Over the past 6 years I’ve watched Chiles-Cerro Negro go through 4 different phases of unrest. Like a toxic lover, no matter how much I try, I can’t shake this volcano. I honestly thought I was going somewhere with Grimsvotn and Iwo-Jima but no. Grimsvotn is stable in the sense that nothing has really changed besides a probable failed eruption in 2023, and there is so little study about Iwo-jima that I can’t say much more than what I’ve already said. Other volcanoes have either failed to deliver on their unrest, or their eruptions just don’t interest me. Chiles-Cerro Negro is different, I don’t think there has been a volcano that I wanted to erupt more than this. 1.3 million earthquakes in 10 years and accelerating deformation are only the tip of the iceberg when it comes to this volcano. It’s funny, in February Chiles-Cerro Negro had an average of 300 earthquakes/day and the only thing I could think of is how relatively quiet things were. A 100 earthquakes/day at this volcano is considered normal and boring. After another year of watching this volcano go through another major shift, it’s safe to say the volcano has met its final and potentially greatest obstacle that precludes an eruption, and I will explain why I believe that this volcano is either going to erupt big or not at all.

Epsilon Swarm

In my previous article for this volcano, I listed 4 major swarms as points of interest.

1. Alpha Swarm (2013-2015)
2. Beta Swarm (2018-2020)
3. Gamma Swarm (2022)
4. Delta Swarm (2023)

After the 2 seismic crisis of 2022-2023, Chiles-Cerro Negro has seemed docile and passive in 2024  with the whole year seeing no more than 40,000 quakes. However, the previous year saw an explosion of VLP earthquakes that had not been seen before at this volcano. Over 1,200 VLP earthquakes and 1,100+ pulses of tremor took place, with the trend continuing this year. Energy levels for these earthquakes are beating the previous record by a factor of almost 5,000. As such, regardless of the low numbers and relatively low energy, I consider this to be a new swarm due to its novelty for this system and what it represents. 

  The location of the strongest VLP quakes has been 3-5 km below the summit of Chiles, where there is almost definitely a plug. It is no longer just my opinion, but the SGC (Servicio Geologico Colombiano) has also pointed out this possibility. No significant changes have been noted with the hydro-thermal system, so this is likely the result of magma and/or magmatic fluid moving within the edifice of the volcano. There have also been significant shifts in deformation, but that topic will be saved for later.  If there is magma accumulating beneath the edifice, the volume probably doesn’t exceed 31,400-100,000 m³/year, so there is no need for immediate concern, as it would take at least a decade for relatively minimal disruptions to the edifice, and there is little chance of significant build-up of shallow magma with these rates. This is of course assuming that the cause of these VLPs is accumulating magma which it may not be.

I’d say an eruption is completely impossible if things continue at this rate, but things rarely stay the same at this volcano, and this swarm could be our potential canary in the coal mine with this system. In fact, with context, I might consider this swarm to be the scariest out of all the swarms so far. 

In order to understand why this swarm might be the scariest of them all, despite being the weakest, we need to understand the extremely convoluted and complicated setup of Chiles-Cerro Negro and how we got to this point in the first place. Before I go into detail about this, I just want to say that this is all my speculation, and to be frank, I am still somewhat confused by this setup, and my hypothesis is my way of reconciling the oddities in this system. It doesn’t help that there is new major information and/or development at this volcano almost every year. Over the past 6 years, I have read almost every weekly, annual, daily, and monthly report from the IGEPN and SGC. After reading hundreds of reports and with some additional perspective I’ve gained from reading about the recent Fagradalsfjall eruptions, I think I’ve come close to a definitive answer to the overall cause of the unrest at this volcano.. I will go over the entire 12+ year history of the unrest so far and list points of interest.  

Alpha Swarm

In 2011, the Cumbal volcano to north of Chiles-Cerro Negro, started a new unrest period relating to it’s hydro-thermal system. Nothing initially spectacular, but the SGC raised the alert level to yellow in 2012 nonetheless. There was no magma intrusion, but this is not required for a restless hydrothermal system. This period of unrest has continued on to this day with variation. The volcano saw 8,000 quakes in 2011, but in the present, it’s not uncommon for there to see over 24,000 earthquakes in a year. We can see this trend even more clearly within in the inclinometer data.

