Mount Etna may be the world’s only known land-based petit-spot volcano.
For decades, geologists have kept a close eye on Etna without ever fully explaining how it came to be. It is Europe’s most active volcano, erupting several times a year, rising more than 9,800 feet above sea level along the eastern coast of Sicily. And yet none of the available geological models could account for its origins.
A new study, led by researchers at the University of Lausanne in collaboration with the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in Catania, proposes an explanation that may finally close that gap.
The Volcano That Defied Classification
Geologists classify terrestrial volcanoes into three broad groups: those that form at subduction zones, where one tectonic plate slides beneath another and typically produce explosive eruptions, like Mount Fuji; those that rise above hot spots, where plumes of mantle material hotter than their surroundings push upward toward the surface, as in Hawaii or Réunion; and those linked to mid-ocean ridges, where plates pull apart.
Etna fits none of these. It sits near a subduction zone, yet its chemical composition resembles that of hot-spot volcanoes — even though no hot spot exists anywhere nearby. That contradiction has puzzled geologists for decades.
To find an answer, the team led by Professor Sébastien Pilet analyzed lava samples collected throughout Etna’s eruptive history. The goal was to trace the chemical composition of lavas from the volcano’s earliest activity, roughly 500,000 years ago.
What they found was striking: the composition of the lavas has remained virtually unchanged over time, despite significant shifts in the region’s tectonic activity.
That pointed to a remarkably stable, deep-seated source. The data confirmed that Etna draws from pockets of ancient magma stored in the upper mantle, roughly 50 miles beneath the surface. As the African and Eurasian plates collide, they bend and fracture the lithosphere, forcing those magma pockets upward toward the surface.
A Fourth Category of Volcano, Hidden on the Ocean Floor Since 2006
Etna may belong to a little-known category called “petit-spot” volcanoes, first identified in 2006 by Japanese geologists — volcanoes fed by magma drawn from pockets in the upper mantle.
Until now, these volcanoes had only been documented on the ocean floor — forming modest structures no more than a few hundred feet tall. Etna, by contrast, towers over 9,800 feet. Etna would be the first documented case of a large-scale petit-spot volcano on dry land — and no one saw that coming.
According to petrologist Sarah Lambart of the University of Utah, as quoted by Live Science, the discovery points to “a new type of volcanism” — one that highlights interactions between the lithosphere and the mantle that scientists had long underestimated.
But the study’s significance extends beyond reclassifying Etna. It raises the possibility that similar volcanic systems exist elsewhere — many still unidentified or misclassified.
On the practical side, a clearer picture of where Etna’s magma comes from will help INGV researchers build more accurate models of the volcano’s future behavior. Its eruptions, though frequent, have historically been less destructive than those of similarly sized volcanoes.
Etna has been active for half a million years. That it can still surprise us says a great deal about how much our planet has yet to reveal.
