Last article we saw a newborn felsic system, Laguna del Maule, whose so far brief history has begun rather impressively, with possibly two VEI-6 eruptions, a number of smaller plinian eruptions, and some sizable lava flows. In the article before that one, we saw Domuyo, a monster volcanic system that is very lazy. It could throw a cataclysmic eruption, but never does anything. Now we will meet two monster felsic systems with a more impressive history behind. Puelche and Calabozos. We are in the Chilean Andes, 200 km south of Santiago de Chile. And this is a land of hidden volcanic beasts.
Puelche is a volcano of which very, very little is known. Not much can be found in scientific literature. The article with the most information on this system is a 1999 article led by Wes Hildreth, who has also been one of the main researchers into Calabozos and Laguna del Maule systems. This 1999 article describes Puelche as the largest cluster of Quaternary rhyolite lava flows known in the Andean South Volcanic Zone.
The area of Puelche is covered in snow much of the year, and is barren, uninhabited, and of very difficult access. Some of the flows are showered in white pumice from the 1932 eruption of Quizapú. Erosion is extensive. Deep gorges cut into the volcanic field. The rhyolite lava flows now form the flat tops of mountains, perched up to a kilometer above fast-flowing rivers, over precipitous slopes.
The composition of the field is bimodal, with most flows being rhyolites, and some flows being basaltic andesites. The rhyolite flows have 72.1-75.5 wt% SiO2, and the basaltic-andesites 54.5-54.9 wt% SiO2. About 21 km3 of rhyolite lava have survived erosion, a comparable volume of pyroclastic material is likely to have been erupted. The flows form a ring of about 15 by 11 km, in a similar arrangement to Laguna del Maule. Two of the flows have Ar/Ar ages of 213 and 354 ka (thousands of years ago).
This earlier information is what is known. However, after inspecting this area in detail, I’m convinced that this volcano has an earlier, much grander eruptive history. I have a map in Google Earth with dike intrusions from this section of the Andes. As part of this map, I studied a remarkable cluster of dikes in the north and south walls of the Puelche River. From the first moment, the dikes stood out for their length and thickness, which, after being used to the few short dikes of stratovolcanoes, struck me as being very prominent. One dike has about 15 meters thick, and at places up to 60 meters thick or more, and can be followed continuously for 6 kilometres, while discontinuously I think extends over 12 kilometres. The dikes are not simple-shaped; they jumped between parallel segments, and sometimes thinner secondary dikes seem to branch off obliquely from the main intrusion. They have variable thickness. Some are a meter wide or less; I can’t see them if they are thinner than this. Other dikes are up to tens of meters thick. Even the same dikes vary a lot along their length. All are very dark-coloured, probably basaltic-andesites in composition. And the swarm is very dense in places. Some brighter coloured portions of the valley walls, where the dikes have strongest contrast and can be pinpointed most easily, show dense intrusive complexes, where you wouldn’t be able to walk any more than 30 meters without running into a dike.
It didn’t take long to realize the dikes seemed to extend from the Puelche Volcanic Field, located immediately to the ENE of the swarm. Presumably the dike swarm would have been the sub-volcanic complex to a field of basaltic andesite cones and lava flows above, in the shape of a plateau, that has been all but removed by erosion. Plateau volcanism has also happened in the area of Laguna del Maule and Calabozos, and judging from the dike swarm in Puelche too, so that it seems that felsic systems in this area are actually bimodal, consisting of plateaus of basaltic andesite lava which develop into calderas or ring-like fields of rhyolite flows, generally located in slightly back-arc positions.
Another clue to the history of Puelche is to be found across the border in Argentina. There, a thick, extensive stack of white-coloured ignimbrites, pyroclastic flow deposits, dominates the landscape. I had long been aware of those ignimbrites, but never bothered to look much into them. I had previously assumed they were probably ignimbrites of Calabozos. But then, upon mapping the ignimbrites of Calabozos, I realized something; they were not from this system. This would have been obvious rapidly. The white ignimbrites are very different in aspect from those of the above-mentioned caldera. Their surface is a lot more worn down and more brightly coloured, but it is their location away from Calabozos that makes it impossible for that to be their origin. The article by Wes Hildreth mentions these ignimbrites as a 650-m thick stack of several welded ignimbrites east of Invernada River. The youngest of them is dated at 1.06 Ma (millions of years ago), too old to be from Calabozos. But there is no more information. The ignimbrites are thickest and most extensive immediately east of Puelche, where they form a broad platform, hundreds of meters thick, that extends 35 km downslope. The distribution, I think, implies an origin in the exact location of the Puelche Volcanic Field. These layers would have been completely removed on the Chilean side by deep glacial erosion that has also taken away the basaltic andesite lavas there, but in the Argentinian side they were better preserved.
