Mount Aso

The collapse happened about ninety thousand years ago, after an eruption whose ash reached Hokkaidō. The central Nakadake crater smokes continuously and its acid lake shifts from turquoise to grey with activity; access closes regularly because of gas emissions. Around it, the plateau grasslands have been burned every spring for a thousand years, a controlled fire called noyaki that keeps the forest from returning and maintains the pasture. The Minami-Aso railway crosses the caldera.