Tacana

Construction of Tacana began sometime before 42 ka.  Later activity took place at the same time as volcanic activity from Chichuj.  The present cone is 8 km in diameter, 0.8 km E from Chichuj and 0.6 km WSW, partly buried by the younger San Antonio and Las Antillas dome.  Base diameter of Tacana is estimated at 3 km with a volume of 25 km3. 

The Tacana Volcanic Complex has been quite active during geologic and historic times, producing both explosive and effusive eruptions.  The complex had multiple sector collapse events and lahars.  The presence of active fumaroles and hot springs indicate an active hydrothermal system and altered rocks, meaning that the complex represents a significant and ongoing debris flow hazard to surrounding villages, particularly those to the S on the coastal plain. 

Construction of Tacana began inside the amphitheater left by the second Chichuj flank collapse to the W.  Initial construction produced andesitic lava flows and summit domes.  These were partly destroyed by either gravitational collapse or Vulcanian events that dispersed pyroclastic block and ash flows around the main cone.  The oldest block and ash flow deposits from Tacana are dated 42 ka.  The oldest explosive products, 32.6 ka, are pyroclastic flows on the N flanks.

Ten volcanic units are identified within Tacana over the last 50 ka or so.  The oldest block and ash flow on the S flank dates 42 – 39 ka.  N flank of the volcano is dominated by a block and ash flow that is stopped by the San Rafel caldera rim.  There are at least four massive units dating around 16 ka.  The E – NE slopes have three pumice fall layers interbedded with pyroclastic flow deposits.  These date 32 ka. 

Tacana summit has a 600 m wide horseshoe crater open to the NW.  The crater was created by a collapse 15 ka, emplacing the Agua Caliente debris avalanche.  The Agua Caliente debris avalanche deposit down the NW flank is 8 km long, covering 6 km3.  It has a volume around 1 km3.  The deposit is up to 200 m thick near its source.  The debris avalanche blocked the river.  It also destabilized the new dome, leading to its collapse and a series of block and ash flows.  Remobilization of this material by water produced debris flows that eroded primary deposits washing into the Coatan River. 

After the collapse, intense effusive activity continued in the crater putting lava flows to the NW (the 12 ka Agua Zarca), and partly refilling the collapse crater.  Around 10 ka, the largest explosive eruption over the last 10 ka took place, sending pyroclastic flows radially around the volcano to its base.  This eruption ejected a low altitude column creating the Once de Abril ash flow. 

At around the same time, the N part of Tacana collapsed creating the Tuimanj debris avalanche into Guatemala to the N.  It was smaller than the Agua Caliente.  Effusive activity resumed, extruding the East (9.3 ka), Southwest (8.6 ka), and the Northwest (8.9 ka) lava domes that filled the crater depression.  The final unit is a 6 m yellow pyroclastic flow topped with another 6 m of reworked (lahar?) material.  It dates 6.9 ka. 

Since then, Tacana produced at least nine smaller eruptions with pyroclastic flows on the upper flanks of the complex.  These date 7.6 ka, 6.1 – 5.6 ka, 2.6 ka, 1.9 ka, 1100 AD, 1000 AD, 1530 AD, 1720 AD, and 1850 AD.  Source for these eruptions is unknown as the summit has been modified over the last 10 ka.

At least two recent eruptions took place along NE – SW fractures between the summit and the Las Ardillas dome.  A phreatic eruption 1240 AD created an 80 m wide crater erupting ashfall and pyroclastic flows.  Today, this crater holds a small lake.  There is another small explosion crater on top of the andesitic lava flow.  The 1949 phreatic explosion vented between these two craters. 

There are two NE – SW landslide scars at Tacana.  One is 350 m wide from the summit domes.  The other is 60 m wide from the andesite lava flow between the Ardillas dome and horseshoe shaped crater WE of the summit.  There is another pair of NW – SE collapses on the NW part of the cone.  Explosive eruptions 5 and 2 ka may be related to gravitational collapse of external parts of the summit domes / lava flow fronts.  Summit dome lavas are highly viscous andesites to dacites with steep edges and are prone to collapse. 