My first motivation after learning about the ignimbrites was to find if there were any signs of a caldera structure in the topography, and I think there are. Valleys in the Puelche area follow a circular structure that runs around the ring of Late Pleistocene rhyolite flows. I think this elliptical structure might be the former caldera. If this is correct, it would have measured 17 by 14 km across. Perhaps the floor inflated upward, which added to later lava flows, largely concealing the caldera.
Puelche would have likely sourced multiple caldera-forming eruptions, possibly VEI-7 events, where pyroclastic flows travelled to distances of over 35 km and covered the landscape in a cumulative thickness of up to 650 meters of pyroclastic rocks. Do we know the age and composition of these massive eruptions? Maybe we do. There are two ignimbrites near Laguna del Maule, the Cajón de Bobadilla and Laguna Sin Puerto ignimbrites, which are dated at 1.5 Ma and 0.99 Ma respectively. I think these ignimbrites could have come from Puelche, since they are found within 20 km of the circular Puelche structure. Because Bobadilla is very thick, it was thought to be a caldera-filling ignimbrite, but I think it could simply be a valley-filling ignimbrite which might be correlative with the one dated at 1.06 Ma east of Invernada River. Both the 0.99 Ma and 1.5 Ma pyroclastic deposits are of rhyodacite to dacite compositions. The earlier one carries fragments of rhyolite lava flows which must have been blown away by the explosive eruptions, while the latter has pieces of andesite.
The Calabozos Complex
The Calabozos Complex lies 40 kilometres north of Puelche, and includes several central volcanoes, a plateau of basaltic-andesite lavas, a well-hidden caldera, a few massive dacitic lava flows, and 1000 square kilometres of a snow-white pumice desert, easily identifiable in Google Earth as a massive white patch from a thousand kilometres eye altitude or more, legacy of the plinian eruption in 1932 that fell just short of a VEI-6. Like other volcanoes of the area, it’s remote, although not as much as Puelche, and it’s little studied and heavily eroded, but also barren and arid which highlights young volcanic features in incredible beauty and detail.
Andesite and basaltic andesite lavas are dated at 2.02, 1.09, 1.08, 0.55 and 0.35 Ma, which makes a lava plateau on top of which have been constructed the later stratovolcanoes. Hildreth mapped three caldera-forming ignimbrite sheets, dated at 0.8, 0.3, and 0.15 Ma. The older ignimbrite only outcrops in a few places and its volume is not well known. The younger ignimbrites, of 0.3 and 0.15 Ma, are estimated at 250-300 km3 and 175-250 km3, respectively. Both ignimbrites are densely welded for the most part, which happens when the searing heat within a pyroclastic flow welds the pyroclasts together. They lack basal plinian deposits. All three ignimbrites have rhyodacite to dacite composition.
I think the reason we know there is a caldera is that there are ignimbrites, because the caldera itself is nowhere to be seen. I’ve looked many times at topographic maps, geologic maps, and Google Earth, and I still can’t picture the exact caldera rim. The ignimbrites point to the area that must have been in the caldera, but topographically the caldera has practically no footprint, with the floor being as high as the surrounding landscape. Two volcanic edifices, Descabezado Chico and Cerro del Medio, are built within the former caldera area. They have probably contributed to hiding the caldera structure. But the main reason the depression is gone is probably a combination of resurgence and glacial erosion.
