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Lake Toba: The Largest Volcanic Lake in the World
Lake Toba Information and Facts
Lake Toba is located in one of Indonesia’s most populous provinces, North Sumatra, in the middle of the northern part of the island of Sumatra, lying at an altitude of 900 meters. It is the largest lake in Indonesia, formed in the caldera of a supervolcano.
Geography and Hydrology
Lake Toba has a maximum length of 100 km and a maximum width of 30 km, adding up to a surface area of 1130 km2. It also has a maximum depth of 505 meters, which is located on its northeastern end. The lake is surrounded by a steep coastline and small valleys. The large island of Samosir found in the middle of the lake was joined to the caldera wall by a slim isthmus, which was eventually cut through to let boats to pass. The lake’s main outflow is the Asahan River, which eventually makes its way and empties into the Strait of Malacca.
Climate, Flora and Fauna
Lake Toba is mostly surrounded by steep, pine-covered slopes. Because of the high altitude the climate is fresh and pleasant, boasting enough rain to support the lush vegetation present in the region. Compared to the tropical heat of the surrounding plains, the climate around the lake is generally cool and dry. The rainy season lasts from October to March.
Local flora is made up mostly of several types of phytoplankton, as well as emerged, floating and submerged macrophytes. The surrounding countryside is covered in rainforest, including distinct areas of Sumatran tropical pine forests at higher elevations.
The fauna is made up of various species of zooplankton and benthic animals. Since the lake is oligotrophic, the native fish fauna is somewhat lacking. The only endemics are the Rasbora tobana and the Batak fish, which is threatened because of the deforestation and pollution in the area, as well as the changes in water levels and the newly introduced fish to the lake’s waters.
Geology and Formation
The Toba caldera complex, located in Northern Sumatra, in which Lake Toba can be found, is made up of four overlapping volcanic craters, which adjoin the Sumatran volcanic front. The youngest one is the World’s largest Quaternay caldera, with a length of 100 km and a width of 30 km, intersecting the other three.
Some 75,000 years ago a major eruption occurred in the area, the last in a series of at least 4 caldera-forming eruptions in the region. The last eruption is considered the largest explosive volcanic eruption happening within the last 25 million years. Scientists of the Michigan Technological University estimate that the total amount of material which was released during the eruption adds up to 2800 km3, of which 2000 km3 is ignimbrite flowed over ground, whilst the remaining amount fell as ash.
New studies based on method-crystal concentration show that Toba possibly released an even larger amount of material, 3200 km3 to be exact. It is also said that the pyroclastic flows resulting from the eruption destroyed 20,000 km3 of land, and the ash deposits were up to 600 m thick by the main vent. The deposited ash layer was said to be up to 15 cm thick all over South Asia. At one site in Central India, the ash layer was up to 6 cm thick, whilst parts of Malaysia were covered in 9 cm thick ash.
The subsequent collapse eventually led to the formation of a caldera, which later filled with water, and the Lake Toba was born. Samosir Island, in the middle of the lake, was created by a resurgent dome, joining two half-domes separated by one longitudinal graben. At least 4 cones, 4 stratovolcanoes and 3 craters are visible in the lake. The Tandukbenua cone, located on the northwestern edge of Lake Toba, has sparse vegetation, which suggests it is just a couple of hundred years old. The Pusubukit volcano, also known as Hill Center volcano, at the southern edge of the caldera, is solfatarically active and is practically a Geology Sanctuary.
According to the pattern of the ash deposits, the eruption must have occurred during the Northern summer, since only a summer monsoon could have relocated a percentage of the ash fall in the Southern China Sea. The massive eruption supposedly lasted more than two weeks, causing a “volcanic winter”, which resulted in the decrease of global temperature by 3-3.5 degrees Celsius for several years.
Mythocondrial studies stated that evidence suggests that humans may have passed through a genetic bottleneck, which reduced the genetic biodiversity below expected, given the age of species.
Stanley H. Ambrose, of the University of Illinois at Urbana Champaign, came up with the Toba catastrophe theory, which stated that the effects of the Toba eruption might have decreased human population to merely a few thousand individuals. His hypothesis is highly debated, since similar effects on other animal species have not yet been observed, and also paleontology studies suggest that no population bottleneck took place at that time.
