El Valle is a broad stratovolcano located some 80 km SW of Panama City.  It is cut by the 6 km diameter El Valle de Anton caldera formed some 56 ka.  The caldera has steep 200 – 300 m walls.  The caldera floor is flat, formed by deposits of a former lake, currently occupied by the town of El Valle.  There is a line of resurgent domes within the caldera.  The most recent activity were phreatic eruptions some 13 ka, which may have continued into the last 10 ka.

El Valle de Anton (Anton’s Valley) is a town of 7,600 located on the caldera floor of El Valle.  It is located at 600 m, making weather there somewhat cooler than neighboring Panamanian lowlands.  There are around 132,000 living within 30 km, 2.1 million within 100 km, most of them in Panama City to the E.

The town is about 25 km off the Interamerican Highway and can be reached by a two-lane road that is generally in good condition.  Panama City is the closest large city, 120 km, about 2.5 hours away via minibus.  Weather here is tropical with averages ranging 10° – 25° C. 

El Valle de Anton is a popular weekend getaway for urban residents.  It is also a small retirement community for some 200 resident expats from more than 40 countries.  There are weekend homes for wealthy Panamanians in the locale.  The town is a growing draw for tourists, with multiple trails and scenic attractions.  There are waterfalls and hot springs near the town, tropical rain forests with birds, orchids and endangered Panamanian golden frog.  The city market is active particularly on the weekends. 

While there are no national dedicated volcano observatory located in Panama, natural disasters are handled by Sistema Nacional de Proteccion Civil (SINAPROC).  These include flooding, hurricanes, landslides and earthquakes.  Their website does not appear to have a dedicated volcano page.  I was unable to find a dedicated webcam for the mountains outside El Valle de Anton.  There is a dedicated webcam on the grounds of the Canopy Lodge that allows viewers to watch local birds feed on cut fruit outside the lodge. 

Region

Panama sits in the break between the Central American Volcanic Arc and the Northern Andean Volcanic Zone in Columbia.  There are the remains of at least 10 stratovolcanoes in the country.  Volcano Discovery lists only four volcanoes in Panama.  All distances will be measured from El Valle de Anton.

Tisingal

Volcan Tisingal (Cerro Colorado, Cerro Pecon) is located some 270 km WNW from El Valle.  It is immediately NW of neighboring Volcan Baru.  The large andesite – dacite volcano was breached to the SW by a massive flank collapse, creating a 7 km diameter wide horseshoe shaped amphitheater.  The 1.66 Ma collapse produced 8 – 10 km3 of debris avalanche.  Activity continued to 520 ka.  Multiple domes were constructed after the collapse.  Cerro Picacho on the NE rim is the high point of the volcano at 2,986 m.  Two large lava domes, andesitic Cerro Totuma and dacitic Cerro Pelon froemd on the NW and E sides of the caldera.  Two more domes are outside the caldera to the SSW.  Cerro Pando is the largest of these.  The final dome is E of the amphitheater.

The area was studied for a hydro project in 2020 that would take water from a local river, pipe it downhill through a power station to generate local electricity.  Note that this is not the typical geothermal power station.  It is rather a run of the mill hydro plant that takes advantage of the vertical development provided by the remaining volcanic cone.

Baru

Volcan Baru (Volcan de Chirqui) is the youngest volcano in Panama.  It is located 255 km WNW from El Valle, 15 km ESE from neighboring Tisingal.  This is also an andesite – dacite volcano.  Like neighboring Tisingal, it also suffered a flank collapse, debris avalanche that created a summit caldera / amphitheater.  This one breached to the W and took place some 9 ka.  The deposit extends onto the Pacific coastal plain. 

Post collapse eruptions constructed domes inside the caldera that rise above the caldera rim.  A strong explosive eruption 700 AD ended human occupation at the Cerro Punta archaeological site NW of the volcano.  There were at least eight eruptions over the last 10 ka.  A strong eruption around 1550 was later reported in 1884.  Later observers decided this report was uncertain, though more recent tephra dating found tephras younger than 500 years, which would have been produced by its most recent eruption.

