Etna keeps changing summit: the volcano whose high point moves
Etna's highest point has changed crater twice in three years and risen more than forty metres. On the summit craters, Valle del Bove and how you survey a mountain that is being rebuilt.
Most mountains have a highest point and keep it. Etna has four summit craters competing, and the lead has changed hands twice in three years.
Writing down a height for Etna is therefore a different kind of problem than for an ordinary mountain. The number is not uncertain. It is perishable.
Four craters on the same summit
At the very top of the volcano sits a cluster of summit craters. For forty years the Northeast Crater was the highest, reaching around 3,350 metres at its peak in the early 1980s. Then it lost height, partly through collapse.
From February 2021 the Southeast Crater went through some fifty violent eruptive episodes in six months. The material built up the crater rim, and in August 2021 INGV established that it had reached 3,357 metres and taken over as Etna's highest point.
Then the Voragine crater woke up after more than three years of silence. Activity escalated from small explosions to lava fountains, and in September 2024 INGV reported that the eastern rim of Voragine had reached 3,403 metres. That is the highest level ever recorded on the volcano.
Forty-six metres in three years. That is the height of a twelve-storey building.
How you measure something that is being rebuilt
Walking up with survey instruments is not always possible on an active crater. Satellite imagery is used instead.
For the 2021 measurement a digital surface model at one metre resolution was built from satellite images and compared against an earlier model from 2015. The difference between two such models shows not only the height but where the material has ended up and how much of it there is. The uncertainty was a matter of a few metres.
Two elevation models of the same place from different years are the same tool used to see how a glacier shrinks or how a landslide has moved. What an elevation model actually is, we cover in the article on elevation models. The difference is that for Etna the year of collection is not a footnote. It is half the information.
Valle del Bove
The largest single feature in the terrain is not the summit but the hole beside it. Valle del Bove is an enormous horseshoe-shaped basin opening to the east, with steep walls and a floor filled by lava from centuries of eruptions.
On an ordinary map it is just an area of tightly spaced contour lines. In relief it is the first thing the eye finds, because it throws a hard shadow right across the flank.
Hundreds of small cones
The other thing that surprises people seeing Etna as terrain is the flanks. They are not smooth. They are covered in small subsidiary craters, so-called parasitic cones, formed where lava found its way out through fissures on the side of the mountain instead of through the summit. There are hundreds of them.
The volcano has been on the UNESCO World Heritage list since 2013, and it is precisely this diversity of volcanic features - summit craters, cones, lava flows, lava tubes and Valle del Bove - that forms part of the justification.
On the Etna piece the summit crater sits in the middle of the frame and the small cones are visible right across the flank. If you want to read more about why mountain heights move at all, there is the piece on measuring elevation.
