Rule of thumb is to stay
at a distance twice the above-water height of the ice. But this is a BIG
calving event and the other rule of thumb kicks in: have the motor
idling.

For these waves, the correct response is to turn and flee. Regular
sea swells are best navigated head-on but these splashes ("seiche" is
the actual term) dissipate quickly as they radiate outward from a
central point. You can essentially outrun the worst of it, and when it
finally catches you it's minor.