Friday, January 22, 2010
Ice Cream Castles in the Air
Several days ago an iceberg that had been floating in the harbor for about a week suddenly “turtled,” which is to say, rolled over. I was upstairs in the gym and happened to be looking out the glass door. It had just rolled over and there were big chunks of ice falling off of it into the water, and circle of small pieces of floating ice was rapidly expanding around it. The (former) underside was deeply furrowed and in places pockmarked like a golfball. This event prompted me to write about a topic I have been looking forward to sharing with you: icebergs.
The first evidence of Antarctica that I saw was in the Drake Passage, with blue water in every direction. A large iceberg was visible about 10 miles away. It was a vision, proof of the frozen land ahead, but seemingly out of place as I stood on the deck in a T-shirt. There were others that we saw in the open ocean, and there was something both dignified and poignant about them. They move, but so slowly that you only know by comparing their position to that of several minutes before. They are so far from the glacier or ice shelf that they came from, alone and proceeding to a certain death, but still they move northward steadily, and seemingly confidently.
The tabular icebergs that I saw at sea were much bigger than those that hang around the harbor and inlets here at Palmer station. Each one has a unique shape and moves around, giving it a personality, a spirit. Icebergs are like clouds: they can be castles, mountains, amphitheaters, turtles, pulpits, hearts, tunnels. One was visible from our window, and we nicknamed it “the Three Musketeers” because of its three spires. It moved a little bit every day, sometimes up the inlet and sometimes down. Then last week a big wind blew the Three Musketeers out to sea. I wish it well in its future endeavors.
I frequently hear the booming sound of the glacier calving. In fact it’s so low that it is more felt than heard, and I look over to see a small trickle of ice falling from the wall. However there is nothing to mark scale on the wall of ice, so actually the “trickle” is not small at all. After a significant calving event, bits of floating brash ice 1-5ft long spread out across the harbor. When the small pieces of ice cover the water completely, the surface hardly rises and falls at all with the waves. Instead, the waves are represented by the pieces of ice rhythmically coming closer together and then separating, like a slow-motion earthquake wave.
Sometimes the floating ice melts into fanciful shapes. My favorites are the ones shaped like the little brown mushrooms you find in the forest, making me think of Alice in Wonderland. Spindles of ice with tilted caps reach up from a mass floating underwater. This shape seems so unusual that I was surprised to see so many, and in all different sizes. I thought about the melting process, and I have a hypothesis of how so many icebergs are shaped like mushrooms. Say an iceberg starts with fairly flat surface. Remember that 89% of it is still underwater due to the density difference between ice and water so most of its mass is submerged. Wave action begins to erode the ice at the water line. Then eventually the berg shifts balance and tips so that the once-flat top is now tilted. The place that was carved by the waves is now exposed to the sun, which continues to melt the ice. Eventually all the ice above the waterline melts away except a thin stalk supporting the original surface, which is now tilted. This hypothesis is just the product of musing while I was trawling for plankton, but the shape seems to be common enough that there must be some explanation even if this isn’t the right one.
Well enough for now. In other news, a penguin jumped in our boat yesterday. It rocketed over the back of the boat, bounced in the bottom and then over the starboard pontoon and back into the water, all in less than two seconds. I think it was a mistake!