A land born from pressure
At the southeastern tip of Shikoku Island, Muroto Cape juts into the Philippine Sea. This peninsula is the leading edge of a slow-motion geological collision. Just 140 kilometers offshore lies the Nankai Trough, a deep trench where the Philippine Sea Plate dives beneath the Eurasian Plate. This process, called subduction, scrapes sediments and rock off the descending plate and piles them onto the landmass above. Muroto Cape results from this process, a landmass built from this scraped-off material, known as an accretionary complex.
The rocks visible along the cape’s 2.6-kilometer Ransho Boardwalk are part of this complex, some formed on the deep ocean floor as far back as 16 million years ago. The immense, unending pressure from the subducting plate squeezes this rock wedge, forcing the entire peninsula to rise. This continuous uplift occurs at a rate of 1 to 2 millimeters per year, among the fastest in the world. Visitors can see the direct evidence of this movement in the striking layers of rock called turbidites. These are alternating bands of sandstone and mudstone, originally deposited horizontally on the seabed by ancient underwater landslides. Tectonic pressure has since tilted and folded these layers, leaving them exposed along the coast as vertical stripes.