The massive Antarctic Ice Sheet rests upon a true continental landmass, unlike the Arctic, which is primarily a frozen ocean. The Antarctic Ice Sheet covers a bedrock continent roughly the size of the United States and Mexico combined. This underlying land is hidden across approximately 98% of the continent, with the ice averaging 1.6 kilometers (1 mile) in thickness and reaching nearly 4.8 kilometers (3 miles) deep in some areas. Far from being a flat plain, this concealed landscape features mountain ranges, deep valleys, and vast subterranean lakes that scientists are only now beginning to map.
The Physical Structure: Continent Versus Ice Sheet
Antarctica is a continent of solid bedrock that has been heavily depressed by the immense weight of the overlying ice. The continent is divided into two major regions by the Transantarctic Mountains, which extend for about 3,500 kilometers (2,200 miles). This range separates East Antarctica from West Antarctica, and the two halves have distinctly different geological histories and structures.
East Antarctica, sometimes called Greater Antarctica, is the larger and more stable region. It consists of an ancient continental shield, or craton, made of igneous and metamorphic rocks that are billions of years old. The bedrock here is generally situated above sea level, though the ice sheet’s weight has caused some central areas to be deeply depressed.
West Antarctica is a much smaller region, essentially a collection of merged continental blocks. Much of its bedrock lies well below sea level, a condition known as a marine ice sheet. If the ice were removed, this western region would largely resemble an archipelago of islands separated by ocean.
Mapping the Subglacial Landscape
Scientists cannot directly observe the bedrock beneath the ice, so they rely on sophisticated geophysical techniques to create a three-dimensional map of the hidden land.
Ice-Penetrating Radar
The primary method used is ice-penetrating radar, also known as radio-echo sounding, which involves transmitting radio waves down through the ice. The radar waves reflect off the boundary between the base of the ice and the underlying bedrock. This allows researchers to calculate the depth and shape of the land surface.
Gravity and Seismic Surveys
Additional information is gathered through gravity and seismic surveys. Gravity measurements detect subtle variations in the Earth’s gravitational field. Denser geological features, like buried mountain ranges, exert a greater gravitational pull, while deep trenches or basins show a weaker pull, revealing the underlying structure. Seismic sounding uses controlled explosions or vibrations to send sound waves deep into the Earth. By analyzing how these waves are reflected and refracted, scientists determine the depth, composition, and density of the subglacial terrain. Combining data from radar, gravity, and seismic methods provides a comprehensive picture of the unseen continent.
The Topography Beneath the Ice
The subglacial landscape is complex, featuring geographical features comparable in scale to those found on other continents. One significant discovery is the Gamburtsev Subglacial Mountains, located beneath the thickest part of the East Antarctic Ice Sheet. This vast range is approximately 1,200 kilometers (750 miles) long, with peaks reaching up to 2,700 meters (8,900 feet) high, similar in size to the European Alps.
This hidden terrain also includes deep troughs and basins, with some areas of bedrock depressed far below sea level. The lowest point on any continental plate is found beneath the Denman Glacier in East Antarctica, where the bedrock floor plunges to about 3,500 meters (11,482 feet) below sea level. This profound depth results from the massive ice load forcing the crust downward over millions of years.
A vast network of hundreds of subglacial lakes and interconnected water systems exists beneath the ice. The most famous of these is Lake Vostok, which is one of the largest lakes in the world, lying beneath four kilometers of ice. These lakes are kept liquid by geothermal heat rising from the Earth’s interior and the insulating pressure of the overlying ice.
Geological Implications of Ice Removal
The sheer mass of the Antarctic Ice Sheet has caused the continental crust to sink into the Earth’s mantle, a process known as isostatic depression. If the ice were to melt, the land would slowly begin to rise again in a process called isostatic rebound. This uplift occurs as the viscous mantle material flows back beneath the relieved crust.
The rate of this rebound is not instantaneous, but it is happening at a measurable pace in areas where ice has already been lost. In some regions, the uplift is measured at up to 5 centimeters (nearly 2 inches) per year. This upward bounce of the land would significantly reduce the water depth in coastal areas, which could potentially slow the retreat of remaining marine ice sheets.
However, the rebound would be insufficient to raise all of the submerged bedrock above sea level. Since much of West Antarctica’s bedrock is already thousands of meters below sea level, a significant portion of this region would remain underwater even after full rebound. The removal of the ice would ultimately transform the continent into a smaller landmass surrounded by a shallow, island-dotted sea.