My post today is about one lovely place of beauty, tranquility and recreation, a well frequented holiday destination in Tasikmalaya, West Java province, Indonesia.
The crater that once spewed hot lava, ash and rocks is now a beautiful quiet lake with clear water, surrounded by lush green forest – today a major icon of Tasikmalaya. From the crater rim visitors can enjoy the natural scenery, decorated with hot streams meandering between the villages and rice fields.
Below the crater there is a natural attraction profiting from the volcano’s hydrothermal system: Cipanas, a hot swimming pool and soaking tubs with water from the crater lake that – supposedly – efficaciously cures various acute skin diseases such as eczema and hives. On weekends, the warm river is normally filled with visitors who bring along the whole family. A nearby shrine is considered the spiritual center of the Kingdom of Sunda, pre-Pajajaran period (~12th century).
On the crater rim, a row of food stalls and stands for vegetables typical for Galunggung, such as fern shoots, Kucay onions and watercress that grow on the cliffs of the mountain. Children’s playground, travel kiosks, gazebo, waterfalls, stage entertainment, camping, and ample parking area around the caldera all make for an attractive holiday destination that can even be reached by rural public transport. In 2014, 200 000 tourists contributed to the local revenues in Tasikmalaya district with about 500 mill. US$. This, of course, is the sunny side of the volcano; remembering its past should – not cast a shadow on the future – but at least should help keeping in mind that this place is not ONLY beautiful but also capable of causing death and destruction.
The stratovolcano Mount Galunggung is part of the Sunda Arc extending through Sumatra, Java and Bali, which is the result of the subduction of the Australian plate beneath the Eurasian plate. Its volcanic rocks are basalt to basaltic andesite. (Yet, on one occasion in 1982 Rhyolite has been erupted; the reason for this is still under discussion, or, at least, I have not found an accessible paper containing an accepted explanation. more below).
Galunggung volcano shares one massif with Telagabodas volcano, directly to the north, which contains a large sulfur-saturated lake. Fumaroles, mud pots, and a warm spring are found around its lake, which also has an elevated temperature. The age of Telagabodas’ most recent eruption is not known.
The physiography of Galunggung volcano may be divided into the volcanic cone, the caldera and the “hilly area”. The volcanic cone is preserved in the western and southern parts, reaching altitudes up to 2168 m, and has an inactive crater known as Guntur crater or “Kawah Saat” (Dry Crater) at the summit. This crater has a circular form, 500 m across and 100 – 150 m deep, and is surrounded by a rim that is in places only 0.5-1 m wide. Directly southeast of it is the horseshoe-shaped caldera of Galunggung which is breached to the SE. Inside is the circular active crater, ~1 km across and 150 m deep. A new cinder cone was formed in it during the final stages of the 1982-83 eruption. As there are many waterfalls carrying debris into the crater but no drainage out from it, a lake has formed around the cinder cone. In Dec. 1986 the cinder cone was completely covered by lake water.
Bronto writes in his 1989 paper: “…access to Galunggung caldera and surrounding areas is only by foot. Geological access to the caldera walls requires a rope. The Galunggung crater is now filled by a lake, so the collection of data on the cinder cone and the crater wall can only be achieved by swimming or by means of a rubber boat“.
In 1993 the volume of water in the lake was estimated at around 10 million m^3. Therefore, in 1994 a tunnel was created through the crater wall to drain most of the water. These efforts served a dual function: reducing the volume of the crater lake water while maintaining some of it as a coolant in the crater, and to utilize the outflowing water to irrigate rice fields and fish ponds downriver. The tunnel is about 650 m long and 4 m in diameter, the water flows into the river Cikunir. In 2005, the volume of water from the crater became stable.
Ca. 2010 the cinder cone fused with the lake shore due to greater sedimentation. Fish have been seeded into the lake, not (only) to suit the visitors for fishing, but they serve as a natural indicator for the healthiness of the lake water: if the fish die, something is afoot in the volcano…
The last we heard from the volcano was that between February and May 2012 an Alert (2) had been called. PVMBG reported that from September 2011 to 8 February 2012 the crater lake water at Galunggung was discolored. In addition, a sudden increase in water temperature was measured, from 27°C on 5 Febr. to 40°C on 8 Febr.. Based on seismic data and crater lake observations, PVMBG raised the Alert Level from 1 to 2 (of 4) and recommended that people stay at least 500 m away from the lake shore.