The northern half of the presumed caldera area doesn’t have any lavas from Descabezado Chico and Cerro del Medio, and instead is floored by the ignimbrites, so the reason that this portion of the floor is as high as the encircling area must be that it has been pushed up from below. Resurgence is common in calderas, after all. A dacite lava flow, possibly from Cerro del Medio, follows the eastern moat around of the resurgent dome, is undeformed, and has been dated at 0.096 Ma. The authors of in the Hildreth article consider that this flow must postdate the main resurgence of the caldera. Main resurgence would have happened within 50,000 years of the last caldera collapse. If the lava flow marks roughly the elevation of the former caldera floor, then the resurgent dome is about 650 meters tall, and given that the dome covers very roughly 100 km2, 16 by 10 kilometres in size, then its volume is 65 km3. My guess is that a volume of 65 km3 flowed into the shallow magma chamber of Calabozos since the last caldera-forming event, but mostly in less than 50,000 years following this eruption. This is larger than the volume of magma emitted during the Tambora eruption in 1815. But it is also less than half the volume of uplift at Domuyo.
A system of ground cracks extends to the NNE of Descabezado Chico. They seem to be the surface scarps of normal faults, with a small downthrow. Most scarps face eastwards. If you have two spots in a balloon and you inflate the balloon, the distance in between the spots will increase, and if you are dealing with an inflating caldera, the same will happen, with the rocky surface getting stretched apart and eventually breaking up, making a graben system along the top of the resurgent dome, typically elongated since most resurgent domes are elongated. This is an axial graben system. So I think the fault scarps were formed during inflation of the Calabozos caldera floor. But we already knew about that inflation, right? The cool thing is that these are scarps are very low but very sharp and sometimes on soft ground, for example there are two low scarps that cut across a debris covered talus but are very well preserved. It is impossible for such scarps to have survived 100,000 years, given that even a small amount of erosion would erase them, and thus I think they are almost certainly postglacial, from the last 15,000 years. That means there have probably been major episodes of caldera inflation during postglacial times and that the magma body is very much alive and kicking.
There are other two other signs of the sleeping monster here. First, there are numerous hot springs which issue along the bottom of the valley, on the east and north sides of the resurgent dome, making an arc along the edges of the presumed caldera structure. Water in the hottest hot springs happens from the northern end of the caldera, which is where the valley cuts down the deepest and probably closest to the magma chamber. These hot springs are known as the Baños de Llolli, and water issues at boiling temperatures in them. There are also reportedly some sinter deposits in this same location, although it is nothing too spectacular as far as I can tell. The second piece of information comes from a mega-thrust M 8.8 earthquake that occurred in 2010.
Following a 2010 M 8.8 mega-thrust earthquake, several volcanoes in the area affected by the earthquake slip experienced deflation. The volcanoes that deflated were Nevados de Chillán, Descabezado Grande, Calabozos, Planchón Peteroa, Tinguiririca, and Cerro Overo (Caldera del Atuel). The volcano that deflated by far the most was Calabozos. Calabozos deflated up to 15 cm over an area 30 by 15 kilometres across, centered on the system of normal faults, and spanning Descabezado Chico and Cerro del Medio. Only Cerro Overo which is possibly a caldera volcano, although probably of smaller caldera size than stated in GVP, deflated by a similar amount of 13 cm, but over a much smaller area of 20 by 12 km. Other volcanoes deflated by smaller amounts and over smaller regions than Calabozos. Watching volcanoes deflate after mega-thrust earthquakes might be a useful way of finding about the location and size of magma chambers. Unfortunately, the study that reported this did not extend its interferograms into the area of Laguna del Maule and Domuyo.
One wonders why the volcanoes deflated. The authors proposed that the release of hydrothermal fluids during the earthquake was the most likely cause for the subsidence. But I would like to propose another option. At Calabozos the deflation area matched very well the resurgent dome, and not the hot spring areas, so I think it could have been magma-driven deflation. The earthquake will have relieved compression built up over decades. It may have thus created extension and opened space for magma underground, causing magma to drain from upper magma chambers into deeper levels of the lithosphere, the volcanoes with shallow storage may have seen some of their magma be removed to fill up space underground, the larger the amount drained, the bigger their magma storage.
Appart from the Calabozos caldera, there are five central volcanoes and numerous scoria cones spread out over the whole area. The central volcanoes are Cerro del Medio, Descabezado Chico, Descabezado Grande, Cerro Azul, and Manantial Pelado.
Cerro del Medio and Descabezado Chico are shield-like edifices made up of lava flows, and with multiple vents, with each volcano having at least 4-5 different scoria cones and or craters, and both are located within the Calabozos Caldera. Cerro del Medio is very eroded and looks relatively old.
