March 28th - The weather cleared up in the evening, so
Christian, Bruce, Marc and Petter flew out to locate a site and
set up the ice camp. It was windy where they landed and apparently it was quite
a lot of work to get some tents up. The following morning Rachel, Chris, Justin and
myself joined them on the ice. Here's a picture of the sea ice off the north coast of Greenland, and then a picture of the camp as we approached:
They had picked a big multi-year floe – thick ice (3-5m)
that had survived last summer’s melt season. Multi-year ice tends to have much
more topography than first-year ice and this floe had a very varied surface.
There were fairly large pressure ridges surrounding us where the floe had be
crushed up against neighbouring floes, large flatter areas where last summer’s
melt ponds had been, hummocks where last summer’s ridges had been, and
everywhere there were wind blown ice drifts and sastrugi. Sastrugi are wind
blown erosional/depositional features of the surface, and appear quite similar
to ocean waves - 10s of centimetres high and a few meters long - but frozen in
time. This pic that Rach took gives an idea of the topography of the ice floe:
Most places there was a fairly thick snow layer – the
deepest we measured was around 90cm but on average it was maybe 30 or 40cm. The
top layer tended to be a firm crust called a wind slab that was maybe 10cm
thick and made walking around much easier. About the bottom 10cm of the snow
pack tended to be depth hoar – larger crystals formed by sublimation of water
vapour due to the temperature gradient between the top and bottom of the snow
pack. The depth hoar is much more loosely packed than the top layers (often the
crystals aren’t bound at all) and the effect of the hard crust and the greater
amount of air left between the spaces of the depth hoar crystals meant that
your footsteps echoed in the snowpack as you walked around. Here's a close up of the depth hoar crystals, thumb for scale!
The flight out to the sea ice was very exciting: the four of us, plus a load of the scientific equipment all
packed into the back of the Kenn Borek Twin Otter. We had excellent views of
the north Greenland fjords and the sea ice all of the way. When we arrived at
the camp the pilot descended to around maybe 100m and made multiple passes over
the floe to get a better assessment of the landing conditions. The landing
itself was great fun, a bit bouncy but if you put out of your mind the
possibility of the plane falling through the ice then it was calm enough!
No comments:
Post a Comment