Our Past (and Future) With Supervolcanoes


As I have stated before, fewer potential civilization-ending natural disasters exist today when compared to our evolutionary past. For example, before we emerged from sub-Saharan Africa 100,000 years ago, an earthquake, tsunami, volcano, famine, or even animal competition could have ended the human experiment. Today, those risks may be locally disruptive, but they do not threaten collective human existence.

But we must remember that there are rare natural events that should still be considered major threats: asteroids and supervolcanoes. Our species has never had to deal with a major encounter with an asteroid, but surprisingly, we have some experience with supervolcanoes. Consequently, by studying how supervolcanoes have affected our species in the past, we may be able to gain a better understanding of their likely impact in the future.

Lake Ilopango Eruption maya-map.gif Location of Lake Ilopango (Southeast of San Salvador) in relation to Classic Maya Civilization

Recently, I interviewed University of Texas paleoecologist Dr. Robert Dull to discuss supervolcanoes. Dr. Dull studies climate change on millennial scales of time and has recently discovered evidence that a major volcanic eruption occurred around 536 C.E. at Lake Ilopango in modern day El Salvador. According to Dull, the Lake Ilopango eruption significantly affected Mayan civilization during the Classic Period and represents the likely culprit of extreme global weather events in 536-537 C.E.

From Dull’s initial research, the 6th century volcanic eruption in El Salvador approached VEI 7 status. The pyroclastic flow from a blast of this magnitude would have destroyed an area 2,000 square km in size. Dull conservatively estimates from the population density of this area during the 6th century that this eruption would have directly killed 40,000-80,000 individuals.

But the effects of the Lake Ilopango eruption go far beyond the initial blast. Although more research is necessary, Dull reveals that a lot changed after 536 C.E.:

Some people lost out and some benefitted. Some cities flourish after this event. All cities were covered in ash, but some had only about 1 cm of ash. I believe that there must have been refugee movement to largely unaffected cities in the north.

It will be interesting to see what future research reveals about how Maya society changed after 536. However, Dull believes this eruption affected more than just local Mesoamerican stability. It may have also caused nearly two years of extreme weather throughout the Northern Hemisphere.

The extreme weather events of 536-537 C.E. is one of the largest historical and paleoecological mysteries. Throughout Eurasia several written records chronicle the events:

The sun became dark and its darkness lasted for one and a half years… Each day it shone for about four hours and still this light was only a feeble shadow…the fruits did not ripen and the wine tasted like sour grapes. — Michael the Syrian

For the sun gave forth its light without brightness, like the moon, during this whole year, and it seemed exceedingly like the sun in eclipse, for the beams it shed were not clear nor such as it is accustomed to shed. — Procopius

…the sun began to be darkened by day and the moon by night, while ocean was tumultuous with spray, from the 24th of March in this year till the 24th of June in the following year… and the following winter in Mesopotamia was so bad from the large and unwonted quantity of snow the birds perished. — Unknown Syrian

So we have had a winter without storms, spring without mildness, summer without heat. — Cassiodorus

If the sun becomes dim because the air is dense from rising moisture—as happened in [536/537] for nearly a whole year…so that produce was destroyed because of the bad time—it predicts heavy trouble in Europe. — John Lydos

Dendrochronological records from Eurasia and South America also show slow growth during these years, which indicates poor growing seasons.

Dull believes that the 18 months of Northern Hemisphere darkness was caused by a global dust vale ejected from Lake Ilopango. If true, this would be the second time in the last 2,000 years that a volcanic eruption prevented summer. Dull notes that:

The Indonesian Tambora eruption in 1815 is the best analogue to Ilopango. They were eruptions that shook the world and produced similar effects. In the case of Tambora it caused a year without summer. In the case of Ilopango it caused the years without summer.

Can this tell us anything about the future?

Perhaps the most frightening aspect of supervolcanic eruptions are their inevitability. If our species plans on sticking it out long-term on planet Earth, we will encounter a supervolcanic eruption. Both Ilopango and Tambora were technically VEI-7 eruptions (or close to VEI-7 eruptions). In the short-term, their impact was locally devastating and globally disruptive. However, neither significantly threatened the existence of our species. Would a VEI-8 eruption be that much worse?

Category 7 eruptions eject about 100 cubic kilometers of volcanic ash. Category 8 eruptions eject 1000+ cubic kilometers of volcanic ash. This difference is significant. Whereas category 7 eruptions have devastating short-term impacts on local and global climate, category 8 eruptions pose serious long-term challenges.

