Toba

You may be amazed by the beauty of Lake Toba. Can you imagine Were it not accommodated in the lake water? If only it could happen, then you will see one of the giant caldera hole that ever existed on earth!
Figure 1: Photograph of Satellite Toba (Image courtesy of NASA / GSFC / MITI / ERSDAC / JAROS, and the U.S. / Japan ASTER Science Team)
Terms that will be used in this paper:

   A. Caldera can simply be defined as a large hole in the earth's surface caused by the sinking of the earth's surface that occur after a volcanic eruption.
   2. Stratovolkano: is a high volcano that formed from layers of lava, tefra, rock pumice and volcanic ash. Lava that spewed from stratovocano usually hardens as it cools, and flows generally are not too far due to the high viscosity of the lava.
   3. Tuff: Tufa: The rock that forms a compacted volcanic ash
   4. YTT: Young Toba Tuff: Tufa youngest Toba
   5. MTT: Middle Toba Tuff: Tufa old Toba
   6. OTT: Oldest Toba Tuff: Tufa is the oldest Toba.
   7. Quartenary: In geology, the geological period quartenary is second in the Cenozoic era, extending from about 2.6 million years ago. In geologic time, Earth is currently at the quartenary of Cenezoic era, and the Phanerozoic eon.
   8.
Toba caldera, located in North Sumatra, Indonesia, is the largest caldera on earth that is created during quartenary. Position extends the Northwest-Southeast direction parallel to the mountains and active volcanoes along the Sumatra. Its size is about 100 km long and 30 km wide (See Figure 2). According to experts, during the last 1.2 million years has occurred 4 times a caldera eruption that spewed tuffs. The youngest tufa spewed out about 74,000 years ago with a volume of about 2,800 km3. The last eruption caused the collapse of the structure of the earth that formed Lake Toba as we see today.
This last Toba eruption issue surrounding the flow tuffs km2 area of ​​20000-30000. Through a series of studies it appears that the younger Toba tuff layer (YTT) gradually solidified attached at the bottom. Samosir island formed of the young post-Toba tuffs contain younger Toba tuff is very solid that fills the caldera.
SETTING tectonicMap location and tectonic setting Toba caldera shown in Figure 2. Stratigraphy pieces taken near Haranggaol, Silalahi, Pangururan, Bakkara, and Siguragura. In the picture can be seen that the Toba caldera (or current Lake Toba) parallel to the fault of Sumatra (the Great Sumatran Fault) which cut the island of Sumatra in the East-West direction, and also almost parallel to the subduction fault in the Indian Ocean.
Figure-2: Tectonic Setting Location Toba (Credit: http://petrology.oxfordjournals.org/content/39/3/397/F1.large.jpg)
Toba caldera FORMATIONToba caldera formation occurred in the vast area which is taken up by the magma pressure is about 20 km beneath, which the experts named Van Bemelen called the Batak Tumor. Batak Tumor is formed in the Miocene. Toba is located at the top of the raised part. At that time 1.3 million years ago, volcanoes formed stratovolkano on the north side of the current caldera. Intake of andesitic rocks floating in the southern part of the caldera at the same time conclude that there is also the focus of intense volcanic activity in the southern part.Toba caldera, according to recent research, the caldera formed from 4 followed one after another that occurred during the last 1.2 million years.
Eruption / pyroclastic eruption of the first known in the Toba caldera formed Haranggaol 35 km3. Of research, it is clear that Haranggaol formed from the caldera in the northern mountains stratovolkano on the 1.2 million years ago (Figure 3b). Tufa produced the experts agreed as Haranggaol Dacite Tuff (HDT) is the current Haranggaol.Then, around 840,000 years ago Porsea caldera located in the southeastern half of the Toba eruption has spewed 500 km3 old Toba tuff, OTT (Figure 3c). This is the oldest tufa or Oldest Toba Tuff (OTT) to the age of 840,000 years.
Eruption activity from happening in the north of Toba about 500,000 years ago that spewed 60 km3 tuffs. Presumably these tuffs erupted from the same caldera that produces Haranggaol older tuffs (Fig. 3d). The experts agreed to name the resulting tufa as Middle Toba Tuff (MTT) is 500,000 years old.
MTT and OTT eruptions occur alternately in the north and south, but usually occurs on the steep caldera wall, and usually attached to its very solid.Finally, 74,000 years ago, Toba had a giant eruption with VEI (Volcanic explosivity index) = 8 which spew younger tuffs, YTT. Last eruption of this spurred the collapse of the structure that resulted in the sinking of the dome above the magma dome, including the two giants, namely blocks and blocks Uluan Naidoo. Debris that creates a giant caldera.This form of the caldera seen today (Figure 3e).
Water and then fill out and meet the caldera. But Naidoo and the Block Island Uluan (Porsea and Prapat) has not been established because it has not raised again. Lake Toba imagined without Samosir Island, and Porsea Parapat area? At some time after a huge eruption, the third area may still submerged under the water that fills the caldera.
After the eruption, magma pressure beneath the caldera formed spaces continue to fill the empty magma that resulted in the removal of layers of the collapsed dome. As a result of this appointment younger tufa content on Samosir Island and the content of the older tuffs on block / area Uluan (Fig. 3f) were raised, and become exposed.
Figure 3: The order of the Toba caldera formation (af) and the spread of younger Toba tuff (g). Taken from: Aldiss & Ghazali, 1984
During the appointment process, the rhyolite domes erupted along a steep fault Naidoo. Dome eruptions also occur along the ring fracture on the plain between the escarpment southwest around Pardepur (Sibaganding) and Mount Pusuk Buhit. Appointment of the chunks is what produces Samosir Island, Island Sibaganding (Pardepur) and Peninsula Uluan that exist today.
Figure 4: The boundaries of the Toba caldera and its age. (Credit: http://www.solcomhouse.com/images/toba-map_l2.jpg)
Toba is located approximately 900 m above sea level. According to the data, Samosir Island has raised about 450 meters of altitude of origin.Smaller magma pressure is still ongoing. Buhit Pusuk volcanoes and Sipiso Piso (near the Horn of Continent) is the result of volcanic mechanisms that are still happening. According to research appointment in the west of the island of Samosir (notice the brown color in Figure-4) and didatakan still happening today.
Super giant eruption that occurred 74,000 years ago at Lake Toba shed pyroclastic flow (high-speed liquid flow consisting of gas, rock fragments, and dust) that buried the region with an area of ​​about 20,000 km2 around Toba caldera. Abu vulaknik continuously shed in the range 2 weeks to fly around the earth, and is expected to accelerate the occurrence of the last ice age is coming on the earth.
Volcanic ash and lava which are then terekat each other to form a cover of rock overlies the caldera area, especially the caldera wall, and is expected to reach 400 m thick.
In South India, the Toba volcanic ash was found with up to 6 m thick and is expected to destroy the life that was there at that time. Toba eruption is also thought to make the "bottle neck" in life and human evolution, namely the reduced number of human populations thousands just to be on earth because of this disaster.