Pockmark (geology)

Pockmarks are crater-like depressions at the bottom of seas or lakes with 10-700 meters in diameter and up to 45 meters deep, in individual cases up to 1.5 kilometers in diameter and more than 150 meters deep. Pockmarks caused by escape of gases or liquids, natural disasters, geological or human activity.

Perhaps the greatest significance could play pockmarks as earthquake indicators, by some, a few days be active before big quake.