Lake Toba is the site of asupervolcaniceruption estimated atVEI 8 that occurred 69,000 to 77,000 years ago,[6][7][8] representing a climate-changing event. Recent advances in dating methods suggest a more accurate eruption date of 74,000 years ago.[9] It is the largest-known explosive eruption onEarth in the last 25 million years. According to theToba catastrophe theory, the eruption had global consequences for human populations as it killed most humans living at that time and is believed to have created apopulation bottleneck in central east Africa and India, which affects the genetic make-up of the human worldwide population to the present.[10] A recent study has cast doubt on this theory and found no evidence of substantial changes in global population.[11]
It was also suggested that the eruption of the Toba Caldera led to avolcanic winter with a worldwide decrease in temperature between 3 and 5 °C (5.4 and 9.0 °F), and up to 15 °C (27 °F) at higher latitudes. Additional studies inLake Malawi in East Africa show significant amounts of ash being deposited from the Toba Caldera eruptions, even at that great distance, but little indication of a significant climatic effect in East Africa.[12]
Batu Gantung (Hanging stone) in Lake TobaMap of the lake
The TobaCaldera inNorth Sumatra comprises four overlapping volcanic craters that adjoin the Sumatran "volcanic front". At 100 by 30 kilometres (62 by 19 mi) it is the world's largestQuaternary caldera, and the fourth and youngest caldera. It intersects the three older calderas. An estimated 2,800 km3 (670 cu mi) ofdense-rock equivalent pyroclastic material, known as the youngest Tobatuff, was released during one of the largest explosive volcanic eruptions in recent geological history.[13] Following this eruption, a resurgent dome formed within the new caldera, joining two half-domes separated by a longitudinalgraben.[7]
At least four cones, fourstratovolcanoes, and three craters are visible in the lake. The Tandukbenua cone on the northwestern edge of the caldera has only sparse vegetation, suggesting a young age of several hundred years. Also, the Pusubukit (Hill Center) volcano (1,971 m (6,467 ft) above sea level) on the south edge of the caldera issolfatarically active.[14]
TheToba eruption (theToba event) occurred at what is now Lake Toba about 73,700±300 years ago.[15] It was the last in a series of at least fourcaldera-forming eruptions at this location, with the earlier known caldera having formed around 1.2 million years ago.[16] This last eruption had an estimatedVEI of 8, making it the largest-known explosivevolcanic eruption in the Quaternary.
Bill Rose and Craig Chesner ofMichigan Technological University have estimated that the total amount of material released in the eruption was at least 2,800 km3 (670 cu mi)[17]—about 2,000 km3 (480 cu mi) ofignimbrite that flowed over the ground, and approximately 800 km3 (190 cu mi) that fell as ash mostly to the west. However, as more outcrops become available, Toba possibly erupted 3,200 km3 (770 cu mi) of ignimbrite and co-ignimbrite. Thepyroclastic flows of the eruption destroyed an area of least 20,000 km2 (7,700 sq mi), with ash deposits as thick as 600 m (2,000 ft) by the main vent.[17] The eruption was large enough to have deposited an ash layer approximately 15 cm (6 in) thick over all ofSouth Asia; at one site in central India, the Toba ash layer today is up to 6 m (20 ft) thick[18] and parts ofMalaysia were covered with 9 m (30 ft) of ash fall.[19]
The subsequent collapse formed a caldera that filled with water, creating Lake Toba. The island in the center of the lake is formed by aresurgent dome.
