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Shikotsu-Tōya NP., Hokkaido
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In 2000, Usu erupted at its foot beside homes and a national highway. Early warnings helped move about 16,000 people to safety before the eruption; nobody died.
Usu’s largest recorded pyroclastic flow swept down in 1822 and burned the coastal Abuta settlement, near today’s Irie. Historical disaster records also count 1,437 horses dead or missing.
Usu’s biggest eruption in the historical record expelled an estimated 2.78 km³ of material in 1663. Its plume was visible from Tsugaru, and the air blast was felt far away in Shōnai.
After Usu erupted in 1910, new hot springs appeared beside Lake Tōya. Those volcanic waters became the starting point for Tōyako Onsen, now a familiar part of local life.
One local pizzeria cooks in a stone oven made from Mount Usu lava, and its seasonal menu has featured pizza topped with sweet corn grown in Usu itself—a very literal taste of the volcano’s neighborhood.
The place-name Usu comes from Ainu words for a bay or inlet. By the Edo period, a large Ainu village, or kotan, stood around Usu Bay, alongside a place for trade.
Usu is sometimes called “the volcano that never lies” because earthquakes and ground cracks have often preceded eruptions by days or weeks. That is not an exact forecast: eruption timing cannot be predicted precisely.
In 1910, police chief Seiichi Iida ordered residents within 12 km to evacuate 2 days before Usu erupted. He acted on warning earthquakes and drew on experience evacuating people during a Tarumae eruption.
The lava dome forming Usu’s main summit, Ō-Usu, began growing after the 1853 eruption. Surveys measured it at 595 m in 1889, 692 m in 1905, and 740 m in 1911.
The 1910 eruption became a milestone in modern Japanese volcano observation. Seismologist Fusakichi Omori used a seismograph and leveling surveys to track earthquakes and changes in the ground at Usu.
At Usu’s eastern foot, local postmaster Masao Mimatsu tracked the neighboring Showa-Shinzan dome with sketches from the same viewpoint. His “Mimatsu Diagram” was presented at an international volcanology meeting in 1948.
During Usu’s 1977 eruption, the column of ash and pumice reached 12,000 m within an hour. The mountain kept rising afterward, forming Usu-Shinzan; ground uplift continued into 1982.
An ancient landslide from Usu reached the sea and helped shape the region’s intricate coastline. Crevices among its volcanic rocks now provide habitat for shellfish, crabs, octopuses, and other sea life.
Archaeological research shows people lived near Usu about 10,000 years ago. The volcano’s springs and ash-created plateaus have supported settlement, farming, and orchards around Lake Tōya.
A historical-geography study found that Ainu residents near Usu had already begun evacuating during the 1822 eruption before the authorities’ order reached them—a striking record of independent action.
