Puyehue-Cordón Caulle: Difference between revisions
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In Cordillera Nevada this volcanism was expressed from about 117 ka ago primarily as dacitic lava flows erupted along [[ring fault]]s. This lava flows partly filled the caldera and flowed north, out to [[Nilahue River]]. In mid or late glacial times cordillera Nevada produced its last lavas wich were andesitic to dacitic in composition. |
In Cordillera Nevada this volcanism was expressed from about 117 ka ago primarily as dacitic lava flows erupted along [[ring fault]]s. This lava flows partly filled the caldera and flowed north, out to [[Nilahue River]]. In mid or late glacial times cordillera Nevada produced its last lavas wich were andesitic to dacitic in composition. |
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Cordón Caulle evolved during this time from being a [[shield volcano]] to a [[ |
Cordón Caulle evolved during this time from being a [[shield volcano]] to a [[graben]] with [[fissure vent]]s. Thisa was accompained by emission of ignimbrites and dacitic lava flows. |
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Puyehue was characterized by eruption of basaltic andesites to dacites until it activity turned [[bimodal]] at around 34 ka [[Before Present|BP]]. The onsed of this change was marked by the eruption of [[rhyodacite]] [[mingled]] with basaltic andesite rich in [[magnesium oxide]] (MgO). The bimodal activity continued with a small [[hiatus]] around 30 ka BP until around 19 ka ago when Puyehues started to produce lava domes and flows of dacitic to rhyolitic compostion, a trend that lasted until 12 ka BP. Between 15 and 12 Puyehue did also erupt basaltic andesite. Duiring the Llanquihue glaciation Puyehue produced some of the most [[bowen's reaction series|primitive]] basalts of the [[Southern Volcanic Zone]] with 14.32 [[wt%]] [[MgO]], which is in equilibrium with melt from [[mantle (geology)|mantle]] [[peridotite]], some of the most primitive [[magmas]] in the [[Andes]].<ref name=lem>{{cite journal |
Puyehue was characterized by eruption of basaltic andesites to dacites until it activity turned [[bimodal]] at around 34 ka [[Before Present|BP]]. The onsed of this change was marked by the eruption of [[rhyodacite]] [[wt:Mingle|mingled]] with basaltic andesite rich in [[magnesium oxide]] (MgO). The bimodal activity continued with a small [[hiatus]] around 30 ka BP until around 19 ka ago when Puyehues started to produce lava domes and flows of dacitic to rhyolitic compostion, a trend that lasted until 12 ka BP. Between 15 and 12 Puyehue did also erupt basaltic andesite. Duiring the Llanquihue glaciation Puyehue produced some of the most [[bowen's reaction series|primitive]] basalts of the [[Southern Volcanic Zone]] with 14.32 [[wt%]] [[MgO]], which is in equilibrium with melt from [[mantle (geology)|mantle]] [[peridotite]], some of the most primitive [[magmas]] in the [[Andes]].<ref name=lem>{{cite journal |
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Revision as of 17:17, 16 October 2009
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Puyehue and Cordón Caulle are two coalesced volcanic vents that form a mayor mountain massif in Puyehue National Park at the Andes of Ranco Province, Chile. In volcanology this group is known under the name of Puyehue-Cordón Caulle Volcanic Complex and hence also the by the acronym PCCVC. Four different volcanoes constitute the volcanic group or complex, the Cordillera Nevada caldera, the Pliocene Mencheca volcano, Cordón Caulle fissure vents and the Puyehue stratovolcano.[2] As most stratovolcanoes on the Southern Volcanic Zone of the Andes PCCVC are located along the intersection of a NW-SE fault with the larger N-S Liquiñe-Ofqui Fault. The volcanic complex has shaped the landscape around and produced a huge variery of volcanic landforms and products over the last 300 ka. Cinder cones, lava domes, calderas and maars can be found in the area apart from the widest variety of volcanic rocks in all the Southern Volcanic Zone and Chile, for example both MgO-rich basalts and rhyolites.
