Although he is sticking safely near the rocks of the South Wall, Stephen can "see the tide flowing quickly in on all sides, sheeting the lows of sand quickly, shellcocoacoloured," and he is acutely aware of the danger posed by the incoming seawater.
In the blog accompanying his photo of a warning sign at right, Dara Connolly writes, "This warning is no joke, and I didn’t take it lightly. I am no stranger to the risks of incoming tide, having got into serious trouble in the past and been lucky to survive. On this occasion I made sure that when the tide turned, we would be on our way back, even if we had not reached the edge of the sand." Beyond the sign, "the sea had retreated very far, almost out of sight. The two ships visible on the horizon look odd, almost as if they are sailing across the sand." But even though the sands stretch on for miles, their shellcocoacoloured shelf will be covered very quickly, and irregularly, by the incoming tide, threatening to trap walkers on rapidly shrinking islands.
Despite his safe position near the boulders, then, the tidal flats give Stephen ample opportunity to contemplate his morbid fear of drowning.