We, humans, are ingenious at finding smart ways to do the impossible. Regarding volcanic eruptions scientists have found a way of figuring out when large volcanic eruptions occurred with incredible precision, large explosive eruptions from anywhere in the world, by looking at ice none less, who would have guessed that? Combined with high-precision geochemical studies you might even find the volcano responsible, although this is not always the case. Learning when large eruptions happened is apparently easier than finding the volcano that made them. There are a bunch of eruptions that we know when they happened, but not where. Among them, there is the mystery eruption of 1808, which I hope I might be able to make into less of a mystery.
In 1808 a large eruption scattered a cloud of volcanic sulfate aerosols across the world, into both hemispheres, depositing the sulfate in both Greenland and Antarctica. Albert is the expert when it comes to volcanic aerosol clouds so I will leave a link to his article on the 1808 eruption at the end that explains many aspects of it better than I could:
I will just mention a few important things for this article. The eruption is thought to have been very large given the major sulfate spike. It must have happened in the Tropics, probably south of the Equator judging from the dispersal of the cloud. There are witness reports, from Peru and Colombia, that describe a haze that obscured the sun in a manner akin to Saharan dust, a pale sun when low on the horizon, and which place the eruption in December 1808 or earlier, which is when the haze first appeared.
There are no historical reports of the eruption itself, however, which is puzzling. Tambora in 1815 was recorded to have been seen and heard by many, yet the eruption of 1808 went completely unnoticed. Which volcanic areas are found within the Tropics that have the potential to produce a large explosive eruption? We have the Central American Arc, the North Volcanic Zone and part of the Central Volcanic Zone in the Andes, the East African Rift, the Sunda Arc, the Philippines, the Bismark Arc (Papua New Guinea), Vanuatu, and the Tonga Arc. That’s a lot right? The thing is that historical records of volcanic eruptions in most of these places go centuries back. Most of these places can be discarded right away based on the existence of those historical records, many can be discarded based on geologic evidence that there were no large eruptions during that time.
The East African Rift is remote, but there is a vast amount of scientific studies, and such an eruption there would have probably been found. Lava flow eruptions of Kone and Fentale, in the Ethiopian Rift around 1820, are reported, so a much more impactful explosive eruption would have probably been written about. Much of the eastern half of the Ring of Fire was part of the Spanish Empire and eruptions were being reported during this time. Sunda was watched over too, as demonstrated by Tambora. All possible candidates I can think of from Vanuatu have been researched, as well as those from Papua New Guinea. The island of Bougainville is one of those places where a massive eruption may have gone fully unnoticed and has a lot of potential for major eruptions. Two volcanoes on the island are surrounded by vast aprons of pyroclastic flows and feature a small summit caldera, the kind of volcano you are normally looking for, but both are well-researched, and their last major eruptions are dated. Finally, there’s Tonga, I used to consider this the best place for the mystery eruption to have taken place, there are calderas all over the place here, but they are underwater. The two subaerial/partly subaerial calderas are studied (Hunga Tonga and Tofua), the rest are all underwater. Usually a few hundred meters underwater. This may pose a problem, since Hunga Tonga, which was an underwater eruption, failed to emit any meaningful amounts of sulfur dioxide into the atmosphere, in fact, its SO2 release was like a VEI 4 eruption, pretty ordinary. Sulfur dioxide later turns into sulfate, and thus Hunga Tonga will have probably failed to leave a sulfate spike in the ice records. The rest, even deeper underwater, calderas, may have faced similar difficulties in sending SO2 into the atmosphere. Not to mention there may be a high likelihood that someone would have heard the explosions or some ship gotten caught in the ash fall.
So where did it happen then? I may have found a very good candidate. A remote volcano in the Andean Altiplano, in an arid deserted region 4 kilometers above sea level, pulled off an eruption that was very big, but very weak. Tambo Quemado.
Edit: Searching the VolcanoCafe comments after publishing the article I found one earlier mention of Tambo Quemado from cbus05, who said that Tambo Quemado was his best possible candidate in the Andes for the eruption of 1808. This comment was in 2016, before I arrived at VolcanoCafé, so I don’t think I could have read it before. That said I must note that cbus05 was the first person to suggest Tambo Quemado as the 1808 candidate, at least to my knowledge.
