While Mount Etna has existed for over half a millennium, this colossal stratovolcano located in Sicily continues to exhibit significant volcanic activity.
This 3,400-meter geological titan stands as Europe’s most active volcano, frequently experiencing multiple eruptions annually.
Indeed, Etna displays an unusually vigorous nature. It is recognized for erupting alkaline lavas, a characteristic divergence from most stratovolcanoes, and does so with a proliferation that defies typical timelines for generating volatile-rich alkaline molten rock.
This phenomenon renders Etna a puzzling subject. Despite its extensive historical documentation—alongside comprehensive modern monitoring and research—no established geological model adequately elucidates its formation or the origin of its consistent supply of alkaline magma that fuels its frequent outbursts.
A recent investigation provides illuminating insights. Etna appears to be sustained by an uncommon magmatic process, identified only in recent decades, which is typically associated with minor submarine volcanoes rather than imposing stratocones like Etna.
The research indicates that Etna’s formation and operational mechanisms differ from those of most other volcanoes, the investigators propose, suggesting it “may constitute a singular locale on Earth” due to its distinctive method of releasing magma trapped within the planet’s low-velocity zone and expelling it to the surface.
These findings offer substantial contributions to the broader field of volcanology, particularly for assessments of the specific risks posed by Etna. This volcano’s proximity to the densely populated cities of Catania and Messina in eastern Sicily, each inhabited by hundreds of thousands, underscores the significance of understanding its behavior.
Volcanoes originate from the melting of mantle material into magma, which then ascends through the crust to its surface, where it solidifies. This process typically occurs through one of three primary mechanisms.
When tectonic plates diverge, mantle material is permitted to rise and melt, resulting in lava extrusion at the plate boundaries that forms new oceanic crust upon solidification.
Alternatively, in subduction zones where one tectonic plate descends beneath another, the subducting plate introduces water into the mantle, lowering its melting point and potentially triggering forceful eruptions.
A third scenario involves hotspots, areas of intensely heated mantle material within tectonic plate interiors, which can rise to the surface, frequently giving rise to shield volcanoes such as those that constructed the Hawaiian Islands.
The majority of terrestrial volcanoes conform to one of these established classifications; however, Mount Etna presents a notable exception.
It is categorized as a stratovolcano situated above a subduction zone, yet the geochemical signatures of its lava align with those of hotspot volcanoes, all without the presence of any identified hotspots in its vicinity.
In an effort to unravel this discrepancy, the study’s authors procured samples from Etna to meticulously reconstruct the chemical composition of its erupted lava over the past half-million years.
Etna’s lava demonstrated a remarkably consistent chemical profile throughout its history, persisting even amidst shifts in tectonic activity that could have readily influenced localized volcanic systems.
This consistency implies that Etna operates through a modus operandi distinct from conventional volcanoes, whose eruptions typically involve recently generated magma.
Instead, Etna appears to receive a slow, continuous influx of pre-existing magma, which has been sequestered in the upper mantle, approximately 80 kilometers beneath the surface, between the mantle and the base of tectonic plates.
The genesis of alkaline lava is contingent upon a limited degree of partial melting within the mantle to preserve alkali concentrations, a process that precludes rapid, large-scale formation. Nevertheless, Etna consistently produces alkaline lava, attributed to its distinctive magmatic reservoir.
As the African Plate subducts beneath the Eurasian Plate, alkaline magma from these upper-mantle pockets is apparently channeled upwards through crustal fissures, akin to water being expelled from a saturated sponge.
Consequently, Etna might be classified as a “petit-spot” volcano, a category initially identified in 2006, characterized by magma sourced from isolated pockets within the upper mantle.
It remains an anomaly, however, as petit-spot volcanoes are typically diminutive, in stark contrast to the immense scale of Etna.
“Our investigation indicates that Etna potentially originated through a mechanism analogous to that which generates petit-spot submarine volcanoes,” states lead author Sébastien Pilet, a geoscientist affiliated with the University of Lausanne.
“This finding is unexpected, given that such processes were previously observed exclusively in very small volcanic structures, typically rising no more than a few hundred meters in elevation.”
