http://www.sciencemag.org/news/2019/12/antarctic-video-reveals-deepest-canyon-earth

SAN FRANCISCO, CALIFORNIA—Despite scientists’ best efforts to probe the land beneath Antarctica’s ice sheets with radar, the continent’s sheer size and remoteness has left many gaps in existing surveys. That changed this week with a new map, called BedMachine Antarctica, released at a meeting of the American Geophysical Union here and published yesterday in Nature Geoscience.

As shown in the video above, the map uses the flow and volume of ice to infer the land below. It has revealed the deepest canyon on Earth’s surface, plunging 3.5 kilometers below sea level under Denman Glacier in East Antarctica, nearly half as deep as Mount Everest is tall.