On Studium Generale public lecture held in Aula Barat of Institut Teknologi Bandung (ITB) on Wednesday (26/9/2018), Dr. Eng. Mirzam Abdurrachman from Petrology, Volcanology, and Geochemistry Research Group of Faculty of Earth Science and Technology of ITB delivered his presentation titled “Why Volcano Erupts? Can Lombok Earthquakes Trigger Surrounding Volcanoes to Erupt?”

“Volcanoes erupt for reasons. There are three things that can cause eruption and all related to the balance of magma chamber in craters,” said Mirzam.

The first factor is the increasing volume of magma over injection of new magma. The second factor is magma crystallization within magma chamber. The third factor is the collapsed wall of magma chamber. These factors significantly raise the volume in magma chamber and force a release.

Other factors aside from the aforementioned ones are the weakening of the volcano’s cap over hydrothermal process as well as the force of attraction of the moon and the sun that reach its maximum during eclipse.

Mirzam also explained that volcano eruption is predictable through two things, the first is short term prediction by looking at the activity of the volcano such as its seismicity, ground deformation, hydrology, and gas content. The second is the volcano’s period of eruptions. These predictions can minimalize the risk from volcano eruption to both casualties and loss.

Mirzam exemplified the period of eruptions of Mount Rinjani in Lombok, NTB. The volcano has an eruption every 26 years in average. Because the last eruption was in 1994, the next eruption is predicted to happen in 2020.

“If we follow the period, the magma chamber will be full again in 2020. Fortunately, Rinjani made small eruptions in 2004 and 2009 which reduce the magma. Hence in 2020 it will only show usual activity,” he said.

Departing from that, Mirzam said that the repeated earthquakes in Lombok will not increase the activity of Rinjani because its magma chamber is not full yet. Meanwhile, Mount Agung in Bali has a period of eruptions every 120 years, and it is not the time yet.

“Eruption is caused by full magma chamber. Hence even if the empty magma chamber is shook, eruption should not happen, and that is what happen at Lombok earthquake several times ago. Five significant earthquakes and hundreds other aftershocks did not make it move, because the chamber is not full yet,” he said.