Continuing eruptions at Volcan de Fuego, Guatemala

In 2016 there have been four eruptions (also called paroxysms). The fourth showed signs of increased activity early March. A few days later, activity levels had decreased to normal levels. They were all marked by Strombolian type eruptions with lava, explosions, some ash, pulsing fountains and lava bombs down the flanks from the summit vent. http://www.volcanodiscovery.com/fuego/news.html

Fuego from neighboring Acatenango volcano http://epod.usra.edu/blog/2015/04/fuego-volcano-eruption-viewed-from-vulcan-de-acatenango.html

Webcams for Volcan de Fuego can be found at the following links:

http://ovfuego-norte.geo.mtu.edu/
http://webcams.volcanodiscovery.com/Fuego

There are over a million people within 30 km of the volcano and nearly 7.7 million live within 100 km of the volcano.

Feb. 7, 2015 from Antigua. Fuego on the left. http://www.infobae.com/2015/02/07/1625501-cerraron-el-principal-aeropuerto-guatemala-las-explosivas-erupciones-del-volcan-fuego

Volcano

Volcan de Fuego is a large andesitic–basalt volcano that is one of the most continuously active volcanoes in Central America. It tops out at nearly 3,800 m. It is one of three large stratovolcanoes overlooking the town of Antigua. Eruptive products are tephra, lava flows, pyroclastic flows and ash.

The three volcanoes are Acatenango, Volcan de Fuego and Volcan de Agua. Fuego’s and Acatenango’s base overlap, while Agua is separated from Fuego by a low saddle.

Volcan de Agua left, Fuego center right, Acatenango to the right. Photo from Guatemala City. https://en.wikipedia.org/wiki/List_of_stratovolcanoes

One of the confusing things (at least to me) is the multiple names for summits, peaks, ancestral mountains, and close neighboring active volcanoes. In this case, we have at least four summit craters identified as parts of two current and one ancestral volcanoes that occupy the same general footprint. Fuego is the currently active vent on the common edifice.

Fuego occupies an ancestral collapse scarp of the older Meseta volcano, which was first of the grouping to start its construction. The collapse is thought to have taken place some 8,500 years ago, making Fuego one of the younger volcanoes in Guatemala.

Construction of Meseta started some 230 Ka ago and continued until some 8,500 years ago when it suffered a flank collapse. Deposits from this collapse extend some 50 km west to the Pacific coastal plain.

Activity for the group has migrated southward, which is described as typical for Guatemalan volcano complexes.

Pyroclastic flow from Fuego, Sept. 2012 http://www.wikistrike.com/article-guatemala-le-volcan-el-fuego-oblige-a-l-evacuation-de-33-000-personnes-110079222.html

Acatenango’s northernmost summit was active between 70 Ka to 20 Ka years ago. The second summit is still active. It is only 3 km from Fuego’s. Last widespread tephra from Acatenango was some 1,900 years ago. The last historic eruption was 1661. Phreatic eruptions occurred 1924 – 1927 and December 1972.

Material erupted has also changed over time, with Acatenango being more andesitic and Fuego being more basaltic. Fuego’s eruptive products have become more mafic over time.

Fuego can produce significant pyroclastic flows. There appear to be 20 – 50 year long clusters of activity with sporadic activity in between. Widespread pyroclastic deposits east of Fuego have been aged at some 980 years BP, 1050 years BP, two some 1350 BP and one at 3530 BP. Lavas on Meseta constrain the age of Fuego at less than 30,000 years old. Lahars from Fuego have been identified over 20 km from the volcano.

Pyroclastic flow deposits near Fuego http://blogs.egu.eu/network/gfgd/2014/10/

The third volcano in the group, Volcan de Agua does not have any recorded historic eruptions. It did destroy a neighboring town in 1541 with what can be best described as a lahar. It was initially thought a crater lake burst and created the mudflow that destroyed old Santiago. A pair of archeologists in 1895 analyzed the volcano and found no evidence of a past crater lake. However, mudflows down the volcano are sufficiently common so it was named Volcan de Agua (with Agua being Spanish for water). It is also tall enough at 3760 m to get snow coverage during the winter.

