Toba Supervolcano discussion
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Toba is a supervolcano in the middle of the Indonesia island of Sumatra.
A large lake, 100km long and 30 km wide, now sits in the calderas.
the Dutch geologist van Bemmelen, in 1949, first found that Lake Toba was surrounded by a vast layer of ignimbrite rocks.
Later researchers found rhyolite ash similar to that in the ignimbrite around Toba in Malaysia and 3000 km away in India. The total amount of volcanic material ejected was found to be about 2,800 cubic kilometres.
The Toba eruption was dated at 73,000 ▒ 4000 years ago and led to a decrease in the average global temperatures by 3 to 3.5 degrees Celsius for several years. This massive environmental change is believed to have created population bottlenecks in the various human species that existed at the time.
Genetic evidence suggests that all humans alive today are descended from a very small population, perhaps around 1,000 individuals that managed to survive.
From the records it seems that Toba produces major eruptions every 300-400,000 years.
Recently, scientists have identified a major climate crisis that struck Africa about 70,000 years ago. Evidence comes from sediments drilled up from the beds of Lake Malawi and Tanganyika in East Africa, and from Lake Bosumtwi in Ghana.
It shows equatorial Africa experienced a prolonged period of drought.
It is possible, this was the reason some of the first humans left Africa to populate the globe.
Certainly, those who remained on the continent at that time would have had to be extremely resilient to make it through such hard times.
What makes the timing so fascinating is that it ties in with the "Eve hypothesis" of human evolution.
However, it should be noted that temperatures at other times during the last ice age fell far lower and did not come close to wiping out humankind; and the exact age of the bottleneck is poorly constrained so that linking it to the Toba eruption is speculative.
Today, Lake Toba is surrounded by two small, active volcanoes as well as several updomed areas and hot springs. These features indicate that there is activity below the surface and that pressure is rising. Samosir Island, too, is evidence for upthrust from below. Seismic readings indicate that two broad regions interpreted to be magma reservoirs lie below the depression.
The volcanoes Pusubukit and Pardepur, lie above the large southern chamber and each have roots that extends to mantle depths.