Futamata Island is entirely made up of columnar joints of a rock called basalt.
These columnar joints are believed to have been created by submarine volcanoes, which were active when Japan was separating from the continent and the Sea of Japan was growing wider. Futamata Island serves as evidence of this submarine volcanic activity.

Although columnar joints can be seen all over Japan, there are not many places where you can stand on top of their cross-section like you can here. The sight is so spectacular that some people liken it to Giant’s Causeway, a World Heritage Site in Northern Ireland.

The surrounding area has a lot of shoals, so even the local islanders do not often go near it. However, if the tide and wave conditions are just right, this island is definitely worth a visit.

Tamasudare Waterfall, another geopark site located in the Sakata area about 40 km from here, is thought to be columnar joints formed around the same time as Futamata Island.