The Dry Valleys

dry valley region The Dry Valleys of Antarctica get virtually no snowfall or moisture of any kind. Researchers come not only to study one of the world's most delicate, yet simple ecosystems, but also to learn more about the unique geological formations and processes occurring there. From south to north, the principal ice-free valleys include the Taylor, Wright, McKelvey, Balham, Victoria, and Barwick Valleys. Similar but smaller valleys also occur farther south, along the coast of McMurdo Sound and the western margin of Koettlitz Glacier; these include, from south to north, Miers, Marshall, and Garwood Valleys, and the Salmon Stream valley.

Glacier-Scoured
  • Antarctic Dry Valley glaciers are clean and white, with a minimum of rock debris, few crevasses, and near-vertical terminus walls.
  • This is due largely to the relatively dry-based nature of these Antarctic glaciers and the fact that they do not move by slipping and sliding on the underlying bedrock, but more by shearing and plastic flow within the ice itself.
  • Also, at such low temperatures, the ice is not able to incorporate rock debris by the pressure-induced melting common to glaciers in temperate climates.

The major Dry Valleys have certain characteristics in common, and some have unique features. They are generally 5-10 kilometers wide (between ridge crests) and 15-50 kilometers long. Only the Taylor and upper Wright Valleys have glaciers at their heads, which connect with the ice of the polar plateau; the other valleys have either barren upper reaches or small alpine glaciers. Only Taylor Valley exits directly to the sea ice of McMurdo Sound, whereas the others are blocked by the Wilson Glacier.

Several lakes occupy parts of some valley floors, their surfaces frozen most of the year. Some lakes are over 30 meters deep and have perennial ice covers several meters thick.

Lake Vanda, which is typical, has 10 percent dissolved solids content in its lower few meters--three times as saline as sea water-while the upper 50 meters has only 0.1 percent. Scientists have noted high water temperatures in the lakes, with temperature inversions resulting in bottom waters as warm as 25°C (75°F). These high temperatures are due entirely to solar heating of the water through the ice, and not to any heat from rocks at depth beneath the lakes.

Glacier in valleyThe lakes are by far the most interesting and diverse habitats in the Dry Valleys. Organisms are found growing on and in the ice cover, in the water, and on the bottom of the lakes. Exploration of lake bottoms by SCUBA-equipped divers, including core sampling of bottom sediments, have disclosed the existence of algal mats on lake floors; in certain respects these are analogous to some of the Earth's earliest life forms. The mats produce gases which render them buoyant in marginal zones of the lake. There they form columns, which detach from the bottom, rise, and then work their way upward through the surface ice layers-as much as 5 meters thick-after which they dry out and blow away, sometimes to colonize in other locations.

The Labyrinth
  • Immediately below the terminus of the Wright Upper Glacier is a much-dissected area of dolerite bedrock, with numerous deeply cut gullies and coulees, known as the Labyrinth.
  • This rugged topography extends down the valley about 6 kilometers and is believed to be the product of either (1) the large, steady flow of subglacial streams, or (2) a sudden release of extremely large volumes of glacial meltwater that had been trapped beneath the ice cap.
  • Scientists do not all agree on the precise explanation for the apparently catastrophic erosion by water, but the effects are nonetheless startling.

Did You Know?
 
  • As in most regions of perennially frozen ground, permafrost patterns often form in the loose sand and gravel of the Dry Valleys.
  • Ice polygons have diameters of between 10 and 30 meters, and associated frost wedges grow in thickness during each annual cycle.
  • Initially, narrow cracks are formed in the ground, with slumping from the sides.
  • As the wedge width increases, the bordering ground commonly forms a trap for wind-driven sediment.