Geology: Ancient Sumatran supervolcano damaged the ozone layer and created a bottleneck for human populations

0

A catastrophic drop in atmospheric ozone levels around the tropics some 75,000 years ago created a bottleneck in the human population, a study concluded.

The ozone level has halved as a result of the eruption of the Toba supervolcano in Sumatra, experts at Germany’s Max Planck Institute of Chemistry found.

Toba, one of the largest explosions on Earth ever, is said to have erupted some 5,097 square miles of material, triggering a 6-10 year “volcanic winter.”

Lake Toba – a body of water measuring 436 square miles – was formed to fill the cauldron-like cavity, or “caldera,” left by the massive explosion.

The cooling of the volcanic winter is said to have had several knock-on effects, including cooler oceans, longer El Niño events, crop failures and disease.

But by blocking the sun and preventing the formation of protective ozone, ultraviolet radiation could have done more damage to people in the tropics, the team said.

According to previous studies, the human population would have declined to just 10,000-30,000 individuals after the Toba eruption.

A catastrophic drop in atmospheric ozone levels around the tropics 60,000-100,000 years ago created a bottleneck in the human population, a study concluded.  The ozone level has halved as a result of the eruption of the Toba supervolcano in Sumatra, experts at Germany's Max Planck Institute of Chemistry found.  Pictured: An Artistic Impression of the Toba Eruption

A catastrophic drop in atmospheric ozone levels around the tropics 60,000-100,000 years ago created a bottleneck in the human population, a study concluded. The ozone level has halved as a result of the eruption of the Toba supervolcano in Sumatra, experts at Germany’s Max Planck Institute of Chemistry found. Pictured: An Artistic Impression of the Toba Eruption

What was the Toba catastrophe?

The Toba super-eruption was the largest volcanic explosion on Earth in 2.5 million years.

It blew its summit about 74,000 years ago on what is now the Indonesian island of Sumatra.

The volcano fired some 720 cubic miles (3,000 cubic km) of rock and ash that spread around the world.

Some scientists believe the eruption wiped out the sky, bringing with it a volcanic winter that lasted a decade.

An eruption a hundred times smaller than Mount Toba — that of Mount Tambora, also in Indonesia, in 1815 — would have brought a year without a summer in 1816.

The Toba eruption devastated life on Earth as the thick cloud of ash blocked out the sun and killed much of the planet’s plant life.

The event was so massive that all that remains is the enormous Lake Toba, which is 100 kilometers long, 30 kilometers wide and 505 meters deep.

The idea that the super-eruption was responsible for slowing the growth of human populations was first suggested by science writer Ann Gibbons in 1993.

“Toba has long been seen as the cause of the bottleneck,” explains author and atmospheric chemist Sergey Osipov of the Max Planck Institute of Chemistry in Mainz, Germany.

But, he added, “initial studies of the climate variables temperature and precipitation yielded no concrete evidence of a devastating effect on humanity.”

Now, however, the link between the supervolcano and the bottleneck may have been established, said study co-author and earth scientist Georgiy Stenchikov of the King Abdullah University of Science and Technology (KAUST).

“We point out that in the tropics, near-surface ultraviolet (UV) radiation is the driving evolutionary factor,” he explained.

Climate effects, such as the cooling caused by volcanic aerosols in the atmosphere blocking incoming sunlight, are only becoming more relevant “in the more volatile regions outside the tropics,” Professor Stenchikov added.

‘The ozone layer prevents high levels of harmful UV radiation from reaching the surface,’ explains Dr Osipov.

‘To make ozone from oxygen in the atmosphere, photons are needed to break the O₂ bond. When a volcano releases large amounts of sulfur dioxide (SO₂), the resulting volcanic plume absorbs UV radiation but blocks the sunlight.’

This, he added, “limits ozone formation, creating an ozone hole and increasing the potential for UV stress.”

In their study, the researchers ran a NASA-developed climate model on a KAUST-based supercomputer to simulate the impact of various eruptions on global levels of ultraviolet radiation.

The team's modeling found that even relatively minor super-eruption scenarios had significant effects on atmospheric ozone — and that Toba's estimated sulfur dioxide emissions likely reduced global ozone levels by as much as 50 percent.  Pictured: ozone changes by latitude in the two years after the eruption.  Exhaustion shown in blue

The team’s modeling found that even relatively minor super-eruption scenarios had significant effects on atmospheric ozone — and that Toba’s estimated sulfur dioxide emissions likely reduced global ozone levels by as much as 50 percent. Pictured: ozone changes by latitude in the two years after the eruption. Exhaustion shown in blue

Their modeling found that even relatively small super-eruption scenarios had significant effects on atmospheric ozone, and that Toba’s estimated sulfur dioxide emissions likely reduced global ozone levels by as much as 50 percent.

This shift would have resulted in higher levels of UV radiation reaching the Earth’s surface, increasing damage to human health and negatively affecting survival.

‘The effects of ultraviolet stress can be comparable to the aftermath of nuclear war,’ explains Dr Osipov.

Lake Toba - a body of water measuring 436 square miles - was formed to fill the cauldron-like cavity, or

Lake Toba – a body of water measuring 436 square miles – was formed to fill the cauldron-like cavity, or “caldera,” left by the massive explosion. Pictured: The location of Lake Toba in Sumatra

Toba, one of the largest explosions ever seen on Earth, is believed to have erupted some 5,097 square miles of material, causing a 6-10 year volcanic winter.  Pictured: Lake Toba, filling the cauldron-like cavity or caldera left by the eruption, as seen in the present

Toba, one of the largest explosions ever seen on Earth, is believed to have erupted some 5,097 square miles of material, causing a 6-10 year volcanic winter. Pictured: Lake Toba, filling the cauldron-like cavity or caldera left by the eruption, as seen in the present

‘For example, crop yields and maritime productivity would decline as a result of UV sterilization effects. Going outside without UV protection would cause eye damage and sunburn within 15 minutes.’

“Over time, skin cancer and general DNA damage would have led to population decline,” he concluded.

The study’s full findings were published in the journal Communication Earth and Environment.

.