There has been interest in geothermal energy development at Baru since at least 2013.  To date, nothing has been constructed. 

La Yeguada

Volcan La Yeguada (Chitra – Calobre) is a massive volcanic complex located some 61 km W of El Valle.  The current system is a roughly circular group of three domes.  These include Cerro Castillo, W and S, Cerro Novillo, E, and Cerro Corero (Cerro de la Charca), N.  Lake La Yeguada and La Laguna are on the W edge of the complex.  There are small hot springs and seeps in the area.  There is speculation that the entire system is set inside a 7 km diameter caldera.  Much more work needs to be done to confirm this, however.

This system has been active for much of the last 15 Ma, erupting primarily andesites similar to El Valle’s Old Group andesites.  The three La Yeguada and Canazas formations erupted 14.7 – 10.5 Ma.  The EL Satro Pyroclastic Flow erupted 11.3 Ma and surrounds the N portion of the complex.  The undated Mano de Pilon is an older rhyodacite pyroclastic flow covered by El Satro.  Most surrounding rocks are Miocene volcanics 11.6 – 7.2 Ma. 

Cerro Picacho is a separate dacite dome complex 1.5 km E of the main complex dating 4.5 Ma.  There was a break in activity from roughly 5.0 Ma – 357 ka.  The youngest dated eruption of the central dome complex was the Castillo dome complex 357 ka.  As both Cerro Novillo and Cerro Corero are currently undated, it is unclear if they were formed before or after the break in activity, though it is possible that the three interior dome complexes formed quickly and close in time to one another.

The Castillo dome complex includes Cerro Castillo and Cerro Novillo.  The 4 x 4.5 km La Yeguada dome includes Castillo unit and Corero unit.  Large fans of debris spread off the dome.  Dome material is highly altered. 

The most recent eruption took place from the Media Luna cinder cone 32 ka.  This eruption was separate from activity at the main dome complex.  It is located 10 km NW from the main complex.  The cone only rises 100 m from the valley floor.  It is breached to the W.  A lava flow breached the cone and flows E for 2.5 km.  The flow is over 500 m wide along its length.   

There is speculation that the system is located in a caldera.  This is fed by multiple similarities to caldera formation.  First is the overall circular shape of the system. Second is the central dome complex similar to other known resurgent dome complexes after caldera formation.  Third is the presence of a large pyroclastic eruption associated with caldera formation.  The El Satro Pyroclastic Flow 11.26 Ma is a silicic welded tuff, the largest mapped in the complex.  Finally, Lake La Yeguada appears to lie within the moat section of the caldera.  However, no detailed fieldwork has been done to verify this speculation, so further investigation is necessary.

El Valle

El Valle is one of three recently active volcanoes in Panama.  It is the easternmost volcano in the Central American Volcanic Arc.  It started out as a stratovolcano, suffered at least one (likely more than one) caldera-forming eruption, and now is topped with a 6 km diameter caldera.  Its activity is divided into the Old Group 10 – 5 Ma and Young Group 3.0 – 0.3 Ma.  Old Group products are mostly andesitic.  Young Group erupted mostly dacites. 

The most recent large eruption was a Plinian one some 32 ka, where caldera lake water interacted with magma, generating a Plinian eruption, sending pyroclastic flows that reached the Pacific coast 25 km S.  Note that this description implies that the caldera existed before that eruption.  The most recent dated activity were phreatic eruptions 13 ka that may have continued to 10 ka.  The caldera has been evaluated for geothermal power over the last decade. 

The caldera is bounded by steep 200 – 300 m walls overlooking a flat floor containing lake deposits.  Cerro Pajita, Cerro Gaital and Cerro Caracoral are dacite dome complexes constructed along an E-W trending lineament on the N side of the volcano.  Cerro Gaital is the high point of the volcano at 1,185 m. 

There may be additional calderas in the immediate region suggested by at least two more ring fault formations.  There is a gravity anomaly beneath the 6 km diameter caldera.  Modeling suggests it is a low-density batholith.  New Group eruptive products filled all the calderas with up to 1 – 2 km thick layer of pyroclastics. 

