First of all, this article is the official start of our celebratory week and we have no less than two things to celebrate since our five year birthday as a beacon light of volcanic science is on Wednesday. More about that later in the week, first we have another jubilee to take care of.
A year ago to the day we started our attempt to re-invigorate the Decade Volcano Program by suggesting a new set of volcanoes. No other series of articles that we have published has had such an impact and over the year that has passed interest in our suggested volcanoes has surged and in a few cases new studies and new equipment has been installed at our suggested volcanoes.
This makes us proud since our intent was to raise awareness of over-looked and under-studied volcanoes that pose a threat to large amount of people, because in the end our only protection against major volcanic events is knowledge.
Back when we planned the series we made a list of ten volcanoes, but one of them disappeared from the final list. The reason for this is awkwardly mundane, and it is time to rectify it and add a final eleventh volcano to the list at a shared second position together with Apoyeque.
The mundane reason is that in the middle of the series I suffered from a small stroke (the first out of two) and Albert and Henrik got stuck with finishing the list (and they did a brilliant job out of it). There are two reasons that they changed the second placed volcano with another, first of all there is a lack of articles written about my suggestion for a number two, and the second reason is that it is my own home-turf volcano. It was also the intent that I would write an additional piece, and what better time than at this anniversary.
As a part of our celebration we have permanently added the list at the top menu of Volcanocafé under the header NDVP.
But, before we get started let us have a reminder of what the prerequisites was to get included in the list. The first thing was that we should give under-studied volcanoes an advantage. The second reason was that they should be active in a way that is pointing towards a future large eruption. The third rule was that the volcano should be awkwardly placed in relation to a large amount of people and that we could fairly accurately predict a death-toll from a maximum historic eruption or a well predicted maximum eruption. As such the original NDVP was a chilling read. Now time to go to the worst piece of property on the planet.
One last thing, I have written an article before that relate to this volcano and I recommend reading it again since it will go through previous disasters of Guatemala City in more detail.
The Capitals of ages past
No country on Earth has had as many capitals destroyed by natural disasters as Guatemala. To date 4 capitals has been destroyed a total of 8 times through 6 earthquakes, 1 lahar and 1 major eruption. Let us go through the list from the latest to the oldest destruction.
The last time Guatemala City (the current and fourth capital of Guatemala in less than 500 years) was destroyed happened during the M7.5 earthquake from the Mixco Fault in 1976. This caused 23 000 fatalities, 77 000 injured and made 1 200 000 people homeless and the rebuilding of the city is pretty much an ongoing project to this day.
Before that Guatemala City was hit by a prolonged swarm of major earthquakes between 1917 and 1927. I have previously covered this in an article that can be found by following the link above.
Prior to that the capital of Guatemala was the third capital after colonization bearing the grand name Ciudad de Santiago los Caballeros, nowadays known as Ciudad Antigua de Guatemala, today it is the only remaining intact Spanish colonial city in the world and it is UNESCO World Heritage Site.
Oddly enough the city was partially saved for our viewing pleasure by being destroyed by no less than 3 earthquakes. The first one was the M7.4 1717 earthquake of Antigua, the next one was a M7 in 1751 and the final strike was the Santa Maria Earthquake of 1773 that had a magnitude of 7.5. For those of us who love pretty historical sites where you can sit with a drink and watch eruptions this is the place to be and I really recommend a visit.
Before that the location of the capital was located in the village of Ciudad Vieja, while it was the capital of Guatemala it was better known by the rather stupendous name of Ciudad de Santiago de los Caballeros de Goathemalan, and just to confuse things it was the second capital of the same name. In 1541 it was destroyed by a non-volcanic lahar emanating from Volcán de Agua. It has erroneously been reported as a crater lake failure in older literature, but that crater lake had already drained in another direction prior to the deadly lahar. Instead the lahar happened after an unusual long rain period where down-flow from the slopes of the volcano had been dammed by rocks and trees. This happens often around volcanoes, but it is one of those hazards that are often over-looked.
As the first capital of colonial Guatemala was slowly starting to recuperate a second disaster struck, this time in the form of a moderate sized earthquake, this time the residents and colonial authority had it and the city was moved to Antigua in 1543.
Now some of you will be pondering what happened to that furtive first capital named Ciudad de Santiago de los Caballeros de Goathemalan? Well, it was placed on an old Mayan capital named Iximche and the Mayans took offence to this and made life seriously miserable for the Conquistadores, so much so that they moved it after just 3 years, so it was not destroyed in a natural disaster. For those interested it was the capital of the Kaqchikel Mayans from 1470 to 1524 when the Conquistadores invaded the place.