Apart from this, the Puyehue-Cordón Caulle area is one of the main sites of geothermal exploration in Chile. Geothermal activity is manifested on the surface of Puyehue and Cordón Caulle as several hot springs and geysers.
Cordón Caulle is notable for having erupted following the 9.6 Mw 1960 Valdivia earthquake the largest recorded earthquake in history.
Geography
Cordillera Nevada is a 9 km wide semicircular caldera and corresponds to the remnants of a collapsed volcano. Its products range from basaltic andesites to dacites and covers an approximate area of 700 km2. From its current structure and lava flows inside it is inferred that Cordillera Nevada caldera developed from a shield volcano and following a collapse it has continued to be active through ring faults in the south and eastern walls.[1]
Cordón Caulle is a NW-SE trending ridge that host a volcano-tectonic where a fissure vent develops. Cordón Caulle runs from the Cordillera Nevada caldera in the northwest to Puyehue volcano in the southeast. Through all its length Cordón Caulles upper parts are above the tree line and at its highest parts it reaches 1,798 metres (5,899 feet). Five different stratigraphic units are recognised on Cordón Caulle apart from fissure lavas of the 1921-22 eruption and the 1960 eruption.[1]
Puyehue Volcano is a stratovolcano located on at south eastern end of Cordón Caulle just east of the main fault of the Liquiñe-Ofqui Fault Zone. Its cone host a 2.4 km wide crater, and products of Puyehue Volcano covers and area of 160 km2. The oldest known rocks of Puyehue Volcano are andesite lavas and breccias piled up in a 150 m thick succession. The rocks at the bottom are ca. 193 ka and those at the top 131 ka. Another succession of similar age is located in the east. Here basalts and andesites are cut several vertical dykes, ages of 245 ka and 103 ka has been obtained for the base respectively the top the succession.[1]
Geologic history
The complex that Puyehue, Cordón Caulle and Sierra Nevada have an long record of active history spanning from 300 ka BP to the present. Volcanism has during this period underwent a series of changes in magmatic composition, locust of activity, output rates and eruptive styles among other things.
Ancestral volcanoes
Some 300 ka BP important chages occured in the area of Puyehue. The old Pliocene volcano Mencheca, currently exposed just northeast of Puyehue's cone declined in activity. This decline was probably due a regional change in the location of the active front of the Southern Volcanic Zone that also afected other volcanoes such as Tronador and Lanín. The relocation of the active front gave origin to new volcanoes futher westward or increased their activity. The formerly rather broad magmatic belt thined retaining only activity in its westernmost parts. Associated to this changes are the oldest rocks of PCCVC those that belong to Sierra Nevada. Sierra Nevada grew over time to form a large shield volcano, during the same time Cordón Caulle was also being built up having rather silicic products if compared to coeval Sierra Nevada and Mencheca. The oldest rocks from proper Puyehue volcano are 200 ka old, being this age then the youngest posssible age for this volcano.
It is estimated that some 100 ka ago in period between Río Llico and Llanquihue glaciation a large ignimbrite called San Pablo was produced. This ignimbrite covers and estimated area 1500 km3 inmediately west of Cordillera Nevada, streaching all across the Chilean Central Valley reaching almost the Chilean Coast Range. The San Pablo ignimbrite has been associated with the formation of the Cordillera Nevada Caldera.
Volcanism during the Llanquihue glaciation
During the Llanquihue glaciation volcanism occured on al three vents Cordillera Nevada, Cordón Caulle and Puyehue volcano. During this most of this time the volcano was covered by the Patagonian Ice Sheet, leaving glacial striae on many lava outcrops and affecting the volcanic activity.
In Cordillera Nevada this volcanism was expressed from about 117 ka ago primarily as dacitic lava flows erupted along ring faults. This lava flows partly filled the caldera and flowed north, out to Nilahue River. In mid or late glacial times cordillera Nevada produced its last lavas wich were andesitic to dacitic in composition.
