Smoke from last Mt. Fuji eruption reached 23 km

November 14, 2012

By HIROTAKA YAMAGUCHI/ Staff Writer

New research into the 1707 eruption of Mount Fuji, the most recent in the mountain's history, has produced troubling results, indicating probable disaster if present-day Japan suffered a similar eruption.

New calculations made by the Hot Springs Research Institute of Kanagawa Prefecture in Odawara found that volcanic smoke from the eruption reached as high as 23 kilometers, much higher than previously believed. The findings suggest tremendous energy may have been released by the eruption.

Experts are now calling for greater preparedness measures because such an eruption occurring today would likely paralyze many urban functions in the Tokyo metropolitan area for an extended period.

Kazutaka Mannen, a senior researcher at the institute, and researchers at Nihon University reviewed the records of the accumulation of volcanic ash and rock to calculate the amount of magma that erupted each second.

Using a calculation formula, they determined the height of the volcanic smoke.

After consulting documents from the time, the researchers calculated that after the eruption began at about 10 a.m. on Dec. 16, 1707, it continued for about 90 minutes, sending smoke as high as 23 kilometers. The eruption weakened for a time, and smoke reached heights between 12 and 22 kilometers by the evening of Dec. 19. After another pause, the eruption resumed, sending volcanic smoke to heights of between 14 and 20 kilometers until the morning of Dec. 30. Officials of the institute said until now, researchers believed that the smoke only went as high as about 15 kilometers.

If volcanic smoke reaches the stratosphere, which stretches from 10 to 50 kilometers above the earth's surface, volcanic ash can be carried great distances by westerly winds.

According to the Meteorological Agency, recent observations of domestic volcanic eruptions did not find any in which volcanic smoke reached the stratosphere.

In the 2000 eruption of Sakurajima in Kagoshima Prefecture, for example, the smoke reached a height of five kilometers, while the eruption on Miyakejima island that same year sent smoke up to a height of eight kilometers. In the 2011 eruption at Mount Shinmoedake, in the Kirishima range in southern Kyushu, the volcanic smoke reached a height of three kilometers.

However, studies have found that ash from the 1707 eruption of Mount Fuji was carried more than 150 kilometers, reaching as far as the Pacific coast of Ibaraki Prefecture.

During the March 2010 eruption in Iceland, volcanic smoke reached heights of at least 10 kilometers, leading to the suspension of flights into and out of 29 nations in Europe. The closure of several airports affected flights to Europe from around the world.

Setsuya Nakata, a professor at the Volcano Research Center of the Earthquake Research Institute at the University of Tokyo, said the latest findings shed new light on the largest eruption in Japan over the past 300 years.

"There is the possibility the effects from the volcanic ash that reached the stratosphere likely had a global impact," he said. "Using those results to think about the situation today, we clearly need to consider the effects on flight routes."

By HIROTAKA YAMAGUCHI/ Staff Writer
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Mount Fuji (Asahi Shimbun file photo)

Mount Fuji (Asahi Shimbun file photo)

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