No rest after the bang: the Toba volcano on the island of Sumatra remained active and dangerous for thousands of years as a result of its gigantic eruption around 74,000 years ago, according to a geological study. In doing so, it evidently threw quite cold material out of its bulging top layer. The results shed light on the development processes at the volcanic giants and can be used to assess their hazard potential, say the scientists.
Disasters that have had a lasting impact on the world: In addition to cosmic impacts, eruptions of so-called super volcanoes in particular have led to abrupt changes in the earth’s climate and thus significantly influenced the history of life on our planet. This category is characterized by a particularly large magma chamber under the volcanic area. If the pressure exceeds a critical value due to the accumulation of magma and gases, an explosion occurs, in which enormous amounts of material are thrown into the environment and the atmosphere. This can change the earth’s climate – a so-called volcanic winter occurs, which can be associated with widespread food shortages and mass deaths.
However, there are still many unanswered questions about the volcanic developments in the context of the gigantic eruptions. For example, it is unclear how the area will develop after the discharge before a super volcano builds up explosive potential again over a long period of time: does it calm down after the massive discharge? So far, it seems clear: When the magma chambers of super volcanoes are emptied, the earth’s crust above collapses, forming a huge basin – a so-called caldera. Later this geological structure often fills with water.
A volcanic monster in its sights
In order to gain insights into super-volcanic developments, an international team of researchers has now looked at the Toba volcano on the Indonesian island of Sumatra. The eruption of this super volcano about 74,000 years ago is considered to be the most devastating in recent geological history. It is even assumed that the climatic consequences have influenced the history of human development. After the eruption, a caldera lake was created with a large island in the middle that is about 100 kilometers long, 30 kilometers wide and up to 500 meters deep. “These dimensions prove the tremendous destructive power of such volcanic explosions,” says co-author Axel Schmitt from the University of Heidelberg.
As part of the study, the scientists examined the minerals feldspar and zircon in the lava stones that can be found inside the caldera. As the researchers explain, conclusions can be drawn about the volcanic activity and when it took place based on the characteristics of these rocks. The scientists were able to use radiometric dating to prove that the Toba was still a long way from resting after its gigantic eruption. According to this, there was still considerable activity over the next 5,000 to 13,000 years. At least for the region, these outbreaks were probably dangerous, say the researchers.
Spit out cool material
Further test results showed that comparatively cold and almost solid material came to the surface during these activities. Modeling of the possible processes showed that it could have been eruptive material that blocked cracks in a bulging top layer of the supervolcano. “After the Toba eruption, the cooled edge of the remaining magma bulged like a turtle shell,” says Axel Schmitt, describing the volcanic development after the big bang. Apparently, this process led to the continued activity.
Using the Toba as an example, the scientists have now been able to prove that super volcanoes can remain dangerous even thousands of years after their eruption. “We need to adjust our understanding of volcanoes in this regard,” says co-author Shanaka de Silva of Oregon State University. “In order to predict a volcanic eruption, we usually try to use geophysical methods to determine whether there has been an accumulation of molten rock underground. Our study shows that volcanoes can erupt even if the magma is solid just below the volcano. This means that we have to adapt our monitoring and early warning systems and also assess their risk potential differently, ”says the scientist.
Source: University of Heidelberg, Technical article: Communications Earth & Environment, doi: 10.1038 / s43247-021-00260-1