It’s Been More Than 300 Years Since Japan’s Breathtaking Mount Fuji Last Erupted

From a photogenic distance, Mount Fuji is a nearly perfect, usually snow-capped cone, protruding out of the Japanese island of Honshu and into the clear blue skies. But another view reveals the site of Mount Fuji’s last confirmed eruption, which began on December 16, 1707, during Japan’s Hoei era.

The image of a tranquil Fuji became enshrined in Katsushika Hokusai’s 19th-century woodblock series Thirty-Six Views of Mount Fuji, which, according to Franz Lidz in Smithsonian, “juxtaposed the mountain’s calm permanence with the turbulence of nature and flux of daily life.”

But viewed from the southeast—the “least admired” view, according to anthropologist Frederick Starr—an imperfection hints at the mountain’s turbulent past. This “excrescence,” as Starr puts it, is the site of the 1707 eruption.

The Hoei eruption, as it’s known, was anything but tranquil. It was likely triggered by an 8.6-magnitude earthquake that struck off the coast of Japan on October 28, one of the most violent seismic events in Japanese history.

The earthquake triggered massive tsunamis that killed thousands of Japanese and compressed magma chambers in Mount Fuji, building pressure and blocking off release vents simultaneously. Over the next 49 days, hot magma from deep within the volcano mixed with cooler magma, and stress within the volcano built until, on December 16, the pressure became too intense and the volcano began to erupt.

The destruction was immense. The eruption spewed tons of tephra—rock fragments ejected from the volcano—into Yokohama and Tokyo, some 60 miles east of Fuji. The cities were blanketed in over an inch and half of ash. The volcano released nearly 30 billion cubic feet of ash, leaving the atmosphere so densely clouded that residents had to light candles to see even during the daytime. Flows of mud, rock and other debris known as lahars devastated farms and villages in the volcano’s proximity, and the buildup of ash in rivers and streams caused further flooding.

While no official death toll was issued for the eruption, which lasted until January 1, many residents suffered respiratory problems related to the ash, especially in densely populated cities. In the countryside, devastated farmlands meant low food supply and starvation. Famine lasted a decade.

The Hoei event was Mount Fuji’s biggest eruption in the Holocene epoch, the past 11,700 or so years of Earth’s history. On the volcanic explosivity index, the eruption scored a five out of eight—“very large,” based on the amount of debris displaced—comparable to the Mount St. Helens eruption of 1980.

Although Fuji hasn’t had any confirmed eruptions since Hoei, it might not be quiet forever. It is still considered an active volcano. Japanese authorities have produced predictions about where craters are likely to occur on Mount Fuji, as well as evacuation areas and guidelines for the tens of millions of residents in Tokyo’s metropolitan area should it erupt again.

Meanwhile, the mark of the Hoei eruption is still evident on Fuji’s face, a reminder of its fiery past. As he hiked up the volcano a century ago, Starr described it as “a regular crater-cone, bare of vegetation, composed of fresh-looking cinders … the result of the last great eruption.” Even that once spewing cavity is tranquil now, too, a silent witness to one of history’s most violent volcanic explosions.

Eli Wizevich | | READ MORE

Eli Wizevich is a history correspondent for Smithsonian. He studied history at the University of Chicago and previously wrote for the El Paso Times.