The Chilean Lake District is a zone in southern Chile defined by multiple lakes in the Andean foothills. It stretches nearly 1,000 km along the Chilean – Argentine border. The region is spectacularly beautiful with multiple lakes interspersed with volcanoes and outcrops of volcanic rocks. Volcanoes stretch 500 km from Llaima in the north to Chaiten in the south. Most of these are on the Chilean side of the border. Two volcanoes, Lanin and the Huanquihue Group are located on the Argentine side of the border, also known as Patagonia. This post will look at the neighboring volcanoes.
Lanin volcano and the Huanquihue Group are separated by 28 km with four long mostly glacial lakes arrayed between them. The largest of these, Lago Heuchulafquen lies mainly to the E of the N – S line between the two volcanoes. Around the line between the two volcanoes, it forks into Lago Paimun to the N and Lago Equlafquen to the S. Both of these lakes lie to the W of the N – Line. A fourth lake Lago Curruhue lies generally to the W of the Huanquihue Group to the S of the larger Lago Huechulafquen.
The area on the Argentine side of the border around the volcanoes has been designated the Lanin National Park. On the Chilean side, it is called the Villarrica National Park. The park is forested, with roads and trails available. Camping and fishing are popular sports activities, particularly fishing for trout and salmon in local lakes, streams and rivers.
Lanin has a thriving climbing business, as the two-day climb is considered to be a great introduction to mountaineering in the Andes. There are two routes up the mountain. The normal route is a relatively easy ascent on volcanic rock and snow. The south face route is more challenging as it traverses glaciers on the volcano. It is only recommended for seasoned, skilled climbers who have ice climbing skills.
Climate is generally moist temperate when not at altitude. Average temps range from 4 C in the winter to 20 C in the summer. Normal precipitation is around 180 cm, though it can be as much as 400 cm in locations. The rainy season is May – Aug and snow can fall anytime from May – Oct.
The largest city near the region, San Martin de los Andes, is 36 km S from the Huanquihue Group at the eastern end of Lake Lacar. It has a population of nearly 24,000 and is considered the gateway into the park and winter skiing. Local logging was phased out decades ago following designation of the region as a park and the economy of the city changed.
This area is sparsely populated with only 3,500 within 30 km and 190,000 within 100 km of the Huanquihue Group.
There are multiple active volcanoes surrounding this region along the Andean cordillera. As such, it is difficult to determine which interbedded fall deposits belong to which eruption. Fortunately, the Lake District has a large number of lakes that mostly preserve fall deposits in order. Once you can figure out which deposit belongs to which eruption, sorting this all out gets much easier. There are multiple papers on precisely this topic in the region around Lanin and Huanquihie. The bad news is that only the two most recent eruptions from Huanquihue left easily determined eruption markers.
Prevailing winds in the region are generally be W – E, so eruptions of northernmost and southernmost volcanoes tend not to deposit significant amounts of ashfall in the region, though the larger eruptions do so. Most of the deposits come from volcanoes to the immediate west.
Close active volcanoes to the region are Caburgua – Huelemolle to the NW, Villarrica and Quetrupillan to the immediate W of Lanin. Mocho – Choshuenco is to the immediate W of Huanquihue, Carran – Los Venados to the SW, and Puyehue – Cordon Caulle farther to the SW. The 2011 Puyehue eruption was large enough to deposit ash across the region.
The Villarrica – Lanin volcanic chain includes three major stratovolcanoes, 5 deeply eroded Pleistocene volcanoes, 20 monogenetic volcanoes and two maars. Villarrica erupts mainly basalts and basaltic andesites. It has an external 6.5 km elliptical caldera that formed before the height of the last glacial maximum. It was remarkably explosive 14,000 – 1,600 years ago, producing at least two major basaltic – andesitic ignimbrites 13,800 and 3,700 years ago. There is a more recent 2 km diameter summit caldera on the NW edge of the older caldera. The present stratocone has been built inside the newer summit caldera by repeated strombolian eruptions. There are at least 30 pyroclastic cones located on its NW and S flanks. Villarrica is considered currently active.
Quetrupillan volcano is a compound stratovolcano built of basalt to dacites. It has extensive postglacial eruptive record with multiple pyroclastic and ashfall deposits. There are at least two nested calderas. As with Villarrica, the older caldera is larger. The most recent one formed during a post-glacial eruption. There are domes and coulees around the caldera walls and scoria cones on the flanks.
The 5 heavily eroded stratovolcanoes along the chain are generally basaltic with noticeable lava flows. In places, they have been eroded down to feeder dikes on the flanks.
