Beneath the subglacial lake lies a massive magnetic anomaly larger than the city of Los Angeles, with no confirmed explanation for what could cause such a strong signal under ice.
Goddard Space Flight Center, Public domain, via Wikimedia Commons
A signal beneath the ice
Deep below the East Antarctic Ice Sheet lies Lake Vostok, the largest of the continent's hundreds of subglacial lakes. It is a vast body of freshwater, approximately 250 kilometers long and 50 kilometers wide, comparable in surface area to North America's Lake Ontario. The water has been sealed off from the surface for at least 15 million years, buried under 3,700 to 4,200 meters of glacial ice. The immense pressure from the overlying ice keeps the water liquid at an average temperature of -3°C (27°F).
In this isolated environment, airborne surveys detected a significant geophysical curiosity. On the lake's eastern side, researchers mapped a large magnetic anomaly measuring 105 by 75 kilometers. This feature is a localized disturbance in the Earth's magnetic field with a strength of over 1,000 nanoteslas. Its existence points to a major geological feature in the bedrock, but the exact nature of this feature is a subject of scientific debate. The ice sheet, which is over four kilometers thick in some areas, makes direct investigation exceptionally difficult.
Competing geological theories
Several hypotheses attempt to explain the source of such a strong magnetic signature. One prominent theory suggests the anomaly is caused by a significant thinning of the Earth's crust. Lake Vostok is situated in a tectonic basin, possibly a continental rift valley similar to East Africa's Great Rift Valley. If the crust here is substantially thinner than in surrounding areas, the warmer mantle would be closer to the surface. This could create the observed magnetic variation and would also explain the geothermal heat required to keep the lake from freezing solid at its base.
Another possibility relates to the composition of the rock itself. The anomaly could indicate a large body of iron-rich rock or an unusual concentration of magnetic minerals. This area of Antarctica is part of the ancient East Antarctic Shield, a craton of Precambrian rock. The anomaly marks a boundary between different geologic terranes or crustal blocks that collided and joined hundreds of millions of years ago during the formation of supercontinents. Without drilling through kilometers of ice to collect rock samples, the precise cause of the magnetic anomaly under Lake Vostok is one of Antarctica's most compelling unsolved questions.
💡Fun Facts
Vostok Station, the Russian research base located above the lake, recorded the lowest natural temperature on Earth: −89.2°C (−128.6°F) on July 21, 1983.
The water in Lake Vostok has been isolated from Earth's atmosphere for an estimated 15 million years.
The pressure at the bottom of the lake is over 350 times greater than at sea level, and the water contains 50 times the concentration of dissolved oxygen and nitrogen found in typical freshwater lakes.
Scientists first confirmed the existence of this massive subglacial lake in the mid-1990s using a combination of ice-penetrating radar and seismic surveys.