Active landslides today are taking place in the E portion of the Ardillas dome and NE part of the main volcano cone.  Mass wasting near tension fractures in the andesitic lava flow and Ardillas dome area continues, highlighting the need for permanent monitoring of the system.

San Antonio

San Antonio was constructed 1.5 km SW of Tacana and the Las Ardillas dome. It is a semi-conical cone built against the Tacana cone, weak and unstable to the SW.  Start of activity here is unknown, though it started after the NW sector collapse at Tacana (Agua Caliente debris avalanche) and before the Agua Zacara lava flow.  San Antonio has an elongated base of 5 – 7 km.  At its maximum, it was 16 km3 with a central andesitic lava dome.  The San Antonio sequence started with several undated basaltic andesitic lava flows. 

The San Antonio eruption around 50 AD started with phreatomagmatic explosions that produced pyroclastic flows around the summit.  Explosions destabilized the cone, triggering a Pelean eruption that destroyed a 30° sector of the SSW flank and the summit dome creating a horseshoe shaped amphitheater.  Dome collapse generated a series of block and ash flows that traveled at least 14 km to the location of the current Mixcun village.  The flow covered at least 25 km2 with a volume around 0.12 km3.  Some ravines were filled with 10 m of material, though most of the fan was less than a meter thick. 

Distribution of the Mixcum block and ash flow deposit to the SW and in the horseshoe shaped crater of San Antonio suggest that a dacite summit dome was destroyed by collapse in multiple stages.  Each stage generated pyroclastic flows with a maximum runout of 14 km, location of the current Mixcum village.  The Mixcum pyroclastic flow deposit has fumarole pipes and juvenile lithics with cooling joints.  Charcoal found in this deposit date around 50 AD. 

Activity following this eruption continued filling the horseshoe shaped crater with several lava flows.  Eruptions ended with a 1 km dacite lava flow and a final summit dome.  These eruptions took place between 50 and 1150 AD.  No other activity from San Antonio took place since these last two dacite lavas. 

Coincident with the 50 AD Mixcum series of eruptions and dome collapse events were a series of lahars that flooded the main ravines S of the complex.  These lahars likely caused Izapa to abandon villages on the lowlands below and S of the complex.  This debris clogged local drainage upstream with loose debris creating a temporary lake.  This lake persisted for some number of weeks to months before breaching the dam and emptying downstream in a series of lahars. 

Plan de las Ardillas dome

The Las Ardillas dome is located between San Antonio and Tacana on the shared flank.  It is an andesitic central dome with two lava flows on the shared flank SW of the Tacana summit. 

The Plan de las Ardillas sequence is exposed between the San Antonio and Tacana volcanoes.  It is an andesitic central dome with two lava flows running along the NW and SE flanks of San Antonio and Taxana.  The most recent lava flow has steep flow fronts and levees.  It dates 30 ka.  The Plan de Las Ardillas domes are younger than the 26ka Agua Caliente debris avalanche.

Hydrothermal

Tacana has an active hydrothermal system.  This includes hot fumaroles (89° C) at the 3,600 m level and several groups of thermal springs (25 – 63° C) at the foot of the volcano 1,500 – 2,000 m.  One of the two fumarole fields was reactivated by the 1986 phreatic eruption.  Another on the San Antonio dome produces diffuse vapor emissions at boiling point. 

Most of these discharge from the NW flank near Agua Caliente village along a fault scarp left after a flank collapse.  All drain into cold streams in the Rio Coatan drainage which in turn discharges into the Pacific Ocean.  A group of hot springs was partly buried by a landslide in 2006. 

Heat discharge is low in comparison with other geothermal prospects in the region, perhaps 40% of that at El Chichon.  The springs are also spread out over a greater area.  There may be additional springs yet to be found.  The hydrothermal system is a stratified reservoir with a deep hydrothermal aquifer under two thermal aquifers. 

