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.
Scars of sudden uplift
The cape's gradual rise is punctuated by moments of violent, instantaneous uplift. The Nankai Trough is a seismically active zone, generating massive earthquakes every 100 to 150 years. During these megaquakes, the tectonic plates lurch, and the coastline at Muroto can jump upwards by over a meter in an instant. The 1946 Nankaido earthquake caused an uplift of approximately 1.15 meters. The 1707 Hoei earthquake was even more dramatic, raising the coast by an estimated 1.8 meters.
This pattern of sudden uplift has created one of Muroto's most distinct features: a series of marine terraces. These are flat, bench-like landforms that were once at sea level, carved by wave action. After being hoisted up by an earthquake, a new coastline forms, and the process begins again. The result is a staircase of old coastlines etched into the landscape. The highest and oldest of these terraces at Muroto sits at an elevation of 180 meters and was formed around 125,000 years ago. Walking across these terraces is like walking through the past, with each step up representing another great earthquake in the region's past. The area's geological significance led to its designation as the Muroto UNESCO Global Geopark in 2011.