Cordón Caulle evolved during this time from being a shield volcano to a graben with fissure vents. Thisa was accompained by emission of ignimbrites and dacitic lava flows.
Puyehue was characterized by eruption of basaltic andesites to dacites until it activity turned bimodal at around 34 ka BP. The onsed of this change was marked by the eruption of rhyodacite mingled with basaltic andesite rich in magnesium oxide (MgO). The bimodal activity continued with a small hiatus around 30 ka BP until around 19 ka ago when Puyehues started to produce lava domes and flows of dacitic to rhyolitic compostion, a trend that lasted until 12 ka BP. Between 15 and 12 Puyehue did also erupt basaltic andesite. Duiring the Llanquihue glaciation Puyehue produced some of the most primitive basalts of the Southern Volcanic Zone with 14.32 wt% MgO, which is in equilibrium with melt from mantle peridotite, some of the most primitive magmas in the Andes.[3]
Postglacial volcanism
Only Puyehue and Cordón Caulle have erupted during the Holocene, and of these only Cordón Caulle has recorded historical eruptions.
In the interval between 7 to 5 ka ago Puyehue had rhylitic eruptions that produced lava domes. this lava domes were later destroyed after sequence of strong eruptions that were part of a explosive eruptive cycle. These eruptions were likely of preatomagmatic and sub-plinian type might have happened around 1.1 ka ago (~850 CE).[4]
Eruptive history
Eruptive records in Cordón Caulle, the only active centre in the Puyehue-Cordón Caulle system in historical times are relatively. This is explained by the geographical position of Cordón Caulle and the history of Spanish and Chilean settlement in southern Chile. In 1558 governor García Hurtado de Mendoza founded the city of Osorno the only Spanish settlement in the zone, 80 km west of Cordón Caulle, but this settlements had to be abandoned in 1602 due to conflicts with native Huilliches. No eruption record is known from this era. From 1602 to the mid 18th century there were no Spanish settlements in a radius of 100 km being the closest ones Valdivia and the mission of Nahuel Huapi both without sight of the volcano. In 1759 an eruption was noticed in the Cordillera, althought this mainly attributed to Mocho. By the end of the 19th century most of the Central Valley west of Cordón Caulle had been settled and an eruption was reported in 1893. Next report came in 1905 but the eruption of February 8, 1914 is the first one there no dubt that have occured.
1960 eruption
On May 24, 38 hours after the main shock of the 1960 Valdivia earthquake, the largest eathquake recorded in history, Cordón Caulle begun a rhyodacitic fissure eruption. The 1960 earthquake had previously struck the whole of Chile between Talca (30°S)and Chiloe (43°S) and had an estimated moment magnitude of 9.6. Being located between two sparcely populated and by then isolated Andean valleys the eruption had few eyewithnesses and recied little attention by local media due to huge damages and losses caused by the propper earthquake.[5] The eruption was fed a 5.5 km long and N135° trending fissure were 21 individual vents have been found. These vents produced an output of about 0.25 km3 DRE both in form of lava flows and tephra.