Tambo Quemado yields no results when searching in Google Scholar. The only written information I’ve seen is the Global Volcanism Program’s description, which itself quotes personal communication, or previous catalogs of volcanoes as the source:
“A low pyroclastic shield near the Rio Lauca forms Cerro Volcán Tambo Quemado on the Bolivian Altiplano. The extremely youthful-looking volcanic complex (also known as Cerro Quemado or Volcán Sacabaya) displays fumarolic activity and is estimated to be of Holocene age. It consists of a broad ignimbrite shield capped by an elongated NNE-SSW-trending vent area about 2 x 3.5 km in diameter formed by three large overlapping craters. The youngest crater lies at the southern end of the summit region and contains a blocky lava dome. The wind has redistributed tephra deposits to the E and S, forming aeolian sand dunes”
Tambo Quemado is in between two major clusters of stratovolcanoes, north is a family of giants that includes the beautiful Sajama and Parinacota volcanoes, the latter, Fuji-like volcano, has been vigorously active in the Holocene. To the south lies a smaller group, that hosts the historically active Isluga, and the very young-looking Augustine-like Tata Sabaya, which, despite collapsing into a huge debris avalanche, later managed to rebuild a very symmetrical cone. Tambo Quemado on the other hand is a low volcanic edifice in a valley, GVP describes it as an ignimbrite shield, although I prefer a tuff cone. It’s relatively isolated, although 30 km south there is a circular massif that might be important as we will see.
The landscape all around Tambo Quemado is covered in ash, the tuff cone itself is gigantic, vast fields of ash dunes extend downwind of the tuff cone for tens of kilometers, and a bright pyroclastic mantle that drapes mountains to the north and south. Overall this area can be seen in satellite images as a big grey blur, perhaps some 50 by 80 km across. The effects on the landscape are dramatic enough to bring attention to this forgotten volcano.
The tuff cone and the cryptodome
Let’s start with the tuff cone. I have inspected the volcano on Google Earth. Tambo Quemado has a complex of craters nested atop a shallow-sloping cone, all features are extremely youthful looking. An outer crater complex measures 4 km long by 2.5 km wide, another crater complex of 2 by 1,5 km is nested inside, and a vent on the southern end of the nested craters erupted a short, viscous lava flow some 200 meters thick. The flow is a of bright brown colour, which if I had to guess is a glassy lava of felsic composition, with a moderate amount of phenocrysts so it’s not a pure dark obsidian. Tambo Quemado stands more than 400 meters above the surrounding ground and has a basal diameter of about 8 kilometers.
I believe the volcano is monogenetic. Both outer and inner craters are very well preserved, but the main reason to me is that both the craters complexes have the same shape, elongated in a N-S direction and with a complex structure that must imply multiple vents along a fissure. Because the shape matches, then the craters may have formed due to an eruption from the same fissure system that waned over time, nesting within itself, something that is not uncommon. So here on I will assume the cone is monogenetic.
Two hills extending west from the cone puzzled me at first. Their relief was unusually round and fit neither with the pre-existing ground nor with the tuff cone. Upon closer inspection, the taller of the two hills had the top rented by numerous grabens and fractures and also featured three small shallow craters 100-300 meters wide. The lower of the two hills also featured some grabens following the crest of the elongated ridge with a rounded top, the fractures were very faint though, and hard to see, I believed they were smoothed over by ashfall during the eruption. I have seen these before, they’re cryptodomes. Magma intrudes just below the ground, as a buried lava dome, pushing up and fracturing it, gas-driven explosions make craters. The 2011 eruption of Cordon Caulle, for example, featured a cryptodome intrusion that was concurrent with the eruption. The cryptodomes resemble two fingers reaching out from Tambo Quemado.
