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Antarctica

Geology

Antarctica is considered both an island—because it is surrounded by water—and a continent. The land itself is divided into east and west parts by the Transantarctic Mountains. The larger side, to the east, is located mainly in the eastern longitudes. West Antarctica is actually a group of islands held together by permanent ice.

Almost all of Antarctica is under ice, in some areas by as much as 2 mi (3 km). The ice has an average thickness of about 6,600 ft (2,000 m), which is higher than many mountains in warmer countries. This grand accumulation of ice makes Antarctica the highest continent on Earth, with an average elevation of 7,500 ft (2,286 m).

While the ice is extremely high in elevation, the actual land mass of the continent is, in most places, well below sea level due to the weight of the ice. If all of this ice were to melt, global sea levels would rise by about 200 ft (65 m), flooding the world's major coastal ports and vast areas of low-lying land. Even if only one-tenth of Antarctica's ice were to slide into the sea, sea levels would rise by 20 ft (6 m), severely damaging the world's coastlines.

Under all that ice, the Antarctic continent is made up of mountains. The Transantarctic Mountains are the longest range on the continent, stretching 3,000 mi (4,828 km) from Ross Sea to Weddell Sea. Vinson Massif, at 16,859 ft (5,140 m), is the highest mountain peak. The few areas where mountains peek through the ice are called nunataks.

Among Antarctica's many mountain ranges lie three large, moon-like valleys—the Wright, Taylor, and Victoria Valleys—which are the largest continuous areas of ice-free land on the continent. Known as the "dry valleys," geologists estimate that it has not rained or snowed there for at least one million years. Any falling snow evaporates before it reaches the ground, because the air is so dry from the ceaseless winds and brutally cold temperatures. The dryness also means that nothing decomposes, including seal carcasses found to be more than 1,000 years old. Each valley is 25 mi (40 km) long and 3 mi (5 km) wide and provides rare glimpses of the rocks that form the continent and the Transantarctic Mountains.

Antarctica. Illustration by Hans & Cassidy. Courtesy of Gale Group.




Around several parts of the continent, ice forms vast floating shelves. The largest, known as the Ross Ice Shelf, is about the same size as Texas or Spain. The shelves are fed by glaciers on the continent, so the resulting shelves and icebergs are made up of frozen fresh water. Antarctica hosts the largest glacier on Earth; the Lambert Glacier on the eastern half of the continent is 25 mi (40 km) wide and more than 248 mi (400 km) long.

Gigantic icebergs are a unique feature of Antarctic waters. They are created when huge chunks of ice separate from an ice shelf, a cliff, or glacier in a process known as calving. Icebergs can be amazingly huge; an iceberg measured in 1956 was 208 mi (335 km) long by 60 mi (97 km) wide (larger than some small countries) and was estimated to contain enough fresh water to supply London, England, for 700 years. Only 10-15% of an iceberg normally appears above the water's surface, which can create great dangers to ships traveling in Antarctic waters. As these icebergs break away from the continent, new ice is added to the continent by snowfall.

Icebergs generally flow northward and, if they do not become trapped in a bay or inlet, will reach the Antarctic Convergence, the point in the ocean where cold Antarctic waters meet warmer waters. At this point, ocean currents usually sweep the icebergs from west to east until they melt. An average iceberg will last several years before melting.

Three oceans surround Antarctica—the Atlantic, Pacific, and Indian Oceans. Some oceanographers refer to the parts of these oceans around Antartica as the Southern Ocean. While the saltwater that makes up these oceans does not usually freeze, the air is so cold adjacent to the continent that even the salt and currents cannot keep the water from freezing. In the winter months, in fact, the ice covering the ocean waters may extend over an area almost as large as the continent. This ice forms a solid ring close to the continent and loose chunks at the northern stretches. In October (early spring) as temperatures and strong winds rise, the ice over the oceans breaks up, creating huge icebergs.

Subantarctic islands are widely scattered across the ocean around Antarctica. Some, such as Tristan da Cunha and the Falkland Islands, have human populations that live there year-round. Others, including the Marion Islands, the Crozets and Kerguelen, St. Paul, Amsterdam, Macquarie and Campbell Islands, have small scientific bases. Others are populated only by penguins, seals, and birds.

Strong winds blow constantly against the western shores of most of the northernmost islands, creating some of the stormiest seas in the world. Always wet in the summer, they are blanketed by snow in the winter and grasses in the summer. Further south in the colder subantarctic, the islands are covered with snow for much of the year and may have patches of mosses, lichens, and grasses in the summer. Seals and enormous populations of sea birds, including penguins and petrels, come to the islands' beaches and cliffs to breed in the summer.

The Falkland Islands, which are British Crown colonies, are the largest group of subantarctic islands, lying 300 mi (480 km) east of South America. Two main islands, East and West, have about 400 smaller islets surrounding them. The islands cover 6,200 sq mi (16,000 sq km). Much of the ground is covered with wet, springy turf, overlying thick beds of peat. Primary industries are farming and ranching of cattle and sheep.


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