It is slightly odd for this volcano’s hydrothermal system to be experiencing such a long and slow increase in activity over 14 years in conjunction with the magmatic system of Chiles-Cerro Negro.  Both volcanoes share a regional fault system, but Cumbal’s unrest started before the first swarm in 2013. I had long since dismissed a possible connection until 2022, when I realized that Cumbal’s hydro-thermal activity was likely regulated by tectonic faults, a lot of which it shares with Chiles-Cerro Negro. In any case, this is our first point of interest.

It is unclear when exactly the swarm started, but seismic activity was first noted in February 2013, and the swarm was recognized in November of that year, as new instruments were added. Unfortunately, as this was the first real sign of life from a long thought dead volcano, there is almost no meaningful data about the volcano before the swarm besides very basic details about its structure. Although the crisis technically started in 2013, it would truly peak in 2014. A strong area of inflation developed to the south of Chiles-Cerro Negro with peak rates of 20 cm observed in May. Interestingly, the swarm would have 3 peaks with significantly low activity in between. Despite the intrusion likely beginning some time in July or earlier in 2013, it wouldn’t be until October-November 2014 that we’d see the peak with 240,000 earthquakes, including a damaging M5.8.  

In the month preceding the crisis, the hydrothermal feature showed a significant rise in heat and acidity, but as the crisis started, the system stabilized despite the escalation in volcanic activity. This gives further support to the fact that the hydrothermal system is more influenced by the tectonic system. As the volcano was building stress, the hydrothermal system was disrupted, but as the stress was released, the system recovered. This fact is very important  in putting current events in context, so keep a note of it. As we move on. Seismic activity would slowly begin to wane, reaching moderate levels in May 2015. Uplift would stop but begin again with no associated seismic swarm. The new deformation pattern that would follow for years to come would be that of 18-20 km long “crack” or tilted dike (Crike, I’ll call it) that would act as a conduit for magma to flow from Potrerillos to the Chiles cone. This will also be extremely important.

From this swarm, there are 3 important facts that are crucial for understanding this volcano.

1. Cumbal volcano started having seismic activity in 2011, 2 years before Chiles-Cerro Negro’s swarms started in July 2013
2. The hydrothermal system reached it’s peak in 2014, likely caused by the buildup of strain preceding the seismic crisis
3. Some type of crack or dike had developed following the seismic crisis that facilitated the transfer of Magma from Potrerillos to Chiles

Geological Neighbors and the 2016-2017 quiet period

Nothing much of note would happen in the 2 years following the crisis. Seismic activity fluctuated but remained mostly stable, and deformation was stable.

We are left with one lingering question. Why is Potrerillos deforming and what is it’s connection to Chiles-Cerro Negro? Is it a coincidence that Cumbal’s hydrothermal activity spike just 2 years before CCN would go crazy? Let’s see. Chiles-Cerro Negro is surrounded by 3 other significant and 2 minor volcanoes. Porterillos, Chalpatan, Cumbal, Horqueta, and Chiltazon.  These volcanoes are within 30 km of CCN and are experiencing interesting shifts. Poterillos and Chalpatan have seen uplift and seismic activity, Cumbal has seen hydro-thermal activity, and these other poorly researched no-names are in the subsidence zone. 

The volcanoes are born from the subduction of the Nazca Plate beneath the South American Plate, which is the progenitor for all of the Andean Volcanoes. This complex is built on top of thick basaltic flows from over 2 million years ago despite CCN proper being far younger. The complex has experienced several eruptions, with the most significant ones occurring around 10,000 to 15,000 years ago. It’s eruptions are a healthy balance between effusive and explosive, with the last eruption possibly happening around 2,000 years ago. Shown by further study, the volcano may not have been as dormant as once thought.

