I’ve been tracking Chiles-Cerro Negro for almost 10 years now and it’s been an interesting ride to say the least, full of great highs and terrible lows. My odd relationship with this volcano is going to be on pause and I will be exploring other volcanoes. As such this will be the final article on the volcano unless it erupts. (I’ll keep you updated in the comments.) I’ve written several articles about this volcano already but I am not happy with their quality. For one I was extremely excited and under a lot of unrelated stress at the time so I wasn’t being very articulate in conveying my ideas. Second, the situation at the volcano has undergone several important changes and developments so we have plenty of new information. This will be my most in-depth analysis on the volcano so you don’t need to read past articles to understand the current situation at CCN. As you might know, I’ve had a bad feeling about this volcano for years, ever since the volcano first made headlines in 2014, there was just something off about it and as the years have passed this volcano has only gotten scarier in my opinion. This volcano is actually a very clear candidate for a future caldera and I will stand by that statement. In order to understand why I am making such a bold statement, we need to go back to the beginning.
In the Pliocene, lava flows started to pour out from deep below at what would be the border of Ecuador and Colombia. A volcanic field was in the making, and soon 2 major volcanoes would be formed, Chalpatan and Potrerillos. Unfortunately, there is little information about the eruptive history of Chalpatan and no information about Potrerillos but these two volcanoes are among the few large calderas in the northern Andes, both being around 6-8 km in diameter, However these volcanoes would lose steam rather quickly and far as we know both volcanoes only produced one major caldera eruption with Chalpatan’s taking place around 2 million years ago. Oddly around the same time these two volcanoes started to wane the two cones of Chiles and Cerro Negro on top of the Pliocene lava flows and a new volcano would be constructed. After years of effusive and explosive activity, the Chiles volcano stopped erupting 160,000 years ago and with few, if any eruptions at the Cerro Negro cone. However, despite no surface activity, the region holds immense geothermal potential as there 3 strong hydro-thermal chambers, 2 at CCN and 1 at Chalpatan.
Before we talk about the recent swarms, we must ask 1 question as an eruption grows more likely, why now? Why couldn’t the volcano erupt in over 160,000 years and why would it erupt now? A 160,000-year dormancy between eruptions at a volcanic system is rare, so rare that I can’t actually think of any more than 3 or 4 other volcanoes where this could’ve happened and none of them were stratovolcanoes. The volcano doesn’t look like it’s lacking any life now and the chamber has a higher melt percentage than other formerly dormant volcanoes so what’s going on? Once again, why is Potrerillos and Chalpatan having volcanic quakes and inflation directly related to Chiles-Cerro Negro? I think we can answer both questions. First off, these volcanoes likely weren’t always connected but they formed very close together and likely shared a deeper source. When magma ascends, it “chooses” the path of least resistance just like all fluids would do under similar circumstances. What decides where this path is, depends on the geological setup of the region. Usually, the path of least resistance is in the vertical direction but this doesn’t always have to be the case. I am thinking that the reason why none of the volcanoes erupted in the past 160,000 years is because the volcanoes started to merge and magma flowed laterally instead of vertically.
The merging of 2 volcanoes sounds dramatic but it doesn’t have to be. As 2 or more chambers get closer, it would gradually become easier for magma and their associated products to move sideways thus relieving chamber pressure without an eruption. If more pressure is lost than gained during the merger, an eruption is completely impossible. This process is usually seen in rapidly developing volcanic regions with relatively high rates of supply (Katmai, Agung & Batur, Samalas & Rinjani, etc) so these mergers usually start and finish relatively quickly. I don’t think our system had high enough rates of supply for a quick merger. This system is millions of years old with nothing very impressive on the surface! Kikai, Toba, Katla, Campi Flegrei, and many more have done more in 100,000 years than this system has likely done in 2 million+ years. Slow supply equals slow merger and it is already hard for magma to break through the crust at CCN because the crust is elastic and compressive, not something that cracks or ruptures easily. Even after the merger was complete, it had been so long that volcanic vents had been sealed shut and the volcano was completely plugged.
Alpha and Beta Swarms
Chiles, Potrerillos, and Chalpatan were all considered extinct up until 2013 when the magmatic intrusion began and the first seismic crisis started. The IGEPN and SGC set up monitoring stations and alerts were raised. The swarms started in November 2013 but it wouldn’t peak until Autumn 2014 when over 250,000 quakes were recorded in just 2 months! Due to limited monitoring, a lot of earthquakes weren’t located but they seemed to be mainly taking place to the SW of the Chiles cone. At the same time, inflation was recorded over not only CCN but also Potrerillos to the SE as well. The seismic crisis would wane but the inflation would remain constant and actually intensify along with moderate seismic activity. The volcano was alive but how alive was the question. After all, the volcano hasn’t erupted in 160,000 years, after the crisis ended no one thought too much of the system, the inflation was widespread but not very fast so nothing seemed too abnormal. I was under the impression that the volcano would do a slow resurgence before it would erupt again if at all. I wouldn’t notice a lot of oddities concerning the volcano until the second swarm started.
