Hōei eruption


The Hōei eruption of Mount Fuji started on 16 December 1707 and ended about 1 January 1708 during the Edo period. Today the crater of the main eruption can be visited from the Fujinomiya or Gotemba Trails on Mount Fuji. Hokusai's One Hundred Views of Mount Fuji includes an image of the small crater at a secondary eruption site on the southwestern slope. This was called Mount Hōei, because the eruption occurred in the fourth year of Hōei.

Extent of eruption

Although it brought no lava flow, the Hōei eruption released some of volcanic ash, which spread over vast areas around the volcano, even reaching Edo almost away. Cinders and ash fell like rain in Izu, Kai, Sagami, and Musashi provinces. In Edo, the volcanic ash was several centimetres thick. The eruption is rated a 5 on the Volcanic Explosivity Index.
The eruption happened on Mount Fuji's east–north-east flank and formed three new volcanic vents, named No. 1, No. 2, and No. 3 Hōei vents. The catastrophe developed over the course of several days; an initial earthquake and explosion of cinders and ash was followed some days later with the more forceful ejections of rocks and stones. Mount Fuji has not erupted since.

Secondary disasters

In the year following the Hōei eruption, a secondary disaster occurred when the flooded due to sediment build-up resulting from the ash fall.
Volcanic ash fell and widely covered the cultivated fields east of Mount Fuji. To recover the fields farmers cast volcanic products out to dumping-grounds making piles. The rain washed material from the dumping grounds away to the rivers again and again and made some of the rivers shallower, especially into the, into which huge volumes of ash fell, resulting in temporary dams. Heavy rainfall on 7–8 August 1708, the year following the Hōei eruption, caused an avalanche of volcanic ash and mud, breaking the dams and flooding the Ashigara plain.