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Shikotsu-Tōya NP., Hokkaido
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Pyroclastic flows from the caldera-forming eruption reached Sapporo and hardened into Sapporo soft stone. Easy to carve and fire-resistant, it became a widely used building material in the city's Meiji-era streets.
The caldera-forming eruption was not one continuous blast: paleomagnetic directions preserved in its deposits indicate 4 distinct eruptions over 240 ± 70 years, with pauses of decades between some phases.
Shikotsu's prized “chip” is kokanee, a landlocked sockeye introduced from Lake Akan in 1894—not a native fish of the caldera. The local hatchery now supplies its eyed eggs to lakes across Japan.
Shikotsu comes from Ainu si-kot, “large depression,” and once named the wider area and river. In 1805, officials renamed the river Chitose (“thousand years”), inspired by local cranes and because Shikotsu sounded unlucky.
The volcanic story continued after the caldera formed: Tarumae began erupting about 9,000 years ago. After months of rumbling and small eruptions in 1909, its present 450-m-wide lava dome formed in just 3 days.
Only 2 of Lake Shikotsu's roughly 14 fish species are native: amemasu char and hana-kajika sculpin. The local fishery credits waterfalls formed on the outflowing Chitose River with limiting which fish could reach the lake.
At about 360 m deep, Lake Shikotsu's bottom lies roughly 115 m below sea level, even though its surface is 248 m above it. That depth helps explain why this far-north lake rarely freezes.
In Japan's lake-water survey, Shikotsu recorded the lowest COD (chemical oxygen demand) for 11 consecutive years through 2017—a measurable achievement behind the lake's reputation for exceptionally clean water.