Now it is time to go back in time to a period prior to the Conquistadors colonizing the local population to near extinction with guns and measles. Back in the dark ages while Europeans muddled around in mud pits thumping their foreheads with bibles Guatemala was the epicenter of one of the greatest High Civilizations on the planet, The Mayan Empire.
Few civilizations have achieved such heights of art, culture, literature and architectonics. If you decide to go to Guatemala I highly recommend a visit to Museo Popol Vuh for the art and culture parts and to the Kaminaljuyu Park that is roughly 1 kilometer away from my mother in-laws house. In that park there is a highly intriguing archaeological dig that is open to the public for a small fee (free of charge if you are a Guatemalteca). As you enter into the rather unassuming corrugated roof coverage you get the dizzying experience of standing looking DOWN the side of a Mayan pyramid.
As the pyramid was built this was the capital of the South Mayan Area that had built a sprawling city near a rather large lake in what back then was a highly bucolic sloping valley. The city was in prominence from 100BC to 400AD and it is the site where the Mayan Empire had one of its high points during the Miraflores Period.
The Mayans got fish and fresh water out of the lake and they farmed the valley for maize and other vegetables. There were also ample grazing grounds for livestock. Living here was so good that they could afford to reach heights of art and culture that still rival anything the western civilization has produced.
In the end not even the mighty Mayan Empire could save their capital from destruction. But, for the Mayans it was not earthquakes that spelled the end. The reason for that is quite simply that they knew very well how to build earthquake safe houses. And for those who would guess that a lahar was the end of the city they would be wrong, the Mayans knew about that danger too.
Most of our readers know that Guatemala City is close by active volcanoes like Acatenango, Fuego and Pacaya. And it would be a pretty good guess that it was one of those that spelled the end of the Mayan capital. Once again the Mayans was too bright and knowledgeable for that. It would have taken a VEI-6 eruption out of Pacaya to produce anything that would have been deadly for the city since it was well located to not be impacted by the recalcitrant volcanoes in the vicinity. In the end we know that there was no such volcanic eruption during that period.
So, where did the ash come from that inundated and filled in the lake completely and that also could cover an entire city with tens of meters of tephra? For an answer to that we need to look at a volcano that they Mayans did not know about. A volcano so big that it took until the 70s before anyone understood the implications of what a large caldera volcano could look like, and what it could do even during a comparatively small eruption. And as chance has it, this large caldera volcano is literally the next valley over.
Here I should Emediately start with contradicting myself and state that it there is no 100 percent evidence of what volcano is responsible for covering up an entire Mayan capital, just that we do know which volcanoes that was not responsible. So, me blaming Amatitlán is a slight conjecture. It could also have been another close by Caldera system. Still, I will walk through the steps and I will even point finger at the likely feature for the eruption and then we can await future research on the subject.
The Amatitlán Caldera
Guatemala has several large volcanic complexes and the second largest is the Amatitlán Caldera. Only the Atitlán Caldera is larger, both in size and in maximum eruption size, to date Atitlán is the only VEI-8 volcano in Guatemala (Maria Tecún Tuff).
Amatitlán is located very close to the Guatemala City depression that has formed as an elongated Graben emanating out from the caldera as a spread center fueling the volcanism at Amatitlán, so in a way the city is within the extended part of the Amatitlán Volcanic Complex.
On another side a volcanic line runs off perpendicular to the caldera that consists of the Acatenango/Fuego double volcano system, Agua and Pacaya. As such this must be one of the most impressive sideshows of a main volcanic caldera on earth. There are also numerous older volcanic edifices surrounding the caldera that most likely have become extinct (even though one or two may be just long dormant).
A major faultline runs through the caldera floor that has created the beautiful Lake Amatitlán, as such it is not a proper caldera-lake like in Atitlán, but it is still a good sign of the high level of seismic activity in the region.
It was on the shore of this lake that the 1917 prolonged earthquake swarm started, and the origin was well and truly volcanic and not tectonic. It is not until after a while the swarm turned tectonic and ran off into the city of Guatemala itself. Before that a rapid intrusion uplifted the village of Amatitlán several meters and creating the hydrothermal system that is today powering the thermal baths (serious tourist trap, be warned).
You can still track that 1917 earthquake swarm in the form of intermittent earthquake swarms under the Villa Santorini suburb of Guatemala City that is located on the caldera wall itself. The view from my wife’s house at Villa Santorini is pretty much second to none when you wish for caldera watching.
I often see people being excited about a few centimeters of uplift at large volcanoes like Yellowstone and I quietly chuckle at their excitement. The reason for my merriment is that I am quite familiar with the amount of landscaping a large volcano can do without erupting.
