Danau Segara Anak is a volcanic lake formed in the caldera of Mount Rinjani
on over 2,000 meters above sea level. The lake spans across an area of
11 square kilometers, and reaches depths up to 230 meters. Danau Segara
Anak is located on the west side of Mount Rinjani in the village of
Lawang Sembalun in Lombok, East Indonesia. The mystifyingly blue colour of the lake gives Segara Anak its name: Small Ocean.
The trek from the Senaru Village, and
through the crater to Danau Segara Anak takes two days and a night. It
begins with a hike through a lush, tropical rainforest, and up the
mountain to the rim of the crater. The trek to the Senaru rim is a
challenging climb up steep terrain and high cliffs, but the exhaustion
is well rewarded by the breathtaking panoramic view of the sun setting
over Mount Rinjani, Bali and the Gili Isles on
the horizon, and the dazzling blue waters of Segara Anak glistening
hundreds of meters below. The top of the crater is a popular camp site
for both foreign and domestic tourists on this journey to spend the
night. It is advisable to set a morning alarm so as not to miss the
magnificence of dawn from atop Rinjani.From the crater’s rim, it is a
sharp descent of about 600 meters to Danau Segara Anak.
Part of Segara Anak flows down a steep
ravine forming one large waterfall and several smaller ones. There are
also four natural hot springs in the lake which are said to hold magical
healing powers, and many make the climb solely for medicinal purposes.
Despite its high altitudes, taking a dip
in the lake is not as cold as one might imagine. 2,010 meters above sea
level, the surface water of the lake is unusually warm for such
heights, at about 20-22 degrees Celsius—well above the mountain’s “room
temperature,” which is about 14-15 degrees Celsius.
Between 2008 and 2009, researchers of
Volcanology and Geological Hazard Mitigation as well as UniversiteLibre
de Bruxells conducted a geochemical and thermodynamic study on Segara
Anak. The tests showed several leaks in the volcanic system of Gunung
Baru; the cone in the center of the lake. These leaks from the magma
chamber seep a large supply of hot water into Segara Anak, indicating a
direct relationship between volcanic activity and the lake’s high
temperature. The geochemical composition of the hot water showed a
number of elements such as chloride, sodium, potassium, and sulphate.
Although rich in elements, rainwater that enters the lake assists in
thinning its chemical content. Segara Anak also maintains excellent
circulation, and is therefore not harmful to life.
Lake water circulation takes place when
the density of the water is higher at the surface than at the base.
Rainwater has a higher density than the hydrothermal water, and
therefore moves downward, while waters from the hydrothermal vent move
up. This is an on-going process providing well-mixed water and bringing
the acid level of the lake to neutral—suitable for breeding fish.
In 1969, volcanologists from the
Directorate of Geology, (London,) examined the lake and recommended the
cultivation of fish. At that time, there were no fish in Segara Anak. In
1985, the Nusa Tenggara Barat provincial government finally began
breeding fish in the lake. The fish bred rapidly and the lake is now
home to millions of tilapia and carp, making Segara Anak not only a
popular spot for fishing, but some locals of the area even make a living
from this.
In the 1980’s, the areas surrounding
Segara Anak pulsated with wildlife. Grouse, hornbill, and barking deer
thrived around the lake. Several species of monkey could be found in the
forests, including the rare black ebony leaf monkey, and the black
crested macaque, indigenous to Indonesia. But human intervention has
changed the ecology of the lake. With more and more people climbing up
the mountain and into the lake, more and more species have begun to
disappear. Initially, people only caught fish, but then grouse, which
soon led to deer hunting as well. Now few grouse remain, and the deer
are no longer found along the route. It is estimated that only a hundred
or so remain.
