Volcanoes of the Andean SSVZ 2, Chile |

We will take a look at the string of volcanoes in the northern portion of the southern segment of the Andean Southern Volcanic Zone (SSVZ).  This segment has one recently active volcano, Chaiten in the middle.  There are 8 volcanic centers along the 194 km volcanic front between Yanteles and Yate.   These volcanoes from N – S include Yate, Hornopiren, Apagado, Huequi, Michinmahuida, Chaten, Corcovado and Yanteles.  There are two groupings of volcanoes within relatively close proximity (20 km or so).  In the N, these include Yate, Hornopiren and Apagado.  In the S, these are Michinmahuida and Chaiten.  The other three are spaced near the average for the SSVZ.

We visited volcanoes in this part of Chile with a few posts, most recently our 2023 Volcanoes of the Andean SSVZ post which looked at volcanoes from Palena to Hudson.  Granyia covered Chaiten in 2018. 

The region is called Los Lagos, Region of the Lakes.  The largest city in the region is Puerto Montt, with a population of over 210,000, located at the NW part of the region.  Puerto Mott is 59 km NW from Yate, the northernmost of our string of volcanoes.  The economy of the region is primarily services and tourism, with aquaculture (salmon farming), forestry and cattle ranching.

Original people in this part of Chile were the Huillche.  Monte Verde is one of the oldest archaeological sites in the Americas.  The Spanish arrived in 1567.  The 48,600 km2 region is sparsely populated, with around 825,000 residents.  Most of these are either in Puerto Montt or in coastal villages connected by the road system.  People generally do not live in close proximity to the volcanoes, with for the most part are unmonitored and unresearched until one unexpectedly erupts like Chaiten in 2008, destroying its neighboring seaside town, Chaiten with lahars and mudflows from the eruption.

The two main national parks in the region are Parque Nacional Hornopiren and Parque Nacionial Corcovado. 

Volcanoes in Chile are monitored by Servicio Nacional de Geologia y Mineria (SERNAGEOMIN). 

Volcanoes

I am somewhat arbitrarily limiting discussion of these systems to those in the northern segment of the SSVZ, with Yate being the northernmost volcano in this post, even though Calbuco, Cayute – La Vigueria, Cuernos del Diablo, Osomo, Tronador, Puntiagudo-Cordon Cenizoz, Antillanca, Cerro Pantoja, and Puyehue-Cordon Caulle are located within 136 km of Yate, mostly to the N and NE.  Sounds like an idea for a future post. 

Yate

Yate is a large, glaciated, heavily eroded stratovolcano located along the major regional Liquine – Ofqui Fault Zone.  It is located 10 km N of the smaller Hornopiern volcano.  The volcano tops out at 2,187 m and has recent parasitic cones on tis flanks.  The volcano is constructed from at least 6 eruptive centers located along a NW-trending fissure 7.5 km long.  The most recent activity was from basaltic andesitic pyroclastic cones on its NW and W flanks.  There are no historic eruptions known, though Smithsonian GVP lists 1090 as the last known eruption, that came from SE flank, producing the Ya2 Tephra.  The cones look fresh and are thought to be at least Holocene.  The area is sparsely populated with 6,100 within 30 km of the volcano and 315,000 within 100 km. 

The volcano is most known for a deadly landslide in Feb 1965 that put a debris flow of ice and rock down a narrow gully.  It descended 1,500 m and flowed into neighboring Lake Cabrera.  This created a seiche, which swept through the community of Lago Cabrera, destroying it and killing 27.  There was virtually no warning.  The event is considered to be the worst volcano-related loss of life in Chile since the 1948 – 1949 Villarrica eruptions.  The debris field is still visible.  The landslide was triggered by heavy summer rains.  There was a second debris avalanche in 2001. 

The ice and rock detached at the 2,000 m elevation, and reached speeds of nearly 145 km/hr before entering the lake.  The seiche was 25 m high with a 60 m runup on the W end of the lake where the settlement was located.  The underlying fault zone appears to control the preferential direction of collapse, weakening underlying rock, and preferentially orienting glacial valleys through a feedback mechanism where collapse events are followed by rapid glacial erosion. 

