Wednesday, 20 July 2011
The World of Ice
Living for many years in Alaska, traveling widely in the Arctic, and doing a lot of climbing and glacier travel, I thought I had seen ice. But I was wrong. I had never seen ice until I went to Antarctica for the first time. Ice occurs there on such an enormous scale and in such an immense variety of forms, nowhere else even compares. Antarctica is the world capital of ice and here are a few reasons why:
• The surface of Antarctica is more than 99 percent ice. Only a few scraps of rock peek out from under the ice cap. • The Antarctic ice sheet is up to 15,000 feet thick, averaging about 6,000 feet.
• It stores the equivalent of 60 years of precipitation on Earth. (Or, the flow of the Mississippi River for 46,000 years.) • The weight of that great mass, bearing down on the South Pole, makes the earth slightly pear-shaped.
If you were going to taxonomically classify ice, the first division you would have to make would be between ice formed from salt water and from fresh water; in other words, sea ice and glacier ice. In the Far South, you’re certain to see plenty of both.
Ecologists call the annual formation of sea ice in the South the greatest seasonal event on Earth. In the late fall it is expanding at the rate of 30 square miles per minute. It effectively doubles the size of the continent for the winter.
The ice is essential for all life in the Southern Ocean, and responsible for its phenomenal productivity. The underside of that extensive plain of frozen water is the breeding ground for a staggering population of algae, which sustains krill and the entire food chain. The surface is a resting place, a floating dock, a nursery, and a hunting platform for seals and penguins.
And then, when summer comes, most of it breaks up. It shatters into ice floes, a huge armada of ice. The loose floes often congregate into great packs, roaming around unpredictably at the whim of winds and currents. What was a clear channel one day might be choked with an impassable mass the next.
The ice in a glacier is not just frozen water; it is compressed snowflakes. It results from snow falling and falling and falling, and not melting, for uncounted millennia, until the sheer weight of the mass crushes and metamorphoses the snow at the bottom. The crystals merge and re-form, and a new kind of ice is born. And it starts to move.
All glaciers move, by definition. Because under pressure, ice does a strange thing: it becomes plastic. It squeezes out like toothpaste, it flows downhill. As it moves, it crushes everything in its path. Glaciers are by far the most rapid agent of erosion on earth. They gouge. They grind. They bulldoze. They carve. The spectacular results of this movement are landscapes like South Georgia. A landscape like that also exists under the Antarctic ice sheet, entombed in ice.
In Antarctica, almost none of that ice ever melts. Most of it leaves the continent in the awe-inspiring form of icebergs. Every year, Antarctica shrugs off some 2,014 billion tons of ice.
Not only do icebergs come in a greater variety of shapes than you imagine; actually, the variety is greater than you can imagine. Explosively calved from glaciers, bergs are pinnacled, castellated, jagged, arched, extruded, angular, towering, tunneled, and any number of other things, sometimes all at once.
But the biggest bergs are not calved from glaciers; they are broken off from ice shelves. Ice shelves are amalgamations of glaciers that carry so much impetus that they do not stop when they reach the edge of land, but thrust out over the ocean and cover it under a vast expanse of frozen freshwater.
Tidal changes cause this raft of ice to flex; cracks form, hundreds of miles long; and chunks float away. Some of these chunks, called tabular bergs, rise several hundred feet above the surface and are larger than Belgium. Early explorers often mistook them for islands, because it defies belief that such enormous objects could be floating. To believe them, you must see them.
To see them, and to see the whole range of possibilities of ice, all of the myriad shapes and forms it can assume, you have to come to the world capital, as I finally did. You have to come to Antarctica.
Join Zegrahm for one of two expeditions to Antarctica, South Georgia, and the Falkland Islands departing December 2011 and January 2012 (Kevin is a lecturer on the January departure). ZE