Looks like a spectacular nose-over, wheels most likely struck a ditch or sank into soft ground and the momentum at the time sent the rear fuselage soaring until it reached the vertical and…. nothing.
Fabulous. I’ve always had a soft spot for Sunderlands as my late father served his apprenticeship at Short’s in Belfast on them. I have his letter of graduation or whatever it’s called and he always used to fondly recall his time at Short’s.