The most important question was finding out how big this eruption was. So I used SRTM data from NASA and plotted it on Google Earth to obtain an accurate estimate. I used topographic contours at intervals of 10 meters and measured the areas within these contours that correspond to eruption material, each area thus represents a 10-meter thickness of ejecta. The results showed how massive the tuff cone is if it is monogenetic compared to other structures of the same kind. It measures some 6.8 cubic kilometers, most of it being pyroclastic material, with a small contribution from the cryptodomes and the lava flow. This alone places the eruption as at least a large VEI 5 size.
The dune field and the ashfall
One of the most striking features of Tambo Quemado is a vast field of sand dunes covering the entire ground for 50-60 km downwind, in cases leaving well-defined trails that radiate from the immediate surroundings of the volcano. They are made of a light grey material that resembles ash. The way that the material is so easily reworked by wind, unlike in any other volcanoes I can think of, might mean the tephra is loose ash with very fine particles, weak and easily eroded.
Apart from the dunes, there is also ash to be found blanketing mountains around the tuff cone. It’s hard to tell how far it reached. It can be seen to extend to at least 30 km SSE, where patches of bright ash contrast with the dark rock it landed on. Ash has been stripped away from the crest of some ridges, while on the steep walls of the valley streams of water have carved away the tephra into dark streaks. Further away from 30 km, there is no clear ash blanket that I could see on hills or mountains. Some mountains which stand in the far reaches of the dune field are also ash-free as far as I can tell, which would mean the dunes carried ash from near the eruption site and distributed it to the east to places where there wasn’t much before.
Without field work estimating the ash thickness seems very difficult, and even with fieldwork it could be complicated given all of the wind reworking and probably lack of good exposures. The only option I could think of was looking at places where the tephra might have been cut by rivers. Near Tambo Quemado runs the Lauca River, so I looked at a number of places, the river seems to incise more deeply into the ground as it approaches the tuff cone. Perhaps this amount of incision can indicate tephra thickness. Using the numbers I obtained tried to approximate the thickness of different areas of the volcano’s surroundings and the dune field, considering the direction of dune movement as the main dispersal axis. I also assumed ash to be 50 centimeters thick in the mountainous areas north and south of Tambo Quemado that have visible, surviving ash cover. Taken together I obtained 3.8 km3 for the volume of ash around the volcano. But unlike with the tuff cone, this estimate is probably inaccurate, since the ash thicknesses are a guess at best, not to mention I’m not including any possible distal ashfall. Assuming it was correct then that would make the eruption’s volume 10.6 km3.
Could Tambo Quemado have done it?
The volume shows the eruption was a very significant event, but enough to produce the sulfur spike? The 1808 sulfate spike is smaller than Tambora, but I’m not sure it was capable. I think the volume, which could very well be an underestimation, could be enough to make it a potential candidate, and it’s not like there are any other known larger eruptions around this time that could have produced the 1808 sulfate spike. Some factors could have aided the eruption, it’s not all about how big the eruption was. For example, the magma could have been extremely sulfur rich. Some volcanoes carry a separate gas phase, more SO2 that they can dissolve, like Pinatubo or El Chichón, this could be an extreme case. Added to this, the very dry climate of the Andean Altiplano may have slowed the transformation of sulfur dioxide into sulfates, perhaps favoring a longer stay in the atmosphere. An eruption altitude of ~4000 meters may have helped in reaching higher levels of the atmosphere.
We expected an eruption in the southern tropics and we have it, Tambo Quemado is 18 degrees south, perhaps a bit more south than ideal but it’s close to where we expected. Additionally, the two reported sightings of the volcanic haze are from South America, Peru, and Colombia, which could suggest the Andes as the source, and Tambo Quemado is in the Andes, in Bolivia to be specific. The eruptive activity could have lasted two months, from mid-December to mid-February, 1808-1809, judging from the reports. Checking some weather maps, from the ECMWF ERA5 Reanalysis, it appears that Tambo Quemado is usually north from the center of an anticyclone during winter, anticlockwise rotation at 9 km height blows the wind around it, first going westward into Peru, and then curving east below the anticyclone. Part of it goes into the subtropical jet stream of the Southern Hemisphere, but part may stay north of it and reach Southern Brazil. There are some weather patterns, in winter, where wind flows northward across Brazil into Colombia, and from there towards Central America, where it reaches the Northern Hemisphere subtropical jet stream so that in such a circulation the volcanic cloud could have drifted across Colombia, and explain the sightings there, and also explain the cloud moving into the northern hemisphere. However other circulation patterns also exist where it seems extremely difficult for the cloud to reach Colombia or the northern hemisphere. Whether or not it made it into the northern hemisphere would depend upon the exact circulation that existed when the eruption took place.
