Footage from Mount Etna

Mount Etna has been erupting again, and some fairly impressive footage of lava fountains have made it onto YouTube:

Both clips at some point zoom out to show that the footage is being filmed from the streets of a town in the shadow of Etna, probably Catania, Sicily’s second-largest city. Despite their proximity, however, these eruptions actually present very little real danger to the population, because unlike other volcanoes in the western Mediterranean region like Vesuvius, Etna tends to erupt runny basaltic lava flows rather than periodically blowing its top, so whilst there’s always a risk of flows overwhelming property, they move so slowly that the people can get out of the way.

When you actually consider the tectonic setting of Etna, this is actually quite odd. The western Mediterranean has had a complicated geological history, but most of the Italian volcanoes appear to be related to the westward subduction of oceanic crust. Water and gases released from the subducting plate trigger melting, and are incorporated into the resulting magma: this generally leads to explosive volcanism. In contrast, less viscous basaltic magmas are generally the result of the melting of unaltered mantle, either due to decompressional melting at rift zones or extra heating by rising mantle plumes (as in the case in Hawaii).

Unfortunately, I’m not in a position to research the whys and wherefores of this anomaly right now. I vaguely recall reading something about the possibility of a slab window – a break in the subducting plate which allows unaltered mantle material to rise to the surface – but I can’t remember the details or even if its relevant. Perhaps one of my geoblogging colleagues can provide the answer…