Pressure Ridges

In a prior blog post, I had made mention of the pressure ridges that form in the sea. Because the sea ice is always moving, the pressure ridges form when the sea ice near land slows down and starts to get squeezed. This squeezing of the ice leads to ridges and crests that form in the ice. If the pressure continues, these ridges eventually buckle and break, thrusting ice upwards along the ruptures. Normally these areas can be dangerous to be near (for obvious reasons), but the mountaineers from the New Zealand Base (Scott Base, which is only a mile or so from McMurdo) scout out and flag paths that you can walk on next to these pressure ridges. Personnel from McMurdo then offer tours to people and take them out for an up-close experience with the ridges. These tours are very popular and fill up quickly so it can be hard to get on them. I managed to catch the signup list right after they posted it this past weekend and signed up for the Tuesday night tour. The group met after dinner and we took a shuttle over to Scott Base and then walked out onto the ice from there. 

Pressure ridge in the ice with Observation Hill in the background. For reference, McMurdo resides on the opposite side of Observation Hill and Scott Base is just outside of the picture to the left.

Once the pressure ridges fractured, all sorts of strange formations occurred as the ice breaks upwards. Some ridges break open with giant cracks running through them. The heights of the ridges varied from a couple feet high to six to seven feet high.

Cracks in one of the ruptured pressure ridges. The blue color was very striking in many of the formations.

Several pressure ridges can be seen in the foreground, with one further back fully rupturing. Castle Rock can be seen in the distance.

Another feature that makes the pressure ridges (and sea ice in general) dangerous are the melt pools that can form. Melt pools are pools of water on top of the ice that can become invisible if the top ices over and snow blows over the top. One minute you can be walking on solid ice and the next you are going for an unanticipated swim (or at least have soaked your foot really good).

On the left side in the foreground is one of the pressure ridges. To the right and just below center you can see one of the melt pools that has formed next to the ridge. The glacier covered mountain in the background is Mount Terror.

Because of the ice fractures, some of which are open down to the ocean, another common site was seals (or as the people down here call them, sea slugs). This afforded me the opportunity to really put my telephoto lens to work after getting it back from being repaired. Most of the following pictures were shot with from that lens (my 80-400 for those photographers out there who are curious).

This seal (aka sea slug) had its belly covered in snow. It rolled on its side to lazily look at us.

More seals laying around the fractured ice.

This one was bashful and kept looking away as soon as I was ready to take the picture. I managed to get this one shot of her/him when s/he looked back.

 Below are a few examples of some of the other crazy ice formations we walked past.

A seal, some broken sea ice and Mount Erebus steaming in the background.

This formation was one of the tallest we walked past. It was at least 15 feet tall.

This formation was mostly by itself and looked like a whale about to breach.

As the tour progressed, the wind picked up to the point it was blowing snow around. We stopped towards the end of the tour to take a picture of the sun shining through a thinner piece of ice. You can see the snow blowing over the top of it.

Thin sea ice with snow blowing over the top of it.

I was thankful to get out on this tour as this was the last tour they have been able to do this week. The weather changed yesterday and Antarctica has shown us what it is capable of. It started snowing yesterday afternoon with temperatures around 18F (-8C) and sustained winds of 25 knots gusting above 30 with snow and blowing snow. McMurdo is currently under travel restrictions and no one is allowed to leave until the storm is over. At least 4-5 inches of snow has fallen (an impressive amount given the temperature) and many of the old-timers have commented that this is one of the worst storms they have witnessed here this time of year. It's expected to last through the day tomorrow at least with the winds to pick up more overnight. There hasn't been a flight from Christchurch to McMurdo in a week now (mostly due to forecasted bad weather). South Pole Station has similarly had bad weather that has prevented flights between McMurdo and South Pole for over a week now. We had noticed in recent days that the galley was still serving fresh salad and veggies ("freshies" as they are called). Rumor has it that because the flights haven't been able to get to South Pole, they are giving us the freshies bound for the South Pole so they don't go bad. No one here is complaining, but if the rumor is true, hopefully the Polies don't find out!

Mark and I are starting to run out of things to do and need to get out in the field soon to finish deployments or we risk getting delayed in coming back. I suspect we'll be working this Sunday and, naturally, the forecast has that day being the nicest of the days in the near term. The next week and a half are going to be busy, let's hope the weather starts cooperating again!