Why does Ontake volcano in Japan suddenly erupt?

The characteristics of the volcanic volcano and the underground eruption believed to have caused Ontake to "wake up" suddenly on September 27 , leaving at least 40 people injured and many missing.

>>>Volcanoes suddenly erupt, causing many deaths in Japan

Ontake volcano suddenly sprayed on September 27, causing ash to cover down the southern flank over 3km. The sudden eruption caused 30 climbers to stop breathing and many flights had to change directions to avoid danger. This is considered a reminder that volcanic eruptions may not be predictable.

White smoke and ash rose from Ontake volcano during the eruption on September 27.(Photo: Kyodo News / AP)

Movement of lava before major eruptions can sometimes cause a warning, such as the case of volcanoes in Iceland in recent times. However, for an active volcano and dust and smoke eruptions like Ontake, this is not always true. According to experts, that's why the incident on September 27 happened without warning.

Ontake has a height of more than 3,000m, is the second highest volcano in Japan and belongs to the group of volcanic formations. These volcanoes form where a tectonic plate folds under a different array, and is characterized by activity again in an unpredictable period.

Eruption caused by volcanic lava is the reason that stratovolcano is particularly dangerous and difficult to give warning. These eruptions caused dust and rock to cling to the slopes, with tremendous speed and up to 700km / h when heading down the slope. This kind of activity happened in Ontake in 1979.

Ontake Mountain is located on the boundary between Nagano and Gifu provinces, about 200km west of Tokyo.(Graphic: BBC)

The dust and smoke movement on September 27 is a smaller eruption, or an underground form with the flow of steam, ash and rock, not accompanied by lava. Carbon dioxide or hydrogen sulfide spilling from the crater can make people suffocate. Since 1979, steam has frequently appeared on Ontake.

Although it does not appear regularly, underground eruptions can still occur on a large scale. The underground eruption in Krakatau, Indonesia, in 1883, is believed to have produced the biggest sound in history.

Ontake volcano is located on the boundary between Nagano and Gifu provinces, 200km west of Tokyo. In the contact position of three tectonic plates, Japan is a country frequently affected by earthquakes and volcanoes.

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