Guest post by Tallis
The more I think about Chiles-Cerro Negro the more I get worried about it and the less simple the answer seems. I can’t seem to make sense of this system and its recent unrest. I have already written a piece on this system but I wasn’t entirely satisfied with it. I spoke from frustration from a lack of conclusive data but know I have concluded my investigation and am sharing the information as well as my conclusion with you. If you would like some more context about what I am talking about then you should read my previous piece. Simply put Chiles-Cerro Negro just had large earthquake swarm the past year but the swarm is currently going on a downward trend. I have recently endeavoured to find what has been causing the swarm but have found roadblocks in my way that has lead to me to giving up on trying to gain more information on this system because the data from the geological surveys concerning the past few months makes absolutely no sense.
The Colombian and Ecudorian governments monitors this system and both have worked together to make reports and share their data. Their geological surveys are call SGC -OVSP and IGEPN respectively. I know that these are poorer governments and they may not have access to enough resources to paint a conclusive picture of what is going on but I am starting to believe something is wrong with these organizations.
The first issue is that they are not reporting the same number of earthquakes and I am not talking about a small difference. Last week, the SGC reported over 400 earthquakes and the IGEPN reported a little bit more then a dozen. You don’t have to be a super genius to know that is a large difference, keep in mind the fact they are monitoring the same area and getting vastly different results. There are no filters or explanations on their websites that would excuse this vast difference in data. One side could have poorer instrumentation and the other better but there is another issue. IGEPN has reported deformation and hydrothermal activity and the SGC-OVSP hasn’t. Whose data shall we trust? I have asked Albert about this and he gave this response.
Anyone’s guess, really. These are two different organizations in different countries each probably operating their own instruments. One report covers 1 week, the other 6 months. One goes down to M=-1(!), for the other I don’t know the limits. The spatial plot has a ‘cross’ of earthquakes: all these must be events where the location is only known in one direction, not in the other.
Feel free to offer your perspective on this peculiar situation. I am not sure if Albert’s answer is correct simply because I can’t verify it but his answer was enough for me to move on until I discovered another issue. Their data doesn’t even match their own reports. At first, I thought I could look at the record of the groups and discern whose data was more trustworthy but that only led me further down the rabbit hole. The October monthly report from the SGC reported that total cumulative seismic energy reached 2.07E+9 joules over energy despite two magnitude 3 quakes taking place in that period not counting the other 3469 earthquakes that month. Two magnitude 3 earthquakes should release almost twice as much of the energy than reported. Same basic issue with the September report. Once again if you have an explanation for this discrepancy feel free to showcase my ignorance
The IGEPN has a different issue. This system has produced over 147,000 earthquakes from last year till the end of summer this year but when I checked the seismic map back in October in only showed 4,000 in past 6 months, and that would mean 143,000 earthquakes would have to have happened in the previous 6 months; something that isn’t corroborated with either groups reports. Unfortunately I didn’t make a screenshot so you are just going to have to take my word for it, discount my claims or stay in a neutral position.
This conflicting data makes it impossible to get a clear picture of what is happening at this system to the point that I will no longer track it unless something changes. The cause of this egregious error is mysterious, is it incompetence, malice, or a lack of resources? Anyone’s guess. Perhaps I should make contact with these groups and inquire on what the issues are but I don’t have the time interest.
There is a lack of concrete data, a mysterious volcanic complex, a lack of papers or interest, and unknown variables. What could come from this system? Nothing and everything. A catastrophic eruption that brings death or just a footnote in the study of volcanoes. So the result of this activity is up in the air as well as the cause at this moment. The current downward trend on this swarm is either really good, really neutral, or really bad. Which one could it be?
The really good
This scenario essentially means that the downturn of this swarm mean that volcanic unrest is coming to an end for good. The past swarm was not as prevalent as the seismic crisis. Theoretically the swarm could mean that the chamber could stabilizing after a decrease of magmatic fluid to the system.
This doesn’t seem to likely because there is no subsidence and the other trends reported still show small increases in heat and uplift. If this scenario were to follow through then we would see a gradual decrease in these signs as well.
The swarm was the result of a plug developing within in the system and the chances of an eruption in the future has gone down substantially. This would have little impact on the other signs and not inhibit the unrest within the magma chamber.
This can’t be proven without more extensive study or monitoring and while it isn’t impossible that this the cause that doesn’t mean there is any proof for this hypothesis.
