Calabozos | |
---|---|
Highest point | |
Elevation | 3,508 m (11,509 ft)[1] |
Coordinates | 35°33′30″S 70°29′47″W / 35.55833°S 70.49639°W[2] |
Geography | |
Location | central Chile |
Parent range | Andes |
Geology | |
Age of rock | Pleistocene |
Mountain type | caldera |
Volcanic arc/belt | Andean Volcanic Belt |
Last eruption | Holocene[2] |
Calabozos (English: Calaboose) is a Holocene caldera in the Maule Region (7th Region) in central Chile. Part of the Chilean Andes' volcanic segment, it is considered part of the Southern Volcanic Zone (SVZ), one of the three distinct volcanic belts of South America. The most active section of the Andes, this runs through central and western Chile, and includes more than 70 of Chile's stratovolcanoes and volcanic fields. Calabozos lies in an area of poorly-glaciated mountains that is extremely remote.
Calabozos and the majority of the Andean volcanoes formed from the subduction of the oceanic Nazca Plate under the continental South American continental lithosphere. Calabozos is in a transitional region between thick and thin lithosphere, and is probably supplied by a pool of magma nearby. It sits on a historic bed of volcanic and plutonic sedimentary rock that in turn sits on top of a layer of merged sedimentary and metamorphic rock.
Calabozos is responsible for the huge Loma Seca Tuff, a body of material that takes up a massive amount of space surrounding the caldera. It accumulated over at least three eruptive periods, beginning 800,000 (0.8 mya) years ago and lasting until 150,000 (0.15 mya) years ago. Each period is distinct for its composition, size, and age.
The volcano's dimensions are 26 kilometers (16 mi) by 14 kilometers (8.7 mi), and it has an elevation of 3,508 meters (11,509 ft).[2] Activity from the volcano has produced multiple other stratovolcanoes and even a complex volcano.[2]
Geography
Calabozos lies in central Chile's Maule Region, near Curicó and Talca, on the western Andes.[3] This is an area of poorly-glaciated mountains that is not permanently populated. There are no roads, and it is only accessible via horse or on foot.[4]
Calabozos is part of the South Volcanic Zone, which runs through central and western Chile and extends south to Argentina. This range includes at least nine caldera complexes, more than 70 of Chile's stratovolcanoes and volcanic fields that have been active in the Quaternary, and hundreds of minor eruptive centers. The South Volcanic Zone is the most volcanically active region in Chile, and produces around one eruption per year. Its largest historical eruption was at Quizapu Crater, located on the north side of Cerro Azul's summit, and its most active volcanoes are Llaima and Villarrica.[5]
Geology
Subduction of the eastern edge of the Nazca Plate under the western edge of the South American Plate occurs about 160 kilometers (99 mi) west of Peru and Chile. This subduction process has resulted in the formation of the Peru-Chile Trench, an oceanic trench in the Pacific Ocean. It has also resulted in the formation of the Andes mountain range in general, and the Andean Volcanic Belt in particular.[6] Calabozos caldera is one of 44 Holocene epoch volcanoes located in central Chile and Argentina.[7] Part of the SVZ, the most active section of the Chilean Andes,[8] the date of its last known eruption is unknown.[2]
Through K-Ar dating, geologist Robert Edward Drake established the age of 66 events in central Chile, and divided them into groups based on the time of their origin. In a publication, he described the location of each group and the west-east-trending movement of volcanism in the range. To the west of the Chilean Andes are an early group of eruptions, dated from the Oligocene and the Early Miocene (33.3-20.2 million years ago). The scale of the eruptive events that produced these features remains essentially unclear. Further east, in the actual range, are huge numbers of eruptions. Between 15.3 and 6.4 million years ago, widespread volcanism took place, followed by extensive folding; this process then repeated itself from 18.4 to 13.7 million years ago during the Miocene. Beginning 6.4 million years ago the Chilean Andes were quiet, though whether or not this quiet took place throughout all of the Andes remains unknown. Central Chilean volcanoes began activity once again around 2.5 million years ago, and have erupted almost continuously since.[9]
Local
Calabozos lies in an area between thick and thin continental crust, suggesting its eruptions are probably fed from a pool of andesitic and rhyolitic magma that sits just under its caldera.[10] The caldera is underlain by a layer of volcaniclastic sedimentary rock from the Mesozoic era coalesced with intrusive and volcanic rocks of Tertiary age, over a layer of Precambrian-Triassic sedimentary and metamorphic rock formed from later plutons (magma intrusions).[11] Under its northeast edge, Calabozos is cut by a north-south trending segment of sedimentary rock such as gypsiferous and carbonates.[12]
