Regarding the eruption of Mount Merapi in Yogyakarta on Monday afternoon, October 14, 2019, at 4:31 p.m. local time, it threw hot clouds with a column up to a maximum of approximately 3,000 meters above the Merapi peak, it has been recorded that, at the same time, there was also tectonic seismic activity in the Indian Ocean.
This tectonic earthquake of magnitude M = 2.8 ° occurred at 16.31.56, western Indonesia time, with an epicenter in the sea at a distance of 38 km southwest of Bantul.
The incident raises many questions from the public, given the possible link between the tectonic earthquake and the eruption of the most active volcano in Indonesia.
In response, the Director of Earthquake and Tsunami Mitigation of the BMKG, Vice President of the HAGI (Division of Land Disaster Mitigation), Dr. Daryono gave his opinion. According to Daryono, if we look at the time of the incident between the eruption and the tectonic earthquake, it seems that the first thing that happened was the eruption of Mount Merapi.
If a tectonic earthquake affects the Merapi eruption, the tectonic earthquake should have occurred first. The current theory is that tectonic earthquakes trigger volcanic activity, not vice versa.
Daryono explained that, in fact, tectonic earthquakes can increase volcanic activity, provided that the volcano is active, contains liquid magma and its interior is rich in gas. If such conditions are met, then the tectonic dynamics around the magmatic sack can trigger volcanic action.
Tectonic earthquakes that originate near volcanoes can create stress tensions that cause changes in gas pressure in the magma bag. Stress tensions caused by tectonic earthquakes around volcanoes can alter the conditions that keep magma and gas content, and induce seismic activity under stress.
This phenomenon can be analogous to a bottle of drink that is stirred to generate gas bubbles that, when moving upwards, press the upper part with such force that they end up releasing it with an explosion.
Meanwhile, if we look at the activity of the tectonic earthquake of recent times in Yogyakarta, the results of BMKG monitoring show an increase in seismic activity before the Merapi eruption last Monday. As an illustration, since the beginning of October 2019.
Seismic activity before the eruption of Merapi on Monday 10/14/2019 (Photo: Inst. Daryonobmkg)