An Appeal for Advice
I thought I was finished with Chiles-Cerro Negro, I have already written two articles on this volcano before detailing my thoughts, issues, concerns, and scenarios. Chiles-Cerro Negro is a volcano that has been restless for almost 7 years now, it has had large swarms and other signs of a potential future eruption and it borders on Columbia and Ecuador. The most recent and extensive swarm since 2015 has come to an end with the activity and earthquakes gone down to low levels since December.
However in January something changed: while Volcanic-tectonic earthquakes went down, LP earthquakes went up representing a change in the volcano’s behavior. Around 300 of these LP and VLP earthquakes have been happening at a depth from 20 km to 46 km below sea level. This contrasts with a relative decrease of shallow volcanic tectonic earthquakes. If you believe that these countries have poor instruments then the real numbers could be larger then reported.
These amount of LP’s have not happened since the first seismic crisis and took place at deep depth, something about this volcano’s unrest has changed recently. This could be the beginning of a new magma intrusion as stated by the IGEPN’s February report but I don’t know how I feel about that.
It seems possible but inflation hasn’t gotten faster. This could be indicative of some type of intrusive body moving into the magma chamber of the volcano.
The LP earthquakes have also been increasing throughout the entire complex however and there has been not a lot of Volcanic-tectonic earthquakes in this area as well but the IGEPN has not mapped all the LP earthquakes so I can’t say anything definitive. There also seems to be a shallowing trend with these earthquakes.
Once again, a lot of LP’s have seem to be taking place to the northwestern part actual complex with the. This could be a reasonable amount of eruptible magma moving through the magma chamber, Unfortunately, most of the quakes have not been located and when I say most I mean more than half. That means that I can’t say anything for certain. Deeper volcanic activity and Long-period earthquakes aren’t my forte, even more so for silicic systems.
The amount of LP earthquakes has also gone down a good deal but they are still there, the exact number will have to wait for the March report. It is my personal opinion that these LP earthquakes are the result of eruptible volatile magma rising to the roof of the chamber. It is my concern that this volcano is hiding a large magma chamber capable of producing a caldera-forming eruption, No one can say that there is not a large magma chamber here because there hasn’t been good studies on this system. Yet this system is stressing regional faults, has a deep chamber, has a connection to 3 surrounding volcanoes, has a long history, and hasn’t erupted in at least 10,000 years. While this evidence is not concrete it should by no means be ignored.
I have recently found out that the hydro-thermal activity to this volcano is controlled and regulated mostly by regional tectonics and not volcanic activity. As the hydrothermal system is becoming unstable that may not be an indication of volcanic activity directly but tectonic strain from the pressure of the magma chamber.
If my propositions are true which I must admit, they are not only somewhat outlandish but also unlikely, then this does not paint a pretty picture of what might happen with this system. I will contact these geological surveys about my concerns and grievances with this system and their data and I would like to ask for your assistance. I am not a scientist and I have never worked in a geological agency so by myself I would probably fail to address my concerns in a professional way or a completely scientific way. Especially since my admitted deficiency with understanding deep magmatic activity, I would like your help in refining my letter and my model to these agencies. Albert and Carl, I ask you to write your own articles analyzing my model and seeing if it is possible and feasible in this situation or unreasonable and unscientific, I would like to have some actual experts to give me their thoughts on my model so I don’t showcase my ignorance when I contact the IGEPN and SGC. I would also ask the readers of this article to give me their thoughts as well.
In 2013, an intrusion started to take place at Chiles-Cerro Negro, The intrusion became more voluminous as 2014 came around and started the 2014-2015 seismic crisis. This, in turn, stressed regional tectonics to the point where the hydro-thermal system started to release gas emissions and resulted in the partial rupture of the southern extension of the Romeral fault, which enhanced the inherently compressive setup of the regional geological area.
As the magma intrusion persisted the pathway to the system had been cleared and seismic activity went down as the system had stabilized somewhat during the intrusion. However, all general activity would remain elevated for a few years. A degree of inflation would take place after the seismic crisis however this is not the direct result of the magma intrusion as the deformation during the seismic crisis was related to the tectonic earthquake. The inflation is due to the magma chamber pressurizing as there was little inflation directly related to the magma intrusion during the seismic crisis.
In 2018 the magma chamber had started to reach its pressure limit and this caused another earthquake swarm. This swarm did not affect the hydrothermal activity or existing deformation by a large degree. However, this swarm would showcase the area under this system’s influence including 3 different volcanoes, Chalpatan, Potrerillos, and Horqueta; a caldera and two stratovolcanoes respectively.
This swarm would include over 139,000 earthquakes but it would come to an end as the pressure limit is reached. A few months after the swarm ends another smaller swarm of LP earthquakes would begin.
This swarm is the result of a plume of reactivated magma rising from the bottom of the magma chamber to the top and after the ascension is complete, the amount of LP earthquakes goes down as the volcanic-tectonic earthquakes go up.
Another seismic swarm could begin as more eruptible and volatile magma could reach the surface of the reservoir leading to more stress for the roof of the magma chamber. More signs for this could be more destabilization to the hydrothermal chamber and slower inflation as the limits of the system’s structure is reached. However, whether this leads to an eruption or not depends on the level of stress reached, if there are one or more large tectonic earthquakes, and if the intrusion continues at this level.
One argument that I know of against the idea of a large magma build-up is that there has been no reported large dome indicative of a large unstable magma body. However, the area this hypothetical dome would occupy is littered with regional ‘junk’: calderas, craters, avalanche deposits, other volcanoes, and mountains. The Uturnucu dome was missed for a while for similar reasons, and I don’t think that this magma body at Chiles-Cerro Negro is as large as the one at Uturnucu.
Even if I am wrong about the cause of the LP earthquakes and it is the beginning of another intrusion, that would still lead to a great deal of additional stress to the system which might not be able to handle. I think an additional intrusion would make a future eruption even more likely than my explanation.
This model I think, answers some oddities about this system’s unrest, such as the lack of gas emissions, relatively slow uplift, protracted seismic activity, the stressing of several regional faults, and the slow destabilization of the hydrothermal system. The issue that worries me the most is the fact that the regional faults are being stressed and over a large area as well. The sheer length of this destabilization might have reached almost 7 years now. That is not indicative of modest or small potential with this system.
If the magma chamber were to start to fail, we would see a HUGE earthquake swarm and accelerating rates of inflation as well as steam explosions and smaller eruptions and we haven’t gotten to that point but if the magma chamber has reached its pressure limit and overpressure is taking place then that means the chance of this happening have gone up. Bold claims require strong evidence and I have some solid negative points but ultimately not enough to say that this model is a fact.
I don’t think that this system has reached the point of return, the intrusion could easily end right now and the stress would slowly dissipate afterward then we could laugh at my fear stoking propositions over some virtual beer and soda (I don’t drink alcohol).