This is a post from my other blog, Clear Sight, published on August 30, 2015. Since then, Fuego (Guatemala) has been very active; Acatenango, not at all.
There are two frequently active volcanoes in Latin America called Fuego (“fire,” in Spanish). English-speakers tend to refer to the one in Mexico simply as Colima, but Spanish-speakers also call it Volcán de Fuego, or just Fuego.
Today we’re going to look at the other famous Volcán de Fuego – the one in Guatemala – and its neighbor Acatenango, both of which are southwest of Atitlan and close to urban areas around Antigua and Guatemala City.
This Fuego is exciting, too!
(I’m pretty sure this video, taken at sunset, also captures the astronomical phenomenon known as the Belt of Venus…basically, Earth’s shadow as the Sun disappears beyond its limb!)
Those people are camping on the Fuego-Acatenango massif, a string of multiple volcanic vents. The massif runs perpendicular to the coast-hugging Central American volcanic front that’s related to the subduction of the Cocos tectonic plate underneath the Caribbean plate.
Indeed, thanks to the complicated plate-tectonic picture in this region, Central American volcanism happens in a number of distinct segments.
The volcanoes in this massif are at least 17,000 years old, fairly young in geological terms. Together with Agua, a third nearby colossus, they are the stereotypical pointy type of volcanoes (stratovolcanoes or composite cones). The ones that concern volcanologists and emergency planners are Fuego and Acatenango. In terms of hazard, briefly, besides the usual eruption effects they also tend to collapse unpredictably over geologic time.
Volcán de Fuego
Almost 4-kilometer-high Fuego Volcano was erupting in 1524 when the conquistador Pedro de Alvarado first saw it. There are many legends and historical reports (Spanish language) about Fuego.
Experts say that Fuego spends many years in basically an open-vent condition. The eruption captured on video above was one of its many small events, but this volcano has also had 60 subplinian explosive eruptions during historic times, most recently in October 1974.
Fuego’s last activity was a month ago, as of this writing, when per the Smithsonian Global Volcanism Program website:
Based on INSIVUMEH notices, CONRED reported that for a 30-hour period during 30 June-1 July activity at Fuego was at a high level, characterized by explosions, high-temperature pyroclastic flows (that began on 1 July), and ashfall. Ash plumes rose 4.8 km above the crater and drifted 25 km W and NW, producing ashfall in 22 local communities. The majority of material deposited by pyroclastic flows was in the Las Lajas drainage. Activity decreased later that day. During 4-6 July, INSIVUMEH reported that explosions produced ash plumes that rose as high as 800 m above the crater and drifted 8-10 km SW and W. Incandescent material was ejected 100 m high, and avalanches descended the Santa Teresa and other nearby drainages.
Michigan Tech has an incredible Fuego web page – check it out!
Although the two volcanoes Fuego and Acatenango are physically joined together in an area called La Horqueta (“the fork”), their magma is very different. Fuego’s magmatic products have become more mafic (like basalt) over time, scientists report.
Fuego (left) and double-peaked Acatenango tower over nearby Guatemalan fields. (USGS)
This volcano sits a little to the north of Fuego and appears like Fuego’s twin, but its magma is the grey explosive type known as andesite. The ridge between Acatenango and Fuego is actually all that remains of a much older volcano called Meseta that may have begun forming some 230,000 years ago and remained active until as late as the last Ice Age.
From what I’ve read, I think Acatenango is a little older than Fuego, but don’t quote me on it. At any rate, both volcanoes are younger than the Los Chocoyos ash that Lake Atitlan laid down some 85,000 years ago. The current edifice called Acatenango is actually the second volcano to form there – the first one collapsed some 40,000 years ago. Twenty thousand years after that catastrophe Yepocapa, the northernmost of the current double summits, was in place. Next came the summit that’s called Pico Central or Pico Mayor.
This volcano’s eruptive history isn’t as well known as Fuego’s. Certainly it has had several prehistoric eruptions, but the first documented one was in December 1924, a VEI 3, on the north slope of Pico Central. Pico Central itself had a VEI 2 deruption from August 1926 to May 1927. The last eruption at Acatengo was on the Pico Central-Yepocapa saddle in late 1972 (VEI 1).
Left: Debris avalanche remnants at modern Acatenango. (Jim Vallance at MTU/Smithsonian) On the right is the ashfall map for a major eruption at Fuego-Acatenango – note Guatemala City and Antigua are both at risk. (USGS)
Volcanic hazards at Fuego and Acatenango
Landslides triggered by heavy rain or earthquakes are as much a hazard at the Fuego-Acatenango massif as are eruptions. So is the possibility of a major collapse on the scale of the flank failure at Mount St. Helens in 1980, which might or might not be accompanied by an eruption.
Magma breaks rock as it moves inside a mountain. This causes seismic activity that seismographs detect. Other eruption precursors include ground deformation and increased gassing. Guatemalan geoscientists are monitoring Fuego for these.
However, landslides and debris avalanches happen without warning. Landslides essentially happen anywhere on sloped ground when downward-moving forces are stronger than forces holding the soil in place. It doesn’t take much to trigger a landslide when the soil is saturated with water from rain or earthquake-induced liquefaction.
Volcanic landslides are much bigger in scale. They were first recognized at Mount St. Helens in 1980 (hard to miss, that!). They are absolutely terrifying both because of their size and their speed (over 60 mph/100 kph).
Such a collapse happened to the first edifice at Acatengo, when some 4 cubic miles (15 cubic kilometers) of material suddenly sped down to the Pacific coast in a huge flow that was over 30 feet (10 meters) deep. It moved so fast that it traveled easily over 19 miles (30 km) of essentially flat ground at the end of its run-out.
Events like this have happened at least twice at Fuego-Acatenango. Now 100,000 people live in the path of the next one.
I’d like to say that everybody is prepared for the volcanic hazards. Unfortunately, I can’t.
Featured image: Fuego, February 2017, from Acatenango, by Arden
at Flickr. CC BY-SA 2.0.