Descabezado Chico is younger than Cerro del Medio. It last erupted during the Holocene, producing the Escorias lava flow that we will see later. Apart from the Escoria’s lava flow, there are two scoria cones that are well preserved and are probably from the latest Pleistocene. One of them forms the summit of the shield structure. From this small scoria cone at the summit extend thin lava flows, I’m guessing of dacite composition (because they look a lot like the Escorias flow), and have preserved channels, wrinkles, and other features. Older, thicker flows underlie the younger, thinner flows. Descabezado Chico is located along the axial zone of the resurgent dome. It seems as if the resurgent dome itself is a massive tongue that extends north from the shield. I would guess that Descabezado Chico is the central vent of the very Calabozos system, and is possibly above the feeder of the shallow magma chamber. Chico means small in Spanish, and descabezado means headless. It’s the small headless volcano, according to its name. But I’d say its not so chico, but rather a monster system, you just need to know where to look.
We have the two shields, and then we have the two stratovolcanoes: Descabezado Grande and Cerro Azul, which are located ~18 km southwest of Descabezado Chico. The stratovolcanoes form steep cones that tower 1-1.5 km above the surrounding lava plateau, made of layers of red and black scoriaceous material interbedded with lava flows. Given the dark, mafic-looking scoria that makes up these two volcanoes, I think they are probably mostly basaltic-andesite in composition, but this is a guess of mine since there is not much data available. Cerro Azul is truncated by a crater 800 meters wide at its top. Descabezado Grande is truncated by an even larger crater 1-1.5 km across. The name Descabezado Grande alludes to its shape. Descabezado means headless, and grande is big. It’s the big headless volcano. The size of these craters indicates powerful vulcanian explosions, and plinian or subplinian activity in their past. Both cones are weathered, and apart from their historical activity and one small dacite flow (Alto de las Mulas), I don’t think they have had any earlier postglacial eruptions.
The fifth central structure, Manantial Pelado, forms a cluster of highly weathered scoria cones, and possibly deeply eroded stratovolcano remnants. The area between Manantial Pelado and Descabezado Grande includes some additional eroded remnants of possible stratovolcanoes.
The postglacial eruptions
Appart from the 5 central edifices, there are a number of scattered monogenetic vents. Most of these vents are old and eroded, but several vents are postglacial, from the last ~15,000 years. Five of the monogenetic vents carry basaltic andesite composition. Among these, are 3 postglacial explosion craters, known as La Resolana, ranging from 500 meters to 1 kilometres in diameter and located to the W of Cerro Azul. Two of the explosion craters are very deep and expose more than 100 meters thickness of bedrock in their walls, which was excavated by the explosions, while the third crater filled up and overflowed with lava. One of the two deep craters is partly filled with water, and the other one is right next to a lake, so the phreatic layer seems shallow and there may have been magma-water interaction. To the SW of Cerro Azul are a pair of postglacial scoria cones, crowned with craters of 150 and 350 meters diameter, and with thick aprons of lava, made of many overlapping 10-15 meters-thick tongues of lava with narrow channels, which were formed during long-lasting lava flow eruptions. The area around the explosion craters and scoria cones, for a length of 15 kilometres or more, is partly covered in a dark mantle of scoria. This shows that some of the postglacial basaltic andesite eruptions were very explosive, probably subplinian.
The Calabozos complex seems somewhat bimodal, with postglacial eruptions of basaltic-andesite and dacite, but with no andesite-only flows. Massive dacite lava flows have issued from vents all over the plateau, making four major lava flows: Escorias, Alto de las Mulas, Lengua de Vulcano (Mondaca), and Quizapú. Only the age of the Quizapú flow is known, which is historical. All four seem young enough to be postglacial, however.
Alto de las Mulas is very modest. Compared to its huge brothers, it is almost insignificant, with 0.1 km3 volume. It erupted from a short, 1-kilometre-long fissure, from the flank of Descabezado Grande. The flow is a simple sheet in shape, some 20 meters thick along the front, and possibly around 10 meters thick along the edges close to the fissure, so it’s among the thinner flows. I don’t see any signs of accompanying explosive activity, although the entire area is thickly covered in pumice from the 1932 eruption, so it’s hard to tell.