El Valle de Anton has an active hydrothermal system with publicly available geysers and hot springs.  Geothermal exploration was suggested before 2000, though as of today, no production wells have been drilled. 

Typical stratigraphy of the region has at least six physical layers.  From basement to the surface, these are the Caribbean Large Igneous Province (CLIP), Llano Tigre, Domes / Iguana, El Hato, EL Valle, and Fan deposits.  The last two layers rework previously erupted material in a wet environment.  A closer inspection of the layers is in order.

Basement

Caribbean Large Igneous Province (CLIP) basement lavas compose the majority of the crust beneath El Valle.  The crust is around 25 km thick.  This unit is a regional basement composed of both CLIP lavas and Galapagos hot spot track and overlying sediments.  Most lavas erupted in this layer erupted below sea level. 

Llano Tigre

The first dated material at El Valle is the Guacamayo dacitic flow 10.2 Ma.  Activity switched to andesite for the next 5 Ma, with andesitic units erupted around 6.92 Ma.  Other Old Group eruptive units include the Piedra Fine and Coarse Grained Andesites, 6.9 Ma, Rio Anton and Iguana pyroclastics.  There was a break in the action with a 5 Ma period without any recorded volcanism starting 5.1 Ma. 

Note that at least one publication has dated the Piedra Coarse Grained Andesites sometime around 1.55 Ma coincident with emplacement of a dacite dome overlooking the caldera.  Given the extensive altering of these volcanic rocks, It would appear that the date of resumed activity is closer to 100 ka than 1.55 Ma.  Either way, it appears that Piedra Coarse Grained Andesites were much closer to 5 Ma, the last Old Group eruptive products.

The neighboring Sora Caldera was active sometime between 10.2 – 6.9 Ma with mixed andesitic and dacitic lavas.  The proposed Las Lagunas caldera between Sora and El Valle is as yet undated. 

Iguana / Domes

Piecing this section of activity in a chronological order is a bit of a festive event based on wildly varying estimates of activity dates.  The beginning of the Young Group eruptions is defined in various places 1.55 Ma – 109 ka.  The El Hato ignimbrite is variously dated 1.33 Ma 0 32 ka.  Worse, there may be at least two caldera forming eruptions, one at the beginning of dome building, and more recent El Hato 32 ka.  All ignimbrites are attributed to El Hato, having similar dacite chemistry.  Variation in dating erupted materials appears to be entirely due to extensive altering of those materials. 

The next period combined Dome building lasting roughly 109 – 85 ka with the Iguana lavas 109 – 56 ka.  There was a 30 ka overlap between the two periods.  All eruptive products after 109 ka are considered to be Young Group dacites.  There are significant chemical differences between the Old and Young Group magmas.  The Young Group magmas may have been derived from slab melting. 

Eruption of the dacite lava domes on the N flank of the caldera (Gaital, Cacacoral and Pajitas) took place 109 ka.  Activity continued with eruption of dacite lava flow units at Guacamaya and Iguana volcanic centers 85 ka.  Volcanic activity shifted E to India Dormida (lava flows) 56 ka.  Volcanism at Guacamaya, Iguana and India Dormida are grouped as the Iguana unit.  Activity reached its climax with eruption of the El Hato unit 56 – 32 ka. 

The first Young Group activity emplaced a dome on the edge of the current caldera.  It is at this point that speculation starts running rampant, with disagreement between multiple dates of caldera formation.  If there was an earlier caldera formation date, this means there were at least two caldera forming eruptions, the first around 109 ka, followed by the El Hato ignimbrite somewhere earlier than 56 ka.  The dome building would then become typical resurgent dome building, post caldera activity.

Various papers discuss emplacement of the initial dome followed by eruption of an extensive ignimbrite, also named EL Hato around 1.33 Ma.  This ignimbrite is the most extensive in the region, blanketing 30 km E and W of the volcano with material over 110 m thick covering the flanks of the volcano.  Subsequent eruptions put 1 – 2 km of material on the floors of the three calderas.  I suspect this estimate is significantly in error, with the first eruption of the Young Group being closer to the 109 ka date of the initial dome construction.

