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Wednesday, February 1, 2012

World Tour Guides to Lake Toba

World Tour Guides: One of the beautiful panoramic tours of Natural is Lake-Toba-Sumatra. It is a lake and super volcano. The lake is 100 kilometers long and 30 kilometers wide, and 505 meters (1,666 ft) at its deepest point. Located in the middle of the northern part of the Indonesian island of Sumatra with a surface elevation of about 900 meters (2,953 ft) it is the largest lake in Indonesia and the largest volcanic lake in the world. Lake Toba is the site of a super volcanic eruption that occurred an estimated 69,000 to 77,000 years ago a massive, climate-changing event. It is the largest known explosive eruption anywhere on Earth in the last 25 million years.

The Toba eruption (the Toba event) occurred at what is now Lake Toba about 67,500 to 75,500 years ago. The Toba eruption was the latest of a series of at least three caldera-forming eruptions which have occurred at the volcano, with earlier calderas having formed around 700,000 and 840,000 years ago. The last eruption had an estimated Volcanic Explosively Index of 8, making it possibly the largest explosive volcanic eruption within the last 25 million years. Smaller eruptions have occurred at Toba since. The small cone of Pusukbukit has formed on the southwestern margin of the caldera and lava domes. The most recent eruption may have been at Tandukbenua on the northwestern caldera edge, since the present lack of vegetation could be due to an eruption within the last few hundred years.

Some parts of the caldera have experienced uplift due to partial refilling of the magma chamber, for example pushing Samosir Island and the Uluan Peninsula above the surface of the lake. The lake sediments on Samosir Island show that it has been uplifted by at least 450 meters (1,476 ft) since the cataclysmic eruption. Such uplifts are common in very large calderas, apparently due to the upward pressure of interrupted magma. Toba is probably the largest resurgent caldera on Earth. Large earthquakes have occurred in the vicinity of the volcano more recently, notably in 1987 along the southern shore of the lake at a depth of 11 km (6.8 mi). Other earthquakes have occurred in the area in 1892, 1916, and 1920–1922. The 2004 earthquake physically rolled the Sumatran Island and altered the shape of the Earth as was detected by the GRACE satellite. Recent highly localized earthquake activity may initiate magmatic activity of this colossal global climate modifier.

The flora of the lake includes various types of phytoplankton, emerged macrophytes, floating macrophytes, and submerged macrophytes, while the surrounding countryside is rainforest including areas of Sumatran tropical pine forests on the higher mountainsides. The fauna includes several species of zooplankton and benthic animals. Since the lake is oligotrophic (nutrient-poor), the native fish fauna is relatively scarce, and the only endemics are Rasbora tobana (strictly speaking near-endemic, since also found in some tributary rivers that run into the lake) and Neolissochilus thienemanni, locally known as the Batak fish. The latter species is threatened by deforestation (causing siltation), pollution, changes in water level and the numerous fish species that have been introduced to the lake.

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