Hornoprien

Hornopiren is located 11 km SSE of Yate, midway between Yate and the town of Hornopiren on the shore of the Gulf of Ancud (Pacific Ocean), another 10 km SSE of the Hornopiren.  The volcano is a young andesitic / basaltic andesitic stratovolcano that tops out at 1,572 m.  Like Yate, it is also built along the regional Liquine – Ofqui Fault System.  There are prominent lava flows stretching beyond the SW flank, onto the graben floor.  The volcano was said to be in eruption in 1835, but there are no known details of either the eruption or the report.  Smithsonian GVP is carrying a VEI 4 eruption around 5.7 ka.  The only other eruption took place around 340 AD. 

Apagado

Volcan Apagado (Hualiaque, Hualaihue) is the third volcano of this loose northern group, located some 13 km W of Hornopiren, 20 km SW of Yate, 13 km W of the volcanic front and the regional Liquine – Ofqui fault system.  It is a basaltic pyroclastic cone with scattered vegetation on its flanks.  It tops out at 1,210 m, with a base diameter of 2 km.  It is topped with a well-preserved 400 m diameter summit crater.  Like Yate and Hornopiren, the region is remote, sparsely populated.  The volcano is located on a peninsula bordered by the Reloncavi Estuary to the N, Reloncavi Sound to the SE, and Gulf of Ancud to the W.  Apagado is the youngest eruptive center of the older Hualiaque volcano.  It is located in a 6 km diameter depression opening to the SW.

There is a single known surprisingly large eruption from Apagado.  This eruption was 2.9 ka, estimated as a VEI 5.3 Plinian eruption that put a plume 13 – 24 km into the atmosphere.  Explosive basalt eruptions are uncommon, especially from scoria cones.  The eruption distributed the Ap-1, Ap-2 and Ap-3 units. 

Ap-1 is a widespread tephra produced in three stages of eruption.  It is generally dispersed to the E and SE of the volcano.  The initial stage was a lithic-rich opening Plinian blast that created a tuff ring.  Deposits are greater than 10 m thick near the vent.  The second stage was scoria rich.  Products of the closing stage are listed as the top visible layer, but not well described.  Ap-2 created scoria flows and surge deposits next to the vent.  These were not widespread.  The final stage, Ap-3 built the current scoria cone and lava flow from the breach in the cone crater.

Huequi

Huequi is a small, unglaciated dome complex in the center of the Huequi peninsula in Ancud Bay, 62 km N of Chaiten.  70 km S of Yate.  The volcano is located in a remote region and was little studied until a 2011 paper by Watt, et al.  The Ayacara peninsula is bounded by a fjord on the E, part of the regional Liquine Ofqui fault zone, and the Gulf of Ancud to the W.  It is inaccessible by road.  The closest settlements are small coastal villages.  1,000 live within 30 km, 108,000 within 100 km.

The volcano is constructed of several coalescing basaltic andesitic to dacitic domes located within a collapse depression.  It is surrounded by debris avalanche deposits extended to the NW.  The complex tops out at 1,318 m.  Field sampling was done in Feb 2008.  The S side of the volcano was inaccessible and not mapped. 

There is a curved depression either caused by regional faulting or an early, large collapse of the ancestral volcano, generating much of the debris to the NW.  The summit is thought to date from the most recent activity in the 20^th Century.  There is a deep valley at the margin between two of the domes that provides a route for multiple debris avalanches creating a fan to the W.  There have been at least three main collapses.  All deposits are densely vegetated with trees not noticeably younger than those on the opposite slopes of the volcano.

The youngest dome is at the head of the NW collapse scar.  This scar exposes older dome rocks which can be traced across the valley.  There are massive columnar jointed rocks, and a range of coloration and fracturing suggesting hydrothermal alteration. 

Repeated dome forming eruptions at Huequi is unusual in the SSVZ.  Volcanoes here are usually much larger (other than Chaiten), with significant lava flows, cinder cones and the occasional large explosive eruption.  Eruptive style here is likely due to the eruption of highly viscous, crystal rich andesites. 

While activity is dominated by repeated dome forming eruptions and collapses, there are tephras around the volcano from moderate explosive activity.  The oldest of these, T1 is up to a meter thick within a kilometer from the present summit.  The thicker T2 deposits, also a white pumice, are thought to have come from the 1890 – 1920 eruptive period.  It is thickest to the E of the summit.  The pumice appears to have come from a series of Vulcanian explosions during the most recent eruptive period. 