Debris fans

There are at least three volcaniclastic fans below the Tacana Volcanic Complex, extending to the Pacific Ocean.  Most of these are as a result of lahar action, though at least one of them is a debris avalanche / debris flow.   The most recent of these, Tapachula is 13 km long, covering 48 km2 with 0.7 km3 of material.  The area is mostly urbanized with Tapachula built 30 km S.  The fan is complex succession of deposits 23 – 1.3 ka formed by remobilization of debris along the Coatan River basin. 

The fans record 34 stacked units and five sequences.  The oldest is Pre-Tacana (Canjale fan).  It is five units of remobilized material produced during formation of the Canjale caldera 1 Ma.  The second, Mal Paso fan is four units deposited 100 – 23 ka.  The Lower Tapachula is two units depodited 23 ka.  The Upper Tapachula fan is 14 units deposited 14 – 1.3 ka.  The most recent Coatan fan is 11 units deposited since 700 AD down the Coatan River valley.  200,000 live on top of the Tapachula fan, making them vulnerable to future lahars from the complex. 

Tacana Eruptions

VOGRIPA lists a pair of VEI 4-class eruptions from Tacana.  The most recent of these was a VEI 4.1 around 70 AD that ejected a little over 0.1 km3 Mixcun flow.  The oldest eruption in the database is the 1 Ma, Chanjate, a VEI 4.0 that ejected 0.1 bulk volume.  The Tacana Volcanic Complex is considered a dormant volcano, though it did produce small phreatic eruptions in 1986 ,1949 and 1881.  There is no trace of materials ejected during these most recent eruptions.

Tacana produced large explosive and effusive eruptions during its history.  Plinian to sub-Plinian eruptions took place 29.5 ka, 23.5 ka, 14 ka, and 850 years ago.  Ashfall from these was distributed primarily on the Guatemala side of the territory.  These eruptions also produced pyroclastic flows, lahars and debris avalanches.  Given the close proximity of neighboring Tapachula, it is important to determine threat posed by future Plinian events.  The tropical climate and rainforest make this difficult. 

Around 29 ka, Tacana began a period of explosive eruptions with Plinian to sub Plinian plumes dispersed mainly NE by prevailing winds.  These produced Pumice fall 1, 29 ka, Pumice fall 2, 24 ka, Ochre Pumice, undated, Sibinal Pumice, 23 ka, and the Tacana Pumice, 14 ka. 

This period of explosive eruptions alternated with effusive eruptions, lava flows and dome extrusion.  Partial destruction of summit domes repeatedly deposited block and ash flows such as La Trinidad, 42 ka, Monte Perla, 28 ka, and San Rafael, 16 ka.

Sibinal Pumice

The 23.5 ka Sibinal Pumice eruption is the best defined of known Plinian eruptions.  It put 10 cm of ash 20 km from the vent.  The nearly 4 m stack of eruptive products found 13 km from the vent has two members separated by a lahar.  The bottom member is seven lapilli fall deposits.  Some of these are rich in lithics.  The lahar layer is topped with a massive, poorly sorted lapilli pumice mixed with hydrothermally altered lithics.  Prevailing winds blew the plume N and NE of the vent.  Minimum tephra volume was 1.9 km3 for the eruption.  Analysis of this eruption allowed geologists to draw initial hazard maps for the region surrounding the volcano. 

The 0.75 m lahar layer was not exposed for long before being buried by subsequent pumice fall.  The pumice fall was produced in a single massive eruption.  It is 2.6 m thick 13 km from the vent. 

The initial eruptive phase was pulsating Plinian with multiple columns that may have been over 19 km high.  Prevailing winds dispersed the column N – NE.  There was conduit erosion during this phase.  Some of there were unstable, interrupted with hydromagmatic explosions to form wet surges.  Others waned over time.  Lapilli and coarse ash was dispersed up to 20 km N of the vent covering a minimum of 432 km2.  After a short period of quiet lasting hours to days, intense rain mobilized part of the loose pyroclastics into a single large flow.  The eruption resumed from a larger conduit as a dry Plinian blast with a column over 22 km high.  1.7 km3 of material was ejected during this phase.  There are no overlying pyroclastics at the end of this phase as the eruption waned until it stopped. 

