This is called a sand art, however, on a much larger scale, and is made at the seashore itself - the primal source of sand used in sand artworks.
The sand art, which Peter Donnelly does on the seashore is actually racing against the tides, and must be done within 3 hours, or else, the shifting tides would wipe it out. It is also said that Peter Donnelly can't view his own artwork at ground level, and he does not use visual aids or plotting tools.
On the video, Donnelly also mentions his experience with a Christian who told him he was never going to get to heaven. "You're going the wrong way, you'll do a much greater work if you're a Christian!" a Christian church goer told him. Apparently, the Christian regarded his work using mounted power shells as an evil number, and wiped out it entirely with his feet. Donnelly later on realizes that the misguided action of that Christian was creating artwork on itself, unfortunately, he wasn't able to get a photo of the sand art.
Well, I guess whatever you do, regardless whether it is reckless or not, is an art when it comes to Donnelly's eyes.