Calabozos seems to be of similar age to Cerro Azul and Descabezado Grande, and its eruptions may correspond to past activity at both volcanoes. Eruption products of very similar composition (including mafic andesite, agglutinates, and dacite) make up the volcanoes. There is also a closeness in size (all are between 40 and 70 cubic kilometers in volume).[13]
Geologic record
In comparison to the rocks of the dry, central part of the Andes, the record that defines the southern sector is poorly-kept. Remnants of Miocene and Quaternary eruptions within the central part are clearly preserved in the rock record. Ash flow sheets constitute as much as 40 percent of the area's total erupted material, suggesting that pyroclastic eruptions were rather important during this time. By examining the eruption rate of individual volcanoes, Hildreth et. al concluded that similar amounts of ash-flow volcanism took place in the southern sector as well. Their study established that particularly silicic ash was missing from the record, and concluded that erosion had probably disrupted deposition of volcaniclastic rock.[3]
While the volcanic history of the area extends back far further, the earliest recognizable events in the region are recorded in the pyroclastic Campanario Formation. This sequence appears to begin at Laguna de la Invernada and ranges from 15 to six million years old. Remnants of magma intrusions as young as seven billion years old can be found at the lake.[14]
The most recent volcanic phase began here approximately 4 million years ago, and produced largely andesitic eruptions. A series of eruptions built up a broad plateau of lava, and extend over the area where Calabozos now lies. Locally, the plateau was composed of mafic andesite with olivine, which, over time, gathered to form 300 meters (984 ft) to 500 meters (1,640 ft) thick layers. Nearby volcanoes sit on top of two million-year-old lavas that formed during this period, while the Loma Seca Tuff lies atop andesitic deposits from Descabezado Grande.[14]
Composition
Calabozos lies in a region between two different types of volcanism—to its north, andesite and rhyolite are the primary constituents of lava while its southern neighbors are composed of more mafic andesite and basalt. It is mainly basaltic andesite and rhyodacite that make up Calabozos, forming a calcalkilic suite rich with potassium. Its lavas are dotted with phenocrysts, which vary from 2 to 25 percent of their mass.[15] These phenocrysts are typically made of plagioclase, but also contain clinopyroxene, orthopyroxene, ilmenite, apatite, and titanomagnetite.[11]
Climate and vegetation
The area's rainfall averages 134 centimeters (53 in) annually, varying from 50 centimeters (20 in) at its lowest to 225 centimeters (89 in) at its highest. Precipitation between May and August (primarily snow) is normally 20 to 35 centimeters, dropping to below one centimeter during summer. Temperature is also variable, typically registering 25 degrees Celsius during the summer, but dropping below freezing at high elevations (>2500 meters).[4]
Vegetation is rare in the area. The 1932 eruption of Cerro Azul's Quizapu Crater reduced much of the land to a pumice desert. Above 1,200 meters (3,937 ft), vegetation becomes even more sparse.[4]
Eruptive history
During the late Pleistocene, Calabozos erupted tuff composed primarily of rhyodacite and dacite. Three distinct eruptions have taken place within the last million years. The sheets of remaining ash left over from each of the eruptions range from 200 cubic kilometers (48 cu mi) to 500 cubic kilometers (120 cu mi) in volume and are known as the Loma Seca Tuff.[2]
The first eruption, which took place 0.8 mya, is distinct from later eruptions in that its product lacks flattened lenticles. The tuff is dotted with predominantly plagioclase phenocrysts, which make up between less than 5 to approximately 15 percent of each particle's mass. After being erupted, the material settled in canyons, where it underwent glaciation. This carved cliffs which drop as much as 100 meters (328 ft). The tuff is limited to just a few kilometers around the complex.[16]
Taking place 0.3 mya, the second eruption was the most extensive. It was probably between 250 cubic kilometers (60 cu mi) and 300 cubic kilometers (72 cu mi) in volume and extended past the reaches of the caldera, down the adjacent foothills. Beyond the caldera, the eruptive products are poor in phenocrysts (unlike those of the first eruption). They are instead rich in lithic material, which makes up as much as 10 percent of the rock in parts (50 percent at the base of the caldera). As the ash was deposited, it accumulated in layers that formed quickly and resisted erosion, but only partially melded together. Other than three sections where very thick or thin rock did not coalesce well, the entire sheet is melded together. Inside Calabozos, the ash resisted welding and contains more phenocrysts. Instead, erosion ate away at it, in the form of acid leaching, and broke down much of its pumice content. Still, the rock layer here contains five to 30 percent phenocrysts, and has high levels of devitrification and lithic content.[16]
