Tatami-ishi, Natural monument in Kumejima, Japan
Tatami-ishi is a rock formation along the south coast of Oujima, composed of thousands of geometrically shaped stones. These stone blocks feature pentagonal or hexagonal forms and stretch for about 250 meters along the shoreline.
The stone formation developed during the Miocene period when hot andesitic lava cooled and contracted. This slow cooling process caused natural cracks to form in a regular pattern, shaping the columnar structures visible today.
The name refers to traditional Japanese tatami floor mats, since the flat, uniform stone blocks lie side by side like mats. This connection to household design shows how people have drawn comparisons between natural forms and domestic spaces.
The best time to visit is during low tide, when the stone surfaces are exposed and fully visible. Checking tide schedules before your trip is important, since accessibility depends heavily on daily water levels.
The stones have a natural inward tilt that resembles the slope of a traditional house roof. This unexpected angle may have been caused by uneven lava cooling patterns and adds an extra dimension to the formation's geometry.
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