I’m guessing its a collapsed lava tube under loose sand.
Actually reminds me of a *cold* solder joint on a circuit board when looked at with a X10 microscope.
In particular the the circular cratering (break) just inside of the outer circumference.
Saw the exact same pattern and look (and I mean exact) when manufacturing didn't use enough heat while soldering.
Cause the type of thermal intermittent that would *eat your lunch* to find :)