Lahar deposit near Fuego. Photo taken 2014. http://blogs.egu.eu/network/gfgd/files/2014/10/1.jpg

The combination of lahars and numerous destructive earthquakes led to the move of the capital of Guatemala from its original location in Antigua to Guatemala City some 40 km away in 1776.

Note that the threat of lahars and debris avalanches exist for all three volcanoes, as significant rainfall will mobilize loose tephra and pyroclastic flow deposits. Add to that the continuing threat of significant earthquakes in the local area. All three of these volcanoes have steep slopes and are weakly held together. The southern flanks of Fuego get over 5 m of rain in a typical Guatemalan rainy season lasting from May through October.

Eruptive plume from 1966 eruption. http://www.geo.mtu.edu/volcanoes/fuego/eruption2.html

Eruptions

Over 70 eruptions / eruptive periods have been observed since Spanish Conquistadors first discovered Volcan de Fuego in the Sixteenth Century. We are in the midst of the longest continuing eruptive period which started in 2002.

The largest eruption on the Smithsonian list was a VEI4 in 1974. There are numerous VEI3s and smaller eruptions.

1974 eruption plume. http://www.geo.mtu.edu/volcanoes/fuego/eruption2.html

The 1974 eruption ejected around 0.02 km3 of tephra and more than 0.2 km2 of pyroclastic basalt. The column was some 15 km tall. It was a relatively small, vigorous and Sulphur rich eruption. Ash was measured some 20 km downwind to the west. There were four distinct 4 – 17 hour long pulses over a 10-day period. As the eruption progressed, chemistry of the magma changed. It was initially poor in mafic crystals and rich in plagioclase. It ended rich in all crystalline phases. This suggests that crystallization began some 5 km below the surface. It appears what erupted was a disrupted / mobilized crystal mush.

Esquintila and La Democracia Debris Avalanche locations. http://specialpapers.gsapubs.org/content/412/105/F1.expansion.html

The largest flank collapse deposit is called the Escuintla debris avalanche. It covers some 300 km2 and measures 27 km long by 18 km wide. The thickness is not well known, though one estimates it as 9 – 15 km3 in total volume. Dating the debris flow based on more recent events leads to an estimate of age between 8,500 – 30,000 years old, with the younger age being the most likely. This means that Fuego potentially has built from the remains of a flank collapse to its current form in a mere 8,500 years. There is clearly a very healthy magma source to this complex. http://www.geo.mtu.edu/volcanoes/fuego/escuintla.html

Cross section of Escuintla Debris Avalanche. http://volcano.si.edu/learn_galleries.cfm?p=14

There is a second debris avalanche called the La Democracia that measures some 2.4 – 5 km3 in volume is thought to have issued from Acatenango based on a scar on its flank. There is some argument which actual volcano this flow came from as its chemistry matches some Meseta / Fuego lavas. So the complex has generated at least two debris flows via flank collapse.

Just to reinforce the active nature of the local area, the next volcano SE is Pacaya. Just NE of the Pacaya – Agua line is a 16 by 14 km active caldera called Amatitlan.  It has at least nine eruptions between 300 – 23 Ka producing over 70 km3 of material.  It is bounded on two sides by faults and filled with pyroclastic materials.  The caldera has a resurgent dome. When the Guatemalans moved their capital, it appears they chose a worse location than it was initially, as it is now within 10 km of the Amatitlan caldera and lake.

Tectonics

Tectonic activity in Guatemala is driven by the interaction of three plates. From the WSW, we have the Cocos plate subducting under the North American and Caribbean Plates at the rate of 50 – 90 mm/yr. The Mid America Trench is the subduction trench in the Pacific Ocean to the west of Central America.

