Cliff face breaks off near climbers - GIF

[Saltfever]

Using the video timeline, or a stop watch, the time is about 14 seconds. The rock had just separated when the video starts so using that as a starting point the smallest rocks hit the water 14 seconds later. Adding 2 seconds gives a height of 3,100 ft and a terminal velocity of about 307 mph (450ft/sec). As Marv indicated density affects velocity in air. While a sky diver is usually 125-150 mph those rocks infer a greater height due to their speed.