The eruption begun in a sub-plinian eruption style creating a column of volcanic gas, pyroclasts and ash of about 8 km i height. The erupting N135° trending fissure had its two crater of mayor activity emplaced at the ends of it; being those Gris Crater and El Azufral Crater. Volcanic vents of Cordón Caulle that were not in eruption produced visible steam emissions. After this explosive phase the eruption changed character to a more effusive one maked by rhyodacitic blocky and Aa type lava flows emited from the vents along the N135° trending fissure. A thirth phase followed with the appareance of short N165° oriented vents transversal to the main fissure which did also pour out rhyodacitic lava. The thirth phase ended temporarly with viscous lava obstructing the vents but continued soon with explosive activity restricted to Gris and El Azufral Craters. The eruption come to an end on June 22.[5]
1921-1922 eruption
Timeline of historic eruptions
| Date | Event |
|---|---|
| 1990 | A small pumice cone in Cordón Caulle is believed to have formed.[1] |
| May 24, 1960 | Following the 1960 Valdivia earthquake whose main shock came on May 22, 1960 Cordón Caulle starts to erupt along its southern flank. |
| March 6, 1934 | Puyehue-Cordón Caulle has a eruption.[1] |
| January 7, 1929 | Puyehue-Cordón Caulle has a eruption.[1] |
| December 13, 1921 | Cordón Caulle has a sub-plinian eruption, with a 6.2 km high plume periodic explosions and seismicity. The eruption had a Volcanic Explosivity Index of 3 and ended on February 1922. |
| 1919 | Puyehue-Cordón Caulle had an eruption that lasted until 1920.[1] |
| February 8, 1914 | Puyehue-Cordón Caulle had an eruption.[1] |
| 1905 | Puyehue-Cordón Caulle might have had an eruption.[1] |
| 1893 | Puyehue-Cordón Caulle might have had an eruption.[1] |
| 1759 | Puyehue-Cordón Caulle might have had an eruption.[1] |
Geothermal activity and exploration
Cordón Caulle is a mayor area of geothermal activity, as manifested on the several hotsprings, boiling springs, solfataras and fumaroles that develop on it. The geothermal system in cordón caulle conists of a vapour deminated system overlain by a moe superifcial steam heated aquifer. The temperatures fo the vapour systems range from 260-340°C and 150-180°C for the aquifer.[6] Hight temperatures and heat flow has made Cordón Caulle is one of main sites of geothermal exploration in Chile.
Approach and ascent
From the south, Cordón Caulle can be approached from Fundo El Caulle on Route 215-CH, which goes from Osorno to Bariloche in Argentina through Samoré Pass. Some 1,000 m up on forested slope there is a campsite and mountain shelter. The acces trough El Caulle is not public as it is not inside Puyehue National Park and entrance fee of 7,000 CLP have to be payed. From the north, there is a trail from Riñinahue near Lago Ranco. It ascends ca 1,000 m through dense forest to the Cordón Caulle area. From the relatively flat Cordón Caulle there is further ca 600 m of ascent over tephra and loose rocks to the summit of Puyehue.
See also
References
- ^ a b c d e f g h i j k l m Lara, L. E. (2006). "Magmatic Evolution of the Puyehue-Cordón Caulle Volcanic Complex (40° S), Southern Andean Volcanic Zone: From shield to unusual fissure volcanism". Journal of Volcanology and Geothermal Research. 157. Elsevier: 343–366. Retrieved April 25, 2009.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Gerlach, David C. (1988). "Recent Volcanism in the Puyehue-Cordon Caulle Region, Southern Andes, Chile (40.5° S): Petrogeneis of Evolved Lavas". Journal of Petrology. 58. Oxford Univeristy Press: 67–83.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ "Geochemical Characteristics of the Southern andes Basaltic Volcanism Associated with the Liquiñe-Ofqui Fault between 39° and 46° S" (PDF). 7° Congreso Geológico Chileno. Actas Volumen II. Universidad de Concepción, Departamento de Ciencias de la Tierra: 1388–1393. 1994. Retrieved April 25, 2009.
{{cite journal}}:|first=has numeric name (help);|first=missing|last=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Singer, Brad S., Jicha, Brian R., Harper. Melissa A., Naranjo, José A., Lara, Luis E., Moreno-Roa, Hugo. Eruptive history, geochronology, and magmatic evolution of the Puyehue-Cordón Caulle volcanic complex, Chile. GSA Bulletin. 2008.
- ^ a b Lara, L.E., Naranjo J.A., Moreno, H. Rhyodacitic fissure eruption in Southern Andes (Cordón Caulle; 40.5°S) after the 1960 (Mw:9.5) Chilean earthquake: a structural interpretation. Journal of Volcanology and Geothermal Research. vol 138. 2004.
- ^ Sepúlveda, Fabián; Lahsen, Alfredo; Dorsch, Klaus; Palacios, Carlos and Bender, Steffen. Geothermal Exloration in the Cordón Caulle Region, Southern Chile. Preceedings World Geothermal Congress 2005.