The pumice cliffs around Dogashima were deposited by subaqueous volcaniclastic currents which came from the explosive eruption of an underwater lava dome.
Tensodo Cave is named after the skylight that was created when the ceiling of the sea cavecollapsed. There is a promenade around the skylight, allowing visitors to viewthe hole from above. Boat cruises regularly travel through the cave as well. It was designated as a in 1935.