But how was it not reported? This volcano is the ideal candidate to produce a massive but unreported eruption. It is very remote. As far as I’ve been able to learn doing some quick search, the closest settlement at the time would have been Putre, 97 km NW, but the very tall volcanoes of Guallatiri and Acotango, 6000 m, stand in between the two locations. Arica is 170 km west, by the Pacific coast, and might be the closest important city of the time, the view from there is also hidden by mountains. Not only is it very remote, but the eruption style may have also been ideal to go unnoticed. This is no Tambora or Krakatoa, quite the opposite. The tuff cone, over 400 meters thick, indicates a prolonged eruption rather than a powerful blast, where ejecta mostly went into weak pyroclastic density currents that did not advance more than a few kilometers, it would take many individual PDCs to build such an immense thickness of ash. In fact, the eruption is somewhat maar-like, and I find it a bit reminiscent of complex, voluminous rhyolite eruptions in the Serdán-Oriental Basin of Mexico (Cerro Pizarro, Cerro Pinto, and Las Derrumbadas), where eruptions often start as cryptodomes and then turn into exogenous domes or maars. Tambo Quemado erupted in an area that is between a sedimentary basin and an alluvial fan. The formation of cryptodomes indicates magma may have stalled below the sediments and formed a horizontal intrusion, interaction with groundwater or simply degassing of the magma may have induced gas-rich eruptions with very high fragmentation, leading to a sort of maar volcanism. A relatively low-intensity, long-lasting explosive eruption like this may not have had much distal impact, perhaps some light ash falls but nothing too dramatic, most damage was done to the immediate surroundings of the volcano that were completely uninhabited. In addition to this, this area in winter is near the center of an anticyclone, and high-altitude winds can be as weak as they get, this would slow the dispersal of ash, limiting its extent.
To sum up, we have a huge explosive eruption, whose location could match the reports of the haze cloud of 1808 and its distribution into the Southern and Northern Hemisphere, and has good chances of not being reported due to its remote location and probably local impact. Added to this, the eruption is very young-looking, clearly Holocene, so makes a very good candidate for being the 1808-1809 event.
20 km south of Tambo Quemado lies an interesting group of mountains. One of the tallest peaks in the group is called Laram Pukara. The mountains form a circular massif, with a diameter of 16-17 km, and along the entire eastern half of the complex lies a near-perfect semicircle of steeply outward dipping strata, of alternating dark and bright colors. The tilted layers form a sort of circular wall that is best exposed on the eastern side of the Laram Pukara mountains. The structure is similar to updomed strata around laccoliths and plutons in many places of the world, like the Trans-Pecos Magmatic Province of Texas, or the Central Montana Alkalic Province. The uplift could be 1-2 km, it could result from the intrusion of a 200-400 km3 pluton.
Around Laram Pukara there are a number of bright-colored lava domes and flows. They are just barely recognizable due to intense erosion that has erased all superficial lava-like features although, on a large scale, they have a smoothed-over lava flow morphology. And because of the bright color, they are probably felsic, somewhere between dacites and rhyolites. I estimated the volume of these domes thinking they might have some relation to Tambo Quemado. Most of them have about 0.5-1.5 km3. But there is an outlier, a huge lava flow erupted from the northern part of the uplift has over 8 cubic kilometers, it is partly incised by valleys, and the distal parts are buried under the alluvial fan of Laram Pukara, which makes it difficult to know the volume precisely. I called it the Long Flow.
