April 17, 2013 | 8
Supervolcanoes are volcanic eruptions thousands of times more powerful than normal volcanic eruptions. These types of eruptions cause significant local ecological disturbances and have profound effects on global climate. On the scale of geological time they occur quite frequently.
Volcanologists categorize eruptions by the amount of volcanic ash ejected upon eruption using the Volcanic Explosivity Index (VEI). The VEI consists of 8 levels, with VEI-8 eruptions considered “supervolcanic eruptions” ejecting 1000 cubic kilometers of ash or more.
Throughout human history our species has encountered one known supervolcanic eruption. This eruption occurred at Lake Toba in Indonesia approximately 74,000 years ago, potentially causing a genetic bottleneck and slowing human expansion into Asia and Australia. However, VEI-7 eruptions (eruptions ejecting 100 cubic kilometers of ash) have occurred with relative regularity (4 in the past 2,000 years).
I recently interviewed University of Texas paleoecologist Dr. Robert Dull to discuss past major eruptions in human history. Dr. Dull studies climate change on millennial scales of time and discovered evidence that a major volcanic eruption occurred around 536 C.E. at Lake Ilopango in modern day El Salvador. He believes that this eruption is responsible for the well-documented extreme global weather events in 536-537 C.E. throughout the northern hemisphere.
I believe that understanding how major eruptions effected human civilization in the past will give us an opportunity to prepare for these eruptions in the future.
Cadell Last: How large was the Lake Ilopango eruption?
Robert Dull: The Lake Ilopango eruption was a magnitude 6.9 eruption. The magnitude scale is more accurate that the VEI. Classifying the eruption as a 6.9 is obviously more precise than labeling it 6 or 7. But it was nearly a VEI-7. However, it wouldn’t take many new data points for that estimate to go up. The more samples we collect the better we will be able to figure out the full volume of the eruption. The magma volume was approximately 39 cubic kilometers.
Cadell Last: Are there estimates on how many people were directly killed as a result of the Ilopango eruption? If so, how were they estimated?
Robert Dull: Between 40,000-80,000 people died during the Lake Ilopango eruption. We used population density assumptions based on settlement patterns in the area. Some of the original density estimations indicated that there were 72 people per square kilometer near the volcano. However, I choose to be more conservative and estimate that there were 20-40 people per square kilometer. Since the eruption affected an area of 2,000 kilometers this indicates that 40,000-80,000 people died in the greater El Salvador region.
Cadell Last: Lake Ilopango was very close to the Maya civilization. Would the entire Maya civilization have been effected by this eruption? And do we know that this eruption caused the “Maya Hiatus” during the Classic Period?
Robert Dull: The entire Maya civilization would have been effected. The entire southeastern Maya highland certainly would have been directly affected. This area was the source of a lot of ceramic types and major obsidian quarry sites. There were a few towns that were completely wiped away. However, we don’t know as much as we could know about the Maya Hiatus. Our findings will spur a lot more research into this. We know that the Maya Hiatus started around 534 C.E. and then lasted for 30 years. These are rough dates but what we know is that this eruption happened right in the middle of the Classic Period. During this time monumental architecture came to a halt. Political alliances changed. One of the most exciting findings is that this eruption coincides with the fall of the largest Mesoamerican city: Teotihuacan. Teotihuacan was a Aztec city with a population of 200,000 people and it fell around 550 C.E. We need to better understand how their alliances with the Maya may have contributed to this collapse.
Cadell Last: Do researchers know why this eruption did not end the Maya Classic Period?
Robert Dull: There were big shifts of power in the Maya lowlands. What seems to have happened was that some regions benefitted and some regions lost out. All cities had a dusting of ash, but some were only covered in about a centimeter of ash. I believe there must have been refugees to a large center of largely unaffected cities in the northern half of the Yucatan Peninsula. I think future research will tell us a lot more about the role of these refugees in the later Maya Classic Period.
Cadell Last: What is your stance on the connection between the Lake Ilopango eruption (536 C.E.) and the Plague of Justinian (541-542 C.E.)?
Robert Dull: It’s certainly plausible. The plague did break out after the volcanic eruption. A global dust vale from the eruption lasts for 18 months in the northern hemisphere during this time. That lasted for two summers. This period of time was also an anomalously cold period. On the whole climate change could have allowed the event to take place.
Cadell Last: There was a VEI-7 eruption in Indonesia in 1815. The Tambora eruption. From the historical record, what do we know about the main parallels and differences between the climatic effects of the 536 eruption and 1815 eruption?
Robert Dull: Tambora is the best analogue to the Lake Ilopango eruption. They were eruptions that shook the world. They produced similar effects. In the case of Tambora it produced The Year Without Summer in 1816. In the case of Ilopango it produced the years without summer: 536-537 C.E. You don’t store food that lasts for two years. In the northern hemisphere you grow it in the summer and save it for the winter.
Cadell Last: Considering how dangerous these eruptions are, have paleoecologists and volcanologists discovered and accounted for all potential supervolcanoes? Is there any possible way that volcanologists will be able to predict the next supervolcanic eruption?
Robert Dull: No we can’t predict when the next supervolcanic eruption will occur. There are known supervolcanoes that have repeatedly erupted. For example, Yellowstone has erupted three times in the last two million years. That is something that we should be concerned about. Of course, Yellowstone is being monitored but we have no way of predicting when it will erupt next.
I believe that Dr. Dull’s research can teach us a lot about how major volcanic eruptions effect human civilization. It is clear that eruptions at or near the scale of VEI-7 have the ability to destabilize civilizations and even alter global climate for multiple years. Also, research by other paleoecologists has shown us that VEI-7 eruptions happen with surprising regularity on scales of thousands of years. Therefore it would be prudent to identify high-risk volcanoes and prepare for such events.
The danger a VEI-8 eruption poses is even higher. They may pose just as significant a threat to our existence as asteroids do. In my opinion there are too many hypothetical situations to know exactly how a VEI-8 eruption would impact our global civilization today. 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.
Finally, I would like to add that I am not trying to be an alarmist. However, if we would like to create a stable global civilization, we must properly prepare ourselves for natural events that occur on larger time scales than we are accustomed to thinking about.