Some people have wondered why I have not written about Sinabung yet. The reason is that so far there has not been any real eruption. What has been seen so far was just a 3 year episode of throat clearing phreatic detonations.
Now it seems like the volcano is closing in on starting the real eruptive phase, something that is heralded by an upgrade of the volcano’s status to a alert-level IV, and the return of the legendary volcanologist Surono who has taken charge of the further proceedings at Sinabung.
Mount (Gunung) Sinabung is situated on the Sunda arc on where the Indo-Australian plate subducts under the Eurasian plate. From a more geographical standpoint Sinabung is located in northern Sumatra in Indonesia, just a mere 25 kilometers from the Toba volcanic system.
Previously the volcano have been erupting magmas ranging from dachite to andesite, mainly depending on how long the period of intermission has been.
The last lava producing eruption occurred 1600, with a later eruption in 1881 that has been discredited. In 1912 a brief phase of activity occurred as a series of fumaroles opened up near today’s active crater.
Phreatic activity 2010 – 2013
On the 25th of August 2010 a period of phreatic detonations started that lasted until the 28th of September in the same year. The detonations lasted between 10 minutes to 20 minutes and produced ash columns not exceeding 4 kilometers in height. Due to the limited knowledge about this volcano the authorities held a very high vigilance and performed evacuations from nearby villages in the 3 km exclusion zone.
For a long period the volcano was at the highest alert level IV even though the activity was fairly benign. In the end the volcano deflated, a sign of magma being withdrawn from the system.
On the 11th September 2013 Sinabung started to suffer yet another bout of phreatic detonations. This time the detonations was more vigorous and at times the ash columns from the detonations reached a maximum altitude of 7 kilometers. Reports of higher columns are from misinterpretations of the VAAC flight warning numbers which are not the same as the actual columnar height.
On the 20th November Surono increased the safety zone around the volcano from the previous 3 kilometers to 5 kilometers as signs of increased volcanic activity started to emerge at Sinabung. According to PVMBG Sinabung have ejected stones 3 – 4 centimeters up to 4 kilometers hitting the villages of Sigarang and Gugung Kuta, this prompted the authorities to evacuate more people. Currently 21 villages have been evacuated with more on standby to evacuate.
On the morning of the 24th November an increase in volcanic earthquakes occured and harmonic tremor increased from the previous level 0.5 – 2mm up to the new level of 0.5 – 5mm. This in conjunction with mountain deformation and increases in gas emission led Surono to taking steps to increase the alert level to IV.
It is currently recommended that residents nearby carry facemasks with them at any time, and if needs be that they use them whenever being outside.
Since so little is known about this volcano it is hard for the authorities to predict how it will behave, instead they have to go on what other volcanoes in the area of the same type have done. And judging from that an eruption ranging up to VEI-4 is likely, with the likelihood quickly dropping off for more powerful eruptions. Do not make the mistake to think that Sinabung is anything like nearby Toba, they are completely different types of volcanoes.
Updates will be forthcoming as deemed pertinent.