Remember the time before 2013, when the volcano-interested world was still guessing at what might have caused that 1257 indelible SO2 trace deep in the pristine Antarctic ice sheet? Well, scientists didn’t just guess but worked out (and a paper was published in 2013) that there was enough evidence for a caldera-forming VEI 7 eruption in Samalas (today Rinjani Volcanic Complex on Lombok/Indonesia) to have been the culprit. Imagine the scale of that eruption: its magnitude was 8 times more powerful than Krakatoa’s and double that of Mount Tambora, so it was one of the largest Holocene eruptions globally. Following the findings of 2013, extensive studies on this volcano were conducted by Indonesian and international scientists, and it was proposed to preserve some areas on Lombok as a geologically important historic district. Tephra of this eruption covers much of Lombok, 35 to 40m high in places. The ash is said to have travelled around the world and caused widespread climate problems, leading to crop failures and starvation in the following years. This assumption is based on many geological, geochemical and petrographical comparative data as well as on points in history as the collapse of the Kingdom of Lombok in the 13th century and the discovery of bones in a mass tomb in London which could be dated to 1258.
1257 – This eruption has destroyed most of the edifice of Samalas, leaving a caldera, now filled with the water of Lake Segara Anak. With time and further volcanic activity a new vent opened in the caldera floor which became the pyroclastic cone now called Baru Jari, son of Rinjani. The cone rises about 370 m above the caldera lake, and along with flank vents and lava flows forms now a large peninsula jutting westward into the lake. All historical recorded eruptions since 1847 have been restricted to this Barujari cone and consisted of moderate explosive activity and occasional lava flows that have entered Segara Anak lake.
1944 – An eruption produced the Rombongan lava dome on the NW flank of Gunung Barujari. It was the source of the lava flow that extends to the NW into the Segara Anak caldera lake. Rumblings and thick smoke with nighttime incandescence began on December 25, 1944. There was heavy ashfall for 7 days, destroying crops and houses outside the caldera.
1966 – Following an earthquake on March 28, explosive eruptions formed a new small cone that fed the lava flows, which eventually covered a 600 x 1700 m area. This eruption produced the extensive barren lava flows that still can be seen extending N and S from the Bajuwari cone into the caldera lake.
1994 – This eruption, the only one marked VEI 3, went from June-October. A glassy bomb from this eruption was a basaltic andesite (55% SiO^2); the two previous eruptions (1944 and 1966) were basaltic. Lake temperatures in April 1994 were 31°C close to the active Barujari cone and 20°C on the W side; temperatures on 9 October 1994 were 36 and 31°C, respectively. Declining lake levels were noted on 9 October (~3 m drop). On 3 November, a cold lahar from the summit area traveled down the Kokok Jenggak River. Thirty people from the village of Aikmel who were collecting water from the river were killed; one person remained missing. No damage to the village was reported. Local volcanologists noted that additional lahars could be triggered by heavy rainfall.
2004-2005 – Fluctuating seismic activity and visual observation conditions made it difficult to determine actual eruptions but in October 2004 Rinjani clearly erupted, causing authorities to immediately raise the hazard status to Alert Level III.
2009 – During May and June, although the volcano was frequently obscured by fog, people still saw impressive eruptions from the observation post at Sembalun Lawang. They noted continuous eruptions with ejected glowing material reaching 200 m in height above the vent, and thrown laterally out to a radius of 500 m from the summit. A great amount of ash, cinders, and incandescent material fell into the caldera, while smaller fragments were blown away. – Same year, about the lake: The lake is neutral (pH: 7-8) and its chemistry dominated by chlorides and sulfates with a relatively high concentration of total-dissolved solids (TDS: 2,640 mg/L). This unusually high TDS value and lake surface temperatures (20-22°C), well above ambient temperatures (14-15°C) for this altitude, reflects a strong input of hydrothermal fluids. Numerous hot springs are located along the shore at the foot of the Barujari cone. Bathymetric profiles showed several areas with columns of gas bubbles escaping from the lake’s floor.
Although, officially, the eruption began on 25 October, this photo (right) is labelled “The first eruption of Mount Baru Jari (23/10)”, which, if true, would indicate that the eruption had already begun at an earlier time. In an later article of that newspaper it was said: “Together with some of the photographers and other climbers, Imran was in the last group of the day (Friday 23/10) who climbed Mount Rinjani“. – Another indication that the eruption might have begun earlier is, IMHO, in the PVMBG report: “In the span of 1 to 22 October 2015: Recorded 17 events Tremor with maximum amplitude of 2-12 mm and quake length of 10-120 seconds, 13 events Earthquake Low Frequency (LF), 3 events volcanic earthquake Shallow (VB), 3 events Volcanic Earthquake In (VA), 4 Local Tectonic earthquake occurrence (TL) and 10 events Far Tectonic earthquake (TJ)”.
25 Okt. 2015 – Gunung Rinjani National Park Authority suspended the activity of climbing Mount Rinjani on Sunday around 10:45 pm. The volcanologist at the Post Rinjani said that the eruption of Mount Barujari was still relatively small. The alert level has been raised from 1 to 2 (alert) later that day, and a restriction zone of 3 km from the caldera was implemented. Officers of Mount Rinjani National Park evacuated hundreds of hikers and climbers of Mount Rinjani to a safe place clear of poisonous gas from the eruption.
Unfortunately, apart from the eruption of Barujari, the savanna-and-pine forest area of Mount Rinjani also burned badly with wild fires at the time.
