The Great Hoei Eruption

Mount Fuji’s last confirmed eruption was in 1707. It is the largest and most recent eruption of Mount Fuji since prehistoric times. Starting from the northern flank of Mount Fuji, eruptions continued intermittently for 16 days. A lateral eruption caused the flank volcano that is now known as Hoei-zan (Mount Hoei). During the eruption, westerly winds resulted in the ash fall being concentrated in the plains of the Kanto region. Hakuseki Arai, a Confucian of the mid-Edo era, wrote of the effects in his autobiographical essay, Oritaku Shiba no Ki (Told Round a Brushwood Fire), describing having to deliver a lecture in a dimly lit room while volcanic ash was falling like snow outside. 

The volcanic ash that fell at the foot of Mount Fuji contained heat and was referred to as ‘burnt sand’. From Oyama-cho and Gotenba-shi, in Shizuoka Prefecture, the burnt sand flowed down onto fields, right through to Kanagawa Prefecture, making cultivation impossible and causing a serious famine. In addition, the volume of volcanic ash raised the water level of rivers, causing floods. 

Odawara feudal lord, Tadamasu Ohkubo, determined that, due to prolonged secondary damage, it would be difficult to recover on his own. He returned territories around the stricken area to the Edo Bakufu and requested assistance.

The Ashigara Plain (currently south-west Kanagawa Prefecture), where the damage was particularly severe, made the rehabilitation project by the Edo Shogunate extremely difficult, and took nearly 100 years to complete.