20 April 2006: British scientists have discovered rivers the size of the Thames in London flowing hundreds of miles under the Antarctica ice shelf by examining small changes in elevation, observed by ESA’s ERS-2 satellite, in the surface of the oldest, thickest ice in the region.
The finding, which came as a great surprise to the scientists, challenges the widely held assumption that subglacial lakes evolved in isolated conditions for several millions of years and raises the possibility that large floods of water from deep within the ice’s interior may have generated huge floods that reached the ocean in the past and may do so again.
The team found anomalies in the ice-sheet surface elevation using ultra-precise measurements from ERS-2’s radar altimetry and radar interferometry. Close inspection of one anomaly revealed an abrupt fall in ice-surface elevation with a corresponding abrupt rise some 290 kilometres away. The scientists state the only possible explanation for these changes is that a large flow of water was transferred beneath the ice from one subglacial lake into several others.
Radar altimeters – originally designed to measure the sea surface height by sending 1800 separate radar pulses down to Earth per second then recording how long their echoes take to bounce back – have been highly successful in measuring large-scale ice surface changes over time. Radar interferometry, known as InSAR, is used to precisely measure the spatial pattern of the changes. Together, they form a powerful ‘instrument’ to investigate the physical causes of changes in the ice surface.
According to Prof. Wingham, Director of the Centre for Polar Observation and Modelling (CPOM), both sensors were essential for the study. “With radar altimetry we can tell how much the lake levels fell and rose, and that it occurred between late 1996 and early 1998, but we cannot determine the area, which is vital for investigating the physics of the flood because we need to know the volume of water involved.
Several groups, under the umbrella of the Scientific Committee on Antarctic Research (SCAR), are currently investigating the prospect of drilling down to subglacial Antarctic lakes where ancient life is thought to exist. However, in light of this discovery, these plans may need to be reviewed.