August 12, 2018: I’ve just read this scientific paper (open-access, freely downloadable from Springer), written by volcanologists in easy-to-understand English, that describes just how difficult it is to manage a potentially violent volcano like Popocatepétl over a long-term “semi-crisis” like the one unfolding there today. Check it out! It really gives you good background on both the volcano and its human setting.
People in central Mexico have always felt a strong personal link with Popocatepétl, which they often call Don Goyo.
As we saw last time, when this volcano broke its five-decade silence with a VEI-2 bang in 1994, local people responded with traditional ceremonies; artists were drawn to the event; government officials took emergency measures; and scientists expanded their monitoring networks.
For almost a quarter of a century now, Don Goyo has been on center stage. People have adjusted to it and are moving on with their lives, as people always do after a natural disaster.
But scientists just updated the official hazard map (Spanish) for Popocatépetl, which we’re going to take a look at in this post.
The volcanologists did reassure everybody that there is no sign of any increased or upcoming increase in activity; the volcano is still at a “Yellow, Phase 2” alert level.
Also, to counter popular rumors, they stated in no uncertain terms that Don Goyo is not connected to Guatemala’s Fuego, which recently had a deadly eruption, or to Kilauea, out in Hawaii, with its spectacular lava flows. Each of these three volcanoes has its own plumbing system and exists for different geological reasons.
The problem with Popocatépetl is that, not only in 1994 but also at any point in modern times, this volcano has never shown the levels of violence that the geologic record proves that it is capable of.
And now Don Goyo has 25 million human neighbors, unfamiliar with its historic power and living less than 65 miles (100 km) away from its summit.
Ashfall risk from Popocatépetl
- The dotted line shows the area that would get at least 4 inches (10 cm) of ash if Don Goyo had another eruption as powerful as one about 14,000 years ago.
- Red: In a big eruption, this unfortunate area could get lots of volcanic ash (up to yards/meters in depth) as well as a bombardment of rocks up to a foot (30 cm) in size.
- Orange: Just a little ash would fall here in a small eruption, but up to 3 feet (1 meter) or more in a big one.
- Yellow: This region isn’t at much risk of ashfall in small eruptions at Popocatepétl, but it could get several inches (dozens of centimeters) in a large eruption.
Seismic sensors, deformation monitoring, and gas/hydrothermal studies can pick up signs of such approaching events, especially the big ones.
Pyroclastic currents and lahars at Popocatépetl
Besides ashfall, Popocatépetl’s Plinian eruptions have produced pyroclastic density currents that raced down the steep slopes and ran out for miles across the lowlands. With these, and also for a century or more after each eruption, came lahars: flows of ashy mud that, at least during Ice Age events, sometimes contained mammoth bones.
Since the bones are all jumbled up, it’s likely that these powerful mudflows remobilized and concentrated the remains of animals that had already died instead of killing a standing herd all at once.
But as this June 2018 video of a lahar at Fuego shows, wet ash, dense as cement and moving swiftly, can easily carry boulders and carve a canyon through the land. Mammoths in its path wouldn’t have had a chance.
Neither did the 23,000 residents of Armero, Colombia, who perished in a lahar when nearby Nevado del Ruiz had a small eruption in 1985.
Here is the lahar and pyroclastic flow hazard map for Popocatépetl today, showing solid-colored or hash-marked areas most likely to be affected today.
- The solid-red area has been hit with lava and pyroclastic flows, as well as lahars, at least twice in the last thousand years.
- The solid-orange area has seen the same things ten times in the last 15,000 years.
- The solid-yellow area is how far flows and lahars have reached at least twice in the last 40,000 years.
- The hash-marked areas show where lahars have gone down canyons and out into the lowlands. The yellow hash-marks extend down to the bottom of the map in some places.
Again, volcano monitoring would pick up precursors of most eruptions early enough to give some warning.
But in addition to these volcanic hazards, people living south of Popocatépetl have something in common with the residents of Tacoma and nearby areas–the relatively flat land they inhabit used to be the flank of a nearby volcano before it collapsed.
Flank collapse at Popocatépetl
A volcano has probably stood here for the last 730,000 years or so, according to rock magnetism studies. But it hasn’t always been the one that we see today.
Here’s a live view (weather and daylight permitting):
This part of Mexico has a belt of volcanoes that stretches obliquely from the southern Gulf of California coast to the Gulf of Mexico.
At least two other stratovolcanoes existed at Popocatépetl’s location before the present edifice began to take shape. Most of the oldest one–called Nexpayantla–disappeared in a huge debris avalanche to the south about 36,000 years ago.
I haven’t come across an explanation for the collapse, but going by what has been reported at Mount Rainier, it probably happened because groundwater, heated and turned acidic by magma, weakened the volcano’s sides until they could no longer support its weight.
After Nexpayantla came Ventorrillo, building on the remnants of its predecessor. This old volcano also collapsed, a little over 22,000 years ago, but you can still see a remnant of it through one of the online volcano cams experts use to monitor Popocatépetl.
So this modern colossus–and El Colosso is one of this beloved volcano’s local nicknames–is around 22,000 years old.
Popocatépetl grew up through what was left of Nexpayantla and Ventorrillo with lava flows both at the crater and also from the flanks, mainly on the northeast and southwest slopes. And it probably will collapse some day like they did.
Here is the area that volcanologists believe will be affected by that collapse.
Unfortunately, just as with Rainier and other volcanoes that are prone to flank collapse, there are no known precursors. One moment the fire mountain will be there, and the next moment, it will be gone in an avalanche. All you can do is try to get out of the way.
For almost a quarter of a century, government experts have been monitoring Don Goyo. That length of time is rough on field equipment. According to news reports (Spanish), some replacements and updates are needed.
However the science budgets turn out, scientists will continue to monitor Popocatépetl as much as possible, both because it is such a dangerous volcano and also because it is complex and even rather personable–for this moment of geologic time, anyway.
Featured image: Popocatépetl at dawn, by phily_100 at Pixabay, public domain.
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Sosa-Ceballos, G., Macías, J.L., García-Tenorio, F. et al. El Ventorrillo, a paleostructure of Popocatepetl volcano: insights from geochronology and geochemistry. (Abstract only) Bull Volcanol (2015) 77: 91
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https://youtu.be/EjcYwQBfHBY UNAM risk map
Popo plume, if needed: https://youtu.be/jXas8TNrF1I