The Potrerillos-Voladero system is encircled by andesitic lava hills, a morphology indicative of a ring fracture from a small caldera collapse. This ring is most prominent along the southern, eastern, and northeastern margins, with the latter segment marking the boundary with the Chalpatán Caldera. While no eruptive deposits are visible within the caldera, roadcuts along the trail from El Voladero Guard Station to Yegua Rusia expose volcanic material linked to gravitational flows. 

Notably, a white ash layer rich in silica and altered to clay under acidic condition was identified in these exposures. This layer, bearing biotite and hornblende, is interpreted as a product of hydrothermal or phreatomagmatic activity from the caldera. Crucially, it lies below the 10,000 years ago  El Soche marker ash  implying Voladero’s eruptive phase likely occurred between 12–20,000 years ago.The Chalpatan caldera, a distinct Plio-Pleistocene volcanic structure formed approximately 2.0 million years ago, represents a significant, albeit comparatively less studied, component of Ecuador’s Northern Andean Volcanic Arc. With an estimated diameter of 6-8 kilometers, it still boast a potent geothermal system with magmatic component and has numerous fault across it.

With so many volcanic features in the region being connected directly or indirectly to the unrest at Chiles-Cerro Negro. I don’t think it’s unreasonable to assume that this could just be one big volcanic field. The area’s history is poorly researched but it’s not without a degree of merit when consider the scale of unrest at this system.

During this period the amount of magma required to cause the observed deformation (pre-gamma swarm) was calculated to be at max 10 million m3/year from 2016-2020 with likely higher rates in 2022-2025. Which means our magma intrusion has likely accumulated 90 million m3 on top of whatever amount of magma it started out with. 

2018-2020 Beta swarm

Formerly the most lacklustre swarm from this volcano, consisting of “only” 210,000 quakes. This swarm would be the most well-documented and the swarm that would spurn my interest in the volcano. The cause of the swarm wasn’t clear; it wasn’t hydrothermal, the magma intrusion didn’t get any bigger, no significant magma movement was noted up until the very end of the swarm, and yet up to 4,000 quakes/day took place during these years. With 2 distinct unrest areas, the most quakes took place at Chiles-Cerro Negro but the fastest deformation taking was at Potrerillos. Chalpatan didn’t miss out either with the activity overlapping into it’s region.

The activity, barring one period, took place right where the “crack” or dike is. The swarm would conclude with a swarm of 30-48 km deep LPs that happened on the other side of the volcano, at Cerro Negro and further NE up to 10 km away from the Chiles cone. Oddly, there was no uplift where these quakes took place, in fact the area of uplift is surrounded by a ring of subsidence of varying rates but usually 1-2 cm/year. INSAR data is not very good in this area due to poor coherence caused by the rough terrain, but the general trend is seen on all available maps and covers an area of roughly 30km by 30km. This subsidence is not seen on any other GPS stations on Southern Colombia or Northern Ecuador outside of the Chiles-Cerro Negro.

Given the events that have followed this swarm, it either had something to do with the pressurization of either the “crike” or magma chamber or heralded the recovery from the 2014 seismic crisis. Spoiler warning for the future events, but what’s happening right now couldn’t be happening without the volcano doing one of these things. After this swarm, Chiles-Cerro Negro chugged out 2 seismic crisis, a 3rd swarm and is likely about to do another crisis. Just think about the scale of this, a potential pressurization or recovery event caused 210,000 earthquakes, I am not aware of anything remotely on a similar scale happening anywhere else. Just due to it’s strength and with that our “Crike” can over pressurize and/or recover without such significant seismic activity. It would seem likely that this was more related to the magma chamber. 

The Great Quiet and 2nd Seismic crisis (Gamma Swarm)

Following the suspicious movement of deep magma, the volcano seemingly shut down. Seismic activity went anaemic with rates as low as 10 quakes/day, and uplift stopped. However, the inclinometers went insane with changes of over 100 microradians/day and the ring of subsidence continued unchanged. At the same time, Cumbal saw an uptick of activity. 2021 would be the strangest year for the volcano, given that the 2nd crisis would happen with just a couple weeks of buildup following this year. It doesn’t make sense for the unrest to have paused, considering that the 1st seismic crisis had over a year’s worth of strong build-up. I am genuinely at a loss on what was happening at this volcano during this time. My idea is that during this period, after the pressurization phase, there was brief stability period as the crust reached it’s limit and briefly stopped stretching and cracking. That ,or magma supply was somehow paused but that doesn’t really make sense to me as the “Crike” was still active following this period. For the later solution to be true, it would mean that the “Crike” would have a pretty significant volume of magma for it not to solidify after over 15 months of no supply.

