Antarctica, a continent almost entirely covered by ice, possesses a hydrological system that defies the conventional understanding of rivers. While the vast majority of its water is locked within the massive ice sheet, liquid water does flow across the landscape and beneath the ice in highly unusual forms. These flows are sustained by unique geological and atmospheric conditions that allow water to remain liquid despite the extreme polar cold. Understanding these rare water bodies is important for scientists studying the continent’s ice dynamics and climate history.
Seasonal Surface Rivers
The most visible, yet temporary, form of river flow occurs during the brief austral summer, typically from December to February. Solar radiation, rather than warm air temperature, provides the energy needed to melt ice and snow, creating meltwater channels that flow across the surface of ice-free land. These flows are highly responsive to daily temperature fluctuations and are considered seasonal streams rather than permanent rivers.
The most prominent example is the Onyx River, located in the McMurdo Dry Valleys of Victoria Land. Stretching approximately 32 kilometers, it is the longest surface meltwater stream on the continent. The Onyx River originates from the melt of the Lower Wright Glacier and flows inland, carrying glacial meltwater for about six to eight weeks.
This surface flow is ephemeral and highly variable, with water volume depending significantly on the intensity of solar energy. The water eventually terminates in Lake Vanda, an enclosed body of water, meaning the flow never reaches the Southern Ocean. Long-term monitoring since 1969 has revealed shifts toward longer flow seasons, though the total annual discharge volume has shown a decreasing trend in some locations.
Subglacial Water Flow
A far more extensive and complex system of liquid water exists hidden kilometers beneath the Antarctic Ice Sheet. This vast network includes interconnected rivers and over 675 identified subglacial lakes, with water flowing between them under immense pressure. The existence of liquid water in this environment is sustained by two primary mechanisms working in conjunction.
One mechanism is the pressure melting effect, where the tremendous weight of the overlying ice sheet, which can be up to 4,000 meters thick, lowers the melting point of ice. This force allows ice to liquefy at temperatures several degrees below zero, such as the calculated -3.06°C at the depth of the largest subglacial lake, Lake Vostok. The second factor is geothermal heat flux, the natural heat radiating upward from the Earth’s interior, which contributes to basal melting.
Scientists first identified these hidden systems using airborne radio-echo sounding (RES) technology beginning in the 1970s, which maps the contrast between ice and water. This radar mapping shows that the subglacial environment is a dynamic, active hydrological system. Some subglacial lakes are known to fill and drain rapidly, causing measurable changes in the height and movement of the ice sheet above them.
Destinations of Antarctic Water
The liquid water produced by both surface and basal melting follows distinct pathways to its ultimate destination. Seasonal surface meltwater typically flows into endorheic basins, filling lakes like Lake Vanda. If this meltwater does not reach an enclosed lake or the ocean, it will eventually refreeze back into the ice sheet structure when the summer season ends.
The permanent subglacial water system has a much larger impact on global ocean systems. This water often pools in reservoirs, with subglacial lakes serving as temporary storage and transfer points. From these lakes, the water moves through a network of channels, sometimes over hundreds of kilometers, before reaching the coast.
The final destination for much of the subglacial flow is the Southern Ocean, where the pressurized rivers vent beneath floating ice shelves. This discharge of freshwater occurs near the grounding line, where the ice sheet meets the sea. For instance, a network of lakes beneath the Thwaites Glacier released an estimated seven cubic kilometers of freshwater into the Amundsen Sea in 2013. The influx of buoyant, fresh meltwater into the ocean cavity can accelerate the melting of the ice shelf base, influencing the stability and flow rate of the entire ice sheet.