Ilopango

Meet a volcano that possibly messed up two empires – Roman and Mayan – very seriously:
 

It's the ones that leave holes in the ground that you have to watch out for.  Today Lake Ilopango fills the caldera.  (Image source)

It’s the ones that leave holes in the ground that you really have to watch out for. Today Lake Ilopango fills the caldera, which sits just east of San Salvador, the capital of El Salvador. (Image source)


 

Many centuries ago, but during the Christian era, Ilopango had a high-end VEI 6 eruption, tens of times more powerful than the 1980 eruption of Mount St. Helens. Ilopango deposited some 20 cubic miles (84 cubic kilometers) of very fine white tephra over what’s now El Salvador and adjacent regions of Central America, the Gulf of Mexico, and the Pacific Ocean. The volcanic deposit is now called Tierra Blanca Joven (TBJ).

In Eruptions That Shook The World (2011), volcanologist Clive Oppenheimer says that radiocarbon dating of the TBJ gives two dates: 150-375 AD and 408-536 AD. He notes, “The evidence has recently tipped strongly in favour of recent versus older ages as new radiocarbon dates have emerged…”

Oregon State University’s Ilopango page goes with the earlier date. They say the caldera formed in 260 AD and killed a hundred thousand Mayans in nearby highlands. Survivors fled to lowland areas in modern Guatemala and Belize, and the Mayan state of Tikal became the new dominant power.
 

You've probably seen images of Tikal's monumental architecture.  This one was taken in 2006 by Raymond Ostertag.

You’ve probably seen images of Tikal’s monumental architecture. This one was taken in 2006 by Raymond Ostertag.


 

That’s bad enough, but OSU is the only major volcanology source online that I could find supporting the third-century date. All others that I checked go with the sixth century date for this Ilopango eruption. This is the most likely date, and it means that Ilopango not only devastated the Mayans in the sixth century AD but also affected global climate in ways that ultimately knocked the declining Roman Empire down for the count.

A low-end VEI 6 eruption.  For scale, those lights aren't a road - they're Clark Air Force Base.  (USGS Cascades Volcano Observatory)

A low-end VEI 6 eruption. For scale, those lights aren’t a road – they’re at gigantic Clark Air Force Base, which here is in the process of being trashed by raging Mount Pinatubo. (USGS Cascades Volcano Observatory)

“Pandemics, famines, and socioeconomic disruptions”

That’s how scientists who recently studied ice cores from Greenland and Antarctica describe the effects of volcanic eruptions on human civilizations during the sixth century. But how can a volcano have effects that go beyond the expected ones of blast and lava/ashfall?

Dr. Oppenheimer says in Eruptions that the low-end VEI 6 eruption of the Philippine volcano Mount Pinatubo in 1991 taught volcanologists how volcanoes influence Earth’s climate. Pinatubo, he tells us, “was responsible for the greatest loading of particles into … the stratosphere … for more than a century. A wide range of ground-based and satellite remote-sensing techniques measured the development, composition, and effects of the volcanic cloud…These studies characterised the nature of the volcanic materials entrained into the stratosphere and demonstrated their profound impacts on atmospheric chemistry and on the Earth’s heat budget and climate.”

At top, a typical side shot of Earth's atmosphere from space.  Black shapes are cloud tops.  Below, taken after Pinatubo's 1991 eruption.  (NASA)

At top, a typical side shot of Earth’s atmosphere from space. Black shapes are cloud tops. Below, taken after Pinatubo’s 1991 eruption. (Images by NASA; inspiration for layout here)

These effects are complex, but as I understand the basic idea, eruptions like Pinatubo’s inject sulfur gases into upper levels of the planet’s atmosphere, where they cause a number of optical and chemical effects that, among other things, affect the planet’s heat budget and lower sea surface temperatures. The overall physical end result is warmer winters and cooler summers until the atmospheric sulfur particles eventually disappear. There are also notable global biological feedback mechanisms as a consequence of the eruption.

The volcano’s location also matters, per Dr. Oppenheimer. Basically, in modern conditions, high-latitude eruptions (like those on the Kamchatka Peninsula) have less global impact than those closer to the equator, like Pinatubo and Ilopango.

A VEI 6 eruption – whether high-end like Ilopango’s pre-1000 AD eruption or low-end like Pinatubo’s in 1991 – is nowhere near a supereruption, but it obviously has bad consequences for us. Crops fail as weather patterns change. Populations of microbes and other small organisms shift, and that can have dreadful results. For example, Dr. Oppenheimer says that Pinatubo’s eruption in the Philippines caused Middle Eastern algal blooms, in the Gulf of Eilat, that killed off much of the local coral.

Historians report that around the Mediterranean, one summer during the reign of Roman emperor Justinian in the sixth century, “The sun gave forth its light without brightness and it seemed exceedingly like the sun in eclipse, for the beams it shed were not clear.”

Justinian himself caught the plague but survived.  (Image by Testus)

Justinian himself caught the plague but survived. (Image by Testus)

Things went downhill after that for 18 months, they say, with climate and weather changes and ultimately a plague that killed one out of every three people there. The resulting social, economic, and military repercussions, in the long run, led to the empire’s collapse.

Meanwhile, in Central America, the Maya at Tikal and other nearby centers stopped recording events for almost sixty years. Things didn’t pick up again for them until the seventh century.

New studies indicate an eruption of Ilopango in 536 AD could have been responsible for the disasters in both Rome and Mesoamerica, especially if it had a little help. Scientists are also looking, thus far unsuccessfully, for a volcano in the tropics that had a 539 AD blast more powerful than Tambora’s VEI 7 blast in 1815.

But if Ilopango erupted, why didn’t the Maya describe it? A high-end VEI 6 eruption in that area, after all, would have devastated nearby regions, killing tens of thousands of people.

Well, put yourself in their place. It took over half a century to recover. The Maya might well have decided to put such a terrible experience behind them as they once more began recording their history in stone monuments for posterity. Perhaps (this is just a guess) they also believed that to describe such an “act of God” might magically make it happen again.

In any event, Nature’s history is also written in stone, that is, in igneous rock and volcanic deposits. The problem today’s volcanologists face is how to find and interpret those geologic records. And in the meantime, hundreds of thousands of people live and work around Ilopango today as El Salvadoran earth science and emergency planning experts monitor it and other nearby volcanoes closely.
 

US and El Salvadoran military exercises over Lake Ilopango in 2014.  Note development on the caldera edges.  Ilopango is a monitored volcano.  (Image:  USASOC News Service)

US and El Salvadoran military exercises over Lake Ilopango in 2014. Note development on the caldera edges. Ilopango is a monitored volcano. (Image: USASOC News Service)

 
 


 

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Categories: Sunday morning volcano

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