Intrusions of magma or hydrothermal fluid shifts can cause rapid uplift on the order of several meters in a day, or in the case of magmatic intrusions entire hills can come into existence in the span of a few weeks. Places along lakes that was at the water’s edge can all of a sudden be a couple of meters up in the air the next time you visit, and houses can be unceremoniously dunked under the surface of the lake. And sometimes houses can be toppled on the side during the night if the volcano in question is having a slight case of constipation. All of these things happens at Amatitlán without an eruption occurring. Now, seriously compare that to an inch of movement over a year in Yellowstone and call me back when you see ten meters of uplift there within a week. General rule, Large Caldera equates Large Movements.
Now, let us get to the meat of the business. As most really large volcanoes Amatitlán itself is not erupting frequently, instead the normal business is attended by its flank volcanoes and among those Fuego and Pacaya are the most prolific together with a few appearances of Acatenango. Agua seems to have gone for a pretty extended nap and is now counted as dormant, but not extinct and may one day erupt again. Among these volcanoes Pacaya is the geographically closest with Agua coming second. Eruptions here occur between once every five minutes to once every 30 years with the five minute thing being more of a general rule.
These eruptions are normally not deadly unless a tourist meanders to close to an active volcanic vent. Sometimes fields and houses are destroyed by lava flows and on rare occasions roof collapses on buildings, sometimes as far away as inside Guatemala City. As the volcanoes ramp up in activity they can be fairly seismically active, something that can destroy nearby houses. Also, lahars and pyroclastic flows can emanate from these volcanoes.
The second most frequent type of eruptions emanate from the caldera itself. These eruptions consist of extrusion of rhyolite to rhyodacite lava domes. No such extrusion has been documented, but it is safe to assume that these events are accompanied by large scale seismic activity before extrusion starts. Other dangers from these eruptions would be gas expulsion and localized pyroclastic flows as the flanks of the emerging dome collapses.
What sets these eruptions apart from other regular lava dome extrusions is the sheer size of the events, they range from creating hills to what can best be described as moderate sized strato volcanoes (even though they are nothing like a strato volcano). And the area is quite frankly littered with them. These lava domes are either extruded at the caldera floor or along the ring fault around the caldera.
Now I will jump over the third most common type of eruptions and instead go for the second most destructive type of eruptions even though they are more infrequent.
Guatemalan strato volcanoes are good at producing devastating flank collapse eruptions, in type they are reminiscent of Mount St Helens, but these events are an order of magnitude larger. Last time this happened was the 1902 Santa Maria VEI-6 eruption, and even that was small compared with the collapses of Acatenango and Fuego, and comparable in size to the collapse of ancestral Pacaya in the year of 800AD (that also helped with covering Kaminaljuyu).
The collapse of Fuego reached all the way down to the Pacific Ocean and reached a projected size of a medium sized VEI-6 eruption and it is here important to remember that the current edifices are equally unstable and that they are likely to fail again catastrophically.
If such a collapse would occur between 100 000 and 1 000 000 people will die either directly or in the aftermath depending on the exact trajectory of the collapse and the pyroclastic base surge. It is though good to remember that events like this happens about once every ten thousand years at these volcanoes. At the same time it is a stark reminder that there is a marked need for studies and more monitoring equipment to study the stability of the flanks of these volcanoes.
Amatitlán Caldera as a supererupter
To the best of my knowledge Amatitlán Caldera is the only known large scale caldera volcano that has two different explosive variants of supereruptions. We know of at least 16 eruptions in the last 270 000 years that have been either large VEI-6 eruptions or VEI-7 eruptions. All of these eruptions have been large enough to form either pyroclastic base surges, welded tuffs or ignimbrite flow sheets.
The reason for there being two different modes of supereruptions is to be found in the rhyolite lava domes and the reason that they are extruded. The ample size of the caldera and that most of the arriving lava going into the side show strato volcanoes makes it into a perfect breeding ground for pockets of magma to rest in. As an intrusion occur it is most likely that it will reside in the caldera crust and that it will take thousands to tens of thousands of years until a new intrusion happens at the same spot. At the same time the intrusions occur at shallow depth, so the magma will fairly rapidly degas and become stale and unable to form explosive eruptions, or even to erupt at all on its own accord.
But, sooner or later fresh volatile rich magma will arrive to the same spot where the rhyolitic mush resides. Here the respective volumes of old and stale magma contra fresh hot volatile rich magma will decide what happens.
If there is a lot of rhyolite and a little andesite the rhyolite will be benignly extruded in the form of a large lava dome and the newly arrived andesite will in turn rapidly degas and then percolate into yet another batch of stale rhyolite.
