Shirasaki Ocean Park
The limestone formations at Shirasaki Ocean Park are part of the karst topography of the Shirasaki Coast. Karst is a type of landscape where the dissolving of the bedrock has created sinkholes, sinking streams, caves and springs. It is associated with soluble rock types.
The landscape dates back 250 million years to the Permian Period and contain fossils of ancient marine organisms. At Shirasaki Ocean Park, visitors can view the formations up close, try and identify fossils, and take in the coastline from an observatory. Within the park, there are dive sites, a campground, and a visitor center with a restaurant serving regional fare.
The park’s geological history
The limestone formations are masses of calcium carbonate formed through the accumulation of biological matter, such as shells and coral. They contain fossils of ancient and extinct marine organisms, including crinoids (also known as sea lilies or feather stars) and fusulinids, extinct single-celled organisms with shells. The presence of fusulinids indicates that the karst topography of the park and surrounding coastline is at least 250 million years old, as this is when they are considered to have become extinct. Fusulinida fossils range from several millimeters to 1 centimeter and resemble grains of rice. In horizontal cross-sectional views, they have a spiral form.
Limestone excavation
Signs of Shirasaki Ocean Park’s past are visible in the appearance and form of the limestone outcrops and in several disused caves that remain. The park was a site for limestone excavation between 1897 and 1972. The limestone excavated there was used in construction and as a raw material in the manufacture of fertilizer and cement. For a brief period during World War II, the excavated caves were used as a secret military base for the storage and launch of crewed torpedoes.
Activities and experiences
The lookout built atop the limestone formations on the western perimeter of the park offers a close-up view of a karst environment. The rock has been eroded by the rain, and calcium-tolerant vegetation grows in clusters between jagged ridges. On a clear day, Awaji Island and the eastern coast of Shikoku are sometimes visible across the Kii Strait. Walking the perimeter of the park, with a stop at the lookout, takes about 30 to 60 minutes.
The park is a popular destination for camping and diving. At the campground, there are both tent sites and cabins with kitchens and basic appliances. Staying overnight offers stargazing opportunities, as the remote location and the surrounding limestone formations block light pollution. The park and its surroundings also have some dive sites, including a beginner-friendly beach-entry point and a boat-entry underwater sea cave exclusively for advanced divers. Dives can be arranged through local diving schools.
