I felt is if this was one of those plots that could've been much better, but when given, we get utter crap.
The Sand draws inspiration from an awful lot of movies, the most obvious of which is Blood Beach 1980 , which bore the memorable tag-line 'Just when you thought it was safe to go back in the water - you can't get to it.
You will enjoy this guilty pleasure but be warned it goes from tense moment to tense moment and try not to let to logic get in the way.
No wonder it glows.
In the morning, the only people left are those that weren't touching the sand.
Finally for the SyFy vibed' part of the film.