Суматрадағы алып жанартау көлі – Тоба жарылысы

Crater lake located in Sumatra, Indonesia

Lake Toba is the site of a supervolcanic eruption estimated at VEI 8 that occurred 69,000 to 77,000 years ago, representing a climate changing event. Recent advances in dating methods suggest a more accurate identification of 74,000 years ago as the date. It is the largest known explosive eruption on Earth in the last 25 million years. According to the Toba 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 a population bottleneck in central east Africa and India, which affects the genetic make up of the human worldwide population to the present. More recent studies had cast doubt on this theory and found no evidence of substantial changes in global population. It was also suggested that the eruption of the Toba Caldera led to a volcanic winter with a worldwide decrease in temperature between , and up to in higher latitudes. Additional studies in Lake 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.

The Toba Caldera in North Sumatra comprises four overlapping volcanic craters that adjoin the Sumatran "volcanic front". At it is the world's largest Quaternary caldera, and the fourth and youngest caldera. It intersects the three older calderas. An estimated of dense rock equivalent pyroclastic material, known as the youngest Toba tuff, was released during one of the largest explosive volcanic eruptions in recent geological history. Following this eruption, a resurgent dome formed within the new caldera, joining two half domes separated by a longitudinal graben. At least four cones, four stratovolcanoes, 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 ( above sea level) on the south edge of the caldera is solfatarically active.

The Toba eruption (the Toba event) occurred at what is now Lake Toba about 73,700±300 years ago. It was the last in a series of at least four caldera forming eruptions at this location, with the earlier known caldera having formed around 1.2 million years ago.—about of ignimbrite that flowed over the ground, and approximately that fell as ash mostly to the west. However, as more outcrops become available, Toba possibly erupted of ignimbrite and co ignimbrite. The pyroclastic flows of the eruption destroyed an area of least , with ash deposits as thick as by the main vent. and parts of Malaysia were covered with of ash fall. The subsequent collapse formed a caldera that filled with water, creating Lake Toba. The island in the center of the lake is formed by a resurgent 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 the summer monsoon could have deposited Toba ashfall in the South China Sea. The eruption lasted perhaps two weeks, and the ensuing volcanic winter resulted in a decrease in average global temperatures by for several years. Ice cores from Greenland 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. 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 and GISP2. They concluded that there was no volcanic winter after the Toba eruption and that high H2SO4 deposits do not cause long term effects. Furthermore, due to the low solubility of sulfur in the magma, the emission of volatiles and climate impacts are likely limited. Evidence from studies of mitochondrial DNA suggests that humans may have passed through a genetic 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 the University 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. However, this hypothesis is not widely accepted because similar effects on other animal species have not been observed, and paleoanthropology suggests there was no population bottleneck. The genetic bottleneck is now recognized to be the Out of Africa founder effect, rather than an actual reduction in population.

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. Some parts of the caldera have shown 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 risen by at least Such earthquakes have also been recorded in 1892, 1916, and 1920–1922. In 2016, a study revealed that the Toba Supervolcano has a magma chamber containing of eruptible magma, about underground. This makes the supervolcano's magma chamber more than four times larger than the volume of Lake Superior in North America, and also larger than the magma chamber underneath Yellowstone. Lake Toba lies near the Great Sumatran fault, which runs along the centre of Sumatra in the Sumatra Fracture Zone.

Parapat is located on the edge of the lake, which is the transit point to travel the lake and Samosir Island. Medan is about 173 km by road from the town and is connected via the Trans Sumatran Highway to Pematang Siantar by a 48 km road. Sisingamangaraja XII International Airport is located about 47 mi (76 km) from Parapat.

The flora of the lake includes various types of phytoplankton, emerged macrophytes, floating macrophytes, and submerged macrophytes, while the surrounding countryside is rainforest including areas of Sumatran tropical pine forests on the higher mountainsides. The fauna includes several species of zooplankton and benthic animals. Since the lake is oligotrophic (nutrient poor), the native fish fauna is relatively scarce, and the only endemics are Rasbora tobana (strictly speaking near endemic, since also found in some tributary rivers that run into the lake) and Neolissochilus thienemanni, locally known as the Batak fish. The latter species is threatened by deforestation (causing siltation), pollution, changes in water level and the numerous fish species that have been introduced to the lake. Among the many introduced species are Anabas testudineus, Oreochromis mossambicus, Oreochromis niloticus, Ctenopharyngodon idella, Cyprinus carpio, Osphronemus goramy, Trichogaster pectoralis, Trichopodus trichopterus, Poecilia reticulata and Xiphophorus hellerii. MV Sinar 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.