Danau Toba

Lake Toba (Indonesian: Danau Toba) is a lake, 100 km long and 30 km wide, and 505 m. (1,666 ft.) at its deepest point, in the middle of the northern part of the Indonesian island of Sumatra with a surface elevation of about 900 m (3,000 feet), stretching from 2.88° N 98.52° E to 2.35° N 99.1° E. It is the largest volcanic lake in the world.

In 1949 the Dutch geologist Rein van Bemmelen reported that Lake Toba was surrounded by a layer of ignimbrite rocks, and that it was a large volcanic caldera. Later researchers found rhyolite ash similar to that in the ignimbrite around Toba (now called Young Toba Tuff to distinguish it from layers deposited in previous explosions) in Malaysia and India, 3,000 km away. Oceanographers discovered Toba ash, with its characteristic chemical "fingerprint", on the floor of the eastern Indian Ocean and the Bay of Bengal.

The Toba eruption (the Toba event) occurred at what is now Lake Toba about 67,500 to 75,500 years ago.[2] It had an estimated Volcanic Explosivity Index of 8 (described as "mega-colossal"), making it possibly the largest explosive volcanic eruption within the last twenty-five million years.

Bill Rose and Craig Chesner of Michigan Technological University deduced that the total amount of erupted material was about 2800 cubic km (670 cubic miles) — around 2,000 km³ of ignimbrite that flowed over the ground and around 800 km³ that fell as ash, with the wind blowing most of it to the west. By contrast, the 1980 eruption of Mount St. Helens ejected around 1.2 cubic km of material, whilst the largest volcanic eruption in historic times, at Mount Tambora in 1815, emitted the equivalent of around 100 cubic kilometers of dense rock and created the "Year Without a Summer" as far away as North America.

The Toba eruption was the latest of a series of at least three caldera-forming eruptions which have occurred at the volcano. Earlier calderas were formed around 700,000 and 840,000 years ago.

To give an idea of its magnitude, consider that although the eruption took place in Indonesia, it deposited an ash layer approximately 15 cm (6 in) thick over the entire Indian subcontinent; at one site in central India, the Toba ash layer today is up to 6 m (20 feet) thick and parts of Malaysia were covered with 9 m of ashfall.[5] In addition it has been calculated that 1010 metric tons of sulphuric acid was ejected into the atmosphere by the event, causing acid rain fallout. The subsequent collapse formed a caldera that, after filling with water, created Lake Toba. The island in the center of the lake is formed by a resurgent dome.

The large volcano island in the middle of Lake Toba is Pulau Samosir (Samosir Island). At 630km², Samosir is also notable as being the largest island within an island, and the fifth largest lake island in the world.

Samosir is a popular tourist destination due to the fantastic vistas it offers. The tourist resorts are concentrated in the Tuktuk area. The island is the centre of the Batak culture and many of this people's artifacts remain on the island.

Source: Wikipedia, Wikitravel