Whenever you have your automatic text translation switched on while reading up on Gunung Raung you will be informed that the roaring mountain is erupting or a great roar has been heard from Mt. Roar. This is what the Indonesian word raung means in English – roar. Which is probably just appropriate as all eruption reports begin with “distinctive rumblings were heard for weeks before” accelerating to “loud explosion sounds and roaring noises accompany the eruption”. Mt. Raung is a quite large volcano on the borders of the three districts Banyuwangi, Bondowoso, and Jember, in Eastern Java, Indonesia.
Due to its remoteness from densely populated areas the media seldom report on Raung, and PVMBG rarely bother to raise its alert level if it displays only moderate strombolian activity. There are just a few small villages at around 10 km distance, and all minor activity takes place at the bottom of the 500-m-deep caldera, so that it often was not even noticed by residents when the volcano erupted.
It’s different this time. The present eruption which began in mid June is still small in terms of VEI, but has a huge economical impact due to the ash plume going in the “wrong” direction.
THE PRESENT ERUPTION
Video via YT by Aris Yanto, taken during an expedition on July 07, 2015.
In their weekly summaries PVMBG reported that, during infrequent times of clear weather white to grey plumes and occasionally weak incandescence had been observed since December 2014, also rumbling sounds were reported by residents. Seismic tremor sharply increased on 21 June. 28 June was characterized by strombolian activity, roaring, ash plumes that rose 300 m, and a loud thumping sound heard 20 km away in the evening. Incandescence from the crater was clearly visible from the observation post in Banyuwangi.
PVMBG raised the Alert Level to 3 (on a scale of 1-4) on 29 June, and a restriction zone was established around the crater within a 3-km radius. During 1 and 3-7 July Darwin VAAC reported ash plumes from Raung to altitudes of 3.7-6.1 km (12,000-20,000 ft) a.s.l. and drifted 25-110 km E, ESE, and SE. On 5 July BNPB reported that roaring sounds were heard from continuous vulcanian explosions and strombolian effusive activity at Gunung Raung.
Volcanologist Burhan Alethea, in the Volcano Observation Post (PPGA) G. Raung in Banyuwangi, said that Mt. Raung currently has two active vents. According to the observation results of NASA satellite Landsat 8, on June 25, 2015 two vents were clearly visible. But when Mt. Raung erupted on October 19, 2012, only one vent was detected in the satellite photos.
Around 200,000 people reside in the potentially affected area, 23 villages across six districts could be affected. So far no evacuations were necessary, but shelters are prepared, just in case. The Head of Geological Agency of the Ministry of Energy and Mineral Resources (DEMR) Mr. Surono calls on people who live around the foot of Mount Raung, East Java, not to panic and not to believe that the mountain will have a disastrous eruption in the near future. Surono explained that the eruption of Raung is of Strombolian type. This means that the eruption, spewing incandescent material, will be like sparks of fireworks seen in the night. He thinks that due to the energy emitted by Mt. Raung gradually since 2011 there will not be a large eruption. This would be different if there were an obstruction in the volcanic conduits, making the eruption dangerous when accumulated energy is suddenly released.
Since 9 July five airports in East Java, Bali and Lombok had been closed; four of them reopened at the weekend, but Bali’s Ngurah Rai airport closed again on Saturday (reopened and re-closed on Sunday, as with other airports). Indonesian volcanologist Gede Suantika said that Mount Raung emitted ash up to 1,000 metres into the air on Sunday and the winds had pushed the ash in a south-easterly direction towards Bali again.
At this time of year the dry season begins and the meeting of cool damp air masses with dry warm air causes higher wind speeds in the unfavorable SE direction. – Reports on 13 July say that the seismic activity of Mt. Raung has somewhat decreased but nevertheless, ash emission is higher and denser now with black plumes abt. 1000m high.
Asked by the press (probably for the umpteenth time) if the eruption of G. Raung could have an effect on the nearby volcanoes of Ijen Complex, Mr. Surono had one convincing answer – he said: I have told you this before, a volcano doesn’t erupt flu viruses, so can not infect other volcanoes!