El Hato

The currently identified El Hato ignimbrite dates around 32 ka and overlies the India Dormida lavas.  This is an extensive ignimbrite sheet covering 300 km2 produced by a caldera collapse event leaving a 30 km2 depression.  El Hato is dated more recently than 56 ka based on stratigraphy.  The 32 ka date may be more accurate based on its fresh appearance in a tropical area. 

As with all things from this period, eruption dates continue to be confusing.  The VOGRIPA database identifies the El Hato ignimbrite, creation of the El Valle de Anton caldera in a VEI 4.0 eruption that produced 0.1 km3 of bulk dacite 56 ka.  The problem is that this is not large enough to create a 6 km diameter caldera and blanket the erupting caldera and neighboring calderas with a kilometer or two of ignimbrite.  There is a possibility that there was at least one other large eruption that has yet to be properly defined.  Sadly, all pyroclastic eruptive products in the area are called the El Hato ignimbrite.

Given the wide variance in estimated eruption dates, 1.33 Ma – 32 ka, we are left with a couple possibilities.  One would be at least two caldera forming eruptions, one on either end of the 109 – 32 ka time period that followed the 5 Ma period of quiet.  This would mean that VOGRIPA missed the first eruption but got the size estimate for the eruption pretty close for the second 32 ka El Hato eruption.  This would explain the previous Iguana / Dome building period as resurgent activity following the initial caldera-forming eruption 109 ka.  The problem with this explanation is the absence of clearly defined multiple ignimbrite layers. 

If on the other hand, there was a single massive eruption at 32 ka, VOGRIPA’s size estimate on eruption size and bulk material ejected is very much on the low side.  The other thing that argues against this is the lack of explosivity for the previous Iguana / Dome eruptive sequence, which was mostly effusive.  In Central America, the longer the magma crystalizes, the more explosive the system is when it starts activity anew.  This one started effusive and went explosive.  Clearly additional work needs to be done here.    

El Valle and Fan Deposits

It turns out that the region is wet, and El Valle held a crater lake for an extended period following caldera collapse.  El Hato deposits and lake sediments were reworked and deposited in the caldera as the El Valle formation, a layer over 90 m thick, he El Valle deposits 32 – 2.4 ka. 

The lake drained through a breach in the SW caldera wall, washing reworked dacite material from the caldera and domes out of the caldera.  Remobilized EL Hato deposits can be found all the way to the Pacific coast.  Sediment transport patterns and crossbedding are visible.  The Fan Deposits were deposited 2.4 ka – present.

Calderas?

Gravity anomaly analysis suggests two additional calderas in the vicinity of El Valle, Las Lagunas and Sora.  Sora is the largest of the group.  Las Lagunas is the smallest.  Topographic maps show ring-like structures around the depressions that correlate to previously known ring faults.  There is very little written about these structures.  While not nested, they are relatively close to one another.

The Munsey 2018 thesis includes a drawing with possible locations of the three caldera structures.  El Valle measures 6.9 x 5.3 km.  Las Lagunas is circular at 4.3 km.  Sora is the largest at 12 x 6.7 km.  The center of Las Lagunas is located 8.5 km E from El Valle.  The center of Sora is located 17 km WNW from El Valle, 10.7 km NW from Las Lagunas.  All of these are discussed in relation to the gravity anomaly beneath the region.  If these depictions are correct, they may indicate a westward migration of activity over time.  

The gravity anomaly was first modeled as the El Hato ignimbrite, with a proposed maximum thickness of 800 m near El Valle.  It extends 30 km E and W from the caldera, thinning toward the Pacific coast.  Turns out that this is not sufficient to produce the observed low gravity anomaly.  Continued research ended up concluding the existence of something now called the Cocle Batholith.  As with all models, things change based on future observations.  If there is indeed a shallow batholith beneath the region, the ignimbrite must be thinner, now thought to be less than 300 m at its thickest.

