Mount Asama Eruption

Background. Mount Asama is an active stratovolcano in central Honshū, the main island of Japan, situated at the conjunction of the Izu–Bonin–Mariana Arc and the Northeastern Japan Arc. Its eruptions mark the span of Japan's recorded history, and the Japan Meteorological Agency classifies it as rank A.

Eruption Sequence. A three-month-long plinian eruption began on 9 May 1783, producing andesitic pumice falls, pyroclastic flows, and lava flows, and enlarging the cone. The climactic phase began on 4 August and lasted 15 hours, containing pumice falls and pyroclastic flows. The 1783 lava flow, later solidified, is remembered on the northern slope as Onioshidashi, 'expelling demons'.

Famine Context. The eruption caused widespread damage and coincided with the Great Tenmei famine of 1782–1788, the worst famine of the Edo period. Many crops were damaged by bad weather, serious cold, and the 1783 eruption of Mount Asama. Between the 1720s and 1820s Japan had almost zero population growth, often attributed to famine, though some historians cite other factors such as infanticide.