Cold fire: in Antarctica's Dry Valleys, the deep chambers and conduits that poured hot lava onto the surface are exposed as nowhere else on Earth

Natural History, July, 2005 by Edmond A. Mathez

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Immediately to the east of the Transantarctic Mountains, the Dry Valleys extend from the polar plateau seaward toward McMurdo Sound, an arm of the Ross Sea, roughly sixty miles away. The reason the valleys exist at all is that the Transantarctic Mountains dam the East Antarctic Ice Sheet, largely preventing it from flowing toward the sea.

At the floor of the valleys the average annual temperature is minus four degrees Fahrenheit (minus twenty degrees Celsius), and the annual snowfall amounts to less than half an inch of equivalent liquid water. The valleys are kept both cold and dry by cold, dense air masses that form on the polar plateau and then tumble down the valleys in what are called katabatic winds, displacing warmer air over McMurdo Sound. As the air descends from the plateau, it warms, amplifying its ability to evaporate moisture. Summer, naturally, is the "warm" season, with temperatures near freezing. In Wright Valley, the summer meltwater collects in the Onyx River, the largest "river" in Antarctica--a rather high flown description for what is hardly more than a trickle in the Antarctic summer and nonexistent the rest of the year.

The lakes scattered throughout the valleys are perennially covered by ice, which is typically ten feet or more thick. They would probably freeze completely were it not for the summer sun that warms them and the ice cover that insulates them during the winter. In fact, the bottom of Lake Vanda, in the heart of Wright Valley, is 226 feet deep; there, the water temperature is a comfortable seventy-nine degrees F (twenty-six degrees C).

Despite being fed by meltwater, most of the lakes are extremely salty. For example, the salinity of Lake Vida, in Victoria Valley, is seven times that of seawater. The basic reason for the high salinity is that the lakes are extremely old--old enough for salt to have built up, even though the waters that enter the lakes bring only minuscule amounts. Fundamentally, the lakes lose water as the top of each lake's ice cover sublimes and is lost to the dry atmosphere. The lost ice is replaced by new ice forming at the bottom of the ice cover. In the process, salt gets left behind in the liquid water.

The glaciers of the Dry Valleys are as exotic as the lakes. The glaciers are said to be "cold-based," which means that, unlike nearly all glaciers outside Antarctica, their bottoms are frozen. That property makes them act idiosyncratically. In places such as Greenland or the high peaks of the Alps, "wet-based" glaciers scrape the bedrock over which they flow, picking up substantial quantities of rocky debris. Where the ice melts, the debris accumulates in ridgelike piles known as moraines. Cold-based glaciers, by contrast, flow mainly by deformation: the ice itself flows like putty, pushed by its own inexorable weight. These glaciers pick up very little debris, cause little erosion, and leave only small moraines. Cold-based glaciers even look different. Instead of being thick rivers of ice full of crevasses, the glaciers within the Dry Valleys are flat and rather smooth; some are even shaped like pancakes. They, too, lose their ice mostly by sublimation, so little or no meltwater issues from them.