Lake Segara Anak: The Charm of Mt. Rinjani's Giant Caldera  

TEMPO.CO, Jakarta - The sun was slowly setting behind Lake Segara Anak, its light flickering on the lake's calm surface. In mid-October, the lake became desolate at dusk. There were only seven tourist tents camped by the lake. "Usually there are dozens. Sometimes we can't find a spot to put up a tent," said our guide and porter, Mastur, 38. The lack of visitors, he said, was due to Mount Barujari's eruption in late September. "Many guests canceled their Rinjani hike," Mastur said. He comes from the hamlet of Torean in North Lombok's Loloan village.

Mount Barujari soars from the center of Lake Segara Anak, about 1.5 kilometers away from where tourists camp out. The active volcano formed almost concurrently with Segara Anak after the ancient Mount Rinjani's (Mount Samalas) massive eruption in 1257. As a result of the 7 VEI (Volcanic Explosivity Index) magnitude eruption, Mount Samalas collapsed, forming a giant caldera with an area of about 7.5 x 6 kilometers, leaving some of the peak intact. The peak, with a height of 3,726 MASL (meters above sea level), is now known as Rinjani's peak.

According to Rachmat Heryadi, a researcher at the Bandung Geology Museum, after 300 to 400 years, Lake Segara Anak began to form in the giant caldera, with water collected from the rain and local springs. After the lake of around 11 million square meters and a depth of 20 to 230 meters was formed, Rinjani's magma has continued to flare. This was marked by the emergence of Mount Barujari's cone from within Segara Anak. "Today it has already reached a height of 2,376 MASL," said Heryadi, who is currently preparing a book on the history of Rinjani's evolution.

Segara Anak, at 2,008 MASL, is the highest caldera lake with an active volcano in Indonesia, and even in the world. The air there is chilly, with temperatures ranging from 15 to 18 degrees Celsius, while at night temperatures may drop to 5 degrees Celsius. A fog can suddenly appear, replacing the clear morning or evening at the crescent-shaped lake, surrounded by the steep cliffs of Mount Rinjani.

Segara Anak's scenic charms are a tourist attraction, making it an icon of Rinjani. In 2004, the magazine National Geographic Traveler and Conservation International named the area the world's best nature destination. Currently, the spot which is part of the Mount Rinjani National Park, is being proposed as one of UNESCO's Global Geoparks.

Since the 2000s, Rinjani and Segara Anak have become increasingly popular with tourists, especially foreigners. Every year their numbers continue to rise, from about 15,000 in 2010 to around 70,000 in 2015. As of September 2016, the number of tourists visiting Segara Anak and Gunung Rinjani went over 87,000.

Arguably, climbing Rinjani feels incomplete if one does not also visit Lake Segara Anak. To reach the lake, two commonly used hiking trails are taken, the Sembalun and Senaru routes. The Torean route is also used quite a lot by local hikers. On our guide's advice, photographer Aditia Noviansyah and I chose the Torean route. "Apart from being shorter and taking less time, that route has nicer, more diverse scenery," said Amak Herni, 57, our guide and senior porter from Torean Hamlet.

It was true. The Torean track offered diverse natural scenery. Along the way, flanked by the rear wall of Mount Rinjani and Sangkareang, we were presented with thick forests, cliffs, valleys, rivers, waterfalls, and natural hot springs, including those flowing in caves. Numerous forest insects, all kinds of birds, monkeys, and other fauna greeted us along the way.

We rested for quite a while at the Plawangan-Torean guard post, surrounded by large and small rocks, and enjoyed our view of the 100 meter-high Penimbung waterfall. The waterfall is about 300 meters from the Plawangan Post and falls from a niche at an elevation of around 1,200 MASL. At the time, a bewitching rainbow arched over the waterfall.

It would have been a great pity to miss such diverse landscapes. We also chose not to go straight to the lake, which is an 8 to 10-hour walk from Torean. We spent the night at the Propok Post, located where the Propok and Propok Putih rivers meet, both originating at Segara Anak. The next day, after climbing a steep ridge and passing through grasslands, we finally arrived at the turquoise lake.

According to one study, the lake's water temperature is 20 to 22 degrees Celsius, relatively neutral, making it suitable for breeding fish. This is because the water continues to circulate. The lake contains hydrothermal chemicals that mix with rain water, making it an ideal habitat for fish.

Since 1985 Segara Anak has been used to breed fish. At the time, the government of West Nusa Tenggara under Governor Gatot Suherman seeded it with nila and mujair (tilapia species). The nila species reproduces very rapidly and is now thought to number in the millions. As we stood on the lake shore, hundreds of young nila milled around close to us. "Fishing in the lake is easy because it has so many fish," said Ruslan, 40, an East Lombok hiker, showing us a palm-sized nila as proof.

TEMPO TEAM