The Antarctic has one of the longest mountain chains in the world,
the Transantarctic Mountains that extend from the tip of the Antarctic
Peninsula to Cape Adare, a distance of 3000 miles (4800 km). In
many places the chain is mostly buried, but the exposed peaks often
have steep snow free faces.
The Transantarctic Mountains cross the
continent, dividing the ice sheet into two parts.
The larger, eastern part of the ice sheet
rests on land that is mostly above sea level.
The eastern ice sheet has been there for
millions of years.
The smaller, western part is on land that
is mostly below sea level.
rise high above the western shore of McMurdo Sound and are considerably
older and of entirely different geologic origin than the Ross Island
volcanics. Many interpretations of the origins of Antarctica have
resulted from studies in these mountains, particularly where the
rocks are best exposed in the Dry Valleys
area. The high, glacier-mantled peaks of the Royal Society Range
to the south, however, provide a more spectacular backdrop to the
McMurdo area, with continually changing patterns of light and shadow
through the 24-hour austral day bringing out both the range's gently
rounded glacial contours and the abrupt rock faces of the higher
peaks. These mountains, and particularly their Dry Valleys, are
within easy access by helicopter from McMurdo Station, and scientists
have found excellent exposures of various geologic units, which
have helped reveal much about the geologic story of the continent.
During the Cenozoic Era, which began about
65 million years ago, the rocks forming the present Transantarctic
Mountains were uplifted, with the sandstone and dolerite layers
being brought to elevations as high as 4000 meters above sea
The rocks of the Transantarctic
mostly a light, buff-colored sandstone-the Beacon Sandstone of Devonian
or Silurian to Jurassic age (400 to 200 million years old)--with
interlayers of dark-colored dolerite (an igneous rock similar to
basalt), which was injected into the sandstone. These injections
occurred about 170 million years ago, during the Jurassic Period,
when molten rock beneath the Earth's crust forced its way upward
into the sandstones.
Where the dolerite split
apart and flowed between (parallel to) the sandstone layers, they
formed the sills, and where they cut across the sandstone, they
formed the more vertically oriented dikes. Locally where the molten
rock reached the surface, it flowed out as basaltic lava, or in
some cases erupted explosively
as ash and pumice to produce widespread volcanic sediments.
Today these rocks are
impressively displayed in the steep eastern face of the Royal Society
Range and in the peaks of the ice-free "Dry Valleys" area. The ice
sheet of the polar plateau was evidently formed during the Miocene
Epoch (5-24 million years ago) and probably has been in existence
in some form for at least 15 million years.
the Dry Valleys formed?
- As the Transantarctic
Mountains were being uplifted, ice flowing eastward from
the margin of the plateau cut deep valleys into the rocks.
- Thus were formed the valleys which transect
the range and provide the pathways for ice flowing from
- Several of these valleys, however,
were later uplifted higher than others and ceased to be
avenues of glacier flow; these became the "Dry Valleys"
of the present day.
- During the final recession of the ice
sheet, its surface dropped to present levels, which allowed
a local dome to form on the ice surface west of the Dry
- As a result of this configuration,
along with the increased aridity caused by the presence
of the ice sheet, very little ice flowed into the valleys.
- They became dry because ice ablation
(down-melting), caused largely by winds, exceeded ice inflow.