The really bad
This swarm is roof of the magma chamber starting to fail and may stress regional faults soon which could precede a large eruption. The low energy nature of the swarm could be indicative of a more subtle but still significant increase in volatility within the magma chamber. The deformation rate hasn’t increased and this weakens the possibility of this scenario, and the earthquakes taking place at great range of depth and area and not being concentrated in the area of the greatest deformation makes me think that this not very likely.
The swarm was representative of the weakening of a deep plug increasing the chances of an eruption in the near future. I absolutely have no proof that there is even a plug let alone it’s weakening, besides some of these earthquakes are shallow and definitely not the result of deep plug weakening
The really neutral
The swarm is not the result of magmatic activity and is hydrothermal in origin as such it doesn’t speak to the condition of the magma chamber. There are plethora of issues within the hydrothermal system that could cause this swarm and could lead to phreatic activity. This could be the result of the disruption of the hydrothermal chamber by the magma intrusion.
The swarm seems to widespread to be hydrothermal in origin and there is so surface representation of this destabilization. While it is not impossible it seems unlikely.
The swarm is a result of a plethora of smaller scale changes within the systems happening at the same time and speaks little to systems future. Possible but no proof or evidence.
Just 6 of the scenarios I have in my head but with the inconclusive data from geological agencies, our imaginations can go wild on what is going on with the system. The eruptive history of this system is poorly constrained as well. Some sources state that this complex likely erupted during the Holocene and others say the last eruption was in the Pleistocene. For heaven’s sake, there might have been an eruption in 1932 but that hasn’t been confirmed. We don’t even have a conclusive history for this system so what I am going say next may seem like it comes from nothing more than my overactive imagination. I believe this system has the potential to produce a large caldera forming eruption in the near future.
I know that’s a bold claim and I have already spent a large portion of this article going over how the data from the IGEPN and SGC only serves to paint a more confusing picture on what is going on but with the reports that we do have I believe this activity somewhat matches the progress of a Phantom Caldera. Before I explain my logic, here are the excerpts from all my sources.
The Chiles-Cerro Negro unrest is perhaps the most intense. Chiles and Cerro Negro are stratovolcanoes on the Ecuador-Colombian border that, until recently, had no historical activity. Since 2013 unrest has persisted at the volcanoes, culminating in a swarm of several thousand volcano-tectonic earthquakes per day in October 2014. At the height of this unrest, there was a M5.6 earthquake just south of Volcán Chiles. CEOS data, in particular, CosmosSkyMed and TerraSAR-X interferograms, showed about 30 cm of ground movement associated with this earthquake and allowed us to estimate the position and slip on the fault plane that ruptured (Figure). Larger earthquakes that occur during volcanic unrest can tell us about changes to the subsurface stress field and are important to understand for assessing volcanic hazard.
Satellite radar data spanning this earthquake detects displacements that are consistent with dextral oblique slip on a reverse fault at depths of 1.4—3.4 km within a SSW-NNE trending fault zone that last ruptured in 1886. GPS station measurements capture ~ 20 days of uplift before the earthquake, probably originating from a pressure source ~10-15km south of Volcán Chiles, at depths exceeding 13 km.
(MEER/CELEC/INP/CGS, 2013) states that Chalpatán is an Early Pleistocene (2 –1.2 Ma) collapse caldera, 8km in diameter. The diameter halves at 1,200m depth and the floor is between 1,600 and 1,800 m depth, indicated by a resistive substratum. Post caldera lavas are andesites and dacites, about 1 Ma in age. The caldera floor is cut by a NNW-SSE fault and basement at the eastern block is uplifted as compared to the western block. Regional NNE faulting affects the caldera and has associated normal faults. Caldera fill is complex and consists of pyroclastic deposits, sediments and lavas, which are less compacted down to 1000m, but compaction increases towards caldera floor at 1,600 m.
According to the GPS bases installed in the field, it is observed that the Chiles – Cerro Negro Volcanic Complex continues with the deformation process recorded since 2015 (Fig. 5). However, since mid-2018, the North component of the CHLW GPS base, located to the southwest of the Chiles volcano, presents a stabilization; while the North component of the CHLS GPS base, located south-east of the Chiles volcano, continues its movement towards the North. This behavior may indicate that the location of the deformation source is migrating. Another possibility is that a new source of deformation, closer to the volcanic complex, has been present in recent months. The East component continues to register a constant separation between the CHLS and CHLW bases. The vertical component shows that CHLS and CHLW continue to rise with respect to the IBEC, COEC and LIEC reference bases, at a rate of ~ 3 cm / year. These signs indicate that the area of Chiles – Cerro Negro, Potrerillos and surrounding sectors, are in a process of inflation.
