Mount Asama
Starting in the 1770s, there was a sharp decline in crop yield in Tōhoku, which is the north-eastern region of Honshū, due to poor and cold weather, so food stocks in rural areas were exhausted. The situation was exacerbated by natural disasters: Mount Iwaki erupted on April 13, 1783 (3rd month, 12th day, in the year Tenmei-3, according to the Japanese calendar), as did Mount Asama on July 6, so volcanic ash was sent down into the atmosphere of Japan. Aside from the direct damage caused by the eruptions, this led to a fall in solar radiation, resulting in cold weather that catastrophically damaged crops. The massive Icelandic Laki eruption of 1783 disrupted weather patterns all over the Northern Hemisphere, and may have worsened matters as well.