Ten years after the eruption of Mount Kirishima Shinmoedake Dangerous “quasi-Plinian eruption” and later –Weathernews

On January 26, a white eruption continued from the morning, but after 2:50 p.m., the appearance of the eruption suddenly changed and the clear sky was covered with black clouds of volcanic ash. It is the beginning of a semi-Plinian eruption. Users of the Weathernews mobile site sent us photos of the eruption one after another, and we learned that something extraordinary was happening.

The meteorological radar (CON radar) installed by Weathernews has shown that the smoke from the eruption has risen to about 7,500 m above sea level. The Japan Meteorological Agency announced that the height of the eruption is 1500 m above the crater (approximately 3000 m above sea level), but it can be judged that it is underestimated even compared to the photos sent, the support of the airlines , etc. for.

The “Vulcan eruption” that occurs most frequently in Japanese volcanoes is characterized by the fact that an eruption can be completed in a few minutes rather than being accompanied by noise and air vibration due to the explosive eruption. This type is the Sakurajima explosion that happens tens to hundreds of times a year. There is also a form called “ash eruption”, which continues to erupt volcanic ash over a long period of time. This includes the continued eruption of Mount Aso.

The “Plinian eruption”, which occurs only once every few years on a global scale, is a very dangerous form despite its low frequency, and a large pillar-shaped eruption rises vigorously for hours or days. Ejections contain pumice stones and can be accompanied by pyroclastic flows and continuous vibrations of the air.

The “explosion” of a Vulcan eruption may seem more dangerous in writing, but it is this Plinian eruption that has the highest risk of widespread death.

The Shinmoedake eruption of 2011 was one of the smaller Plinian eruptions (also known as a quasi-Plinian eruption). In the photo at the beginning of the article, you can see how the eruption is swept by the wind, but in a large-scale Plinian eruption, the enormous thermal energy causes the eruption to stand upright, ignoring the wind. If the eruption column becomes too heavy to support, it can collapse and create large pyroclastic flows that can destroy cities (such as Pompeii, Italy).

Fortunately, the 2011 Shinmoedake eruption did not cause fatalities, but a large amount of volcanic ash accumulated mainly in Miyazaki Prefecture, which had a great impact on people’s lives and agriculture. Many people are said to fear the haunting continuous vibration of the air.

In Shinmoedake Crater, there was an emerald green crater lake called Shinmoedake Pond, which disappeared in the 2011 eruption.

The activity had been calm for several years after that, but starting in 2017, the activity was re-activated and an eruption occurred causing an eruption, and in March 2018, lava began to accumulate in the crater. One part hung from the rim of the crater to the outside of the crater like a tongue, but it did not reach the base and the outflow stopped.

As of January 2021, you can see on surveillance camera that this lava from 2018 is filling the crater like a hot pie. White fumaroles rise from the hollows of this lava and near the crevices of the western slope.

At Shinmoedake, crater area warnings (eruption alert level 2, crater area regulations) are posted continuously. The number of volcanic earthquakes is increasing and decreasing, and it is unknown when an eruption will occur. Of course, it is not possible to climb Shinmoedake, and the surrounding Shishikodake is also within the regulation range, so the mountain trails are restricted.

Even a very small eruption can cause casualties such as the Mount Ontake eruption and the Mount Kusatsu-Shirane eruption. Even if it is outside the regulation range, when approaching the volcano’s vicinity, make sure you understand the risk and wear a helmet etc. before acting.