Michinmahuida

Volcan Michinmahuida (Michinmavida) and Chaiten are separated by only 17 km.  Michinmahuida is located on the main Liquine – Ofqui Fault Zone.  Chaiten is located to the W of the main volcano.  Some papers treat these two volcanoes as part of the same system.  Some do not.  I will treat them as related, but separate systems for purposes of this post.

Like most other volcanoes in this part of the SSVZ, Michinmahuida is a heavily glaciated, andesitic / basaltic andesitic stratovolcano.  It tops out at 2,452 m.  The massive structure is topped with a 3 km wide caldera.  The edifice is elongated in the NE – SW direction.  There is a recent eruptive center on the ENE side of the complex.  8,000 live within 30 km, 64,000 within 100 km. 

Michinmahuida generally erupts andesites, basaltic andesites, and the occasional dacite.  Basaltic andesites are erupted from the flank scoria cones.  Andesites and the single dacite were erupted from the main vent or the upper flank.  In contrast, major eruptions from Chaiten are all rhyolites.

There are multiple tephra layers from eruptions from Michinmahuida.  Some of these are major eruptions.  Some are smaller tephras from smaller cones on its flanks.  The oldest of these is an andesite dated around 10.8 ka.  It was closely followed by the Amarillo ignimbrite at 10.5 ka.  There were at least three other layers, one an andesite (main vent) and two basaltic andesites (flank scoria cones) between 10.5 ka and the Mic1 andesite 7.2 ka.  There are at least four Chaiten rhyolite layers among these from Michinmahuida erupted in the last 9.7 ka. 

The Amarillo ignimbrite is a dark, unwelded pyroclastic deposit.  It typically flattened erosion features on the flank of the volcano.  The deposit is up to 80 m thick and well preserved up to 20 km from the present-day summit.  The eruption is dated around 10.5 Ma and may be the largest in the SVZ over the last 10 ka.  Pre-erosion volume is estimated at around 10 km3.  This is considered to be a preliminary estimate that should rise with additional research.  Tephra fall deposits associated with the eruption have not been definitively found.  However, there are extensive fall deposits in the region around the date of the eruption that have yet to be analyzed.  There was an event that put enough ash to collapse roofs in a couple archeological sites in Patagonia that may be connected to this eruption or more likely its immediate predecessor.  Clearly, additional work needs to be done to tie the bits and pieces of data together.  This VEI 6 eruption ejected at least 10 km3 of material and is thought to have created the summit caldera. 

The Mic1 deposit came from a VEI 5.2 eruption around 7.2 ka.  The deposits are a coarse reddish andesitic scoria fall.  The deposit is 20 cm thick 10 km SE from the volcano.  It is one of the coarsest grained fall deposits from this volcano at this distance.  The deposit has been identified 70 km E of the volcano, with a layer less than 10 cm.  Volume of this deposit is estimated at 2 km3. 

The originally designated Mic2 deposit around 5.0 ka ended up coming from Chaiten and is now referred to as Cha2 or Cha2/Mic2.  It was originally tied to an eruption from Michinmahuida.  However, as Chaiten is the only volcano in this part of the SSVZ that erupts rhyolites, the source of this deposit was reassigned. 

There are another five scoria / tephra layers found in close proximity to Michinmuhuida since the Mic1 eruption 7.2 ka, four of these within the last 1,200 years.  One of these is the 0.1 km3 F2C dacite around 4.0 ka from a VEI 4.0 eruption.  Eruptions were reported in 1742.  Charles Darwin observed activity in 1834.  The most recent eruption was the 1834 – 1835 eruption sequence from one of the flank scoria cones.  The Feb – Mar 1835 part of this produced a lava flow from a flank vent.  Lahars from this eruption sequence reached the coast at Punta Chana. 

Chaiten

Chaitan is located some 20 km W of the main edifice of Michinmahuida.  It is topped with a 3 km post-glacial caldera.  A rhyolite obsidian lava dome was built within the caldera.  The caldera is drained to the W by the Blanco River.  This river flows into the Gulf of Corcovado.  The volcano tops out at 1,122 m and is the only volcano in the region that erupts rhyolites.  Magma storage beneath the volcano is at 10 km. 