The structure of Laram Pukara resembles a large silicic complex, with a central pluton surrounded by a ring of lava domes erupted from cone sheet intrusions. However, it is heavily eroded. Given the poor state all the domes and flows are in, I’d say they are likely well over a million years old, there are no signs of recent deformation/uplift either. However, the proximity of Tambo Quemado to Laram Pukara may not be coincidental. Is there a link? A satellitic vent of Laram Pukara? More likely Tambo Quemado might just be a successor of this ancient silicic system, but this is hard to know.
Based on an otherwise complete lack of good volcanic candidates for the event of 1808-1809, Tambo Quemado volcano, a youthful-looking tuff cone in the Andean Altiplano of Bolivia, is not a bad guess at all, I think. Historians and meteorologists have probably as much to say about this as much as volcanologists do, and as a volcano guy, there are many things I can’t know. So what do you think? Could Tambo Quemado be the eruption of 1808? Could there be some forgotten historical records to be found now that a possible location has been pinpointed? Would the location be right for producing the cloud of volcanic sulfate? Are there any other good volcanic candidates that I haven’t considered?
If Tambo Quemado is the eruption of 1808 then that would open many interesting questions. Can large maar eruptions have disastrous consequences on climate? Perhaps we ought to widen our view. We recently saw how Hunga-Tonga did something we did not expect, a volcano that injects vast amounts of water into the stratosphere. We know a lot about Krakatoa/Tambora-like events, and now we know about Hunga Tonga events, but what about Tambo Quemado-like events?
Albert’s previous article on the eruption:
Topography data, including NASA’s SRTM:
Tambo Quemado’s GVP page:
Reanalysis of weather maps:
On the volatile excess of El Chichón and Pinatubo:
Update on current events
There are quite a few things going on in the volcano world, if I hadn’t just published an article, then I would make a new one. I will just add updates here.
23 UTC update 13 August:
First, Etna volcano in Sicily has entered a paroxysm. The activity started several hours ago and is ramping up as I write. These are not too uncommon, they consist of strombolian activity of increasing vigor until a continuous lava fountain forms, intensity keeps increasing that can even build up to a subplinian climax, and afterward ends abruptly. Probably won’t be long before the eruption climaxes and ends.
Second, a powerful swarm started in the Reykjanes Ridge at 19:40 UTC. The first 10 earthquakes had magnitudes of only 1.5-2.2. 27 earthquakes into the swarm we had the first star, > M 3. This shows the swarm started with small earthquakes before going into the stronger ones which is usually a sign of volcano-tectonic swarms, this means swarms where magma is involved, like dike intrusions. Tectonic swarms would open with a big earthquake. There have been nearly 200 located earthquakes already. It is good to keep in mind that this swarm is far offshore Reykjanes, SW of Fuglasker, in an unnamed volcanic system, some 35 km away from the tip of the Peninsula, so smaller earthquakes are not located here, only larger events, mostly larger than M 1.7. The swarm is weakening but this would not be uncommon for dikes, given that dikes grow fastest at first and slow exponentially. It could be a dike, but I can’t fully confirm this time because the earthquakes are far from the seismic monitoring network and poorly located. That said the chances we are dealing with a dike are high, I think. We don’t have a webcam here so if it erupts we won’t know right away.
Lastly, Kilauea is undergoing a small magma intrusion. After a few days of increased inflation, the tiltmeter at Uwekahuna has experienced a rather abrupt deflation of half a microradian that has now stabilized. The deflation coincided with over half an hour of continuous tremor and earthquakes visible in north caldera seismic stations, with many tiny, sharp earthquakes per minute visible in their seismograms. The intrusion started very gradually around 21:47 UTC. There are some chances an eruption might happen in a matter of hours, but there are as many chances or more that the intrusion will stop without anything happening. So far we have a smallish intrusion that is deflating Uwekahuna, and not a large intrusion that inflates Uwekahuna, which always happens before eruptions. These smallish intrusions often fail to erupt, last time, however, one of the smallish intrusions changed into a major eruptive event, so we will see. M 3 earthquakes are likely, since they have accompanied both types of intrusion.