Hoei Crater was added to Your Favorites!
Fuji-Hakone-Izu NP, Shizuoka
Claim this place to tell your story your way.
The little mountain beside Hoei Crater isn’t an ancient lump pushed up by magma: a 2022 geological study found it is a cone built from material erupted during the 1707 blast.
Hoei’s largest vent, No. 1, is about 1 km across—wider than Fuji’s summit crater. This enormous bowl opened halfway down the mountain during the 1707 eruption.
Hoei’s eruption changed color as it progressed: pale pumice burst out first, then dark, bubbly scoria began erupting from No. 1 crater that evening as the magma’s composition shifted.
Hoei’s ash traveled more than 100 km, reaching Edo (today’s Tokyo) and the Boso Peninsula. Historical accounts describe daytime darkness so deep people lit lamps as ash fell.
Hoei Crater is a line of 3 vents. The eruption began at the lower, southeastern No. 2 and 3 craters, then shifted upslope toward No. 1, closer to Fuji’s summit.
About 0.7 km³ of magma in total was released in the 1707 eruption—and roughly one-quarter of that total came out during its first day. The activity then pulsed on for 16 days.
Despite carving out a vast crater, the 1707 eruption produced no recorded lava flows or pyroclastic flows. Its pumice, scoria and ash were blasted into the air and fell back as volcanic debris.
A magnitude 8.7 Hoei earthquake struck on October 28, 1707; 49 days later, this crater opened. Researchers have modeled a possible trigger link, but the timing alone cannot prove cause.
The damage kept traveling after the ash stopped falling: rain washed debris into the Sakawa River, whose floods repeatedly battered the Ashigara Plain. Records show impacts continued until 1783—76 years later.
The blast buried Suyama trail’s fifth station and wiped out the route. Local leaders began rebuilding it in 1779, and it reopened in 1780; the present trail was restored in 1997.
The ash-and-gravel slopes may look bare, but hardy Fuji thistle, Fuji-hatazao and other plants grow there. Their gradual spread makes the Hoei area a valuable natural site for studying plant succession.
Hoei’s walls are a geological cutaway: vertical dikes show magma that froze in cracks, while fragments of gabbro on the crater floor came from deep inside Fuji’s magma system.