There are obsidian cobbles found throughout the length of the Blanco River.  These cobbles were used as prehistoric artifacts along the Pacific coast, as far away as 400 km N and S of the source.  Some of these historic sites are dated as old as 5.6 ka. 

The former town and regional capital of Chaiten is 10km SSW from the caldera.  It was destroyed by flooding and lahars produced by the 2008 eruption.  The river flooded, destroying much of it as it chose a new channel through the center of town.  The town was completely evacuated in early May when Chaiten erupted.  The regional capital was also moved.  In 2009, the Chilean government proposed to rebuild Chaiten on the coast about 10 km N of its current location.  The proposed relocation has since become the center of a national political controversy. 

Chaiten is a surprising volcano, in that it was thought to be inactive for the last 9 ka prior to the 2008 eruption.  Instead, it has at least four VEI 4-5 eruptions over that period.  Two of these (Cha1 and Cha2) are among the largest in the SSVZ over the last 11 ka.  A smaller eruption took place between Cha1 and Cha2 (before 7.6 ka).  There are multiple lahar deposits along the Chaiten River not connected to volcanic eruptions. 

The largest of these eruptions, a VEI 5.5 ejected 5.5 km3, Cha1 fall deposit which was incorrectly thought to have come from the only Holocene eruption of Chaiten prior to the 2008 eruption.  This was a white to yellow coarse pumice layer, and a pink – white coarse ash found over 100 km from the volcano.  Dispersion of the ash N and E was complex and changed a bit during the eruption.  There is 5 cm thick yellow, fine lapilli fall deposit over 70 km SE from the volcano.  There are no unconsolidated fall deposits from Cha1 above 1,000 m elevation.  The best estimate for the date of this eruption is 9.7 ka, slightly younger than the Amarillo ignimbrite.  The Cha1 tephra is estimated at 5.5 km3.

The newly designated Cha2 eruption took place some 5.0 ka, producing the Cha2/ Mic2 fall deposit. This is a coarse-grained yellow pumice layer found 85 km E in Argentina, where it is a few tens of cm thick.  There is a proximal pyroclastic layer at Chaiten dated 4.95 ka.  Paloesol under the fall deposit is dated 5.4 – 5.1 ka.  There is a several meter thick pyroclastic deposit a few kilometers N of the crater that contains pieces of the underlying soil.  There are some peat layer dating results that suggest this may have come from two closely spaced eruptions.  No fall deposits support this conclusion.  Estimated tephra volume for this eruption is 4.7 km3.  Magma for Cha2 was stored at 7 km. 

The first layer of the Cha2 deposit is a coarse debris flow deposit containing rocks and large chunks of wood (no charring), pumice and obsidian chops.  This flow is covered by a sequence of pyroclastic flow, surge and fall deposits.  It is topped with a pale-yellow fine ash fall deposit.  The early debris flow may have come from destruction of an old dome and vent clearing during the opening stages of a large explosive eruption.  The flow cleared vegetation from the slopes of the volcano.  This is the largest volume tephra deposit in the SSVZ. 

There are deposits from small, young eruptive events younger than Cha2.  These have been named Cha3 and Cha4.  They are each a few centimeters thick separated by soils.  Neither of these layers have been dated or characterized.

The 17^th Century eruption from Chaiten took place some 300 years ago, 1625 – 1685.  It was a VEI 4.7 that produced 0.5 km3 of material, about the same size as the 2008 eruption.  There is a soil directly on top of the ash layer.  This eruption deposited pyroclastic material 20 – 30 km SW of the volcano and triggered lahars down the Chaiten River.  Note that the Chaiten River, which drains to the S is called the Rio Blanco in some papers and reports, particularly describing the 2008 eruption.  I believe this to be in error, as the Rio Blanco is located to the N of the volcano, draining generally due W.

The 2008 eruption was a VEI 4.9 that produced 0.75 km3 of material.  The eruption progressed quickly with seismicity only a day before it erupted.  The eruption started May 2 with a plume that quickly grew to 21 km.  The eruption produced significant ashfall over the next several days, with a plume estimated at 30 km.  Evacuations were ordered for anyone within 50 km of the volcano.  Lahars and floods inundated the nearby town of Chaiten.  Most evacuation out of Chaiten was done by boat. 

