About everybody knows that Guatemala has three very active volcanoes: Fuego, Pacaya and Santa Maria’s dome Santiaguito – but did you know that a staggering 324 eruptive centers have been identified in that country?
I read this number in a 1969 study which attempted to create an overview of all the volcanoes and other eruptive centers in Guatemala. However, the author stressed that the result was only preliminary and therefore was to be taken with a heap of salt rather than just a few grains. Further research should confirm or change these results.
Most of these correspond to small cineritic and lava cones in the south-eastern part of Guatemala (cineritic = violent Strombolian). I haven’t found a corrected actual number though, and there is no guessing whether following field work has revealed even more volcanoes, or found that many “volcanic” features had to be dismissed as such.
Whatsoever, curiosity led me to look at some of the confirmed volcanoes from the list, and the last one to have been in the news was Tecuamburro.
OF FAULTS AND GRABENS
Tecuamburro volcanic complex, or montaña de Chiquimulilla, is located in the South of the country, roughly 50 km south of Guatemala City, in the department of Santa Rosa (which has no less than 42 eruptive centers listed). It sits about 30 km from the Pacific coast and 20 km S of the main volcanic chain.
Guatemala is divided into two major tectonic blocks, the Maya block (North American Pl.) and Chortís block (Carribean Pl.), juxtaposed along the present-day Polochic-Motagua Valley fault zone. Tecuamburro Volcano lies within the Chortís block on the west-tapering tail of the Caribbean plate. In Guatemala this plate is bounded in the south by the Middle America Trench and its NE-dipping subduction zone. The Central American chain of active volcanoes along the coast are fed by magma from this subduction.
Active tectonics in southern Guatemala include the formation of a system of roughly north-trending grabens and horsts. This results in a crudely corrugated fabric to the landscape. Tecuamburro Volcano lies within the south-central part of a roughly 20 km wide graben that terminates northward against the (trench‐parallel) major regional Jalpatagua fault system. Motion analysis of a 1979/80 earthquake swarm indicates further downthrow at the graben faults – the Tecuamburro graben continues to grow.
Many more complex fault patterns become apparent within the graben. Lines of warm mud volcanoes located 1 km west of Ixpaco crater, fissures from which hot springs issue along the banks of Rio Los Esclavos, and the alignment of some volcanic vents including those of Tecuamburro Volcano and two adjacent domes, all follow a north-west fault trend.
One interesting fact is that north-trending valleys within the Tecuamburro graben are partly filled by rhyodacitic ignimbrites and tephra fallout. The nonwelded ignimbrites are from a few to several meters thick. They consist mainly of ~15 cm sized pumice lapilli. These are interpreted as products of caldera-forming eruptions at Amatitlán, ~50 km to the northwest!
Volcán Tecuamburro is the youngest within a cluster of four Pliocene to Pleistocene volcanoes. Due to the presence of several zones of active hydrothermal alteration it is known that the volcano is currently still active. However, there is no historical record of volcanic activity for this area. A radiocarbon study indicates that the last major upheaval in the volcano occurred about 38,3 ka. At that time the modern Tecuamburro formed inside the 4 x 6 km caldera of the ancestral stratovolcano, called Miraflores. The latest known activity was the phreatic eruption of the Ixpaco maar crater to the N ~2900 years ago.
At some stage the old caldera breached to the east by a devastating structural failure. The Miraflores debris-avalanche deposit covers roughly 10 km² opposite the scarp on the flanks of Ixhuatán volcano across the Río Los Esclavos, some 5km to the east.
Because the exposed deposit is not large enough to account for the roughly 4 km³ collapse scarp, it is likely that the Miraflores avalanche was deflected down-valley and travelled many kilometers onto the Pacific coastal plain. A corresponding deposit has not been confirmed, but, unlike other rivers, after reaching the coastal plain the Río Los Esclavos turns to the SE, parallel to the volcanic front. This could mean there is a subtle topographic high to the west, which could indicate a possible underlying avalanche deposit from Tecuamburro.
THERE’S MAGMA BELOW!
Modern Tecuamburro is a small, densely forested andesitic-to-dacitic stratovolcano, or lava-dome complex, of mostly Pleistocene age. The eastern part of the elongated volcano consists of the younger lava domes C. Peña Blanca with 1850 m a.s.l. and C. El Soledad with a height of 1845 m a.s.l. at the eastern end. These were constructed during the late Pleistocene or early Holocene within the east-facing caldera. The highest peak is Cerro Miraflores in the western part, 1945 m tall.
