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). Segara Anak has a natural hot spring.
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.
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.
 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.
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.
 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.
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.
 Get in
Most visitors arrive via the village of Senaru (600 m), on the northern side of the mountain and thus closer to the main resort areas of the west coast including Senggigi. The other possible entry point is Sembalun Lawang (1,150 m), on the eastern side, which is closer to the summit.
Both villages are accessed from the main north coast road.
Entry to the park costs Rp 150,000 per person. This fee is split up as follows: 13% to the national park authority, 62% to the Rinjani ecotourism trekking program and 25% for trek route maintenance etc.
 Get around
Within the park the only way to get around is to hike. Porters can be arranged to carry your supplies.
[add listing] See
[add listing] Do
 Climbing Mount Rinjani
 The basics
At 3,726 m, Rinjani is the second highest volcano in Indonesia after Sumatra's Gunung Kerinci. It is very climbable by visitors with a high level of physical fitness. Critical is to understand and respect this great mountain: sadly, visitors have died here through failing to follow sensible procedures and make all necessary preparations.
Few actually make the very strenuous effort required to reach the actual summit but instead stop at the crater rim (approx 2,700 m) where the views of the crater lake are mind blowing. To make the extra 1,000 m ascent to the very top requires a considerably higher level of fitness, not to mention strength of spirit and sense of adventure.
Typically, a trek to the crater rim involves two days and one night on the mountain. The longer ascent to the summit can be done with just one night's camping but is often part of a longer trek of 3-4 days and two or three nights.
The current park entrance fee is Rp 150,000. Of this 13% is allocated to the Gunung Rinjani National Park, 62% to the Rinjani Trek Ecotourism Program and 25% to support the Rinjani Trek operation and maintenance program.
An organised trek is by far the easiest, safest and most popular option but it is also quite possible to make all of your own arrangements and just hire a guide and equipment from one of the trekking centres on the mountain. Rinjani Park regulations stipulate the use of a certified guide so even the most experienced and well prepared mountaineers will still need to climb Rinjani with the services of a professional guide. The mountains Licensed Guide Association (HPI) issues certification to the Rinjani guides and porters but it should be understood that the certification standards and required training are no where near as rigorous as would be expected in many other countries. Serious accidents including fatalities do occur on Rinjani treks when led by these accredited guides.
Proper sturdy climbing/hiking boots are an absolute necessity as is a substantial waterproof, windproof jacket, and a head lamp. If you are going to the top, use of poles (walking sticks) for getting through the scree (loose rock) at the top are also highly recommended. By 2,000 m, you will feel like you are not in the tropics any more as rising wet, hot air loses its temperature and may fall as rain. If inappropriate clothing becomes wet difficulties will set in as air temperatures towards the summit are as low as 4⁰C, often with a significant extra wind chill factor. You must prepare accordingly.
 Guides and trekking providers
At times it seems that everyone in Lombok is a trekking guide for Mount Rinjani, especially on the main tourist strip in Senggigi.
Take most of what you are told with a pinch of salt and you will find the most experienced and reputable guides at the main trekking centres at Senaru and Sembalun Lawang. It does happen that tourists who are highly experienced hikers or climbers may find themselves far better prepared and skilled for mountain conditions than the local guides. Codes of conduct have been developed for the local trekking support community that include climbing safety, environmental awareness and responsible use. Some of the guides and trekking organisations are better than others at respecting these agreements and guidelines. It is also a good idea to independently check for any volcanic alerts that may have been issued for Mount Rinjani.
Many visitors have found it is preferable to avoid package deals purchased away from Senaru, and instead negotiate either with one of the four trekking providers listed below or with the guides themselves to ensure that they are actually competent. If there is a problem, you can then find a different guide company in Senaru or Sembalun.
To help you judge the experience, abilities and equipment provision of a potential guide and support team it may assist to consider the following:
Guide fees are generally negotiable. Only the Rp 150,000 park entrance fee is set by the park authority. A sensible package price range would be:
These trekking fees will vary though according to how busy the guides are, how many people are in your party and if a commission is due to a referring person or agency. Some guide companies will charge as little as Rp 900,000 per person for a 2-night trek in the off-season, but it is important to check they are properly experienced, equipped and provisioned. Ensure your trek price is all-inclusive of any extra charges for transportation, provisions, porter fees and the park entrance fees.
The following all offer organised treks with accommodation, transport to the mountain, return to your accommodation and can also help with hiring a private guide if required:
 Ascent routes
Serious trekkers should explore the options of staying on the mountain for 3 nights or more with a planned trek that takes in the crater rim, down to the lake shore, the absolute summit and more. Such treks normally start in either Senaru or Sambulan Lawang however in the last couple of years some other routes have opened including the Benang Stokel, Timbanuh and Torean routes.
