For decades satellites crisscrossing over Antarctica have been peering under the ice by bouncing microwave pulses off the rocky surfaces below. In December 2019 scientists finally stitched all these images together. Below Denman Glacier in East Antarctica they discovered what is believed to be the deepest land canyon in the world; 3.5km below sea level, 20 km wide and 100 km long. This geometry exerts influence on the motion and melting of the surrounding glaciers.
(https://bbc.in/2RRFjLT)