Another flow, Escorias, erupted from the heart of Calabozos, from Descabezado Chico volcano. A 1.8-km-long fissure opened cross the shield volcano of Descabezado Chico and erupted from both sides of the mountain, each side sourcing lava flows. The flows are thin. From the west side of the mountain erupted a flow that only reaches 10 meters thickness at the very tip of the flow, 5-km downstream from the vent, and is thinner than 10 meters elsewhere along the edges. A larger flow erupted from the eastern side of the descabezado, which is 20-30 meters thick along the edges, as far as 16 km downstream. GVP estimates the Escoria lava flow at a volume of 5 km3, which I think is too much. The flow is not thick enough, and the volume is more likely to be around 2 km3. This shows, I think, exceptionally high effusion rates that produced thin flows with scarce crust thickness. The lava flows are dacites with 64 wt% SiO2, but they have a very dark brownish colour, which is almost black. This shows the lavas are high in molten material with few crystals, when that happens felsic melts freeze into a glassy black-coloured material, like obsidian. Explosivity during the Escorias flow eruption was minimal. The west vent formed a minuscule crater, 100 meters wide. The east vent formed a shallow crater a little under 300 meters wide, with a subtle ring of darkish pyroclastic material. Eruption was basically effusive, with pyroclastic volume being minimal in relation to the lava. Ejecta from both vents is dark-coloured, which I suspect could be andesitic or basaltic-andesitic in composition.
Next to the Manantial Pelado volcano, lies Lengua the Vulcano, which, as the name implies, is a gargantuan lengua (tongue) of lava. It consists of two slightly overlapping sheets of lava that fill a deep glacial valley, with the longest tongue reaching over 100 meters thick at the lava flow front. My guess is that the overall flow averages 150 meters thick or more. At the vent, lava piles up to a height of over 100 meters despite being on the very steep slopes of the U-shaped valley. The total volume, I believe, is probably a bit below 2 km3. The large thickness could suggest this flow may have erupted more slowly, however, the channels are very wide, which could suggest high eruption rates. Maybe it was actually its composition that was different and favoured a strong viscosity and increased thickness. Its composition is rhyodacite with 70wt% SiO2, which is more strongly silicic than the Quizapú and Escorias eruptions. The appearance of the flow seems different too, of a cream colour, much brighter than other flows, although there are some parts and bands which are dark like the Escorias flows. I’m not sure whether the colours could have been given by overlying pyroclastic material, but the cream tone of the flow is different from the pure white pumice of the 1932 eruption, and the Lengua de Vulcano eruption doesn’t seem to have produced substantial explosions, so I think the flow is bright because it is very crystal-rich, because it has felsic minerals that give the flow a brighter tone than the glassy lavas of Quizapú and Escorias, but only close inspection could confirm this. The eruption had very little explosivity, with no cone or crater visible around the vent at all. There is only some possible pumice upslope. One article mentions the Lengua de Vulcano eruption as happening around 1760 and cites personal communication as the evidence. However, without more information, I’m skeptical whether this is accurate.
The Quizapú eruption sequence.
On 26 November 1846, a new eruption broke out from the flank of Cerro Azul stratovolcano. The new vent opened 1.5 km north from the centre of the large summit crater of Cerro Azul. Quizapú was born, or reborn, as this may have been the return from the dead of Cerro Azul. The name Quizapú means “who knows?”, which is what a local said after being asked about the name of the volcano. There was no fumarole or volcano in the place the eruption happened, so of course no one had a name for it. Within 15 days of the outbreak, lava had flowed 7 kilometres to the east.
Not many contemporary details are known of this eruption. No ashfall was reported, so the eruption must have been predominantly effusive. The date of the stop is not entirely clear. Some lavas may have flowed westward until 1853-1854, with the eruption lasting several years, erupting a total volume of about 5 km3, according to existing estimates. The flow field is very complicated. Many tongues of lava were active at different times, most of them with thicknesses somewhere 25-50 meters along the edges, and with up to three overlapping sheets of lava in some areas. The final lavas of the eruption seem to have formed somewhat thicker flows, with 50-150 meters, and in one location up to 150 meters thick along the edge, which only advanced 2-3 km from the vent. The morphology shows this eruption was longer lasting than any other postglacial flows of felsic composition in Calabozos or Laguna del Maule volcanic fields.