The differences between these two deposits can be accounted for by a few factors, including time of eruption and placement. The material inside the caldera must be younger and erupted from a pool of magma that had larger crystals. Its extensive erosion can be explained by the presence of hydrothermal vents, and its high levels of lithics probably originates from either being exposed to the rocks after they were erupted, lying adjacent to them while they underwent subsidence, or just formed slowly and over a long period of time. Any of these reasons would also effectively account for the poor mixing of the lavas.[16]
Activity continued for approximately 150,000 years in the form of quiet andesitic eruptions, as glaciation took place. About 0.15 mya (150,000 years ago), a third and final ash flow was ejected from Calabozos vicinity. With a volume of 175 cubic kilometers (42 cu mi) to 250 cubic kilometers (60 cu mi), it was smaller than the second eruption, but traveled in a similar format, and had much more densely-welded tuff. The ash was thickest at 300 meters (984 ft), at Loma Seca, and the top of the deposit has undergone erosion. It is densely-welded in crevasses, but not at thin 50 meters (164 ft) layers, where much of the material is barely welded or not welded at all.[16]
The beginning layers of the last deposit were alternating belts of light and dark-colored material, and were densely-welded. They appear to have been erupted in pulses, and continue for hundreds of meters until they disappear. Deposition was continuous except for one interruption, which can be seen at proximity to the caldera, where the layers are replaced by thin, non-welded sheets of lava. Another zone of nonwelded material, about 20 meters (66 ft) and near Cajon Los Calabozos, underwent no erosion, suggesting that activity stopped, then began again.[16]
High in fiamme, the third tuff layer differs from the second in that it has even higher phenocryst content, but poor lithics. In the fiamme, phenocrysts constitute between five and 15 percent of the rock, increasing to 25 to 30 percent near the caldera. In the younger emplacements, clinopyroxene is evident along with an increase in mafic content.[17]
Later events
Holocene activity produced the Cerro del Medio complex (elevation: 3,508 meters (11,509 ft),[1] made chiefly of andesite and dacite. It takes up a volume of 20 cubic kilometers (5 cu mi) to 25 cubic kilometers (6 cu mi) and is located on the southern rim of the caldera. On the southwestern edge activity created the Descabezado Chico volcano (elevation: 3,250 meters (10,663 ft),[1] which consists of four overlapping volcanic craters.[2] It last erupted during Holocene time, and produced a 2.5 cubic kilometers (1 cu mi) lava flow (dacitic in origin) which extends for 30 kilometers (19 mi).[2] Another cone in the complex is Cerro Colorado (elevation: 2,928 meters (9,606 ft).[1]
Towards the center of the caldera, hot springs including Cajon Loz Calabozos and Banos de Llolli[1] are present.[2] These were produced as a result of uplift caused by re-occurring activity in the caldera.[2] They occur in clusters and are located along the margin of a fault or at the southwestern edge of the caldera. Hildreth et al. (1983) evaluated that Calabozos could potentially be useful for the harvesting of geothermal energy.[18]
Threats and preparedness
Calabozos is in the South Volcanic Zone, which includes potentially deadly and active volcanoes like Mount Hudson, Llaima, and Villarrica.[19] Villarrica and Llaima together have more than 80 reported episodes of volcanism since 1558, and at least 40 South Volcanic Zone volcanoes have had Holocene-age eruptions.[5]
If Calabozos were to erupt, though this is unlikely, relief efforts could be orchestrated. The Volcanic Disaster Assistance Program (VDAP) formed in response to the famous eruption of Nevado del Ruiz in Colombia and saved lives following the 1991 eruption of Mount Hudson in Chile by organizing evacuations. The team's stated aim is to "reduce eruption-caused fatalities and economic losses in developing countries". Made up of various USGS offices, such as the Cascades Volcano Observatory (CVO), which are responsible for monitoring Mount St. Helens, the team is outfitted with equipment that they can use to monitor any volcano. This equipment allows them to effectively predict volcanic eruptions within a short period of time and evacuate nearby homes.[20]
See also
References
- ^ a b c d e "Calabozos: Synonyms and Subfeatures". Smithsonian Institution. Retrieved January 15, 2011.