After over 2 years of relative quiet, another uptick in seismic activity began in 2018 and lasted until the end of 2020. On an ironic note, the least intense swarm recorded at this volcano would be the one to seriously catch my attention. Most of the quakes took place at CCN proper in the beginning but as the swarm progressed, more and more quakes would take place at Potrerillos and Chalpatan. Around 200,000 quakes would compromise this swarm making it much weaker than the last but still very significant. Despite this swarm’s relatively low intensity, it would produce more fluid-based earthquakes than its predecessor by a wide margin. While I tracked this swarm I started to have major questions. First off, why was there more uplift at Potrerillos then at CCN and why wasn’t more seismic activity taking place at Potrerillos if that is where the bulk of the uplift is? What is causing these deep LPs( around 25 km below the surface or more ) and why are they clustered away from the VT quakes and inflation to the NW of the Cerro Negro cone? This swarm never got an official explanation but the IGEPN postulated that the changes of pressure within the magma reservoir were the most likely culprit. Inflation didn’t get faster, no tectonic quakes, and the hydrothermal systems didn’t seem to change that much so whatever caused the swarm was expansive and significant but subtle at the same time.
As you can clearly see, the area of inflation is actually very large, and we have new studies concerning the size of the magma reservoir. The studies give the chamber the dimensions of 15 km wide and 8 km deep which give a volume of around 1,400 km3 with 14% or 196 km3 of melt. These are just 2 studies so this measurement is not absolute but I am very sure that this number underestimates the chamber’s size. The dimensions that this study gives for the magma chamber are substantially smaller than the inflation area. If you were to use the dimension of the area of uplift i.e. 25×15 km as a proxy for the magma chamber (assuming that the melt percentage and chamber depth is correct), you’d get around 2,300 km3 with around 322 km3 of melt. The first studies on volcanoes are usually the most inaccurate but in any case, evidence is supporting my claim that this volcano is far bigger than it looks.
After the Beta swarm ended, inflation abruptly stopped and seismic activity fell to new lows and for the entirety of 2021, nothing major happened. I’d honestly thought that the intrusion had ended when it took place but something still didn’t seem right to me. As Chiles-Cerro Negro waned, the nearby volcano of Cumbal to the north grew more notably agitated. Nothing major but nothing insignificant. This along with continued instability on the inclinometers gave me the impression that CCN wasn’t quite finished. The current seismic activity at Cumbal is driven by a hydrothermal system that is influenced by regional faults. CCN and Cumbal share the same regional fault system so it’s not a crazy claim that Cumbal would see a modest increase in activity due to the unrest at CCN. However if Chiles-Cerro Negro caused the uptick at Cumbal that would have to mean that it significantly destabilized the regional faults in its quietest year.
This is actually supported by the inclinometer data, as the Cerro Negro Inclinometer showed insane motion for 2021 shifting over 45,000 micro-radians in 1 ½ years! Sometimes moving at speeds of 150 micro-radians a day! After consistent reports of this data, I have no reason to suspect a broken instrument.
Gamma and Delta Swarm
In 2022, another swarm would begin and would be the most energetic swarm since the seismic crisis back in 2014, starting at May and lasting into October, consisting of around 180,000 quakes. Once again, the number of LPs and other fluid motion quakes in this swarm beat both of the past swarms combined. The formerly deep LPs shallowed greatly from 32 km below the surface to just a few km at depth. Fast uplift began in April rising at rates at over 3x the speed of the 2014-2020 inflation period. While no official explanation has been given for the cause of this swarm it would be safe to assume that ascending magma played a major role in this period of unrest. Somehow, uplift stopped again in Nov 2022 and seismic activity subsided. One might think that after the insane movements on the inclinometer, this swarm would bring dramatic shifts on the instruments but on the contrary! The Inclinometers showed less instability during and after this swarm.
Inflation would begin again Feb 2023 but would either stop or wane by the end of March. Following the uplift would come the most recent swarm, which began abruptly on March 9, peaking as soon as it started on March 10 and 11. This swarm didn’t last, only lasting 3 months, with total quake numbers roughly reaching 190,000.