If the respective amounts are more balanced you get a champagne cork effect, first a happy little rhyolite dome will extrude before it is blown to smithereens by the volatile rich andesite. If both of these volumes are large you get a pretty large eruption well into the VEI-6 range like the Ojos de Agua eruption.
If the amount of fresh magma is larger than the old stale magma there will not be time for a dome extrusion, you just get very rapid inflation and then that part of the caldera goes off.
This type of eruptions would produce a pyroclastic base surge covering everything fifty kilometers out to a depth between 1 and 20 meters. Currently there is not enough monitoring equipment in place to detect an upcoming eruption of this type, and due to the high population ratio contra routes of evacuation it is dubious if it would even be possible to get the population of Guatemala City evacuated. And, as monstrously as it sounds, even if you could evacuate the population there is no realistic place to evacuate 6 million people to. If an eruption like this occurs between 1 and 3 million people would die.
The other version of supereruption is more normal, but with a twist. The caldera of Amatitlán has formed in a series of caldera forming explosive eruptions. Normally a volcano will do a large caldera collapse during an eruption and during later stages you have smaller intra-caldera eruptions transforming the large caldera into a nested caldera.
Due to the intricate faulting of the Amatitlán Volcanic Complex you instead get intrusions running in under the caldera walls themselves and as pressure reaches the breaking point you get an explosive caldera enlargement. If you ride a boat along Lake Amatitlán you will see semi-circles gouged out of the caldera wall, one after another. Some in the VEI-6 range and a couple of them is in the 150 cubic kilometer range. If a large eruption of this type would occur Guatemala City would be a complete loss since the base surge would devour the city and cover it with between 20 and 100 meters of ignimbrites within minutes, there would also probably be a 50 percent loss of life extending from 50 kilometers to 100 kilometers. The death toll here would be in excess of 6 000 000 people.
With the knowledge in geology and volcanology that we have today nobody would place the capital where it is. Still, there is a reason that both the Mayans and the colonial powers wanted the city where it is.
The region is the most fertile in the world and the elevation produces a climate that is as near to perfect as is possible. There is a reason that Guatemala City is nicknamed “The City of Eternal Spring”. The coastal area towards the Pacific Ocean is very warm, so much so that only sun craving Swedes think it is a good spot to be at. And the Atlantic coast is even warmer and also infested with mosquitoes, which is sad since that would be the safest spot for the next capital city.
The last large eruption occurred outside of the caldera itself and was of the champagne cork type. It happened on the way to Pacaya and it left a couple of nice hydrothermal lakes and this is the most likely source for the demise of the Mayan Capital.
At the beginning of the article I wrote about things moving about in the Amatitlán Caldera, and this occurs in an area stretching from Ciudad Amatitlán all the way to Pacaya. Here hydrothermal springs and hydrothermal field’s crop up, hills inflate, beaches lift or sink and generally tend to refuse to stay in place as hydrothermal fluids move about and magma shifts around or intrudes.
To me this is an area that is in dire need of instrumental coverage. Sadly Guatemala does not have the money for that and they have to use the money they have to monitor the more frequently erupting strato volcanoes around the city.
I can understand and relate to the hard decisions the local agency has to do, but at the same time as both a geophysicist and a resident of this beautifully dangerous city I find it heartbreaking. I understand that the amount of equipment needed is just too much for the funding, and I can relate to the hard decisions made. But at the same time I know that it is really just a question of time before one of the larger eruptions comes knocking on the door, be it a flank collapse or an explosive caldera eruption.
There is though hope, the local volcanologists are pretty sharp and there is a new breed of even sharper volcanologists in training (I know some of them and they are sharp cookies indeed). If they could just get their hands on a steady supply of equipment they would perform miracles.
So, here is a wish list from me for the volcanologists of Guatemala. 10 complete borehole strainmeters drilled and ready. 6 complete gas measuring stations and 1 water chemistry station permanently located in the lake itself. 20 state of the art seismometers and 20 research grade GPS-stations. Or in other words, about half of what Iceland has.
Yes, we are talking about a few million dollars or Euros here, but put that into relation of 6 000 000 people and the price per life would equate to less than 1 dollar per person.
At the same time as we add Amatitlán Caldera and Guatemala on the New Decade Volcano Program on a shared second place I would also recommend going to Guatemala. It is a country of intense beauty, untold cultural riches and by gosh if the volcanoes are not outstanding both in beauty and in richness of its eruptions. I can’t think of a place on earth other than this where you are guaranteed to see eruptions while visiting a world heritage city with a drink in hand. It is the paradise for a volcano lover and for me it is my personal Garden of Eden, even though it has a large dragon at its heart.