Two nested craters, the larger of which is Chupadero, lie at the NW end of the complex. The smaller inner crater is a phreatic tuff ring, Laguna Azufrada de Ixpaco, with an acidic crater lake as well as hot springs, fumaroles, and boiling mud pots around. On GEarth I saw another hydrothermal area that used to contain a ~200-meter long lake in 2005 but had completely dried up after 2014.
Studies of the youngest volcanic rocks say it seems likely that a partly molten, or a solid-but-still-hot, near-surface intrusion still resides within the crust beneath Tecuamburro volcanic area. Chemical geothermometry suggests that a hydrothermal convection system is centered over this crustal heat source. An 808 m deep drill hole, completed in 1990, yielded temperatures of up to 300°C. These investigations had been made 1988-1992 in preparation for a geothermal plant but so far, none has been built in the area.
LAGUNA DE IXPACO 2019
Video by ‘Laguna de Ixpaco’ on FB from 30/12/2018 (Video opens in new Tab. If it doesn’t work, try it in Facebook HERE)
The crater lake Laguna Ixpaco is an important attraction in the municipality of Pueblo Nuevo Viñas, at 1,105 m a.s.l.. It is one of the craters of Tecuamburro volcanic complex, 5 km NW of Tecuamburro proper. This crater was created about 2900 years ago within the 4 km Chupadero crater (or possibly a small caldera) of Pleistocene age. It formed as a maar tuff ring, during the last phreatic explosions of Tecuamburro.
It is thought that the lake bottom connects to an aquifer below and so to the hydrothermal system of the volcano. Due to sulfur and other minerals in the lake water, its colour is usually mint green, but can turn milky-white occasionally. The water temperature is variable, it ranges from 30 to 100 °C, and has a pH of ~3. At times, vigorous upwelling can be seen on the lake surface. Prolonged exposure to the fumes coming off the water can be harmful; people with breathing problems should probably not visit the Ixpaco lake.
On 8 January 2019 CONRED Guatemala tweeted that they, “in coordination with municipal staff, today carry out an evaluation of a conical geological structure where sulfur smell and vapour with high temperature emanates on the banks of the Ixpaco lagoon”.
On 16 January they add that “INSIVUMEH staff is currently conducting a geothermal study on the newly formed geological structure on the shore of the Ixpaco lake […] with the aim of obtaining more scientific details” on a new vent at the lake’s shore that had fast grown in size and had increased emissions of gas and mud. A last tweet in February blandly stated the unchanged situation at the new mud vents.
I searched both the websites of INSIVUMEH and CONRED to find the results of the studies, or at least a “back to normal” sign, but no luck. If I searched correctly, there hasn’t even been a single mention of Laguna de Ixpaco on either website. Judging by private photos of the lake shore from August and September this year, the new mounds have been eroded somewhat since, and degassing activity was much less than before. But that were just snaps of a moment, so, we don’t know nothink…
Comparing the GEarth imagery of previous years with the image from January 2019, no obvious changes show up in the vents visible at the lake shore. Perhaps the area looks a bit more elevated, but that could be due to varying water levels. Of course there is the new vent which seems to have appeared before summer 2018 and only increased its activity in January.
Knowing that there is, in all probability, a red-hot blob below the the volcano, there are as usual two possibilities: either Tecuamburro volcano begins to prepare for a new eruption in the near or far future – or, if not, the magma will cool down to remain there as a nice lump of a diorite pluton. In the latter case, the Guatemalan electricity industry may go ahead winning energy from it for ages. Maybe some uncertainty about the future behaviour of the volcano has so far prevented them from already building the plant? Either way, this certainly is an interesting volcano and I look forward to new findings about it.
Disclaimer: I am not a scientist, all information in this (and any of my other posts) is gleaned from the www and/or from books I have read, so hopefully from people who do get things right! 🙂 If you find something not quite right, or if you can add some more interesting stuff, please leave a comment.
Enjoy! – GRANYIA
SOURCES & FURTHER READING
– GVP, Tecuamburro
– Los Focos Eruptivos Cuaternarios de Guatemala
– Geology and Geothermal Potential of the Tecuamburro volcano (1992, paywalled)
– Estudio Técnico y Recategorización del Áreas Protegida Volcán Tecuamburro (2015, Presentation)
– Large-volume volcanic edifice failures in Central America (2006, paywalled)
– An evaluation of the geothermal potential of the Tecuamburro (1990)