On June 15th, 1991, the Pinatubo volcano located in the Philippines erupted in what would later become one of the three most powerful volcanic eruptions of the 20th century. Situated on the island of Luzon, the volcano is part of a volcanic chain along the western tip of the island. The prediction of the impending eruption led to the evacuation of the surrounding areas, which affected tens of thousands of people. Despite the evacuation efforts, at least 875 people died as a result of the outbreak and its consequences. After lying dormant for a period of about 550 years,[1] the volcano spat more than ten cubic kilometres of ash, along with another 17 million tons of sulfuric acid into the sky. This was disseminated in a large radius, and suffocated all plant life within its reach. Vast quantities of the small airborne particles traveled around the Earth, affecting regions far beyond. Volcanic eruptions of this magnitude have an impact on the global climate by reducing the amount of solar radiation reaching the Earth’s surface. The massive outpouring of gases and ash enveloped our planet in a grey dirt veil that damaged the Ozone layer and blocked the sunlight, resulting in cooler temperatures. The global average of that year was 0.6 degrees Celsius below the long-term average.[2]
A 2020 study using well-dated volcanic fallout records in six Arctic ice cores identified one of the largest volcanic eruptions of the past 2,500 years in early 43 BCE. The eruption of the Okmok volcano in Alaska caused pronounced changes in the hydro climate, including seasonal temperatures specifically in the Mediterranean. Temperatures dropped as much as 7 °C below normal during the 2-year period following the eruption as well as unusually wet conditions. This probably caused crop failures, famine, and disease, exacerbating social unrest and contributing to political realignments throughout the Mediterranean region thus accelerating if not causing the downfall of the roman republic.[3]
Anthropogenic Emmisions
Due to man-made, or “anthropogenic” emissions, the consequences of volcanic eruptions and the impact on global climate can become even more severe. For instance, the chlorofluorocarbons (CFCs)—which in accordance to the Montréal Protocol, were used in refrigerators and propellants until the 90s when they were internationally phased out of production due to detrimental effects on the Ozone—can cause chemical chain reactions with the volcanic aerosol particles. This can destroy Ozone molecules in the stratosphere, thus intensifying the depletion of the Ozone layer.[4]
Major volcanic eruptions affect the radiative balance of our planet, because the volcanic aerosol particles absorb terrestrial radiation and block a significant amount of solar radiation. This effect is called “radiative forcing,” and depending on the scale of the incident, it can last for two to three years,[5] or even decades. The largest type of volcanic eruptions are the so-called “super-eruptions,” which are capable of annihilating all life and infrastructure over tens of thousands of square kilometres, and disrupting or destroying agriculture over millions of square kilometres, affecting global climate for years, decades or more.[6] The Pinatubo eruption was one of the mightiest of its kind in the 20th century. It’s effects were felt worldwide, and yet it was a rather marginal event in comparison to what happened during the Toba eruption in Sumatra roughly 75,000 years ago.
In the largest volcanic event in the past 2 million years, an estimated 2,800 cubic kilometres of tuff (volcanic rock) were ejected. In comparison, the well-known recent volcanic eruption of Mount Saint Helens in 1980 had a mere 1 cubic kilometre, while the Pinatubo had 10 cubic kilometres, respectively. Around the caldera, the collapsed surface crater of Toba which is an incredible 100 km long and 30 km wide—the layer of tuff is more than 600 metres thick. The volcanic ash of the super-eruption covered an area of more than 4 million square kilometres, which is about half the size of the United States.[7]
The Toba Catastrophe Theory
According to the Toba-Catastrophe-Theory, the eruption in Indonesia caused such mayhem and destruction to the biosphere, that it came close to wiping out the entire human species.[8] Planet Earth experiences volcanic eruptions every now and then that are on an entirely different magnitude than those we have witnessed in historic times. Those events that yield more than 450 cubic km are considered super-eruptions. The exact number of these events in the past is unknown. According to our current understanding of geology, the most recent eruption of this scale happened 26,000 years ago at Lake Taupo, New Zealand. While these extraordinary eruptions may seem quite rare from a human perception of time, it is however far more likely that our planet experiences another super-eruption, than being hit by a large asteroid of 1 km diameter or bigger. If such an event would occur, the consequences would be felt worldwide. [9]
Super eruptions – not if but when…
In a recent study from the scientists of the University of Bristol, the period between super-eruptions that are of the highest magnitude lies between 5,200 and 48,000 years, which is considerably shorter than previous estimates. Considering the last known event was 26,000 years ago, the potential risk for human civilization as we know it could be far greater than previously thought.[10]
In conclusion, Earth will almost certainly experience another super-eruption within the time span of 100,000 years. With a growing global population of 10 billion by 2050,[11] an increased dependency on technology, and energy demand and urbanization, the modern society is increasingly vulnerable to catastrophic events. If we as a species survive long enough to be confronted with such odds, the survivors will be faced with untold challenges in the aftermath of a super-eruption.[12]
References:
Lowenstern, J. B., Smith, R. B., and Hill, D. P. (2006): Monitoring super-volcanoes: geophysical and
geochemical signals at Yellowstone and other large caldera systems.
McConnell, J. R., Sigl, M., Plunkett, G., Burke, A., Kim, W. M., Raible, C. C., Wilson, A. I., Manning, J. G., Ludlow, F., Chellman, N. J., Innes, H. M., Yang, Z., Larsen, J. F., Schaefer, J. R., Kipfstuhl, S.,
Mojtabavi, S., Wilhelms, F., Opel, T., Meyer, M., and Steffensen, J. P. (2020): Proceedings of the National Academy of Sciences oft he United States of America, June 2020.
Nasa (2006): https://asterweb.jpl.nasa.gov/gallery-detail.asp?name=toba
Rougier, J., Stephen, R., Sparks, J., Cashman, K. V., and Brown, S. K. (2018): The global magnitude-frequency relationship for large explosive volcanic eruptions. In: Earth and Planetary
Science Letters Volume 482, 15 January 2018, Pages S. 621-629.
Self, S. (2006): The effects and consequences of very large explosive volcanic eruptions. In: Philosophical Transactions of the Royal Society A. 15. August 2006.
Spektrum (2009): Der Tag, an dem die Welt unterging. Spektrum – Die Woche, 48. KW 2009.
Vanderbilt University (2012): Press-Release 2012: Super-eruptions may have surprisingly short fuses. https://news.vanderbilt.edu/2012/05/30/super-eruptions
Wikipedia (o. J.): https://de.wikipedia.org/wiki/Pinatubo
Wolfe, J. (2000): Volcanoes – Climate Change. https://earthobservatory.nasa.gov/features/Volcano
Worldometers (2019): https://www.worldometers.info/world-population/#pastfuture
[1] Wikipedia (o. J.)
[2] Spektrum (2009)
[3] McConnell et al. (2020)
[4] Wolfe (2000)
[5] Wolfe (2000)
[6] Lowenstern, Smith and Hill (2006)
[7] Nasa (2006)
[8] Vanderbilt University (2012)
[9] Self (2006)
[10] Rougier, Stephen, Sparks, Cashman and Brown (2018)
[11] Worldometers (2019)
[12] Lowenstern, Smith and Hill (2006)