21 December 2011

Accretionary Wedge #41: Geology in progress

Posted by Jessica Ball

Ron Schott is hosting Accretionary Wedge #41, and he’s asking us to do a little reminiscing:

Right, then. Your mission, should you choose to accept it, is to relate the story of the most memorable or significant geological event that you’ve directly experienced.

What we seek for AccretionaryWedge #41 is an account of a geologic event that you experienced firsthand. It could be an earthquake, a landslide, a flood, a volcanic eruption, etc. (but don’t feel compelled to stick to the biggies – weathering, anyone?) – some geologic process that you were able to directly observe and experience.

Because of my background, this pretty much means I get to chose from eruptions or earthquakes. I’ve gone on and on about my field area in Guatemala, so I’ll try to venture a little further afield for this Wedge. Two years ago, I went on a field trip with one of my professors and a couple of grad students, where we toured volcanoes in Southern Italy. It was a whirlwind trip – we went all the way down the ‘boot’ and off it completely, visiting Vulcano, Etna and Stromboli before making our way back up to Vesuvius and the calderas around Rome. It was on Stromboli that I had a truly heart-stopping experience.

At one time, hikers had been allowed to go to the top of Stromboli at will, but several accidents prompted the island’s authorities to limit summit visits to scientific teams and specific tour groups. We joined one of these tour groups for a forced-march hike to the summit of Stromboli (an experience that I don’t want to repeat – it would have been much nicer to take a more measured pace, but the tour guides were trying to get us up there in time for sunset so the lava would be glowing). When we reached the top, several of Stromboli’s vents were erupting with small bursts of incandescent lava. This is interpreted to be the result of ‘slugs’ of gas rising to the top of a magma-filled conduit and bursting. When it’s dark, you can see a sort of intermittent spattering from these vents, with bright sprays of hot rock arcing into the air and collecting on the slopes.

The bursts were usually small, but every so often there were larger ones. After about half an hour at the summit watching the lava spatter, the guides were getting ready to start herding us down the slopes of the volcano. And then there was one huge burst that sent lava high over our heads:

(The video above is courtesy of one of my fellow UB graduate students, Sonja Melander, who you can hear exclaiming in excitement when the explosion happens. Thanks for the quick filming, Sonja!)

That ‘fwoom’ sound, and the instant jolt of adrenaline that I felt when I saw the molten lava over my head, will stay with me for a long time. It provoked a very visceral reaction of wanting to get the hell off the top of the volcano, because it wasn’t just erupting in the distance, it was erupting right in front of me. The guides, as well as the rest of the group, seemed to agree with this, because we were on our way downhill pretty quickly after that.

I think this moment was when I really, really realized just how dangerous it can be to get that close to a volcano. Even in my field area, we had always been a relatively safe distance away – but here we were sitting on top of one that was erupting. It was a real kick in the gut, which I view as perfectly healthy and possibly life-saving, because forgetting that you can get hurt or killed by geologic processes is a very, very bad thing to do. Still, it was a particularly thrilling experience, and one that I’m not likely to forget for a long time.

 

I just managed to capture the explosion – one of my last photos from Stromboli’s summit!