Mount Rinjani or Gunung Rinjani is an active volcano in Indonesia on the island of Lombok. Administratively the mountain is in the Regency of North Lombok, West Nusa Tenggara (Indonesian: Nusa Tenggara Barat, NTB). It rises to 3,726 metres (12,224 ft), making it the second highest volcano in Indonesia.
On the top of the volcano is a 6 km by 8.5 km caldera, which is filled partially by the crater lake known as Segara Anak (Child of the Sea). This lake is approximately 2000 metres above sea level and estimated at being around 200 metres deep, the caldera also contains hot springs.
In Lombok, Rinjani volcano lies approximately 300 km north of the Sunda Trench (also known as Java trench) and is situated about 170 km above the active north dipping Benioff zone. Based on the composition of andesites which have very low Ni concentrations and low Mg/Mg+Fe It is suggested that the Rinjani suite is of mantle origin, but that all the andesites and dacites as well as many of the basalts have probably been modified by fractional crystallization processes.
It is concluded that the Rinjani calc-alkaline suite, which in many respects is typical of many suites erupted by circum-pacific volcanoes, probably originated by partial melting of the peridotite mantle-wedge overlying the active Benioff Zone beneath Lombok Island.
The Pleistocene-Recent calcalkaline suite from the active volcano, Rinjani is composed of a diverse range of lavas. These include: ankaramite, high-Al basalt, andesite, high-K andesite and dacite. Sr-isotopic and geochemical constraints suggest that this suite was derived from the sub-arc mantle. Geochemical models suggest that fractional crystallization is an important process in the suite’s differentiation, although the series: ankaramite-high-Al basalt-andesite-dacite does not represent a continuously evolving spectrum of liquids.
Recent activity Rinjani erupted three times on May 22, 2010 with activity continuing until early on May 23. According to the volcano’s official monitoring agency, ash from Mount Barujari was reported as rising up to two km into the atmosphere and damaged crops. The volcano did not threaten villagers at that time. Lava flowed into the caldera lake, pushing its temperature up from 21°C to 35°C, while smoke spread 12 km.
In February 2010 observers at the Gunung Rinjani Observation Post located 12.5 km (4000 feet) NE northeast of G. Rinjani saw one whitish-colored plume that rose 100 metres (328 ft) from the volcano. Dense whitish plumes (and possibly brown) rose 500 metres (1,640 ft) – 900 metres (2,953 ft) in March 2010 on 26 occasions and as high as 1,500 metres (4,921 ft) in April 2010 on 41 occasions. Plumes seen on 1 and 2 May 2010 were “chocolate” in color and rose a maximum height of 1,600 metres (5,249 ft). From February 2010 through April 2010 seismicity decreased, although the maximum amplitude of earthquakes increased. CVGHM (Center of Volcanology and Geological Hazard Mitigation) also noted that ash eruptions and ejected incandescent material fell within Rinjani caldera, but some ash was blown out of the caldera.
The activity in early 2010 centred about Gunung Barujari a post-caldera cone that lies within the Rinjani’s caldera lake of Segara Anak. The Volcanological Survey of Indonesia reported on 1 May 2010, that a column of smoke was observed rising from G. Rinjani “issuing eruptions 1300-1600 metres tall with thick brown color and strong pressure”. Their report Evaluasi Kegiatan G. Rinjani of 4 May also stated that on 1 May 2010 at 10:00 four events of Explosve Earthquake were recorded with a maximum amplitude of 6–53 mm and 110 seconds long earthquake, earthquake tremor events with a maximum amplitude of 1 mm and 55 second long duration, 15 Local Tectonic earthquake events and two events of tectonic earthquake.
The Volcanic Explosivity Index (VEI) Alert Level was raised to 2 (on a scale of 1-4) on 2 May 2010. Level 1 is “Normal” and Level 2 is “Advisory” with an Aviation Alert color of Yellow-Advisory. Based on analysis of satellite imagery, the Darwin VAAC (Volcanic Ash Advisory Center) reported that on 5 May a possible ash plume from Rinjani rose to an altitude of 5.5 km (18,000 ft) a.s.l. and drifted 150 km NW. The plume was not seen in imagery about six hours later. CVGHM (Center of Volcanology and Geological Hazard Mitigation) advised the VAAC that intermittent activity could produce ash plumes to 1.5 km (5,000 ft) above the caldera.
On 27 April 2009 Gunung Barujari became active with activity continuing through to May 2009. The mountain was closed at that time as the eruptions intensified with plumes of smoke and ash as high as 8,000 m (26,250 ft). A Volcanic Explosivity Index (VEI):2 rating was issued for the activity between 2 May 2009 and 20 December 2009. The activity during this period was described as having the characteristics:of central vent eruption, flank (excentric) vent, explosive eruption and lava flow(s).
Rinjani National Park
The volcano and the caldera are protected by the Gunung Rinjani National Park established in 1997. Tourism is increasingly popular with trekkers able to visit the rim, make their way into the caldera or even to make the more arduous climb to the highest point; fatalities, however, are not uncommon. In July 2009 the summit route was closed due to volcanic activity at that time and subsequently reopened when the activity decreased. During early 2010 up to and including May 2010 access to Rinjani was at times again restricted due to volcanic activity.
The park is popular for mountain climbs and trekking and represents an important nature reserve and water catchement area. The park is officially 41,330 hectares within the park boundaries and includes a further 66,000 hectares of protected forest outside. The mountain and its satellites form the Mount Rinjani National Park (Taman Nasional Gunung Rinjani) – officially 41,000 hectares within the park boundaries and a further 66,000 hectares of protected forest outside. In 2008, the Indonesian government proposed to UNESCO that Mount Rinjani be one of the world’s official geoparks. If this was approved by UNESCO, Mount Rinjani would become the first such geological park in Indonesia.
It has been claimed that the preliminary documentation required for UNESCO registration has not received sufficient support from the Nusa Teggara Barat government offices. Among the requirements to become a geo-park sufficient information must be supplied to show that the location has sufficient and appropriate management, information services, access to educational instruction to facilitate “knowledge-based geotourism”, the implementation of a sustainable regional economy, biodiversity conservation, and to have established public access to the park area.
Mount Rinjani has obtained the World Legacy Award from Conservation International and Traveller (2004), and was a finalist for Tourism for Tomorrow Awards (2005 dan 2008) from the World Travel Tourism Council (WTTC).
Best time to trek in Rinjani : April to November
Designated : Minister of Forestry, SK.No.280/Kpts-II/97, a total area of 41,330 hectares Location : Regencies; West Lombok, Central Lombok and East Lombok, Province of West Nusa Tenggara
Temperature 23° – 30° C Rainfall 2,000 mm/year (on average) Altitude 550 – 3,726 m asl. Geographical location 116°18? – 116°32? E; 8°18? – 8°33? S