Lesley standing next to the pressure ridge.
This past weekend I was fortunate to catch a tour out to the pressure ridges by Scott Base, the New Zealand research station. People can only explore the pressure ridges with a trained guide because they are very dangerous. Tour guides are trained to spot hazards such as cracks in the ice and to gauge melt water pools on the surface of the ice. A safe route through the ridges is marked by green flags. Unsafe areas are marked with red or black flags. Areas considered to be unsafe are snow bridges over cracks/crevasses and melt pools of unknown depth and bottom integrity.
Green flag marking a safe trail through the pressure ridges. For scale, the flags marking the route are about 5 feet tall, on average.
There were 10 of us on the tour (they keep the size-limit to 12 for safety reasons). We all piled into a van and took a 10-minute drive out to the field. The hike itself was almost two hours long. We walked up one side of the ridges, took a somewhat meandering path through/across the ridges, and then back along the opposite side. On the far side of the ridge (the Ross Ice Shelf side) we were fortunate enough to see a couple of seals lolling about on the ice.
Pressure ridge with western Antarctic mountains in the background
Close up of edge detail on a pressure ridge.
Seal looking very contented on the Ross Ice Shelf.
Pressure ridges are formed where the sea ice on McMurdo sound meets the Ross Ice Shelf. As winter approaches, and extremely cold temperatures arrive, the sea ice begins to reform. Where it is in contact with the ice shelf, water in the crack where the two meet expands as it freezes, and forces itself upward. The motion of the upthrust ice blocks are similar to lithospheric plates being deformed during plate tectonic collisions. The pressure ridges continue to grow throughout the winter. As the height of the austral summer approaches (December 21st) the pressure ridges become unstable was the sea ice begins to melt. The ridges are continually changing with the currents of water flowing along the margin of the ice shelf, surface temperature (if it thaws and refreezes), and wind. The ridges will diminish in size until winter along with its sub-zero temperatures returns again.
Melting edge of a pressure ridge.
Pressure ridges with Mt. Erebus in the background. Mt. Erebus is the most southerly active volcano in the world.
Close up of pressure ridges.
Hiking among these giant, twisted blocks of ice was truly magical. It was yet another amazing view of this beautiful continent.
Looking back toward the pressure ridges from Scott base.