• NASA scientists have discovered a gigantic cavity, almost 300 metres tall, growing at the bottom of the Thwaites Glacier in West Antarctica, indicating rapid decay of the ice sheet and acceleration in global sea levels due to climate change.
  • The findings highlight the need for detailed observations of Antarctic glaciers’ undersides in calculating how fast sea levels will rise in response to warming.
  • Researchers expected to find some gaps between ice and bedrock at Thwaites’ bottom where ocean water could flow in and melt the glacier from below.
  • The size and explosive growth rate of the newfound hole, however, surprised them.
  • It is big enough to have contained 14 billion tonnes of ice, and most of that ice melted over the last three years.
  • We have suspected for years that Thwaites was not tightly attached to the bedrock beneath it,”
  • Thanks to a new generation of satellites, we can finally see the detail.
  • The cavity was revealed by ice-penetrating radar in NASA’s Operation IceBridge, an airborne campaign beginning in 2010 that studies connections between the polar regions and the global climate.
  • The researchers also used data from a constellation of Italian and German space-borne synthetic aperture radars.
  • These very high-resolution data can be processed by a technique called radar interferometry to reveal how the ground surface below has moved between images.
  • (The size of) a cavity under a glacier plays an important role in melting.
  • As more heat and water get under the glacier, it melts faster.
  • Thwaites Glacier is currently responsible for about 4% of global sea level rise.
  • It holds enough ice to raise the world ocean a little over 65 centimetres and backstops neighbouring glaciers that would raise sea levels an additional 2.4 metres if all the ice were lost, they said.
  • The huge cavity is under the main trunk of the glacier on its western side — the side farther from the West Antarctic Peninsula.
  • In this region, as the tide rises and falls, the grounding line retreats and advances across a zone of about three to five kilometres.
  • The glacier has been coming unstuck from a ridge in the bedrock at a steady rate of about 0.6 to 0.8 kilometres a year since 1992.
  • Despite this stable rate of grounding-line retreat, the melt rate on this side of the glacier is extremely high
  • On the eastern side of the glacier, the grounding-line retreat proceeds through small channels, maybe a kilometer wide, like fingers reaching beneath the glacier to melt it from below.
  • In that region, the rate of grounding-line retreat doubled from about 0.6 kilometres a year from 1992 to 2011 to 1.2 km a year from 2011 to 2017
  • Even with this accelerating retreat, however, melt rates on this side of the glacier are lower than on the western side.