Lake Toba Eruption Lake Toba.jpg

Surprisingly, modern humans have encountered a VEI-8 eruption before. Approximately 74,000 years ago Lake Toba in Indonesia erupted and ejected 2,800 cubic kilometers of volcanic ash. This eruption blanketed South-east Asia, South Asia, and the Arabian Peninsula in ash. Recent studies indicate that it also led to prolonged cooling and deforestation throughout Asia.

Consequently, many evolutionary theorists have posited that the Lake Toba eruption could have had profound effects on our emergence as a species. Genetic evidence suggests that our species suffered a severe genetic bottleneck sometime before 60,000 years ago. Our population may have dropped to as low as 1,000 breeding pairs. Although more research needs to confirm the hypothesis, the Lake Toba supereruption was the likely cause of the bottleneck. At the very least this eruption slowed our expansion into East Asia and Australia.

By a fluke of geography, we evaded extinction. Had the eruption occurred in East Africa, we may not have been so lucky. What if it happened today?

Supervolcanoes Today

From my perspective I am not sure whether a VEI-8 would threaten our species with extinction, but I am sure that it would seriously destabilize our global infrastructure.

As we have learned from Dull’s research at Lake Ilopango, “some people lost out and some benefitted” in Mesoamerica after 536 C.E. Would we expect the same if a VEI-8 volcano erupted at say, Yellowstone National Park? Certainly all of North America would be negatively impacted if the Yellowstone Caldera erupted with comparable intensity to previous eruptions. As a result would we see North American refugees heading to whatever European, South American, African, or Asian country would have them?

yellowstone-surface-cendre.jpg Yellowstone Eruption Radius

There are too many hypothetical situations to know for sure. However, it is conceivable that what occurred locally in Mesoamerica in 536 C.E. could repeat itself globally if we encountered a VEI-8 in the near future.

During our interview, Dull acknowledged that a VEI-8 eruption would be “horrific.” He added that:

We can’t predict [supervolcanic eruptions]. There are known supervolcanoes that have repeatedly erupted. Yellowstone 3 times in the last 2 million years. That is something to be concerned about. We know it has erupted in geologic history in a devastating way.

We may not be able to predict supervolcanic eruptions, but a recent study published in the journal Nature indicates that there are characteristic processes that occur decades (perhaps even a century) before a major eruption. If volcanologists can gain a better understanding of these pre-eruption processes, we may be able to detect the next supereruption decades before the event. This would at least give us time to prepare (possibly avert?) disaster.

Currently NASA leads a program to categorize all “potentially hazardous objects” (PHO) (e.g., asteroids and comets). Of course, this program is extremely important for the future stability of our civilization and planet. But why are we not preparing in the same way for supervolcanic eruptions? We already know that eruptions on the scale of Lake Toba 74,000 years ago happen with much higher frequency than asteroid impacts. Yet we have no plan to deal with VEI-8 eruptions. Even the Long Now Foundation, an organization focused on promoting a 10,000 year framework to build our global civilization has no official stance or plan for dealing with a VEI-8 eruption.

So what should we do? I would argue that our current knowledge of past supervolcanic eruption events indicate that they pose a significant risk to global stability. I also feel that it would be enormously irresponsible if our species did not develop a program analogous to the NASA PHO effort. So here is what I propose we must do:

  1. We must gain as much data and knowledge of past supervolcanic eruptions as possible.

  2. We must attempt to understand whether supervolcanic eruptions occur in any recognizable pattern on geologic time scales so that we can roughly estimate when we should expect the next major eruption.

  3. We must fund volcanology research into better understanding the processes that occur decades (and even centuries) before a major eruption.

  4. And we must start to hypothesize about technology and/or methods that could be used to prevent supervolcanic eruptions.

As Dr. Dull’s research shows us, eruptions at or near the scale of VEI-7 have the ability to destabilize civilizations and create years without summer. Research by other paleoecologists have shown us that supervolcanic eruptions happen with surprising regularity on scales of thousands of years. Therefore it would be prudent to prepare for such events.

Finally, I would like to add that I am not trying to be an alarmist. I am sometimes accused of being overly optimistic about our future as a species. But I believe all evidence indicates that our species has tremendous potential and the possibility for a very bright future. However, if we would like to create a healthy and stable global civilization, we must properly prepare ourselves for natural events that occur on larger time scales than we are accustomed to thinking about.

If we invest in more research, take the necessary precautions, and develop the right technology, we can knock another natural disaster off of the list of events that threaten the human experiment.

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