 The Senaru ascent route
This is by far the most used route as it allows the (relatively) less strenuous trek to the crater rim only. You start at an elevation of 600 m in Senaru village, normally in the late morning or early afternoon and make the 6 hour ascent to the crater rim before dark. The route passes through POSII at 1,500 m, breaches the treeline at 2,000 m (POSIII) and then it is a bit of slog up gravel paths to the camp site just below the crater rim at 2,600 m. Wake before dawn to make the 20 to 30 minute final climb to the crater rim to enjoy sunrise and the iconic view across Segara Anak to Gunung Baru.
If that has not sapped all of your energy you can then make a very precarious descent down to shores of the crater lake and bath in the hot waters. You need some confidence to do this as it is a steep descent of 600+ m using handrails and ropes.
And then it is back to Senaru the way you came.
There is an option to go on to Plawangan II where you overnight again before making the ascent to the absolute summit. This is not especially recommended from the Senaru side though. If you want to get to the top, the climb to Plawangan II is best made from Sambulan Lawang.
 The Sembalun Lawang ascent route
Starting in the morning from the Rinjani Trek Centre in the village, the climb to Plawangan II at 2,638 m will take about 8 hr via POSI (1,300 m), POSII (1,500 m) and POSIII (1,800 m). Overnight at the campsite here and go for the summit starting at 3AM the next day. You need to be well rested as this is a stiff task - the final climb is nearly 1,100 m on difficult ground.
 The Benang Stokel route
Departs from the village of Aik Berik in Central Lombok and is is about 27km east of Mataram or a little less than an hour’s drive. Locally Benang Stokel is well-known for its 2 waterfalls, the Benang Kelambu waterfall and Benang Stokel waterfall. Treks normally depart from this waterfall location. The ascent up to the crater rim takes around 6 hours. From there a descent to the crater lake requires a further 3 hours. This track offers lots of variety and includes the Tiara Dewi Anjani waterfall. This is an route suitable for experienced trekkers.
 Other activities
You do not have to climb to the summit of Mount Rinjani to enjoy the splendours of the national park. Indeed unless you really think that you are physically capable it would be foolhardy to even try. You will find plenty of guides in either Senaru or Sembalun Lawang to suggest lower level treks through beautiful valleys.
There are also other activities centred around the park including eco-walks and tree planting treks. Choose the provider carefully to ensure they do actually have an understanding of the local environment and an informed and genuine commitment to environmental sustainability practice. One long term Rinjani trek provider, Rinjani Trekking Club, has attempted to shift the focus of activities upon the mountain to one of environmental respect and sustainability. Programs such as carrying out rubbish and maintaining clean camp sites and trails is a stated objective of the more eco-sustainable trek providers. It is important though to ensure that if a trek marketed as eco-friendly is taken that the trekking guides' do conform to their own stated objectives and policies during the trek.
[add listing] Buy
In and around Sembalun Lawang you will have the opportunity to purchase unique and high quality hand woven cloth.
[add listing] Eat
If you are trekking outside of an organised group, you should carry in all necessary food for your trek. Fresh fruit and high energy foods are especially appropriate. If you are planning to make the ascent to the absolute summit try to carry a special food item with you for celebrating your achievement of reaching the top.
Trekking packages usually include food which is carried and prepared by the porters.
There are simple restaurants at the lodges in Senaru and Sembalun Lawang.
[add listing] Drink
If you are trekking independently, stock up with some liquids at Senaru or Sembalun Lawang. A flask of hot tea or coffee is very appropriate.
There are a lot of fresh springs on both routes and these determine the positioning of the campsites. You therefore do not need to carry large quantities of water with you. The springs can run a little dry sometimes but all guides should know the status of each spring beforehand.
[add listing] Sleep
There is no lodging in the park itself, but some simple places to stay can be found at Senaru & Sembalun Lawang.
Tanjung on the nearby northwest coast has several more upmarket offerings, and both it and the Gili Islands are reasonably close to Mount Rinjani. Many visitors choose to stay in the Senggigi region and travel north to Mount Rinjani by road.
 Accommodation for the Senaru route
 Accommodation for the Sembalun Lawang route
Camping is possible at designated rest shelter areas on the ascent routes, and at the crater rim.
 Stay safe
This is a very active volcano. Always be aware of the current assessment of eruptive activity. Sources worth keeping an eye on include local media and The Smithsonian Institute's weekly Volcanic Activity Report . Do not always take the word of a trek organiser as gospel on safety issues.
Rinjani is high enough that altitude sickness is a concern. Be aware of the symptoms and treatment.
It is also very cold up on the summit (4 to 5°C), so warm, windproof clothes are a must as are appropriate hiking boots and a head lamp. The sun can be very strong during the day and severe sunburn is a risk.
Make sure that your guide is carrying a radio with him and that it is fully charged and working. A test call to the trek centre is advisable. The trek centre has a satellite telephone and it can be used by visitors - ask to see the chart of charges.
 Get out