Earth sciences professor Yoshiyuki Tatsumi and associate professor Keiko Suzuki of Kōbe University recently released a study showing that in the worst case scenario, a colossal eruption within the next century could kill all Japan's population of 127 million, the Wall Street Journal, Niconico News and other sources report.
Despite having the slim probability of only 1%, professor Tatsumi was quoted saying, “it wouldn't be unusual for such an enormous eruption to occur.” In fact, he claims, the same low risk percentage was ascribed to the Great Hanshin earthquake that struck Kōbe in January 1995, devastating the city and killing more than 6,000.
The researchers' findings were based on the frequency and scale of volcanic eruptions that occurred in the Japanese archipelago within the past 120,000 years. Calculating the Weibull distribution of the 447 eruptions of magnitude 4 or above led to the conclusion that in the next 100 years, there is a 1% chance that a magnitude 7 eruption could gush out more than 100 billion tons of magma, causing a massive caldera to form. Within two hours, this would leave approximately 7 million people underneath molten rock and lava. Many others would perish from the ensuing pall of ash. The Daily Mail reports such a toxic cloud would make the main islands of Japan “unlivable”.
Calderas are collapses of large amounts of land triggered by huge volcanic eruptions. During the Jōmon Period, circa 7,300 years ago, the 8.1 magnitude Akahoya Eruption completely obliterated the Jōmon culture, forming the Kikai Caldera. Recovery from the disaster took one thousand years. Another example, the Aira Caldera, is located near the major city of Kagoshima in the south-most part of Japan. It was created some 22,000 years ago and has an area of approximately 20 square kilometers.
Prof. Tatsumi's study also reveals that 7% of all volcanic eruptions in the past 10,000 years are located in Japan.
This news comes several weeks after the eruption of Mount Ontake in central Japan, which claimed the lives of 56 people when it suddenly erupted on 27 September. It also comes at a time when Japan is rethinking its relationships with nuclear power plants and the threat posed both by tsunamis and volcanoes.
According to Asahi News, “new safety standards requires electric power companies to consider possible influences from volcanoes located within a radius of 160 kilometers from nuclear power plants.”
Despite there being several calderas near the Sendai area – where the Fukushima power plant is located – electric power companies said the interval between the last catastrophic eruption and the next is exceptionally low. However, some experts remain skeptical of this optimistic view since eruption predictions in Japan have historically had a poor accuracy rate of only around 20%, the Japan Times reports.