A photograph made available by Nasa shows an oblique view of a huge rift in the Larsen C ice shelf.
A giant iceberg, with an area equivalent to Trinidad and Tobago, is poised to break off from the Antarctic shelf.
A thread of just 20km of ice is now preventing the 5,000 sq km mass from floating away, following the sudden expansion last month of a rift that has been steadily growing for more than a decade.
Icebridge, an airborne survey of polar ice, completed an eighth consecutive Antarctic deployment in November 2016 when this photograph was taken.
Photograph: John Sonntag/IceBridge/Nasa/EPA