Japan’s Volcanoes Under Watch — Scientists Caution of Impending Large-Scale Eruptions

What lies behind the increasing volcanic activity in Japan

On August 26, a booming doon echoed as Sakurajima in Kagoshima Prefecture sent up a column of ash about 1,700 meters high.

This year alone, the volcano has erupted nearly 300 times.

Masato Iguchi, former head of Kyoto University’s Volcano Disaster Prevention Research Center, explained:

“Beneath Sakurajima lies the Aira Caldera, where magma has accumulated sufficiently — it’s ready for a major eruption. During the great eruption of January 1914 (Taishō 3), the total discharge of volcanic material was about 30 billion tons.

By comparison, the 2014 eruption of Mount Ontake in Nagano–Gifu, which claimed around 60 lives, released only about 1 million tons. If Sakurajima erupts again on that scale, the amount of material expelled would be a thousand times greater.”

Japan, experts warn, may now be entering an era of heightened volcanic activity.
Behind this trend are the frequent earthquakes occurring in nearby regions such as the Tokara Islands and the Kamchatka Peninsula.

Kyoto University honorary professor Hiroki Kamata, a volcanology expert, added:

“Mega-earthquakes of magnitude 9 or greater can trigger volcanic eruptions by changing the stresses on the Earth’s crust and activating magma movement.

For example, after the 2004 Sumatra earthquake (M9.1) in Indonesia, several volcanoes — including Talang and Merapi — erupted within three years, killing hundreds. Similarly, the Krasheninnikov Volcano on the Kamchatka Peninsula, which erupted this August for the first time in about 500 years, may have been influenced by the M8.8 earthquake that struck the same region in July.”

Particular attention is now on the link between the predicted Nankai Trough earthquake (expected within the next 30 years with about an 80% probability) and Mount Fuji.
Kamata continued:

“Beneath Mount Fuji, the Philippine Sea Plate is subducting beneath the Eurasian Plate.

The Nankai Trough earthquake occurs along this same plate boundary, so there’s a strong mutual relationship between the two phenomena. The last eruption of Mount Fuji was about 300 years ago, in 1707 — and notably, the Nankai Trough earthquake struck just 49 days earlier, in October of that same year.”

The harmful effects of volcanic ash extend even to communication systems

At the beginning, the enormous scale of Sakurajima’s eruptions was described. However, records from the Edo period reveal that during Mount Fuji’s Hōei Great Eruption, the amount of volcanic ash released over two weeks was equivalent to 200 years’ worth of Sakurajima’s average annual emissions (about 5 million tons), blanketing a wide area across southern Kanto (see figure below).

Yoshiaki Kawata, a disaster prevention expert and specially appointed professor at Kansai University, warns:

“The effects of volcanic ash are not limited to respiratory or other health problems. Ultrafine, high-density suspended ash particles—called aerosols—can adhere to the circuit boards of air-cooled electronic devices, causing short circuits. This could lead to sudden, catastrophic failures across key sectors such as communications, healthcare, railways, and aviation. The capital could become paralyzed for an extended period. In addition, if large amounts of lava flow from new vents, major highways like the Tōmei Expressway could be severed.”

It’s not only Mount Fuji and Sakurajima that are cause for concern. Based on data from the Japan Meteorological Agency and expert analysis, ten “high-risk volcanoes” have been identified (see second figure). Professor Hiroki Kamata of Kyoto University explains:

“At Shinmoedake, part of the Kirishima mountain range (in Miyazaki and Kagoshima Prefectures), frequent earthquakes have been occurring since March this year, and ground deformation indicating swelling of the mountain has been observed. The Japan Meteorological Agency has raised the eruption alert level from 2 to 3.

Miyakejima (Tokyo) has erupted in 1940, 1962, 1983, and 2000—roughly every 21 years. Since the last eruption came slightly early, statistically this year falls within the danger window. There’s no doubt that another eruption is approaching.”

Japan, the volcanic archipelago, has clearly entered a new active phase.