History
This is a very active volcano.
The oldest recorded historical eruption was in 1847. Previous to that this was a very remote region indeed, hence the lack of records.
There was a spate of activity from 1994 to 1995 which resulted in the further growth of the crater cone Gunung Baru, since renamed Gunung Barujari Finger Mountain.
On 27 April 2009 Gunung Barujari became active again with that activity continuing through to May 2009. The summit ascent routes were closed at that time as the eruptions intensified with plumes of smoke and ash as high as 8,000 m. A Volcanic Explosivity Index VEI:2 rating was issued for the activity between May and December 2009. The ascent routes re-opened on September 14th 2009 but hiking routes down into the crater lake were still deemed unsafe and remained closed.
In February 2010 observers at the Gunung Rinjani Observation Post detected a smoke plume that rose 100 m from the volcano. The activity in early 2010 is centred about Gunung Barujari. On May 1st 2010 a column of smoke was again observed rising from Rinjani issuing eruptions 1,300-1,600 metres tall with thick brown color and strong pressure. On May 5th 2010 a possible ash plume rose to an altitude of 5.5 km 18,000 ft and drifted 150 km NW. Accordingly the Center of Volcanology and Geological Hazard Mitigation advised that intermittent activity could produce ash plumes to 1,500 m 5,000 ft above the caldera. In light of this The Volcanic Explosivity Index Alert Level was raised to 2 with a recommendation that there be no activity within a radius of 4 km from the eruption at Gunung Barujari.
Understand
At 3,726 m, Rinjani is the second highest volcano in Indonesia, second only to Mount Kerinci on Sumatra, and it dominates the landscape of the relatively small island of Lombok.
Within its huge 50 km² caldera sits the crater lake Segara Anak Child of the Sea. Eruptions within the caldera have formed a new small cone called appropriately enough, Gunung Baru New Mountain.
The mountain and its satellites form the Mount Rinjani National Park Taman Nasional Gunung Rinjani (http://www.dephut.go.id/I...) - 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.
Climate
Rinjani is best climbed during the April-November dry season. It is possible to climb during the rainy season as well but treks are often cancelled at short notice if the rain is heavy.
It gets very cold on the mountain above 2,000 m and nears freezing at the summit. Warm clothing is an absolute must.
Recent activity
Rinjani erupted three further times on 23 May 2010 with activity continuing until 24 May 2010. According to the volcano's official monitoring agency, ash from Mount Barujari was reported as rising up to 2 km into the atmosphere and damaged crops. Lava flowed into the caldera lake, pushing its temperature up from 21°C to 35°C, while smoke spread 12 km. The volcano did not directly threaten villagers during any of the eruptive activity in early 2010 however access to some sections of the Mountain was officially closed or restricted at some times.
Flora and fauna
The lower and middle elevation slopes are densely forested with typical tropical species. Fig trees are especially apparent. Casuarina forest cemara takes over higher up and eventually these give way to an alpine flora above the treeline.
Lombok is east of the Wallacean Line and some Australian bird species are therefore apparent. These include a lot of sulphur crested cockatoos and green hanging parrots. Bird life is generally not easy to observe here though due to the density of the forest.
The familiar long-tailed grey macaque the Bali temple monkey is common right up to the crater rim. Of much more interest is the rare ebony leaf monkey which inhabit these forests. Rusa deer and muntjacs are more often heard than seen.
Landscape
The lower and mid levels of the mountain are quite heavily forested. Above the tree line though the slopes are barren and rugged scree slopes and volcanic rock. The views of the crater lake are quite breath-taking from the caldera rim, as is the sunrise. From the absolute peak you can see Bali to the west and Sumbawa to the east.