The temperature today is a very pleasant minus 23. And we’ve got continuous, thick cloud cover, which is nice for me as as it puts up the humidity and the chronic dry inflamation in my nose settles. No blood in my nose, sleep stops being restless and disturbed, I swear even food tastes better! And as we walked in poor visibility alongside the power line suspended on wooden posts out to the Seismology shelter, it was quite like being in the hills behind Kingussie in the wintertime, on a flat top following a fence.
We - Summer campaigners Sergio, Roberta, Alessia and I were being taken to visit the seismo cave by the seisomology investigator for the coming winterover, Eric.
The theory behind the seismo cave is that, if you want to measure tremors in the earth – ie earthquakes occurring thousands of kilometers away - you need a really solid substance to put your sensor into that will transmit vibrations very well. And snow of course is not a particularly good substance for that. What’s better is to dig down fifteen metres or so to where the snow has been pressured and aged into ice, the top layer of a single sheet of ice 3.2km thick that makes almost perfect contact with bedrock below. A sensor placed at this depth gets much better coupling and therefore is much more sensitive.
The cave is, for me, one of the last fascinating things to see around here. It is is a kilometer from the station and rarely visited. From a hatch in the floor of the shelter you climb down a series of ladders, platforms and a tunnel until you get down to where the sensor is placed and the temperature is a fairly constant, minus 54. The sensor itself is the same as the ones I helped Pascal and Maxim dig out last year. It’s been a while since I’ve felt cold like this and I had to cover my mouth again, and my gloves made the sharp crackling noises they only make below minus fifty. The walls of the final descent have been made by three containers stacked one on top of the other buried below the surface. The top two are oriented normally with the floor and roof cut off respectively to make a single space, and the one below them placed on end and the doors, now at the top, cut off. So we stood at the bottom of a metal lined shaft that disappeared into darkness above us. The grey metal walls around us seemed solid but distinctly unwelcoming, functional.
The most interesting thing about the Seismo cave, though, is back up near the top, in the long horizontal tunnel cut perhaps four metres below the surface. It has no lining, and so it’s walls are just the snow. Eric shut the hatch and turned off the lights, and we could see the walls and ceiling gowing blue as sunlight filtered down through the snow to us. People before us had written their names in the snow of the tunnel walls and, although practically invisible with the lights on, they stood out clearly a different shade inthe blue glow. Beautiful.
And another surprise for me, as we walked back to the base, it did something I thought it would never do here. It snowed! It’s rare and remarkable, but it’s warm enough and cloudy enough that it could actually snow. A little summer treat.