THE VOLCANO – GUNUNG RAUNG or Raoeng | Rawon | Roung
Raung volcano is rising from a ring fracture around the SW part of the rim of Ijen caldera, but is usually considered not to be part of the caldera complex.
Mt. Raung is part of the oceanic island arc in the Java-Sumatra subduction system, where the Australian plate subducts beneath the Eurasian plate. There are a lot of controversial theories published concerning the detailed contemporary processes as well as the geological history of the systems involved (see link to bibliography below). It produces Andesite/Basaltic Andesite lavas and Basalt/Picro-Basalt. Since 1586 Mt. Raung had 69 recorded eruptions, the largest among them were: 1x VEI 5 (1593), 2x VEI 4, 3x VEI 3. Its last eruption took place in 2008.
The 3332-m-high summit of Gunung Raung is truncated by a dramatic steep-walled, 2-km-wide caldera that has been the site of frequent historical eruptions. The upper part of the mountain is unvegetated which gives the appearance of a grey collar. Raung contains several eruptive centers constructed along a NE-SW line, with Gunung Suket and Gunung Gadung stratovolcanoes being located to the NE and W, respectively. The formation of Gunung Raung itself is not dated but a pyroclastic flow deposit produced by the Gunung Suket, sampled in the Caldera of Ijen (itself dated to about 50,000 years) gives an age of 37900 +/- 1850 years.
Though it is not immediately obvious, Raung is actually a huge volcano on the flanks of another older, bigger volcano named Gunung Gadung. Gadung is the ‘ancestral’ volcano that formed before Raung, but Gadung has since collapsed. The timing of this collapse is unknown (tens of thousands to hundreds of thousands of years), but the numerous hills (debris-avalanche hummocks) scattered along the curving 79 km path between the old mountain and the Indian Ocean indicate that it was one of the largest volcano avalanches in the known geologic record. At some point before, during, or after the collapse of Gadung, magmatic material began to come out of the east flank of Gadung. This eventually built the edifice that is Raung today (Is it possible that the building of Raung on the east flank caused Gadung to collapse towards the west flank?).
Because Gadung has since collapsed, an untrained eye only sees one large volcano: Raung. There are several things you can look for, however, to clearly identify the remaining presence of Gadung. One, there is actually a jagged cirque on the west flank of Raung. This is the cavity left behind from Gadung’s collapse. A small, resurgent cone sticks out of that cirque in the same spot that Gadung used to sit (J. Wellik).
To get an idea of this wonderful mountain I recommend watching this 7min video of climbing Raung, with heart-stopping lofty scenes and a short round view of the crater interior. The description on YT reads: “Oct 18, 2014 “Gunung Raung” One of the extreme mountains in Indonesia, located in East Java Province, Mount Raung is infamous for its difficult terrain and technical climbing requirement to attain the highest peak (Puncak Sejati). Standing 3344m asl, Raung has 9 Checkpoints […] and 4 Peaks; Puncak Bendera, Puncak 17, Puncak Tusuk Gigi, Puncak Sejati. 3 days are required to attain the summit […] Mount Raung offers ultimate breath taking views from Puncak Bendera to Puncak Sejati, where technical climbing skills and extreme caution are a must since failure might lead to death. […] Raung Sejati, Push Your Limit!” By “HK”.
Enjoy! – GRANYIA
SOURCES & FURTHER READING
– Detik News
– Encyclopedia of Earthquakes and Volcanoes; A. E. Gates, D. Ritchie
– Ndeso Adventure/Aris Yanto Blog – Mt. Raung
– ACTIV – L’Association … Connaissance … Transmission de l’Information en Volcanologie
– Catastrophic Landslides: Effects, Occurrence, and Mechanisms
– John (Jay) Wellik’s blog
– Structural architecture of oceanic plateau subduction offshore Eastern Java…
– Segmented Volcanic Arc … in Java Island, Indonesia
– NASA Earth Observatory, Raung
– Bibliography of the Geology of Indonesia and surrounding Areas