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Lake Toba

2007 Schools Wikipedia Selection. Related subjects: Geography of Asia

                  Lake Toba, Indonesia
   Lake Toba, Indonesia - Landsat photo of Lake Toba

                         Landsat photo of Lake Toba

   Coordinates       2°37′N 98°49′E
   Basin countries   North Sumatra, Indonesia
   Max-length        100 km
   Max-width         30 km
   Surface area      1130 km²
   Max-depth         505 m
   Water volume      240 km³
   Surface elevation 905 m

   Lake Toba ( Indonesian: Danau Toba) is a large lake, 100 km long and 30
   km wide, in the middle of the northern part of the Indonesian island of
   Sumatra with a surface elevation of about 900 m (3000 feet), stretching
   from 2.88° N 98.52° E to 2.35° N 99.1° E.

Geology

   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, 3000 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 eruption

   Location of Lake Toba shown in red on map.
   Enlarge
   Location of Lake Toba shown in red on map.

   The Toba eruption (the Toba event) occurred at what is now Lake Toba
   about 71,500 ± 4000 years ago. It had an estimated Volcanic Explosivity
   Index of 8 (described as "mega-colossal"), making it possibly the
   largest volcanic eruption within the last two 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 2000 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 cubic km of material, whilst the largest volcanic eruption in
   historic times, at Mount Tambora in 1815, emitted the equivalent of
   around 100 cubic kilometres of dense rock and created the " Year
   Without a Summer" as far away as North America.

   The Toba eruption was the last 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.
   Landsat photo of Sumatra surrounding Lake Toba
   Enlarge
   Landsat photo of Sumatra surrounding Lake Toba

   The subsequent collapse formed a caldera that, after filling with
   water, created Lake Toba.

   The eruption lasted perhaps two weeks, but the ensuing "volcanic
   winter" resulted in a decrease in average global temperatures by 3 to
   3.5 degrees Celsius for several years. Greenland ice cores record a
   pulse of starkly reduced levels of organic carbon sequestration. Very
   few plants or animals in southeast Asia would have survived, and it is
   possible that the eruption caused a planet-wide die-off. There is some
   evidence, based on mitochondrial DNA, that the human race may have
   passed through a genetic bottleneck within this timeframe, reducing
   genetic diversity below what would be expected from the age of the
   species. According to the Toba catastrophe theory proposed by Stanley
   H. Ambrose of the University of Illinois at Urbana-Champaign in 1998,
   human populations may have been reduced to only a few tens of thousands
   of individuals by the Toba eruption.

More recent activity

   Children playing in Lake Toba
   Enlarge
   Children playing in Lake Toba

   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 metres
   since the cataclysmic eruption. Such uplifts are common in very large
   calderas, apparently due to the upward pressure of unerupted 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. Other earthquakes have occurred in the area in 1892, 1916, and
   1920-1922.

   Lake Toba lies near a fault line which runs along the centre of Sumatra
   called the Sumatra Fracture Zone . The volcanoes of Sumatra and Java
   are part of the Sunda Arc, a result of the northeasterly movement of
   the Indo-Australian Plate which is sliding under the eastward-moving
   Eurasian Plate. The subduction zone in this area is very active: the
   seabed near the west coast of Sumatra has had several major earthquakes
   since 1995, including the 9.3 2004 Indian Ocean Earthquake and the 8.7
   2005 Sumatra earthquake, the epicenters of which were around 300 km
   from Toba.

People

   Most of the people who live around Lake Toba are ethnically Bataks.
   Traditional Batak houses are noted for their distinctive roofs (which
   curve upwards at each end, as a boat's hull does) and their colorful
   decor.

   Retrieved from " http://en.wikipedia.org/wiki/Lake_Toba"
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