Even though the rock in this area is, just from the look of it, hard and unyielding, still, in a contest with the water, it does not stand a chance. To begin with, notice the two dark areas just to starboard of the tourist vessel. The are two locations where the water, gradually and over eons is dissolving away the calcium of the calcite rock.|
Eventually what had happened, as the cave became larger was that the unsupported rock's weight became too heavy and collapsed. As a result of these two processes - the dissolving of the calcium, and the collapsing of the rock, - these water channels over a long, long period of time became, what today is called the calanques.
In this photo, just to starboard of our vessel, there are two spots where the Mediterranean water is dissolving the calcite rock and over eons of time is causing caves to form.