You may have noticed a trend with the first 3 swarms, they all started off kind of slow but gained in intensity after some time, peaking then slowly losing intensity before the swarm ended. The quakes took place all over CCN, Potrerillos, and even Chalpatan at times. This swarm was the weirdest because as soon as it started it peaked and the quakes were mostly concentrated in one area. Inflation preceded both the 2022 and the 2023 swarm which is also something we don’t usually see. Since 2018, there’s been a change in activity every year with major swarms for 4 out of 5 years since then of ever-increasing intensity. So whatever caused the 2018 swarm marked a changing point in the volcano’s unrest. You’ll also notice that one area saw the most quakes in all 4 swarms and that area is near an intersection of several regional and local faults which is almost certainly no coincidence.
There are three options, either this zone is where a volcanic vent is forming, a small destabilized volcanic chamber, or the result of volcanic stress on the 3 faults
Tons of swarms but can we get some explanations? I’ve thought about this volcano for a while and I’ve got an explanation. I believe that the 2018-2020 swarm was the result of stress from the newly merged chamber being pressurized and the 2021 quiescent period was the result of the chamber going past its “safe” pressure limit. When you stretch an elastic object to its limit, right before it breaks it loses its flexibility and stops stretching. It didn’t seem odd when it happened but in hindsight, the quiescent period was the weirdest year for the volcano. Why in the world would a volcano under intrusion stop producing inflation and quakes only for strong swarms to begin again the next year with no clear explanation? I initially thought that the intrusion may have gotten plugged but I’ve never seen or heard of that happening before, and the inflation at this volcano has so far been on/off since 2022 with an atypical swarm for 2023. In both the previous swarms, the quakes started AFTER uplift began, several weeks after which is something that doesn’t typically happen when a volcano goes under intrusion. In fact, when the uplift rapidly accelerated in February 2023, there were no extra quakes or anything more than 14 VLF earthquakes.
There has been no official explanation for the Gamma and Delta swarms, not even an official guess, or postulation has been given. I have my own hypothesis but I am not in a position to confirm it. It is of my opinion that these swarms were the result of cracks and/or ruptures at the magma chamber, and honestly, I can’t think of any other potential cause. Ruptures at the magma chambers would be preceded by inflation, causing strong earthquake activity including fluid quakes as the magma rushes to occupy the newly made space, and this all could happen without an eruption If this is actually the case then an eruption is more likely than not at this volcano. The sudden stabilization of the inclinometers during 2 seismic crises could easily be caused by the loss of crustal elasticity and would fit with my hypothesis
. Let’s just think about this for a minute, this volcano is likely as evolved as you can get, has no vents, has not produced any measurable gas emissions of any kind, and the geological setup is hostile to volcanoes, working against magma ascension but despite this, an eruption is becoming more and more likely with every swarm and year under intrusion. Just think about the pressure required to punch through 6-8 km of solid rock, that is a tall order for any volcano. If Chiles-Cerro Negro erupts soon then it has likely been building pressure for centuries or thousands of years. Data on the recent intrusion at this volcano shows that this intrusion is not that big and is almost definitely not large enough to break a volcano like this. This is how large eruptions happen, the condition at the volcano becomes hostile towards eruptions i.e. pressure is gained much quicker than is lost before something breaks, relieving mass amounts of pressure quickly. The volcano has almost all of the markings of a pre-caldera volcano.
- Evolved system?
- Past caldera events?
- Large reservoir?
- Large amounts of eruptible magma?
The last point is the most significant and I can’t answer this question. The amount of eruptible magma is unknown and since this volcano seems to have been lacking large amounts of supply for most of its lifetime it is completely possible that this volcano doesn’t have enough good magma for a large eruption.
This volcano has produced over 1 million quakes from 2013-2023 and chances are that another swarm is going to happen sometime in the next couple of years. What will the final swarm look like? If we’re assuming that my hypothesis is correct then the final swarm would be preceded by massive uplift. Not 12cm/yr but 12 cm/week or more. Volcanoes that erupt at newly made vents have massive local uplift and there is no reason to assume that this volcano would be any different. The peak uplift speed seen at this volcano was 36 cm/yr so this tells us that if the past 2 swarms were caused by ruptures, they were small ruptures which gives us an idea of how bad the final swarm would be if a small rupture would cause 180,000+ quakes. The fracturing quakes would be followed by fluid quakes and magma would rush to the surface. It would be pretty obvious that an eruption is on the cards.
It’s possible that this “Omega swarm” has already started! On August 5th 2023 another(!) swarm would begin and unfortunately, I don’t have enough information on this to make a detailed analysis on it but we have an official cause for this swarm! This swarm is the result of significant disruptions to the hydro-thermal chamber. Which is indicative of either tectonic and/or crustal instability from ascending magma or an influx of volcanic fluid into the chamber. In either case, this means we’re getting closer to an eruption. I don’t know how fast things are going to move from here but this volcano needs to be monitored like a hawk. This volcano has too many oddities and red flags to be ignored.
Tallis, August 2023