Lanin is the easternmost volcano in a 60 km long NW – SE chain of three stratovolcanoes – Lanin, Quetrupillan and Villarrica. The alignment appears to be based on an underlying fault at right angles to the generally N – S alignment of the Andes. There are a number of older eroded remains of stratovolcanoes along the lineament. Lanin is the least active of volcanoes along the chain.
Lanin is a large, simple stratovolcano. It tops out at 3,747 m, 2,500 m above surrounding ground level. It covers around 220 km3 and has an estimated volume of 180 km3. The steep slopes are partially glacier covered. There is dome that produced a blocky lava flow in the summit area on the N flank. There are multiple flank vents, pyroclastic and cinder cones on the flanks of Lanin. There is at least one flank collapse amphitheater on its flanks.
The oldest Lanin structural Unit 1 is generally massive dacitic lavas. All of these show columnar joints and are up to 300 m thick. Vents for these lavas have not been observed. Age is unknown but should be older than 200,000 years. Lanin Unit 2 is interbedded basalt lava flows and volcaniclastic units. These form the base section of the current volcano. They are significantly glacially eroded. The oldest dated flow is 207,000 years old. These layering show pyroclastics, lahars, lava flows typical of ice-covered stratovolcanoes. Some of the layers were emplaced below the glacier cap. Upper levels of Unit 2 should be older than the last glacial advance in the region 33,500 – 14,000 years ago.
Lanin Unit 3 are lava flows that built the main inner structure of the present cone. These basalts and andesites are discontinuous and partially covered by younger Lanin Unit 4 flows. These do not show glacial erosion features, rather deep river erosion and gravitational collapse scarps. These likely erupted from the summit, are up to 150 m thick in places, with a maximum age of 14,000 years.
The final Lanin Unit 4 was erupted post glacially and produced multiple lava flows and pristine pyroclastic deposits. Multiple flows were extruded from the flank and cover a structure on the cone slope interpreted as a caldera collapse rim that likely formed in Lanin Unit 3. There is a dacitic lava dome on the N flank with coulees up to 6 km that produced a block and ash flow dated around 2,170 years ago. There is an extensive basaltic field on the N flank that reached all the way downslope to neighboring Quillelhue Lake. This field produced multiple pahoehoe basalts, with low effusion rates and tube-fed lavas. There is a pyroclastic flow deposit dating 1,650 years ago that covers the basalts.
Activity at Lanin has been different from its neighbors. It is a simple stratovolcano built by repeated effusive cycles. The suspected caldera on the N and W flanks may be a Hawaiian style collapse caldera rather than an explosively formed one. Lanin does not show visible volcanic activity or a recent eruptive record like its neighbors. The eruptive mechanism for Lanin is effusive and thought to be closely related to crystallization in a shallow magma chamber. The intermittent magma pulses may be related to a magma source some distance from the volcano. The steep sides of Lanin make it a hazardous volcano mainly due to lahars and sector collapses.
The most recent activity from Lanin took place in the vicinity of the Arenal Volcano in the W end of the basement foothills S of Lanin. This is a tuff ring that produced deposits as far as 3 km E and SE. Exposures are scarce and not easy to reach. Estimated thickness of deposits near the cone are 20 – 30 m. Rocks show hyaloclasts, indicating the eruption took place in the presence of water.
The Smithsonian GVP lists little in the way of eruptive history for the volcano, with 6 smallish eruptions between 2,500 – 1,500 years ago. Older eruptions took place some 8,300 and 11,200 years ago. There was a seismic swarm of 59 long period volcanic – tectonic events that lasted for 45 minutes on Feb 15, 2017. This prompted SERNAGEOMIN to raise the Alert Level to Yellow. ONEMI raised the Alert Level to Yellow for the neighboring community of Curarrehue 32 km N for a time. Both Alert Levels have long returned to Green.
The Huanquihue Group is a group of at least four volcanic structures in the Andes in western Argentina (Patagonia). The two most recent eruptions took place from the La Angostura cone on the northern side of neighboring Epulafquen Lake and from Achin – Niellu to the S of the lake. There are at least three other eroded basaltic stratovolcanoes in the immediate region, with Huanquihue to the S. Volcanism appears to be associated with the Liquine – Ofqui Fault. The two most recent eruptions produced basaltic trachyandesite ashfalls and an a’a lava flow.
