Last week I joked with a new student as he got into our 1991 Dodge 150 pick-up that this was our helicopter. The handbrake doesn't work, it has no spare tyre, no four-wheel drive, one functioning seatbelt, a leaking radiator and when the rain leaks in through the gap where the door won't close properly it smells like sweaty dogs. Nevertheless, it manages to trudge over the 4000 m pass in Nevado, to traverse streams and to take us to within reasonable walking distance of the things that we want to do. Yes, things are a bit different in Colima.Or they were up until now. The university may not have any cash, but the Protección Civil agency of Jalisco state has plenty and they spend it wisely to fund their boys-with-cool-toys lifestyle. They have a fleet of trucks, cars and speedboats decked out in orange and blue in which they race around the state, sirens blazing, boots shining and emblazoned uniforms looking smart and macho. They also have an 800hp Eurocopter. Today they were using it to check some instruments that they have located on the side of the volcano. When we have been there on foot it is has been a journey of over 6 hours of driving and hiking. In the helicopter it takes 15 minutes.
Protección Civil were interested in reports from their previous flight that there was a new dome growing in the crater of the volcano. A lava dome is a small hill of lava, with a hot interior and a broken, rocky crust. It forms when the lava comes out too cool and viscous to flow away to the side. For as long as I have been here, the volcano has been exploding multiple times per day. Each time it throws out some gravel and ash which was gradually filling the crater like a bucket of sand. But last week they had seen a rocky mound in the centre. They wanted us to take up our thermal camera to see if it was hot or not. If it was hot, it could suggest that it was a dome. As my boss couldn't make it today, I was the lucky one that go to go. Futhermore, as the thermal camera doesn't work behind glass, I got to ride shotgun where the only openable window was.
Clouds came and went from the volcano's summit as climbed towards it. The landscape surrounding the volcano consists of a large flat plain cut by deep ravines (barrancas) and flush with crops of sugar cane, agave cactus and maize. During the wait to fly I had explained to the mayor of the local town, to the civil protection officers and to the armed police that had turned out to protect the helicopter that the plains had formed when the whole volcano had collapsed about 4000 years ago. I even got to use the old shake-up-the-bottle-of-coke routine to demonstrate how the pressure of gases exsolved from the magma drives the expulsion of material from the crater.
As we closed on the mountain we crossed barrancas in the thick tropical forest which had been filled by both lava flows (the upper one, 1975) and pyroclastic flows (the lower one, 2005). In recent years the volcano has switched from producing one to the other. A machete is no longer a required field-tool when you travel by air. The crusty viscous lava flow deposit appears thicker and more rugged than the stream of rubble that made up the pyroclastic flow.
Climbing further we entered the clouds. I was changing the settings on the thermal camera as we rose through them then began to hover. I got a bit of a shock when the clouds cleared and I saw the crater through the glass panel at my feet. It was extremely close. On the crater rim the fumaroles were steaming strongly and had stained the rocks with sulphurous yellow. All year I have watched ash bursting explosively from this crater and now I was about 300 m directly above it. It felt exactly like looking down the barrel of a gun. Through the steam and the clouds I could just about make out some forms in the sandy landscape. I held the thermal camera to the open window.
In the bottom of the crater we saw the rocky lump. It was low and grey and flattish with a blocky and broken up surface. It is about 60-80 m wide and less than 20 m tall. It wasn't steaming and it didn't look hot, but on the thermal images it showed up white and the maximum temperature indicator jumped about within it, reading temperatures in the cracks of 220C, 280C, even 380C. The crater rim was defined by the fumaroles, which we have been monitoring from afar; these were a frigid 60C in comparison. The most exciting thing about our rocky patch was that it appeared clean - everything else nearby is draped in grit. This, combined with the high temperatures is a pretty strong indication that it is indeed a dome.
I don't really know what will happen now. I was quite surprised to see the dome there, and had you asked me this morning, I would have bet my last quesadilla that the crater would have been empty. The fumarole temperatures have been dropping, we aren't detecting much gas and the seismicity has been relatively low. It seems like I need to rethink what I thought that I knew about the volcano. The only indication is that recently even small explosions have been lobbing hot scree over the crater wall. Perhaps these were parts of the dome that were caught up in explosions from the hot-looking hole on the western (left-hand side) edge.
Some previous domes have quickly grown to overflow from the crater producing lava flows and rockfalls. Others have grown slowly over periods of years. Some fat, lazy, photogenic lava flow would bring the tourists flocking. The bottom line is that domes = ascending magma and ascending magma = action. The most direct way to return from a dome-inside-the-crater scenario back to a no-dome-inside-the-crater scenario involves blasting hot ash and boulders many kilometres into the sky and sending pyroclastic flows down the barrancas. The neighbouring populations would then potentially be in a lot of danger. 'Potentially' is the keyword here, as on the other hand the volcano might just do nothing and go back to the old routine. Nobody actually knows, but many people will be very keen to find out as much as they can.
Whatever happens, I'll try to keep things up to date on this page. Watch this space.
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