of melting and magma transfer to the Earth's surface. A prominent example is Mt. Etna, eastern Sicily, offset from the asthenospheric tear below the Malta Escarpment proposed as its melt source. The nearby Hyblean volcanism, to the south, and the overall northward migration of the eastern Sicilian volcanism are also unexplained. Here we simulate crustal magma pathways beneath eastern Sicily, accounting for regional stresses and decompression due to the increase in the depth of the Malta Escarpment. We find non-vertical magma pathways, with the competition of tectonic and loading stresses controlling the trajectories' curvature and its change in time, causing the observed migration of volcanism. This suggests that the Hyblean and Etnean volcanism have been fed laterally from a melt pooling region below the Malta Escarpment. The case of eastern Sicily shows how the reconstruction of the evolution of magmatic provinces may require not only an assessment of the paleostresses, but also of the contribution of surface loads and their variations; at times, the latter may even prevail. Accounting for these competing stresses may help shed light on the distribution and wandering of intraplate volcanism.
Keywords: intraplate volcanism; fault shoe; dike propagation; Malta Escarpment; Hyblean volcanism; Etna.
Figure 1 – A lava flow from Etna expands on the high eastern flank of the volcano. The box at the bottom left shows in a simplified way the source of the Etna magma, located under the faults of the Malta Escarpment
Figure 2 – The active craters at the summit of Etna, taken from the southeast