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Fuji-Hakone-Izu NP, Tokyo
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The last evacuation bus cleared Ako only about 10 minutes before lava crossed the road. Around 80 people were still cut off; local fishing boats ferried them out, and no one died.
This was no single-crater outpouring: a fissure on Oyama’s southwest flank stretched 4.5 km and opened more than 90 vents. Lava fountains burst from its upper part as flows ran down several valleys.
The 1643 eruption also destroyed Ako. Geological Survey of Japan maps show that the 1643, 1763 and 1983 flows partly followed the same routes—older lava now hidden beneath newer rock.
1983 lava buried homes, shops and schools in Ako’s former hot-spring quarter. Completed in 2007, the trail crosses the flow beside the remains of the old elementary and junior high schools.
Firefighters sprayed about 4,700 tons of seawater onto the lava’s 300-m front over 3 days, hoping to slow it. Researchers found it had likely stopped before pumping began, so the experiment’s effect remains uncertain.
On August 24, 1983—40 days before the eruption—Tokyo held a major island eruption drill with about 3,000 people from 30 organizations. Government records say the practice helped guide the real evacuation.
The jagged, blocky flow is ʻaʻā basalt, a lava type named from Hawaiian usage and contrasted with smoother pāhoehoe. The University of Tokyo’s collection includes a specimen from Miyakejima’s 1983 eruption.