The trends described by the time series of the GPS stations are consistent with what was observed by means of the InSAR satellite interferometry technique. Figure 6 shows the deformation detected in the El Ángel Ecological Reserve area between October 2014 and June 2019. The red areas correspond to those that show a displacement in the Satellite Observation Line (LOS) equal to or greater than 10 cm during this period (approx. 3 cm / year). The time series in Figure 7 corresponds to the deformation at one of the points of greatest inflation (indicated by a blue triangle in Fig. 6).
Based on the data of two electronic inclinometers, Cerro Negro –CER- and Chiles –ICH, the time series of the inclination components in the N and E directions between January 2016 and July 2019 are illustrated in Fig. 8. The E component of the ICH inclinometer shows a stable trend, with variation less than 20 μrad, while the North indicates an upward trend that accumulates about 400 μrad since May 2016. The Cerro Negro inclinometer shows variations that are not easily associated With volcanic activity, however, the change that was recorded between January and June 2018 in component E with an accumulated of 420 μrad and in March 2018 in component N with 133 μrad stands out.
The resulting deformation vector of the ICH inclinometer from May 2016 to date shows an inflation towards the S of the top of the Chiles volcano. On the other hand, the direction of the resulting vector of the CER inclinometer shows an inflation trend towards the NE zone with respect to the top of the Cerro Negro volcano, parallel to the trace of the Cerro Negro-Nasate fault, which may be associated with the movement in the Cerro Negro-Nasate fails in response to the activity of the Chiles volcano (Fig. 9).
The most interesting part of this unrest is the fact the surrounding sectors are uplifting as well, this is so easy to overlook that it took me several reading of the reports to notice that fact. The area of the greatest uplift encompasses several different volcanoes including Chiles – Cerro Negro, Potrerillos, and Chalpatan. Not only that but there has been copious amount earthquakes at the Chalpatan and Potrerillos as well. This probably means that there is some type of connection between these volcanoes. The Chalpatan caldera is likely the result of a major VEI 7 or 6 eruption as it roughly is the size of the Ilopango caldera and if these systems share a source then that means that this source has already produced a large eruption and might have capability to produce another.
Unfortunately, the surrounding volcanoes does not have any public data or even a page dedicated to it.
The first excerpt mentions pressure source at depths either matching or exceeding 13 km. The reports from the IGEPN seem to acknowledge this as fact. At that depth, a large magma chamber could be being reactivated and influencing unrest on the volcanoes it feeds. This would explain the faults being stressed by the activity over a long period despite more benign surface signs.
I am going to give my idea of what I think is happening, I believe the major earthquake during the seismic crisis inhibited deformation and gas emissions. It enhanced the compressive nature of the geological setup but didn’t limit the magmatic intrusion. This is because even after the earthquake, the swarm continued at high levels for months and the recent swarm is the result of the magma chamber pressurizing.
This is the reasoning I gave in the previous piece to explain the current swarm and the lack of deformation after the seismic crisis but it didn’t seem complete to me because it felt too simple. The magma chamber must have been pressurizing for years so why is there a swarm now? Because the magma chamber is approaching it’s limit. Which caused the earthquakes and now that the limit has almost been reached so the swarm is on a downward trend. This would explain widespread and somewhat low energy nature of this swarm but why hasn’t the rate of deformation increased? Because the deformation is a result of the magma chamber reaching its pressure limit to begin with. I am not saying that the volcano is going erupt soon. This uplift and swarm is most certainly not result of the failure of the ceiling of the magma chamber before an eruption.
If this is truly the case then this system has had unrest in the past which might be able to be detected with study and diligence. The lack of gas emissions could be explained with unrest taking place on a deeper level and with a large felsic magma chamber, the gas from reactivated system could be stuck in the magma chamber. The gas emissions during seismic crisis could be from the hydrothermal system.
I think this idea is plausible but not the only solution. I do want to contact these geological organizations to inquire them about issues concerning their reports. After all you can only make so many assertions with data this inconsistent. Maybe I should stop listening to this music as I track volcanoes.