The La Angostura Cone is located on the northern shore of Epulafquen lake. It built into the lake itself from the north creating a feature locally known as La Angostura (The Narrowing). The widespread deposits indicate the structure is best described as a tuff ring with significant involvement of water during its eruption. The crater shows two rims. There are hyaloclasts indicating water involvement during its eruption. There is an earlier ashfall with no known terrestrial exposures noted, was also produced by a VEI 3 eruption that ejected perhaps 3 km3 of material. This material made it perhaps 65 km from the source. This one was dated some 4,117 years ago. It was identified via lake sediment drilling and core sample analysis. The source of this eruption has not been identified that I could find but may have been La Angostura.
The most recent activity from the Achin – Niellu (Cerro Escorial or Huanquihue volcano) cinder cone produced strombolian fall deposits. The cone is a steep, asymmetric pyroclastic cone. It is constructed of well-sorted black lapilli. There are consolidated beds within the main crater and evidence of fumarole activity. There are three units associated with the cone.
The lava unit (El Escorial) is a basaltic a’a flow with open feeding channels. It appears to be very new and fresh. As the region is a humid zone, this it thought to be clear evidence of its youth. The flow enters neighboring Epulafquen lake to the north, building a flow peninsula into the glacial lake on part of the southern shoreline. The lava flow is layered between explosive deposits. There are also oral reports of a recent eruption the end of the 17th Century that may have created the recent lava flow from the base of the Achin – Niellu cinder cone dated around 200 years ago.
Pyroclastic deposits related to this unit cover glacial till surrounding the volcano to the S. There are two units 0.8 – 1.0 m thick. The orange – brownish lower unit is strongly weathered lapilli alternating with finer grained pumice. The upper unit is very similar to material found in the crater itself, black and well-sorted. Thickness of both units is uniform, coating the slopes nearly to the summits with little variation in thickness. This is a coarse ash to small scoria fall deposit associated with a a’a lava flow. It was erupted from a VEI 3 eruption that produced an estimated 3 km3 of material. Fall material has been identified as far as 80 km from the vent. Estimated age is 359 years ago.
Final unit is fluvial, caused by erosion, measuring 10 – 15 m thick in some places. It is cut by a creek along the E side of the lava flow and mainly includes lapilli and ashes.
The Andean Lake District is part of the Southern Volcanic Zone (SVZ). Lanin and Huanquihue are located in the Central portion of the SVZ (CSVZ).
Tectonic activity in the SVZ is driven by the subduction of the Nazca Plate under the South American Plate. Its northern boundary is defined by the subduction of the Juan Fernandez Ridge into the Chile – Peru Trench. This location also defines a change in subduction angle of the Nazca Plate beneath the South American Plate. The southern boundary of the SVZ is defined by the intersection of the Chile Ridge with the trench. Convergence angle is oblique (20 – 30 degrees) and convergence rate is 7 – 9 cm/yr.
The age of the Nazca Plate is quite young, 45 Ma in the N to 0 Ma in the S. Subduction angle increases from around 20 degrees to the N to 25 degrees to the S. Trench distance from the volcanic front decreases from around 290 km in the N to less than 270 km in the S. This in turn moves the volcanoes from the high Andes in the N to the western portion of the Andean Cordillera in the Central Valley, an extensional basin in the S. Crustal thickness decreases from 55 – 60 km in the N to less than 35 km in the S.
The northern end of the CSVZ is around 120 wide with intra-arc basins and arc volcanoes in Argentina. The CSVZ narrows into a chain about 80 km wide without intra-arc basins. This portion of the arc is W of the drainage divide between Chile and Argentina. The volcanic front has either migrated W or the magnitude of volcanic activity increased significantly. The front consists of mid-late Pleistocene to Holocene stratovolcanoes built on deeply eroded older edifices. To the S, modern stratovolcanoes are allocated along the W margin of the main cordillera.
The CSVZ is the most volcanically active segment of the Andes, with two of the most active and largest individual volcanoes in South America – Llaima and Villarrica. Tronador, while not quite as active, is just as massive, all three over 400 km3 in volume. The largest volcanic fields in the CSVZ are the Codillera Nevada caldera, Cordon Caulle fissure range, Puyehue, Mencheca and Carran – Los Cenados clusters covering over 1,500 km2.
The Lanin – Huanquihue Group region has been recently active with substantial eruptions in the last several thousand years. While Lanin appears to be monitored, Huanquihue, source of the two most recent eruptions, both perhaps VEI 3, is not. Fortunately, the region is sparsely inhabited. As it is surrounded by active volcanoes capable of large eruptions, the possibility of future volcanic activity should not be discounted.