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Shikotsu-Tōya NP., Hokkaido
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Toya’s caldera-forming eruption, about 110,000 years ago, was among the largest in an island-arc setting—one of only 9 such eruptions in Japan in the past 120,000 years. Its crater later filled to form the lake.
The caldera wall shapes local flavor: around Lake Toya’s north and west shores, it blocks harsh late-day sun, helping red shiso retain its vivid color and aroma. The herb is now one of Toyako’s signature crops.
Only 4 Nakajima islands break the lake’s surface; geologists have mapped 11 volcanic bodies above and below water, including lava domes, a buried dome and a tuff cone made by explosive magma-water encounters.
In Ainu, to-ya means “lake shore.” Ainu scholar Mashiho Chiri also recorded that the lake itself was called simply to, “lake”—a name rooted in the shoreline, not volcanic geology.
Three sika deer brought to Nakajima in the 1950s–60s escaped and multiplied on the isolated island. Today, fewer than 30% of plant species recorded in 1977 are confirmed; a restoration plan aims to revive the forest.
Ash from Toya’s eruption spread across northern Japan. Its distinctive layer now serves as a geological bookmark: researchers match it in distant deposits to date and correlate events far beyond Hokkaido.
Geologists divided Toya’s 80–100 m-thick pyroclastic deposit into 6 units with no break between them, reading one continuous eruption in the layers. Caldera collapse began in unit 4 and reached its climax in unit 5.
Toya’s kokanee, known locally as “chip,” usually measure 20–30 cm, but the fishery cooperative records a 52 cm specimen. They feed mainly on animal plankton and sometimes even eat smelt.
Toya’s kokanee fishery grew from hatchery work: fishing associations in Abuta and Usu formed in 1917, then united as the Lake Toya Fishery Cooperative in 1924—a local institution still managing and selling lake fish.
In an Ainu account recorded by Ainu scholar Mashiho Chiri, Lake Toya’s master appears as a winged serpent swimming amid whitecaps—a vivid lake legend, not a geological explanation for the caldera.
The caldera also sets Toya’s celery calendar: farmers plant at different heights—from lakeshore to mid-slope to upland—so harvests are staggered and the season lasts longer.