Tectonics of Guatemala showing northern boundary of Caribbean Plate. http://ontario-geofish.blogspot.com/2015/11/the-tectonics-of-guatemala.html

The movement between the North American Plate and the Caribbean Plate is 20 mm/yr to the west. Note that both plates are moving, with the Caribbean Plate also moving ENE. It is a strike-slip motion and created the major fault feature in Guatemala, the Motagua Fault. Finally, there is a relatively poorly defined triple junction between all three plates offshore southern Mexico at the western end of the Motagua Fault where it intersects with the trench.

The Caribbean Plate is a relatively young mainly oceanic plate. Its origin is still debated. Best explanations appear to be either a thickened oceanic plate due to the presence of the Galapagos hot spot or thickened oceanic plate due to the presence of a complex area of spreading junctions a bit farther west in the Pacific. The motions of the North American and South American plates have essentially squeezed the Caribbean Plate between them. The northern boundary is mostly a strike – slip boundary. The easternmost boundary is a subduction region marked by the Lesser Antilles. The westernmost boundary is marked by a subduction trench off the western coast of Central America. Finally, the southern boundary is complex and not offshore South America. It has subduction in places; strike slip in places, and overthrust folding of continental collisions that has not yet turned into subduction.

Caribbean Plate blocks and boundary action http://www.intechopen.com/books/new-frontiers-in-tectonic-research-general-problems-sedimentary-basins-and-island-arcs/the-caribbean-plate-evolution-trying-to-resolve-a-very-complicated-tectonic-puzzle

While both North and South America are generally moving westward, it was long thought that the Caribbean Plate was moving eastward. This seems to be relative motion only, as there is at least one paper that describes its actual motion as westward.

Volcanic activity in Guatemala is driven by the subduction of the Cocos under the Caribbean Plate. There are at least 29 volcanoes in Guatemala, most to the south of the fault line and to the east of the trench. 23 of them have been active in the Holocene. At least four of them are considered currently active.

Motion along the fault averaged 13 mm/yr over the last 10.3 Ma. It is currently estimated at 6 – 10 mm/yr.

A car rides near the Volcan de Fuego (Fire Volcano), located 3,763m above sea level in the Escuintla-Sacatepequez border, some 60km from Guatemala City, 25 December, 2007. AFP PHOTO/Orlando SIERRA

Conclusions

Volcan de Fuego is a young, vigorous, very active volcano. It has a history of flank collapses. It has a history of multiple widespread pyroclastic flows and of lahars. The only thing I haven’t found about it was a caldera formation event, which may be in front of us rather than behind us in time. It has a robust and vigorous magma source. It has exhibited eruptive episodes (like 1978) that indicate destabilization of crystal mush leading to explosive eruptions.

The 7.7 million living within 100 km of this volcano may be living a bit too close. This is one of the nastiest systems I have reviewed and should be treated with a great deal of respect.  One of the great dangers of Fuego is that it has a large number of small, unobtrusive eruptions.  These tend to teach those nearby (residents and visitors) that the mountain is not a significant threat.  You can see that from the close locations some of the photos were shot.  This works right up to the point where it pops off into a large eruption like 1974 or 1966 or even larger.  At that point, a lot of people end up getting hurt.

Fuego, April 1, 2015. http://photography.nationalgeographic.com/photography/photo-of-the-day/fuego-volcano-guatemala/

 

Additional information

http://specialpapers.gsapubs.org/content/412/105.abstract
http://geology.gsapubs.org/content/29/10/911.abstract
https://www.researchgate.net/publication/222074490_The_October_1974_basaltic_tephra_from_Fuego_volcano_description_and_history_of_the_magma_body_J_Volcanol_Geotherm_Res_43-53

Click to access of2001-0431.pdf

http://www.geo.mtu.edu/rs4hazards/links/Seismicity-Rudiger/seismicity_guatemala.htm
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.693.9074&rep=rep1&type=pdf
http://www.geo.mtu.edu/~raman/VFuego/VFuego/Welcome.html

 

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