The initial eruption destroyed part of the old dome.  A second dome (Dome 2) started being extruded as the eruption wound down.  There were pyroclastic surges in addition to lahars, mudflows and ashfall.  The new dome was first observed on May 24, confirmed by Nov.  By Dec 2008, the new dome had mostly replaced the pre-eruption dome.  It was briefly topped by a tephra cone by May 26.  A scar on the side of the ancient dome was observed in late July 2008.  It was ascribed to a lateral blast from the dome. 

Seismicity diminished though July.  Activity continued through Nov at a lower level with dome growth, plumes, and seismicity.  Plumes were generally less than 2 km high with the occasional puff to 4 km.  There was a pulse of higher activity in late Oct, likely due to a landslide from the active dome (Dome 2).  The growth of a second new dome (Dome 3) was first observed Sept 2009. 

Heavy rains struck the region in early Nov, flooding Chaiten once again.  New lahars followed the flood waters.  The alert level was finally lowered from Red to Yellow May 2010.  It was again lowered to Green May 2011. 

It is unusual for a volcano active several times over a 10 ka period to have erupted virtually identical magmas.  Chaiten is erupting rhyolites, producing tephras, pumices, obsidians, and lavas.  This is in stark contrast to the diverse range of magmas erupted by neighboring systems.  Whatever is happening it taking place 20 km closer to the trench than a large, typical front arc andesitic stratovolcano (Mchinmauhuida).  Chaitan erupted explosively more frequently than its near neighbors Michinmahuida, Corcovado, Yanteles and Huequi.  Several large explosive eruptions from volcanoes in this region could remain unrecognized.  Eruption frequencies at several of the remote volcanoes of the SSVZ may be higher than currently though. 

Corcovado

Volcan Corcovado is a heavily eroded basaltic / andesitic basaltic stratovolcano that tops out at 1,826 m, 32 km SSW from Chaiten.  While the core is heavily eroded, it has multiple relatively recent cinder cones on its flanks.  There are lava flows around the base that appear to have come from the cinder cones.  These flows are heavily vegetated, so are not all that recent.  There were historic reports of an eruption beginning in Nov 1934, ending in 1935 with a lava flow from one of the flank cones.  However, no such new lava flow exists.  The eruption is now thought to have come from neighboring Michinmahuida volcano, which was active at the time.  The observations were by passing mariners in the Gulf of Corcovado.  Once again, the region is sparsely populated, with 5,500 within 30 km.  62,000 within 100 km. 

There are three tephras associated with explosive eruptions of varying size (Cor1, Cor2 and Cor3).  Cor1 is the oldest layer, with small particle size, and accretionary lapilli.  It was produced by a VEI 4.6 eruption that ejected 0.4 ikm3.  Products suggest a water-rich eruption.  It is 50 cm thick at 25 km NE of the volcano.  The layer is estimated at 9.6 ka and overlies the Yan1 tephra from the 9.2 ka Yanteles eruption. 

It is in turn covered by the Cor2 tephra at 8.0 ka.  This tephra came from a VEI 4.8 eruption the ejected 0.6 km3 of material.  It is thinner, 35 cm at 25 km NE.  It may also be present as a thin layer 120 km E. 

The youngest tephra (Cor3) is the thickest, 70 cm thick at 25 km NE of the volcano.  It was erupted form a VEI 5.0 eruption that ejected at least 1.0 km3 of material.  It consists of fine to medium lapilli mixed and weathered to a yellow color.  It is also visible 120 km NE of the volcano.  The layer is dated 6.9 ka. 

Yanteles

Volcan Yanteles is a glaciated volcanic massif locates dome 60 km S of the city of Chaiten, 30 km S of Corcovado.  The 1,790 m massif is about 10 km long, with the higher eroded peaks located 5 km E.  The Yanteles vent is located at the NE end of the structure.  There are several Holocene tephra layers attributed to this volcano.  There were reports of an eruption Feb 1835 that may be connected to an earthquake.  There were black areas observed on the mountain after the earthquake, but never explored.  This region is also sparsely populated with 1,300 within 20 km, 45.000 within 100 km. 