The 1982/83 eruption
|This eruptive period was noted for four types of eruptions (Bronto 1988):|
A major eruption had started in April 1982, a VEI 4 event with 68 fatalities, many of them due to indirect causes; 22 villages were left uninhabitable. This eruption also brought to worldwide attention the dangers of volcanic ash to aviation, after two Boeing 747 passenger jets flying downwind of the eruption suffered temporary engine failures and damage to exterior surfaces: a British Airways aircraft had all four engines jammed due to the buildup of volcanic ash; it descended for 16 minutes, losing 7,500 m of its 11,500 m altitude, until the crew managed to restart the engines and land in Jakarta. The other was a Singapore Airlines aeroplane; three of its four engines stopped but the crew succeeded in restarting one of the engines after descending 2,400 m.
It began with a brief explosive eruption on 5 April, ejecting incandescent tephra and “stones as big as a human head”, a weather satellite image showed an eruption column about 50 km (!) in diameter.
Hundreds of villagers fell ill from the poisonous gases of Galunggung volcano during the first three days. Intermittent explosions began. Lahars and nuées ardentes flowed SE through the breach onto the upper portion of the major prehistoric landslide deposit. Hot mud flowed at 60 km/h as far as 11 km down the SE flank, buried houses in at least six villages, and destroyed a bridge over the Cikunir River. The highest reported ash column reached 16.5 km. Ash fell as far away as the Yogyakarta-Solo area, ~300 km to the E.
After the 6th eruptive episode, on 13 May, over 90% of the 1918 lava dome (Gunung Jadi) was still intact, but the next explosions, on 17-19 May, left only 10% of the old dome in the crater. According to a preliminary estimate of the VSI, magma was located about 3 km below the surface (late June 1982).
By July, Galunggung’s explosive eruptions have forced the evacuation of 62 000 persons from the densely populated area close to the volcano. Houses, rice fields, fish ponds and roads have been destroyed. Ash clouds of over 900 km length have been reported. Ash from the larger explosions has been reported as reaching Australia, causing brilliant sunsets and twilight enhancement in Sydney. The eruption went on, partly with strong explosions, through November 1982. Monsoon rains threatened to remobilize the loose materials and form destructive lahars. In the primary danger zone, residents have been given 40 000 plastic bags, which were to be filled and used as a protection against flooding. Authorities even have warned residents of the city of Tasikmalaya (17 km away, 700 000 residents) of the danger of lahars.
Activity declined somewhat from November on. Within the crater, a tephra cone ~200 m in diameter and 70-80 m high has developed in the area once occupied by the 1918 lava dome (Gunung Jadi). A 20-30-m-diameter vent in the new cone ejected pyroclastics to several tens of meters height. Strombolian activity occurred from this vent in Jan. 1983. Then, after one year quiet, the eruptive period ended in Jan. 1984 with a phreatic eruption that lasted about two weeks.
Changes in magma composition
– GVP note in their Bulletin June 1982 (SEAN 07:06): Chemical analyses show a consistent decline in SiO2 content, from 55.7 weight % in samples from the first explosion to 49.2% in the June tephra. A significant increase in MgO, FeO, and CaO content was also noted between early April and late June. This change in chemical composition also became visible in the deposits: Pyroclastic fall deposits erupted in the initial stage, from April to May 1982, are grey and composed of andesitic materials. But later, from September to December 1982, the materials become darker and basaltic in composition (see photos in Bronto 1989).
– Although neither pre-1982 Galunggung rocks nor other volcanic rocks around Galunggung have rhyolite compositions, on 16 September 1982, a Galunggung eruption ejected rhyolite pumice clasts. Bronto suggests that it could be derived from the melting of pre-existing dacite in the crust by the high temperature magma (1300°C); and there is Miocene dacite exposed to the south of Galunggung.
