Mount Aso Caldera – Aso, Japan - Atlas Obscura
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Aso, Japan

Mount Aso Caldera

The largest volcanic caldera in Japan holds an entire city in its maw. 

Accessed by an aerial tramway, the lake at the top of Mount Naka is a thing to behold: smoking, steaming and churning. Mt. Naka, or Nakadake, is an active volcano which has grown, along with 16 other currently inactive peaks, inside one of the world’s largest volcano craters, itself the creation of a volcanic eruption 90,000–300,000 years ago.

Each year, the community sets the mountainside ablaze in the Aso Fire Festival in March, creating the shape of the kanji ‘hi’ (or “fire”) in flames. The ritual is known as noyaki is ceremonial but also practical: the flames keep the native grasses healthy over time.

The entire city of Aso is contained within the massive caldera which is about 80 miles in circumference. Natural hot springs and a geothermal plant also get their energy from the volcano. Visitors flock to the top of Mt. Naka-Dake for the view of the inside of the volcanic crater.

Since the volcano is active, and has been known to take lives without warning, concrete bunkers (of questionable functionality) sit near the crater, just in case.