There is a tephra (Yan1) over 1 m thick some 35 km NE of the volcano, erupted from a VEI 4.8 eruption that produced 0.6 km3.  There is a thin layer of the same tephra found in Argentina, some 120 km NE of the volcano.  The deposit is a yellow andesitic pumice and medium diameter lapilli.  The tephra is dated around 9.2 ka.  There are younger and smaller tephras attributed to this volcano. 

Tectonics

A more complete discussion of tectonics in this part of Chile can be found in our original post on the SSVZ.  What follows is a truncated version of that discussion. 

Volcanic activity in the Andean SVZ is caused by subduction of the Nazca Plate beneath the South American Plate.  Oblique subduction takes place along the Chile Trench parallel with the South American coastline.  The subduction is complex as there is a triple junction between the two plates and the Antarctica Plate to the south.  This has created a triple junction just offshore, some 280 km E of Hudson Volcano.  Over the last 15 – 20 Ma, this junction migrated northward along the continental margin due to the oblique collision between the ridge and trench and the northern movement of the Antarctica Plate.  The age of the Nazca Plate subducting into the Chile Trench offshore, is less than 33 Ma. 

Volcanism in southern Chile takes place in two zones – the Southern Volcanic Zone (SVZ) and the Austral Volcanic Zone (AVZ).  The SVZ is a 1,400 km long chain with 60 stratovolcanoes, three large caldera complexes, and numerous monogenetic eruptive centers.  It is divided into four segments:  The Northern (VSVZ), transitional (TSVZ), central (CZVZ) and southern (SSVZ).  Segments are differentiated by geometry of the volcanic arc and chemistry of erupted magmas, though the exact segment boundaries are still debated.  Crust thickness in this zone is around 30 km.  Erupted magmas vary generally with location along the zones, with more evolved magmas to the north in the Central Volcanic Zone. 

Stratovolcanoes appear to be located in the middle of surface block segments between surface fault lines.  Monogenetic volcanoes appear to be located along NNE – SSW or NE – SW fault segments, generally parallel with the Liquine – Ofqui fault system.  Erupted magmas in the SSVZ are thought to be from mantle fluids and melted subducted sediments.  Average extrusion rates of volcanic activity in the Andes decrease southwards. 

Conclusions

The southern segment of the Southern Andes Volcanic Zone (SSVZ) is an example of volcanic activity in a complex tectonic environment.  Sadly, this part of South America is remote, sparsely populated and generally not monitored.  But there are volcanoes, one particularly dangerous and active volcano in Chaiten.  As with many other parts of the world, the more we know about the region, the more active and dangerous seemingly quiescent volcanoes are found to be.  The 2008 eruption of Chaiten was a huge surprise.  I don’t think it will be the last one.  This is a part of the world where remote sensing will be among the first notification of an imminent or active eruption. 

Additional information

Holocene tephrachronology of the southernmost part (42°30’ – 45°S) of the Andean Southern Volcanic Zone, Naranjo & Stern, Dec 2004

Holocene tephrachronology of the Hualaihue region (Andean southern volcanic zone, ~ 42°S(, southern Chile, Watt, et al, Dec 2011

Tehprachronology of the southernmost Andean Southern Volcanic Zone, Chile, Weller & Stern, Aug 2015 

Geology, petrology and geochemisty of the dome complex of Hueque volcano, southern Chile, Watt, et al, Jul 2011

Apagado volcano scoria cone (Southern Andes, 42°S): a basaltic Plinian eruption at 2,480 yB.P, M Mella, Jan 2013

Paleoecology of later Quaternary deposits in Chiloe Continental, Chile, Heusser, et al, 1992

Holocene record of large explosive eruptions from Chaiten and Micninmahuida volcanoes, Chile, Amigo, et al, May 2013

Evidence of mid- to late-Holocene explosive rhyolitic eruptions from Chaiten volcano, Chile, Watt, et al, May 2013 

Chaiten (Chaiten Volcano) – Chile, J Ball, Geology.com

A thicketeering mission on Hornopiren volcano, DC Haney, voyageoftherascal.com, Jan 2016

The 2008 eruption of the Chaiten Volcano, Chile: a preliminary report, LE Lara, Jan 2009