Further down the timeline: 1918 – 1822
– The eruption in 1918 was a small one, preceded by earthquakes, with ash emissions limited to the crater and the southern slope. This was followed by the extrusion of an andesitic lava dome in the lake. In the course of a few months it grew to 560 x 440 m and 85 m height but was destroyed in the 1982/83 eruption.
– In the 1894 eruption pyroclastic flows and lahars followed the same paths they had taken in 1822 but people must have been more cautious as no deaths were mentioned. Yet this eruption destroyed 50 villages, most of the house collapsed, crushed by heavy ashfall. It took place from three eruptive vents within the crater, and created a new crater about 300-400 m across and several explosion holes.
– The first recorded eruption, 1822, was relatively short, but was the cause of nuees ardentes (pyroclastic flows) and lahars that killed more than 4,000 people and destroyed 114 villages. The nuees ardentes extended up to 10 km away from the volcano and ash/lahars rendered agricultural land unusable to the E and S as far as 40 km from the summit.
– Radiocarbon dating suggests that before 1822 Galunggung had a longer dormant period; the next deposits below would have been laid down 590 ± 150 years BP.
The shadowy past
– In front of the caldera opening are the “Ten Thousand Hills of Tasikmalaya”, more than 3600 hummocks of 10-80 m height in an area 6.5 km to 23 km from the crater – they are the result of a huge debris avalanche. More than one-third of the SE part of the volcano slid onto Tasikmalaya high-plain to form a fan-shaped hummocky topography covering about 170 km^2, and comprised more than 20 km^3 of material. According to radiocarbon dating this event occurred about 4200 years ago. Originally, it was thought that either the hills had been caused by a lahar through the sudden release of crater lake water, or that they were man-made. Gorshkov (1959) compared the hills below Galunggung with the 1956 gigantic “directed blast” of Bezymianny in Kamchatka. The hummocks have been long considered great to build houses on since they provided good defence against hostile people, and being above the paddy fields they were – free of mosquitoes and rats!
– The earliest known eruptions of Old Galunggung (50 ka – 10 ka ago?) ended with the intrusion of a ~250 m wide and ~500 m high cryptodome (lava dome that didn’t break through the surface) below the crater. The cryptodome then blocked the existing vent and subsequent activity moved to the weakest part of the old cone, to the ESE, resulting in the destructive eruption in which a horseshoe-shaped caldera was formed 4000 years ago.
ARE YOU READY FOR THE NEXT LAHAR?
The post-eruption period (1984-1990) was a time of rehabilitation of disaster areas, mainly to restructure the road network that was disconnected in many places. Lahars and tephra fall had brought thousands of tons of sand/gravel that damaged houses and infrastructure and clogged the streams. They had to be rebuilt and dredged, and many dams (lahar pockets) were constructed for protection. For all this, the usefulness of and easy access to volcanic sand for construction works was much appreciated. Unfortunately, the sand digging business has gone on since and grown, to the present day, legally as well as illegally. Not only is the damage to the environment in general huge, the sand miners also seem not to be particularly considerate as to where they are digging – in press articles of recent years one reads again and again complaints about river banks and protective dams along them being damaged or already collapsing.
One blog post concludes with the sad sentence “However, it turns out that ‘Ten Thousand Hills’ is now increasingly disappearing because it continues to be mined away.” Local authorities are now forced to order repairs and re-building of dams. Hopefully, this can be achieved before Gunung Galunggung gears up for her next eruption…
Enjoy! – GRANYIA
SOURCES & FURTHER READING
– GVP, Galunggung
– Neumann van Padang M., 1951. Indonesia. Catalog of Active Volcanoes of the World…
– Geological and tectonic implications […] Lembang fault (2015)
– Kompas.com – Travel – Galunggung, 05/2015
– Volcanic geology of Galunggung, West Java, Ind. (1989, S. Bronto, PDF, opens download)
– West Java – The Galunggung (Earth of Fire, Bernard Duyck)
– Traces of Disaster in “Ten Thousand Hills” (Blog)
– UPI News, 07/04/1982
– John P. Lockwood, Ph.D., eyewitness report Galunggung 1982