Russell Glacier, Greenland
Each ridge on the channel sides represents about a days worth of melt from the water flow. For scale, the channel is about 8-10 m deep here. Upstream lies a huge lake ~3km^2 in a depression on the ice-sheet surface. As the stream keeps eroding down, it would eventually cause the lake to drain rapidly within a matter of hours. The stream eventually flows to a huge moulin, where it then likely reaches the bed of the ice sheet, ~1000 m below.
Lake-drainage events like these are common, and are currently being studied by scientists at Aberystwyth and Swansea Universities.