Eruptions the last 10 ka

Activity at Tacana continued until 10 ka, with an eruption that produced a sustained pyroclastic fountain of ash and pumice that collapsed producing a widespread pyroclastic flow, the Once de Abril ash flow.  This event continued with hydromagmatic activity and pyroclastic surges.  The pyroclastic flows reached 8 km from the crater to the S and 7 km to the NW.  It is not clear if this eruption caused collapse of the N flank of Tacana and the Tuimanj debris avalanche. 

Activity continued after this collapse with eruption of 4 – 5 km long lava flows.  The 10 km Agua Zarca lava flow extruded from the summit down the collapse scar.  Effusive activity from Tacana alternated with explosive eruptions and pyroclastic fountains that dispersed pyroclastic flow deposits.  Eruptions are dated 7.6 ka, 6.9 ka, and 5.9 ka.  The explosive eruptions alternated with extrusion of summit lava domes and lava flows downslope from the summit. 

The earliest documented native settlements in the vicinity of Tacana are 3600 and 3100 BC (5.6 and 5.1 ka).  Over that period, Tacana erupted at least 11 times leaving ashfall / pyroclastic deposits. Milder lava flow eruptions are not so readily apparent.  Over that period, there were at least six eruptions.  The first of these around 970 BC produced pyroclastic surges that filled the Tacana summit crater.  A 1170 AD eruption put a scoria flow W of the volcano.  An eruption in 1270 AD produced pumice fallout and pyroclastic surge deposits.  More pyroclastic surge deposits and flows were erupted 1270 AD, 1630 AD and 1680 AD.  The largest of this group of recent eruption was the 1270 AD pumice fall.  All of these should have been visible from the native settlements S of the complex. 

A hydromagmatic eruption 2.7 ka produced pyroclastic surges confined in the summit.  Later activity was confined to the summit with extrusion of three domes of varying composition (andesite, basaltic andesite and dacite). 

Minor explosive eruptions took place at Tacana over the last 1,000 years, 1080, 1630, 1720 and 1850 AD.  These were most likely low fountaining of pyroclasts without high eruption columns.

About 1150 AD, a low altitude eruptive column dispersed fall deposits on the summit domes and upper flanks of Tacana.  This deposit is thickest SW of the summit.  There is a lake at 3,784 that resembles an explosion crater separating las Ardillas dome from the SW base of Tacana cone.  The crater occupied by the lake it thought to be the vent of this eruption.

Smithsonian GVP lists multiple Bulletin Reports 1986 – 1988.  The first of these Jan 1986 reported shallow earthquakes beginning Dec 1985.  These damaged local adobe structures and a concrete school building.  One of these quakes was a M 5.0.  There was no change in temperatures at the summit lava dome or hot springs at the foot of the volcano.  Fumarole activity was also unchanged.  Earthquakes continued through April.

By May, earthquake frequency increased, and 23 hours of thunder-like noise was heard starting 7 May.  A moderate phreatic explosion opened a vent on the upper NE flank 8 May.  This ejected a small amount of fine ash, destroying vegetation a couple hundred meters from the new 20 m diameter vent.  Vapor emissions continued from active fumaroles.  Most seismicity was shallow, within 3 km of the new vent.  There was no observed deformation or increase in hot spring temperatures during this event. 

Seismicity decreased after the 8 May explosion to 1 – 2 events / day by June.  The active vent emitted steam to 500 m with an audible roar.  There was no gas sampling but H2S odor was noted.  Samples of ejecta were found to be strongly altered.  No glass was found in any of the samples. 

Residents reported that the 1986 activity seemed stronger than the previous event 1949 – 1950.  That activity was on the upper SW flank from numerous small fumaroles rather than a single vent and much shorter in duration. 

There were three small seismic swarms near Tacana late Jan 1987.  Seismic activity continued through July. 

Tectonics

Tectonics in the SE Mexico – NW Guatemala region is driven by the triple junction between the impinging Cocos Plate to the SW, the North American Plate to the N and the Caribbean Plate to the S.  While most depictions of this junction place it offshore of SW Guatemala, its actual location is still a bit controversial.  Further complicating the process is the subduction of the Tehuantepec Ridge into SE Mexico. 

