Sicily’s Mount Etna began erupting a decent amount of lava – peppered with the occasional ash column – towards the end of February of this year, and plenty have gathered around it to watch the fireworks. A BBC News team happened to get a little bit too close to it today, though, and a sudden explosion almost took them out.
As tweeted by the BBC’s Global Science Correspondent Rebecca Morelle, lava and steam erupted from somewhere near the summit as they were gallivanting around there. Superheated rock and ash flew towards them and a few people nearby, but thankfully – despite a few injuries – everyone’s alive and well.
“Running down a mountain pelted by rocks, dodging burning boulders and boiling steam – not an experience I ever ever want to repeat,” Morelle tweeted earlier today.
This type of volcanic explosion sounds a lot like a phreatomagmatic blast, which involves water interacting with lava. If you just pour lava onto water or ice, the lava lets off a bit of steam and that’s about it. When lava erupts into water along a divergent plate boundary (see: Mid-Atlantic Ridge), the lava balloons outwardly, cools rapidly, and again – that’s about it.
However, if you wrap water up in lava – say, snow-melting down into the volcanic soil and near or into some magma quite close to the surface – something strange happens. The water turns into vapor pretty quickly, which briefly acts as an insulating film between the rest of the water and the lava/magma.
This is known as the Leidenfrost effect, and can be seen when you pour a tiny amount of water onto a very hot kitchen stove.
This mechanism temporarily stops the water instantly boiling. Eventually, though, the vapor film collapses, and the temperature difference between the water and the magma balances out rather rapidly.
This sudden appearance of steam is dangerous enough, but when this happens within volcanic systems, it’s normally underground. The added presence of a high pressure environment often leads to some explosive results, as was observed today on Mount Etna.
Many people have died as a result of these explosions in the past, especially when they destabilize the volcano and things escalate rather quickly. The BBC team – and a 78-year-old woman who was also there at the time – were very lucky to have escaped with their lives this time around.
If anything, it’s clear that these adventurous reporters seem to have a better instinct of self-preservation than some others might have. Take this group of skiers, for example, who recently chased one of Etna’s lava flows down a slope.
Today's blast and subsequent lava flow captured by ESA's Sentinel-2A satellite. ESA