Recent Volcanic Activity
Because Lake Toba lies in an earthquake-prone zone, a number of smaller eruptions have occurred since the major eruption. The most recent eruption happened at the northwestern edge of the caldera, at Tandukbenua, suggested by the lack of vegetation. Parts of the caldera have been uplifted because of the partial refilling of the magma chamber, such as Samosir Island and the Uluan Peninsula. The lake sediments on the island were at least raised by 450 meters, since the cataclysmic eruption. Similar uplifts can be observed in large calderas, mostly because of the pressure of the magma below ground.
Toba is the largest resurgent caldera in the world. Larger volcanic activities have been recorded in the region in 1892, 1916, 1920, 1922 and in 1987 along its southern shore. The region is located in the Great Sumatran Fault, along the center of Sumatra in the Sumatra Fracture Zone. The volcanoes of Sumatra and Java are part of the Sunda Arc, which is the result of the northeasterly movement of the Indo-Australian Plate. The subduction zone in the area is very active.
A couple of years ago the lake has lost a significant amount of its water levels. This fact was due to deforestation and overconsumption of water by a pulp factory and a hydroelectric power plant near Porsea. After a number of protests, the factory was shot down. This action contributed to Lake Toba regaining its original water level.
Locals and Legends
The area is mostly inhabited by the Bataks, who are mostly Christian today, after encountering Christian missionaries in the 1850’s and 1860’s from the Netherlands. The first European to see the lake and actually report it was H.N. van der Tuuk, a Dutchman. Traditional Batak houses are noted for their variety in color and their special roofs, which curve upward and each end as a boat’s hull does.
A local Batak legend exists regarding the creation of the lake. As legend has it, a fisherman once caught a large fish and took it home. It was the largest catch he’d ever seen. Once at home, the fish actually turned into a beautiful princess, with whom the fisherman eventually fell in love with. When he proposed to the princess, she only had one condition before marrying him: the man should never tell anyone that she was once a fish. If he did, disaster would strike.
The man immediately agreed to keep her secret. After they got married, they had a daughter. When she was a bit grown, she’d bring lunch daily to his father. As she was greedy, one day she ate her father’s lunch and showed up on the fields empty-handed. His father got upset and yelled “Damn daughter of a fish!” to her. The girl went home crying, and the mother was shocked to hear what her husband has said to their child. She sent the girl up to the hills to safety, and started praying. Soon a large earthquake occurred, rain fell and springs appeared from everywhere, flooding the area, forming the lake. The princess turned back into a fish, while the fisherman transformed into Samosir Island.
Tourism and Recreation
The easiest way to get to Lake Toba is by flying in to Medan Kuala Namu International Airport. From the airport you can get to the lakeside town of Parapat in less than four hours by car. Getting there is also possible through public transportation, either by train or by bus. Getting around is easiest by bicycle, motorcycle (which can be rented by locals) or buses.
The lake area is very popular among Chinese tourists around the Chinese New Year, when rooming availability drops dramatically and accommodation costs skyrocket. The best thing to do at the lake is to relax, admire nature and unwind. Numerous hot springs can be found on the western part of the lake, where tourists can enjoy a relaxing day bathing in hot waters. Numerous resorts offer great spa deals. Mount Pusuk Buhit (1981 m) overlooks the hot springs, and is sacred to the Batak people, since their first ruler, Si Raja Batak has descended from heaven right to the mountain.
The town of Balige in the southern part of the lake is home to a famous mausoleum to Raja Sisimangaraja XII and a large museum dedicated to local Batak culture at the TB Silahali Center. Tourists can go hiking in the surrounding mountains and hills, swimming in the lake or sailing.
In the middle of Samosir Island you can find a small mountain, with a height of 780 meters, which is easily accessible to anyone, offering stunning views of the lake and the lakeshore towns. Simanindo houses a museum which organizes traditional Batak dances performed twice a day. Tomok is the best place to get souvenirs, mementos and Batak handicrafts, which consist of weaved clothes, sarung, scarves and other traditional Bataknese handicraft elements. The area is also home to numerous waterfalls, which attract a large number of tourists.