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. photo of Sumatra surrounding Lake Toba 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.
More recent activity 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. 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 9.1
2004 Indian Ocean earthquake and the 8.7
2005 Nias–Simeulue earthquake, the epicenters of which were around from Toba. ==People==