Starting Late May 2022, the 2nd crisis would begin with over 200,000 quakes in 4 months and another damaging magnitude 5.6 quake. Interestingly, deformation rates quadrupled from it’s previous rates to 12 cm/yr before the swarm started. At the same time, the swarm of rapidly shallowing LPs quakes took place indicative of magma rising from the depths of down to 38 km below the surface to just a few km below sea level. Once again activity was concentrated exactly where the “Crike” is. Uplift would abruptly pause and restart following the swarm, and the inclinometers would start to stabilize after the swarm ceased. The most seismic energy was released at Potrerillos and Chalpatan although CCN proper still saw major seismic activity.

With the fact that significantly more magma movement and uplift was noted with this swarm than with the years before, it’s safe to assume that something big broke and the “crike” expanded allowing more magma to flow through it and once again, all of the activity lined up with Crike perfectly. At this point, it should be pretty clear that the deformation and seismic activity that we’ve been seeing is related to whatever structure developed after the first seismic crisis and not to the magma chamber directly. As we’ve established, the deformation follows the crack or dike perfectly and without error. A measly >10,000,000 m³ isn’t going to do much for a 1,200+ km³ magma chamber but it would keep a small magmatic structure from solidifying. This isn’t just my speculation; this is the official explanation. The following is from Pilicita Masaband, Mothes, 2025:

On average, vertical deformation reached ~40 cm of uplift over ten years, and continued even during non-swarm periods (Figure 12a). Both GPS and InSAR methods showed the same trends (Figure 12b), distributed across several stations or control points in the InSAR time series located between Voladero and Lagunas Verdes. Given this specific case, the deformation sources were modeled using SarScape software, concluding that the Potrerillos deformation source is 18 km long and 5-6 km wide, resembles a “crack” opening, and its depth drops between 6-8 km below the surface (Figure 13a). The other source is Lagunas Negras, which is shallower, and its displacement suggests a tilted dike (71°). In both cases, a magmatic intrusion is considered to be the cause of the deformation observed at the surface.

The mostly seismic activity and most visible deformation that has taken place since 2015 has never been directly related to intrusion into the chamber proper; the accelerating deformation and increasing seismic activity is the direct result of a magma intrusion from the magma chamber. The subsidence that surrounds the volcano is likely the result of magma leaving the magma chamber. This is somewhat similar to the current situation at Fagradalsfjall, where the activity we see is the result of a deep magma chamber sending a constant supply of magma to a shallow level that would later serve as the main source for an eruption. The implications for this happening at Chiles-Cerro Negro is not pretty, this would mean that we don’t need to wait on the chamber to be pressurized or get more and more molten. The magma reservoir is already primed and ready to erupt and what we are seeing how is not the system oiling it’s gears like other volcanoes, we’re seeing it try to break through the crust and relieve itself. This notion is supported by current events and what happened the following year.

3rd Seismic Crisis (Delta Swarm)

Not even 6 months after the end of the second crisis, the third crisis began on March 11, peaking immediately with 11,000 quakes on the next day. This swarm would almost be entirely be located at Chiles, right at the top of our proposed “Crike” and would have more LP quakes than any other swarm before it. Despite peaking early, it lingered throughout the entire year producing over 270,000 earthquakes, more than the previous swarm but not as intense. Uplift abruptly paused and restarted no less than 3 times during this year but a peak speed of 36 cm/year was observed at Lagunas Verdes to the south of Chiles. Towards the end of the year inclinometers would start to show more instability, a trend that has maintained itself until now. Shallow LPs, VLPs, and tremor has been observed within the edifice of the volcano following this swarm mainly taking place 2-5 km below the summit.