The Cocle Batholith is now thought to be centered beneath El Valle.  It measures 35 km E-W, 15 – 20 km N-S, wide, 5-11 km thick, and 3.5 – 14 km deep.  The batholith spans 515 km2 with a volume around 36,000 km3.  The depth estimate comes from crystallization depths in this particular segment of crust. 

Tectonics

Panama is located on one of the more complex tectonic environments in the world where the Cocos and Nazca Plates are subducting under the Caribbean Plate.  From this relatively simple beginning, we end up with a subducting spreading center between Cocos and Nazca Plates, a triple junction working its way eastward along the Middle America Trench, and a Panama Microplate.  The Central American Trench is located offshore to the S and SW of Panama. 

The most recent major tectonic event took place 4 – 3 Ma with the collision with the South American Plate that created the land bridge connecting North and South America 3.5 MA.  Today, the Panama microplate is moving N in relation to the Caribbean Plate.  Its ongoing collision with South America is 1 – 2 cm/yr.  The previous tectonic event took place 10 – 5 Ma, with suspected detachment of the subducted Nazca slab beneath Panama and South America. 

Note that despite the overall tectonic complexity, Panama only has four recently active volcanoes, though It does have remains of at least 10 extinct major stratovolcanoes.  Today, most remaining volcanic activity is W, on the Central American Volcanic Arc, and E in Columbia in the Andean Northern Volcanic Zone.  This will change as the collision progresses.  The triple junction between the Cocos, Nazca and Caribbean Plates is working its way eastward along the Middle American Trench.  Over time, this will extend volcanism similar to that in Costa Rica into Panama from the W.

One of the reasons for current lack of volcanism in Panama is subduction of the cold, thick Cocos Ridge beneath S Costa Rica and W Panama.  This uplifted the non-volcanic Talamanca Mountain range.  Panama has much larger spacing between volcanic front volcanoes and less frequent eruptions.  It is considered to be geologically separate from Central America.  

It is relatively common for researchers to divide major tectonic plates into various blocks and microplates as a way to understand their motion and interaction with one another.  The Panama Plate is described as a microplate, a chunk of the Caribbean Plate located between the Cocos and Nazca Plates.  Most of its borders are convergent boundaries and included present day Panama and Costa Rica.  It was a piece of the Central American Volcanic Arc that split off from the rest of the Caribbean Plate.

Conclusions

El Valle has been inactive for perhaps the last 10 ka, though it still has enough heat to power a vigorous hydrothermal system.  Depending on which analysis you embrace, it had 1-2 caldera-forming eruptions over the last 109 ka.  Worse, the surrounding region is active with two or more additional caldera forming eruptions suspected over the last 10 Ma.  Despite activity spreading from the W, there is nothing that suggests that El Valle is a threat for activity in the near future.  As with all things volcanic, these systems always have the capability to surprise. 

Additional information

Gravity and geochemical constraints on the structure and evolution of the El Valle volcano, Panama, KR Munsey, 2018

Origin of silicic volcanism in the Panamanian arc:  evidence for a two-stage fractionation process at El Valle volcano, Hidalgo, et al, May 2011

Petrology and geochemistry of El Hato silicic ignimbrite, El Valle volcano, Panama, PJ Hidalgo, 2007

Preliminary evaluation of thermal and nonthermal waters at selected sites in Panama, Central America, Los Alamos National Laboratory, LA-11103-MS, UC-000, Nov 1989

Advanced pre-feasibility studies of El Valle de Anton Geothermal field, Diaz, et al, Jun 2000

Panama Plate, Wiki 

Isthmus of Panama formed as result of plate tectonics, K Donovan, Florida Museum, Mar 2009

Lower Miocene stratigraphy along the Panama Canal and its bearing on the Central American Peninsula, Kirby, et al, Jul 2008

Structure and tectonics of the Panama-Nazca plate boundary, Westbrook, et al, Jan 1995Seismicity and tectonics of southern Central America and adjacent regions with special attention to the surroundings of Panama, B Wolters, Aug 1986