The Tehuantepec Ridge is an important feature, with the Cocos Plate behaving differently on either side of it.  This is a recently aseismic ridge, with no earthquakes over M 7.6 over the last two centuries.  Subduction of the ridge began some 8 Ma.  It is a narrow ridge rising 2,000 m from the sea floor.  It also delineates shallow sea floor 3,900 m to the NW from deeper seafloor 4,800 m to the SE (Guatemala Basin).  The ridge also separates two different ages and subduction angles of the Cocos Plate, 12 Ma and 25° to the NW and 28 Ma and 40° to the SE.   The plate does not break into two segments at the ridge, rather, it transitions smoothly between regions.

In S Mexico, the Cocos Plate subducts 7.6 cm/yr.  The Tacana Volcanic Complex is located some 240 km from the Middle America Trench.  The slab is some 100 km below the complex.  The subduction of the Triple point appears to stop volcanism of the Central American Volcanic Arc in S Chiapas.  There are only two sites of scattered volcanism immediately NW of Tacana in S Mexico between the main volcanic structures of the Central American Volcanic Arc and the Trans Mexican Volcano Belt to the N.  These are El Chichon in N Chipas and Los Tuxtlas Volcanic Field near Veracruz.

Conclusions

Tacana is a complex, unstable, highly active volcanic system.  While recent activity has been small phreatic explosions, the system is quite capable of eruptions up to Plinian in size.  The edifice is unstable with ongoing landslides and has an extensive history of everything from rockslides to massive flank collapse / debris avalanches.  It has an active hydrothermal system busily altering volcanic rocks, making it easier for those rocks to collapse sending them downhill.  Appears activity is primed to continue for the foreseeable future.  Do not take this volcano lightly.

Additional information

Smithsonian GVP – Tacana

Late Holocene Pelean-style eruption of Tacana volcano, Mexico and Guatemala:  past, present and future hazards, Martin, et al, Geological Society of America Bulletin, 2000

Tacana volcano, Guatemala / Mexico, Volcano number 1401-13

Tephra fallout hazard assessment at Tacana volcano (Mexico), Vazquez, et al, Apr 2019

Study area – The watersheds of the Tacana volcano, Freie Universitat Berlin

Eruptive history of the Tacana volcanic complex, Macias, et al, Feb 2015

Geological evolution of the Tacana volcanic complex, Mexico – Guatemala, Garcia-Palomo, et al, Jan 2006

Risk management of El Chichon and Tacana volcanoes:  Lesons learned from past volcanic crises:  Chapter 8, De la Cruz-Reyna and Tilling, 2015

Active volcanoes of Chipas (Mexico):  El CHichon and Tacana, Solamacchia & Macias, Editors, Oct 2016

The ~14 ka Plinian-type eruption at the Tacana volcanic complex, Mexico Guatemala, Arce, et al, Dec 2008

Late formative flooding of Izapa after an eruption at Tacana volcano, Macias, et al, Sept 2018

Petrology and geochemistry of the Tacana volcanic complex, Mexico – Guatemala:  evidence for the last 40,000 yr of activity, Mora, et al, Jan 2003

Evidence of volcanic activity in the growth rings of trees in the Tacana volcano, Mexico-Guatemala, Allende, et al, Sept 2019

Volcaniclastic sequences at the foot of Tacana volcano, southern Mexico:  Implications for hazard assessment, Murcia & Macias, Jul 2014

New chronological constraints on intense Holocene eruptions and landslide activity at Tacana volcanic complex (Mexico), Alcala-Reygosa, et al, May 2021

Chemical and isotopic compositions of thermal springs, fumaroles and bubbling gasses at Tacana volcano (Mexico-Guatemala):  implications for volcanic surveillance, Rouwet, et al

The analysis of the seismic Tacana volcanic complex in 2017 – 2018, AYA Pacheco, 2023

Petrogenetic and tectonic implications of major and trace element and radiogenic isotope geochemistry of Pliocene to Holocene rocks from the Tacana volcanic complex and Chiapanecan volcanic belt, southern Mexico, Verma & Verma, May 2018