Sand

I had another real quick dream this morning (I think).
There were several people from my martial arts there. There was this big ocean-like area, but instead of water it was filled with sand. The sand moved like an ocean with waves. When a big wave would come, then after the wave a big depression would be left in the sand. Like after a real wave in the ocean, but instead of lasting for a few seconds the depression was permanent - until another big wave came later.

The only real detailed thing I remember is that a big tidal wave pulled CM out to sea and we were all trying to pull her back in. Her husband, AM, was trying to get her and I was pulling on her arm. But she was trapped under the sand because the tidal wave had covered her up with sand. And she was suffocating because she was under the sand.