26 Oct. 2015 – That day, Hindus gathered at the temple Jagadnata, solemnly sang a song of Earth Atonement, and recited prayers and sacred dance to the world Dewanata. This ritual is the beginning of the Cultural and Natural Pekelem Sudha, a Hindu prayer procession with participants arriving from Bali, Java, and Borneo as well. This big ceremony for Hindus is conducted every five years on the island of Lombok. For three days they will climb Mount Rinjani to reach Lake Segara Anak, which is believed to be the spiritual center in the Land Sasak.
The sanctity of Mount Rinjani was believed by Hindus since the sixteenth century: At that time, faced with a long drought that resulted in deaths and disease, the King Anglurah got the whispers to perform Yajna Earth Sudha and Pekelem on Fifth Month Moon at Lake Segara Anak Gunung Rinjani. Miraculously, after the ritual was held, it rained on the earth and brought back the blessings of health for the local community. Since then, the Hindus in Lombok continued this ceremony until now. – What a nice background to such a ceremony an erupting volcano is!
31 Okt. 2015 – Activity has increased again on Saturday morning, with at least ten explosions and plume hights up to 700m, moving N.
3 Nov 2015 – Authorities have prepared several scenarios for evacuation, there are 40,000 residents living around the mountain! Also, the previous day first reports came in from pilots of local aircraft that the heat from the eruption and first ash particles disturbed the air space over Lombok. Since this morning activity of Rinjani is increasing, accompanied by tremors which tend to rise to amplitude of 22.5mm, dominant 12 mm. A total of seven villages in North Lombok are affected by volcanic ash, with the ash plumes going now up to a hight of 1300m. Face masks have been distributed and extra personnell is making sure that nobody enters the restriction zone of 3km.
4 Nov. 2015 – The ash plume from Rinjani is travelling west and closing one airport after the other on the neighboring islands. According to Dr. Devy Syahbana Kamil, since November 2, seismic tremor was recorded continuously and the eruption energy increased significantly. Visual observations indicate strombolian explosive eruptions and lava flows from the crater. Height of the eruption column was at a maximum of ~2,000 m above the crater or 3400 m a.s.l.
5 Nov. 2015 – Dr. Surono, expert for Disaster mitigation, estimates that the eruption of Mount Rinjani will not be very explosive. “Mount Rinjani no longer has significant power to make an explosive eruption,” he said in Yogyakarta on Thursday, because “after the latest eruptions the magma plumbing system is already open. In addition, the volume growth of the lava dome of Mt. Rinjani also tends to lower the maximum flow rate which reaches 18 m^3/s (3 Nov. 2015), unlike in Mt. Merapi where the growth of the lava dome reached 38 m^3/s in 2010”. (translated by Google).
The results of MODIS data processing showed that the magma heat flux increased since two days ago to the present. The maximum rate of discharge of lava to the surface ranges from 1-18 m^3/s with a rising trend. The primary potential hazard at this time is in the form of lava flows and pyroclastic fallout within a radius of 3 km and in all areas in the Rinjani caldera. Indirect hazards may include flash floods in the river if pyroklastic materials and lava flows fill up the lake as happened in the eruption of 2009.
06 Nov. 2015 – The latest report for 12:00 to 18:00 pm:
Visual: The weather was overcast, winds calm, clear mountain-0III fog. Air temperature 26°C, humidity 84%. Thick white to gray plume, height ± 2500 m leaning to the south. Earthquake: Tremor constantly Amax: 3-44 dominant 16 mm.
Conclusion: G. Rinjani Level 2 (Alert). Recommendation: No public activity in all areas in Rinjani caldera and in a 3 km radius of the crater G. Barujari. Communities are to prepare masks in anticipation of volcanic ash. Communities that are around the river to be aware of potential flooding [White crowing Floods] if an increase in the water level of the lake occurs due to eruption material filling in.
Having written in all this length about an eruption that is so far certainly bothering many, but not dangerous to the local residents and, on the other hand, interesting to volcano enthusiasts all over the world: this is a small eruption and hopefully will remain so. But I would like to ask everybody to please spare a thought for those many thousands of people who used to live in sight of Mt. Sinabung in northern Sumatra and who have lost their homes and livelihoods in that eruption, which still goes strong since 2013. Many of them still live in shelters with nowhere to go to… they might just have a sad smile for the “tiny” eruption of Mt. Rinjani.
Ooh, how beautiful Mount Rinjani is even without an eruption!
07 Nov. 2015 –
10 Nov. 2015 – Updates on the eruption come in very sparsely. What I gather from the media is: The eruption is going on in a moderate fashion, with still continuous hightened tremor and strombolian, explosive/effusive activity. The closing of Praya Lombok International Airport was extended until Wednesday, November 11, 2015 at 8:45 pm, all its operations including arrivals and departures were cancelled. Other Indonesian airports were able to re-open.
11 – 16 Nov. 2015 – The eruption has been going on but with less intensity, and flight conditions are back to normal. Lava flows down the E and N of the cone. It is estimated that a total of 4.5 million m^3 (0.0045 km^3) of pyroclastic material has accumulated in this eruption. – With the increased volume of erupted material in Lake Segara Anak water level has risen. There is an imminent danger of spilling over and flooding along the river Kokok Putih, especially in heavy rain conditions.
Enjoy! – GRANYIA
SOURCES & FURTHER READING
– Various news sources, Twitter, FB, Instagram etc.
– Kicknews Today (news)
– Samalas in Indonesia Identified as Source of the 1257 A.D. ‘Missing’ Eruption
(2013, E. Klemetti blog)
– Source of the great A.D. 1257 mystery eruption unveiled… (PDF, 2013)
– Eruptions at Rinjani Cancel Flights Across Indonesia (5/11, E. Klemetti blog)
– New PVMBG webcam Rinjani (accessible in some elected countries only!)
– The enormity of the eruption of Mount Samalas… (Tempo.co, newspaper article)
– PVMBG Report on Rinjani, 25 Oct. 2015