History of Mount Toba

Samosir-Mount Toba Lake Toba is now a complex which is the caldera with the island of Samosir in the middle.
Mount Toba is the giant volcano is an active volcano in the category of very large, estimated to last erupted about 74,000 years ago leaving a lake that is Lake Toba, North Sumatera, Indonesia as the world's largest caldera.
Scientific evidence
In 1939, Dutch geologist Van Bemmelen reported that Lake Toba, a length of 100 kilometers and 30 kilometers wide, surrounded by relics of pumice from the eruption. Therefore, Van Bemmelen concluded, Toba is a volcano. Later, several other researchers discovered dust rhyolite (rhyolite) are the same age as rocks Toba in Malaysia, even as far as 3,000 kilometers to the north to Central India.
Some marine experts have also reported finding traces of Toba rocks in the Indian Ocean and Bay of Bengal. The researchers start, Van Bemmelen also Aldiss and Ghazali (1984) has been created through a suspect Toba eruption mahadahsyat. However, other researchers, Vestappen (1961), Yokoyama and Hehanusa (1981), and Nishimura (1984), assumed the caldera was created by several eruptions. Researchers later, Knight and colleagues (1986) and Chesner and Rose (1991), provide an estimate of more detail: the Toba caldera created by three giant eruptions.
Research around Toba is not over until now. So, there are still many mysteries behind the sleeping giant. One of the newest generation of researchers Toba is Fauzi from Indonesia, seismologists at the Meteorology and Geophysics Agency. Degree in physics from University of Indonesia, 1985 graduates earned a doctorate from Renssealer Polytechnic Institute, New York, in 1998, for research on the Toba.
Being in three tectonic plates
Location of the Mount Toba (now: Lake Toba), in Indonesia is prone to disasters. This is related to the position of Indonesia which is located at the confluence of three tectonic plates, the Eurasian, Indo-Australian and Pacific Plate. As many as 80% of the territory of Indonesia, located on the Eurasian plate, which includes Sumatra, Java, Kalimantan, Sulawesi and Banda.
This continental shelf life, every year they shifted or mashing other plate with a certain distance. Eurasian Plate is a continental shelf is always a target. Indo-Australian Plate for example mashing the Eurasian plate as far as 7 cm per year. Or the Pacific Plate are shifted relative to the Eurasian plate as far as 11 cm per year. From that shift came the series of mountains, including the Toba volcano.
If there is a collision, slab ocean sediment layers containing infiltrate beneath the continental shelf. This process is then called subduction or infiltration.
Mount the subduction, one Mount Toba. Although now no longer shaped mountain, remnants of eruptive kedasahyatan still looks today. Lake Toba is a caldera formed by the eruption of Mount Toba is about three times the first 840 million years ago and the last 74 000 years ago. The part that was thrown by the eruption reached the area of ​​100 km x 30 km square. The remaining area and then forming the caldera. In the middle and then came the island of Samosir.
Previously Mount Toba erupted three times ever.
The first eruption occurred about 840 million years ago. This eruption produced the caldera in the south of Lake Toba, covering area Prapat and Porsea.
The second eruption that has a smaller force, occurred 500 million years ago. This eruption formed the caldera in the north of Lake Toba. Precisely in the area between Silalahi with Haranggaol. From these two eruptions, the eruption of the most fierce ketigalah.
The third eruption 74,000 years ago produced a caldera, and be present with Lake Toba Samosir Island in the middle.
Mount Toba is classified Supervolcano. This is because Mount Toba has large pockets of magma that erupted kalderanya if huge. Volcano kalderanya hundreds of meters, while Supervolacano is tens of kilometers.
What is interesting is the gravity anomaly in Toba. According to the law of gravity, from one place to another will have the same force of gravity when has mass, and the relativity of the same height. If any other material that was in there with different masses, then the tensile force is different. Imagine the mountain erupted. A lot of material that comes out, which means mass loss and tensile force is reduced. Then going up-lifting (removal). This is what led to the emergence of Samosir Island.
Magma below continued to urge upward, slowly. He has no power to erupt. This movement is trying to adjust to normal gravity. This happens within a period of thousands of years. Only Naidoo who was taken because it is the weakest area. While other regions is the caldera wall.
by: History of Lake Toba