The chemistry of this effusive phase is very interesting, the lavas include dacites, andesites, and basaltic andesites. Silica ranges from 53 wt% to 68 wt%, but you can seemingly find every intermediate value. Phenocryst content is about 15 vol%. The more silicic lavas are slightly more crystal poor than the more mafic types. Presumably the lavas erupted are a mixture between the basaltic-andesite and dacite end-members of Calabozos. The flows are very dark coloured.
Starting around 1907, Quizapú started making frequent ash clouds and steam plumes. In 1914, it sent a plume of ash to 7 km in height. Between 1916 and 1926 explosions became more frequent, sometimes happening daily, and incandescence lighted up the volcano at night-time. Explosions weakened a little but continued until 1932.
Suddenly, on 10 April 1932, Quizapú reinvented itself. The postglacial dacite eruptions of the Calabozos Complex have been entirely almost entirely effusive, but the 1932 eruption would be the entire opposite, a fully explosive eruption. A column of ash rose to 30 km high and spread out into an enormous umbrella. Booming sounds rattled doors and windows in Santiago de Chile during 18 hours of continuous plinian eruption, but fortunately, no one was anywhere near the event when it happened. There wasn’t much property damage either. A catastrophic release of water from a lake impounded by 1846-53 lavas, which took place a few months after the plinian eruption, was actually the most destructive event related to the eruption, and caused damage along the Maule River. Total volume erupted is estimated at 9.5 km3. The eruption opened and ended with minor volumes of basaltic-andesite and andesite, but the bulk of the volume is dacitic with 66 wt% SiO2 and 15 vol% phenocrysts.
Quizapú painted the landscape in a white dacite pumice, which turns pink close to the vent. I presume the pink colour is due to high-temperature iron oxidation. Two pyroclastic flows are visible as pink, fluid-looking deposits that run following the steepest lines of descent from Quizapú to a distance of 6 km westward, and some other possible flows reach 7 km down the opposite side, to the east. Interestingly, there are very few pyroclastic flows. Almost all the ejecta went airborne and then came down as showers of pumiceous material that still today mantle the ground for tens of kilometres downwind. A crater 600 meters wide and 200 meters deep formed in this eruption. Given the size of the crater, I expect the intensity of the eruption was lower than that of plinian rhyolite eruptions of Laguna del Maule, even though, perhaps due to its great duration, the volume was very substantial.
Two weeks after the plinian eruption, activity shifted to Descabezado Grande, with plumes of steam rising from the flanks of the headless volcano for the first time in recorded history. At some point during June-July 1932, Descabezado Grande’s north flank started producing explosions. These explosions gouged out a massive crater 900 meters wide, and 200-300 meters deep. Explosions continued into 1933, producing plumes of ash, at times up to several km high. The new crater, now known as Respiradero (literally meaning vent), ejected only lithic material, old lavas of the headless volcano blown to ash-sized bits.
I think the activity of Descabezado Grande is very interesting and poorly understood. Quizapú is 1.5 km north of Cerro Azul summit crater. Respiradero is 1.5 km north of Descabezado Grande summit crater. Each of the new vents represents the reactivation of its respective stratovolcano, which had been dormant since pre-glacial times. I believe this is what happened: the plinian eruption of Quizapú, of the Cerro Azul conduit, decompressed the entire magmatic system, and Descabezado Grande is part of this system, which in turn, when affected by this plinian-induced decompression, had a buildup of gas bubbles, pressurized magmatic gasses trapped in the volcanic conduit eventually broke upwards, blasting out a gaping hole in the side of Descabezado Grande in a series of repeated gas explosions.
