Mt. Iwadosan was born by underwater eruption.
You can observe the deposits made by phreatomagmatic eruptions, which occurred due to the direct contact of hot magma and cold seawater.
Since it is located on the land jutting out into the sea, it is subjected to continual coastal erosion. It has been also increasingly weathered. The trail route to the Anakannon cave was collapsed in 2019 and is now closed.