The exact year of the eruption is unknown, but the pattern of ash deposits suggests that it occurred during the northern summer because only thesummer monsoon could have deposited Toba ashfall in the South China Sea.[20] The eruption lasted perhaps two weeks, and the ensuing volcanic winter resulted in a decrease in average global temperatures by 3.0 to 3.5 °C (5 to 6 °F) for several years.Ice cores fromGreenland record a pulse of starkly reduced levels of organiccarbon 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. However, the global cooling has been discussed by Rampino and Self. Their conclusion is that the cooling had already started before Toba's eruption. This conclusion was supported by Lane and Zielinski who studied the lake-core from Africa andGISP2. They concluded that there was no volcanic winter after the Toba eruption and that highH2SO4 deposits do not cause long-term effects.[21][22] Furthermore, due to the low solubility of sulfur in the magma, the emission of volatiles and climate impacts are likely limited.[23]
Evidence from studies ofmitochondrial DNA suggests that humans may have passed through agenetic bottleneck around this time that reduced genetic diversity below what would be expected given the age of the species. According to the Toba catastrophe theory, proposed by Stanley H. Ambrose of theUniversity of Illinois at Urbana–Champaign in 1998, the effects of the Toba eruption may have decreased the size of human populations to only a few tens of thousands of individuals.[24] However, this hypothesis is not widely accepted because similar effects on other animal species have not been observed, andpaleoanthropology suggests there was nopopulation bottleneck.[25][26] The genetic bottleneck is now recognized to be theOut-of-Africafounder effect, rather than an actual reduction in population.[27]
Since the major eruption ~70,000 years ago, eruptions of smaller magnitude have also occurred at Toba. The small cone of Pusukbukit 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, suggested by a lack of vegetation that could be due to an eruption within the last few hundred years.[28]
Some parts of the caldera have shown uplift due to partial refilling of themagma chamber, for example, pushingSamosir Island and theUluan Peninsula above the surface of the lake. The lake sediments on Samosir Island show that it has risen by at least 450 m (1,476 ft)[16] since the cataclysmic eruption. Such uplifts are common in very large calderas, apparently due to the upward pressure of below-groundmagma. Toba is probably the largest resurgent caldera on Earth. Largeearthquakes have recently occurred in the vicinity of the volcano, notably in 1987 along the southern shore of the lake at a depth of 11 km (6.8 mi).[29] Such earthquakes have also been recorded in 1892, 1916, and 1920–1922.[16]
In 2016, a study revealed that the Toba Supervolcano has a magma chamber containing 50,000 cubic kilometres (12,000 cu mi) of eruptible magma, about 30–50 kilometres (19–31 mi) underground.[30] This makes the supervolcano's magma chamber more than four times larger than the volume ofLake Superior in North America, and also larger than the magma chamber underneathYellowstone.[31]
Batak canoes near Haranggaol on Lake Toba (circa 1920)
Most of the people who live around Lake Toba are ethnicallyBataks. 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.[32]
Theflora of the lake includes various types ofphytoplankton, emergedmacrophytes, floating macrophytes, and submerged macrophytes, while the surrounding countryside is rainforest including areas ofSumatran tropical pine forests on the higher mountainsides.[33]
On 18 June 2018, Lake Toba was the scene ofa ferry disaster, in which over 160 people drowned.[37]MVSinar Bangun was an irregular operating vessel on the lake which capsized with many passengers on board. The incident caused the death of 167 people and injuries to a number of others. Preliminary reports found the vessel was in operation with irregularities. Ignoring overloading on the vessel and operating in rough weather conditions were concluded to be the main reasons leading to the disaster.
The Origin of Lake Toba is a folk story about the lake, in which once upon a time, there was a fisherman who caught a golden fish. Samosir Island is believed to be the golden fish's son.[38]
^Ninkovich, D.; N.J. Shackleton; A.A. Abdel-Monem; J.D. Obradovich; G. Izett (7 December 1978). "K−Ar age of the late Pleistocene eruption of Toba, north Sumatra".Nature.276 (5688):574–577.Bibcode:1978Natur.276..574N.doi:10.1038/276574a0.S2CID4364788.
^Scrivenor, John Brooke (1931).The Geology of Malaya. London: MacMillan.OCLC3575130., noted by Weber.
^Bühring, C.; Sarnthein, M.; Leg 184 Shipboard Scientific Party (2000). "Toba ash layers in the South China Sea: evidence of contrasting wind directions during eruption ca. 74 ka".Geology.28 (3):275–278.doi:10.1130/0091-7613(2000)028<0275:TALITS>2.3.CO;2.{{cite journal}}: CS1 maint: numeric names: authors list (link)
^"Yellowstone Is a Supervolcano?".Biot Reports (164). Suburban Emergency Management Project. 11 January 2005. Archived fromthe original on 13 January 2008. Retrieved21 February 2008.
^Petraglia, Michael D (2012). "The Toba volcanic super-eruption, environmental change, and hominin occupation history in India over the last 140,000 years".Quaternary International.258:119–134.Bibcode:2012QuInt.258..119P.doi:10.1016/j.quaint.2011.07.042.
^Lumbantobing, Daniel N (2010). "Four New Species of the Rasbora trifasciata-Group (Teleostei: Cyprinidae) from Northwestern Sumatra, Indonesia".Copeia.2010 (4):644–70.doi:10.1643/CI-09-155.S2CID86114358.
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