Mount Asama erupted in 1783 (Tenmei 3), causing widespread damage. The three-month-long plinian eruption that began on 9 May 1783, produced andesitic pumice falls, pyroclastic flows, lava flows, and enlarged the cone. The climactic eruption began on 4 August and lasted for 15 hours, and contained pumice falls and pyroclastic flows. The complex features of this eruption are explained by rapid deposits of coarse pyroclastic ash near the vent and the subsequent flows of lava; and these events which were accompanied by a high eruption plume which generated further injections of pumice into the air.