The origin of the dacite magmas
A 2012 article uses thermobarometry to estimate that the magmas of Quizapú were stored at about 5-6 km depth, while a 2021 article estimates an even shallower depth of 4 km. In either case, the origin of the dacites seems to be from a very shallow magma chamber. The depth of this magma chamber seems to be slightly more shallow than that of Laguna del Maule, as far as I can tell. But where is the magma chamber located exactly? The only place with good evidence for a shallow magma chamber is the Calabozos resurgent dome where there is topographical evidence of a ~65 km3 resurgence that continued into postglacial times, large-scale deflation during the 2010 mega thrust earthquake, and numerous hot-springs that are found around it. Quizapú erupted almost 10 km3 DRE of magma in less than a century. It must have drawn its magma from a very substantial magma chamber, and the only clear option is Calabozos. Descabezado Grande must be part of the system too, given its behaviour in 1932-33, and, by extension, the Lengua de Vulcano lava and Alto de las Mulas lava flows may have fed from the resurgent dome too. This shows an unusual, largely unrecognized, behaviour. Though it could be similar to the Katmai-Novarupta eruption of 1912. A shallow, felsic magma chamber which regularly supplies magma to three neighbouring stratovolcano systems: Cerro Azul, Descabezado Grande, and Manatial Pelado. In fact, Calabozos itself rarely erupts, unless it does so through the shield volcano at the southern end of the resurgent dome, Descabezado Chico. Unlike Laguna del Maule, which has a ring of cone-sheet-fed vents around its chamber, Calabozos doesn’t erupt around the resurgent dome and instead sends magma to nearby well-established conduits. Calabozos is also a volcano proficient at building up magma through resurgence, and eventually producing VEI-7 eruptions, while having a less silicic dacite-rhyodacite composition than the rhyolite of Laguna del Maule. I’d say Calabozos has a greater subduction influence in its volcanism, and in fact is a stratovolcano complex, while Laguna del Maule is more intra-plate-like.
The silicic trio of the Maule-Neuquen
Domuyo, Laguna del Maule, and Calabozos, the three silicic volcanoes of the Maule-Neuquen, are next to each other and have silicic compositions, but are very different to each other. Combined, they make up a vigorous ongoing silicic flare-up. Domuyo, in the Neuquén Province of Argentina, has the most magma but the least eruptions. Laguna del Maule, has the least magma and the most eruptions. While Calabozos has very different eruptive dynamics to the other two, and is also predominantly dacitic, while the other two are predominantly rhyolitic.
This is my take on the three systems potential:
Domuyo I think has the potential for the largest eruption, some 150 km3 of magma, but this is probably a volcano with a really, really long history behind, and that resurgent dome may have been there for many hundreds of thousands of years. In the scale of human lifetimes, the possibility of Domuyo going caldera seems insignificant.
I don’t think Laguna del Maule has enough magma for a VEI-7. Although many would disagree with this. Only a small VEI-6, and maybe not even that at present. I‘m not too sure what to expect from this system in the future. The youngest two eruptions have probably been rhyodacitic. Could it be that the system has “weakened” from its former rhyolitic eruptions to rhyodacitic ones? I don’t know.
Calabozos has rapid caldera cycles. The previous two ignimbrites happened 150,000 years apart, and 150,000 years have passed since the last one. The system has been overflowing dacite from multiple satellite systems, and the historical series of eruptions is incredibly rare. Something is going on, although I’m not sure what. I think Calabozos will be the next one to do a major caldera-forming eruption, a low end VEI-7, possibly. Thankfully, this volcano is in a remote uninhabited area where direct effects of the eruption will not be too damaging, and in the southern hemisphere so that the impact of a volcanic winter impact will be lessened. The volcano is also probably spent after the whole Quizapú sequence, and it might very well take a few centuries or more for it to erupt again.
And thus this series about the Payenia Volcanic Province, and the Maule-Neuquén silicic volcanoes comes to an end. Although there are many questions that remain about this region. Like, for example, flat slat or no flat slab? I’m not as sure as I was during the past article about this question. I ended up talking a lot more about this region than I meant to, but nowhere near as much as I wished I was capable of.
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Hildreth, W. y R.E. Drake, 1992. Volcán Quizapu, Chilean Andes.
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Hildreth, W., Grunder, A. L., & Drake, R. E. (1984). The Loma Seca Tuff and the Calabozos caldera: A major ash-flow and caldera complex in the southern Andes of central Chile. Geological Society of America Bulletin, 95(1), 45. https://doi.org/10.1130/0016-7606(1984)95
Pritchard, M. E., Jay, J. A., Aron, F., Henderson, S. W., & Lara, L. M. (2013). Subsidence at southern Andes volcanoes induced by the 2010 Maule, Chile earthquake. Nature Geoscience, 6(8), 632–636. https://doi.org/10.1038/ngeo1855
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