Pit craters

Pit craters are circular depressions up to one hundred metres deep, which at first glance look like a classic volcanic crater. But, unlike the latter, there has never been any eruptive activity in the pit craters.
They are formed by sinking due to a movement of magma in the area below. As a result, a small gap is created below which is filled by the sinking and the consequent formation of the pit crater.