{{cite web}}
: Text "work-Global Volcanism Program" ignored (help) - ^ a b c d e f g h i j "Calabozos". Global Volcanism Program. Smithsonian Institution. Retrieved January 15, 2011.
- ^ a b Hildreth et. al, p. 45.
- ^ a b c Hildreth et. al, p. 47.
- ^ a b Stern et al., pp. 154–156.
- ^ "Volcanoes of South America: Highlights". Global Volcanism Program. Smithsonian Institution. Retrieved January 16, 2011.
{{cite web}}
: Cite has empty unknown parameter:|1=
(help) - ^ "Volcanoes of South America: Central Chile and Argentina". Global Volcanism Program. Smithsonian Institution. Retrieved January 16, 2011.
- ^ Moreno, T. and Gibbons W, ed., page 154.
- ^ Drake, Robert E. (November 1976). "Potassium-argon dating of igneous activity in the central Chilean Andes — latitude 33°S". Journal of Volcanology and Geothermal Research. 1 (3): 285–295.
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:|access-date=
requires|url=
(help); Unknown parameter|coauthors=
ignored (|author=
suggested) (help) - ^ Grunder, p. 71.
- ^ a b Grunder, p. 72.
- ^ Hildreth et. al, p. 47.
- ^ Hildreth, et. al, p. 51.
- ^ a b Hildreth et. al, p. 48.
- ^ Grunder and Mahood.
- ^ a b c d e Hildreth et. al, p. 49.
- ^ Hildreth et. al, p. 50.
- ^ Hildreth et. al, pg. 53.
- ^ Topinka, Lyn (March 4, 2002). "Description: Chile Volcanoes and Volcanics". United States Geological Survey. Retrieved February 25, 2010.
- ^ "The USGS/OFDA Volcano Disaster Assistance Program". United States Geological Survey. March 21, 2001. Retrieved February 25, 2010.
Bibliography
- González-Ferrán, Oscar (1995). Volcanes de Chile (in Spanish). Santiago, Chile: Instituto Geográfico Militar. ISBN 9562020541.
- Grunder, Anita L. and Mahood, Gail A. (1988). "Physical and Chemical Models of Zoned Silicic Magmas: the Loma Seca Tuff and Calabozos Caldera, Southern Andes". Journal of Petrology. 29 (4). Oxford University Press: 831–867.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - Hildreth, Wes (January 1984). "The Loma Seca tuff and the Calabozos caldera: a major ash-flow and caldera complex in the southern Andes of Chile". Geological Society of America Bulletin. 95. Geological Society of America: 45–54.
{{cite journal}}
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ignored (|author=
suggested) (help) - Simkin, T; Siebert, L (1994). Volcanoes of the World (2nd ed.). Tucson Arizona: Geoscience Press (in association with the Smithsonian Institution Global Volcanism Program). ISBN 9780945005124.
- Stern, Charles R.; Moreno, Hugo; López-Escobar, Leopoldo; Clavero, Jorge E.; Lara, Luis E.; Naranjo, Jose A.; Parada, Miguel A.; Skewes, M. Alexandra (2007). "5. Chilean Volcanoes". In Moreno, Teresa, and Gibbons, Wes (ed.). Geology of Chile. Geological Society of London.
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: CS1 maint: multiple names: editors list (link)