In my opinion, the swarm was the result of shallow magma hitting the plug and destablizing the area. Cracks around the volcano following the swarms have been noted, but still no direct effects on the hydro-thermal system. It should be noted how quickly the volcano recovered from its tantrum in 2022 to produce another one just 5 months later. This speaks to how quickly the volcano,”the crike” more specifically, is now accumulating strain. During this period, the trend of subsidence surrounding the volcano might have completely reversed with more areas undergoing uplift that we’ve not seen before. As a result of these swarms, the top of the “Crike” is now just 1-2 km below the surface with magma or related products potentially leaking into the edifice.

The fact that this swarm took place so soon after Gamma Swarm with no build-up and no seismic activity relating to pressurizing gives credence to the notion that if pressurization processes were the principle cause of Beta Swarm it would be from the magma chamber. In the 10 month span encompassing the totality of Delta swarm, only 6 months had high seismic activity and the other months saw only moderate levels of activity. If we were to assume that the “Crike” was accumulating strain in the weaker months and add up the 5 months repose period between the swarm we find that at minimum 1.47e+12 Joules of seismic energy was gathered in 11 months. This would give the “crike” a minimal seismic energy accumulation rate of at 1.37e+11 joules/month. If we were to assume that all of swarms’ energy was accumulated during the repose period, then double the number.

The 4th seismic crisis and the Current Swarm

Now that we have context, it becomes clear why the Epsilon Swarm is the scariest so far. These unending VLPs are indicative of the “Crike” being capable of effectively delivering magma right to surface, only being stopped by a strong plug. A large felsic pressurized magma chamber is trying to break through a strong plug and erupt. We also know that the area is rapidly accumulating strain given that the system completely recovered from a seismic crisis and produced another in just 6 months. Since February, a general uptick in VT quakes have been noted, in pulse like miniswarms lasting about 1-2 weeks. This signals that things are starting to break again. Whether the plug will fail or not is a different story. About 3 of these mini-swarms have taken place, each one stronger than the last, with the recovery time in between dropping quickly from months to weeks.

It would seem that something has happened with our “Crike”, the uplift at Laguna Verdes, where the top of “crike” is, has completely stopped and the uplift at Potrerillos has slowed significantly but inflation surrounding this area has increased. Normally, this would be seen as good but last time something like this happened we got a large swarm a year later. As general deformation and fluid-motion related seismic activity hasn’t stopped, it’s obvious that magma hasn’t stopped flowing through our “Crike”.

After over 10 years, the fumaroles and hot springs are now once again reaching temperatures close to what we saw in 2014 preceding the 1st and biggest seismic swarm at the volcano. The Alpha and Beta swarm were probably the only recent swarm that was directly associated with the chamber and the recent activity was related to expansions and instability in the “Crike”. This could mean that the chamber could be reaching stress levels not seen since 2014. Remember, Fagradalsfjall had to produce multiple failed dikes before ultimately erupting, it took 2 years of this before we got magma. The pressure was always there but after producing failed dikes, the chamber would need to accumulate strain to create more. The process paused but never stopped. The dikes and swarms helped the volcano by weakening the crust. Something similar is likely happening at Chiles-Cerro Negro but instead of producing multiple dikes or intrusions, it is expanding and strengthening one. This fact is also supported by the fact that the areas surrounding the “Crike’ reversed from deflation to inflation. So we not only have our “Crike” directly stressing the plug and accumulating strain on its own, but the magma chamber itself may throw it’s hat in the ring. Just one of these things would cause another seismic crisis, but the potential of these 2 things happening around the same time might cause the biggest seismic swarm in this volcano’s in it’s 12 years of unrest.

We have 3 options for the current swarm, either the current swarm continues to escalate into a full blown seismic crisis akin to delta swarm, the aforementioned simultaneous Crike and Chamber crisis, or it maintains it’s relatively moderate scale before tapering off. In my opinion, the first option is the most likely. 

