Pierre Thomas is a geologist from the Earth Sciences Laboratory of l’Ecole Normale Supérieure at Lyon in France. We asked him about the particular characteristics shown by the volcano which last erupted in 1821. How long could it be active, and could it trigger its much more dangerous neighbour?
Pierre Thomas, Geologist:
“Nobody is capable of predicting like that when it’s going to stop. Icelandic geologists had perfectly predicted the start of the eruption. The pressure gently began to build up 15 years ago. So they knew, they monitored the volcano. The eruption began a month ago in mid-March, but at the beginning it wasn’t at all explosive. It was an eruption like they have every two to three years in Iceland. And then when the cracks had opened up and reached the glacier it became very explosive. But the explosion wasn’t a surprise – that was forecast too.”
“Last time the eruption went on for between a year and a half and two years. There are not many descriptions, but if the lava always emerged from the same point, the glacier melted all around, and overall there would have been less ice there where the lava appears.
So progressively, if the lava always surfaces in the same area, one would hope that the explosivity would diminish. If the volcanic fissure creeps on to touch another part of the glacier, then that’s it.”
“If the glacier is very thick, there’s lots of water, and that, if you like, drowns the volcano. It’s like an eruption deep under the sea, the lava solidifies immediately, and there’s no explosion.
If there’s not much water, it vapourises to begin with, but nothing special. That’s just what’s needed to create something like a series of pressure cookers that explode ever five minutes.
As there’s always water, the pressure cookers explode over and over and that sends the ash- cloud five, six, maybe ten kilometres.”
“Volcanoes are not contagious. Just because there’s a volcano here doesn’t mean there’ll be an explosion elsewhere. But historically – twice I think – the activity started in our volcano with the unpronouncable name Eyjafjallajökull, and just afterwards Katla began to erupt. OK, twice isn’t statistically significant — it could be just chance — but maybe there is something in it, and that would be very tricky, because that volcano is much more explosive. That would be under a glacier, and that would make it explosive in itself. But it also has its own explosivity because it’s not the same lava. It could be rhyolite and that is extremely explosive.”
“If you want to make yourself scared, let’s talk about Laki’s eruption in 1783. For two years, it poured out lava equivalent to the flow of the River Rhine – 2000 cubic metres of lava per second. Imagine that over two years… and it unleashed a cocktail of toxic vapours that poisoned the Icelandic vegetation and livestock.
A quarter of the population died. But that was extraordinary volcanic activity, the biggest eruption of lava ever witnessed by mankind since records began.”