Caldera chances and Conclusion

I don’t know if I am 100% correct in my assessment but the fact is that we’re not waiting on the magma chamber to ready itself, it is already primed. I can’t help but to hammer this fact in, a large felsic pressurized magma chamber has triggered a magma intrusion that has remained active for a decade and is still trying breakthrough a plug. Thanks to the plug, the volcano is expanding it’s intrusion and gaining pressure. This is somewhat of an unprecedented situation for a felsic system in modern volcano monitoring.  Even if the plug maintains itself for another 12 more years, as long as the chamber is capable of sending magma to it’s intrusion and stays overpressurized, the danger level won’t change. Only an eruption or a larger, failed dike can stabilize the chamber now.  

I’ve warned about this volcano’s chance of producing a caldera-forming eruption for years and I’ve only grown more confident in this possibility but there could be one saving grace for this volcano. The magma chamber is deep, 8 km below sea level and 10-13 km below ground. This isn’t a favorable setup for caldera-forming eruptions, the deeper the chamber the more pressure it takes for it to produce a caldera. A shallow chamber needs less pressure to produce a caldera than a deeper chamber. With a chamber as deep as this, it should take a lot of pressure to produce a caldera forming eruption, pressure that may not have had enough time to build. With recent studies highlighting the possibility of eruptions within the Holocene. The dormancy argument is far weaker now. The fact is that this system has only produced 2 calderas at the most so far, so we know that this system has a high threshold to cross before it can do such a thing.

We don’t know the current pressures of the chamber but we might be able to calculate how much pressure it would take for caldera collapse with this formula:

Pu = 1/2 μρg L/Sc H^2

μ is the static friction coefficient of the fault, ρ is the density of the host rock, g is the gravitational acceleration, Sc is the basal area of the caldera block, L is the perimeter length of the caldera block, H is the depth to the magma chamber. Unfortunately for me, I don’t know how I would calculate the static friction coefficient of a fault but if anyone else wants to throw their hands on this issue I’d be happy. The official numbers for structure of the Magma chamber is that it’s 15 km wide and 8 km deep. I doubt this because the dike is sourced nearly 20 km away from Chiles but the chamber still produced LPs another 10-15 km away from top of the dike which could indicate of a minimal width of 30-35 km and consistent magma movement was noted with depths up to 48 km which could indicate a maximum chamber depth of 40 km. It wouldn’t be very scientific of me to use these numbers like they’re confirmed by study but it’s not crazy to say that the chamber size is underestimated with some of these inconsistencies. The most important information that we need now is how much pressure the chamber has now and what are the dimensions of it’s magma chamber? 

Chiles-Cerro Negro has consistently defied expectations and thrown us many curveballs, and now as more information is uncovered, the less conventional the volcano becomes. The undeniable fact is that we are in desperate need for more information concerning this volcano.

Images

The images above are from Patricia Mothes et al., Variable Ground Deformation Rates Since May 2022 at Chiles-Potrerillos Volcanoes, Ecuadorian-Colombia Border, presentation given in 2023. https://fringe2023.esa.int/iframe-agenda/files/presentation-488.pdf

References

Pilicita Masabanda, Mothes, 2025: https://bibdigital.epn.edu.ec/bitstream/15000/26268/1/CD%2015044.pdf

Geshi et al. 2023: https://www.nature.com/articles/s41598-023-34411-5

Insar modelling of Chiles Cerro Negro, EO Open Science, YouTube presentation, Yepez, Mothes et al:

Koch et al. 2021: https://www.sciencedirect.com/science/article/abs/pii/S0895981121001784

SGC 2023: https://www2.sgc.gov.co/Publicaciones/Informes%20tcnicos/Informe_tecnico_volcanes_del_sur_dic_2023.pdf

IG-EPN bulletin 2025: https://www.igepn.edu.ec/servicios/noticias/2246-informe-volcanico-especial-complejo-volcanico-chiles-cerro-negro-no-2025-001 

COMET deformation portal: https://comet-volcanodb.org/volcano-index/South%20America/Colombia-Ecuador/Chiles-Cerro%20Negro/S1_analysis

insar map: https://insarmaps.miami.edu/