Galán
Galán | |
---|---|
![]() Galán viewed from space | |
Highest point | |
Elevation | 6,100 m (20,000 ft) |
Coordinates | 25°56′S 66°55′W / 25.93°S 66.92°W[1] |
Geography | |
Location | Catamarca Province, Argentina |
Parent range | Andes |
Geology | |
Age of rock | 2.08 ± 0.02 million years |
Mountain type | Caldera |
Last eruption | Unknown |
Cerro Galán is a
Volcanic activity at Galán is the indirect consequence of the subduction of the Nazca Plate beneath the South America Plate, and involves the infiltration of melts into the crust and the formation of secondary magmas which after storage in the crust give rise to the dacitic to rhyodacitic rocks erupted by the volcano.
Galán was active between 5.6 and 4.51 million years ago, when it generated a number of ignimbrites known as the Toconquis group which crop out mainly west of the caldera. The largest eruption of Galán was 2.08 ± 0.02 million years ago and was the source of the Galán ignimbrite, which covered the surroundings of the caldera with volcanic material. The volume of this ignimbrite has been estimated to be about 650 cubic kilometres (160 cu mi); after this eruption much smaller ignimbrite eruptions took place and presently two hot springs are active in the caldera.
Geography and geomorphology
The Galán
Galán is part of the
The
The Galán caldera lies on the eastern margin of the Andes, where the Sierras Pampeanas begin.[24] The region is characterized by the Puna, a high plateau similar to Tibet in Asia.[25]
Local
![](http://upload.wikimedia.org/wikipedia/commons/thumb/d/d5/Cerro_Galan.jpg/280px-Cerro_Galan.jpg)
Galán is a caldera with topographic dimensions of 38 by 26 kilometres (24 mi × 16 mi), of which about 26 by 18 kilometres (16 mi × 11 mi) are part of the caldera proper.[26] Such dimensions make Galán one of the biggest calderas on Earth;[18] it has been described as a supervolcano.[27] The floor of the caldera reaches an elevation of 4,500 metres (14,800 ft)[2][17] or about 4,600 metres (15,100 ft),[28] and the whole caldera has an elliptical shape[17] extending in the north–south direction.[29] Only the western margin of the caldera structure appears to be a true caldera margin, however,[30] with different landforms forming the rest of the caldera walls[31] and the actual collapse caldera covering only a portion of the topographic caldera expression;[32] the latter has been defined to be a volcano-tectonic depression.[33]
The caldera contains a
Summits along the caldera margin include Cerro Aguas Calientes (a lava dome[39]) to the north, Cerro Leon Muerto to the southeast, Cerro Pabellon to the southwest and Cerro Toconquis to the northwest.[4] On the western rim, elevations of 5,200 metres (17,100 ft) are reached.[29] Younger volcanoes have developed on the western and northern rim of the Galán caldera.[35]
Hydrology
The caldera contains a 7 by 3 kilometres (4.3 mi × 1.9 mi) lake
Rivers in the caldera and neighbourhood display
Geology
The
About 14.5 million years ago volcanic activity started in the region, first west of Galán but by 7 million years ago it shifted to the future caldera, forming the Cerro Colorado, Pabellon and Cerro Toconquis
Mafic volcanism occurred south and west of Galán both before its large eruption and afterwards, in the valley of Antofagasta de la Sierra and may have continued to less than ten thousand years ago.[54] The positions of the exact vents are controlled by recent fault systems in the region.[63]
Since about 10 million years ago, the area has been subject to
Composition
Galán has erupted mainly
The formation of the Galán magma has been explained with melting of lower
Based on the presence of two separate populations of pumice in the Galán ignimbrite it has been inferred that there were two types of magma in the magmatic system during the Galán eruption, a larger volume of so-called "white" magma and a "grey" magma which was injected into the "white" magma pool and eventually rose above the latter.[76] More generally, it appears that before each eruption there were two batches of magma present beneath the volcano[74] which however were very similar owing perhaps to a homogenization process that took place deep in the crust.[77] Before the eruption, the magma is estimated to have been 790–820 °C (1,450–1,510 °F) hot.[69]
Climate and biology
Galán lies in a region of arid climate, with annual precipitation amounting to about 65 millimetres per year (2.6 in/year).[78] Frosts occur year-round.[79] Climate data are known for Salar de Hombre Muerto north of Galán; average temperatures there are 8–23 °C (46–73 °F) in summer and winter, respectively. Precipitation occurs mostly during the summer months.[46]
At high elevations there is no vegetation.
Eruptive history
Volcanic activity at Galán occurred in two separate stages,[54] which are separated by an erosional unconformity[80][28] during which the ignimbrite apron of the Toconquis group was incised by deep valleys.[81] Mechanistically, the onset of the eruptions has been explained with delamination events during which parts of the lower crust broke off, asthenospheric material replaced the crust lost by delamination and basaltic magmas penetrated the remaining crust.[82][83]
These stages have left an ignimbrite plateau that surrounds the caldera[4] except on its southern side, and which is noticeable on satellite images.[28] It covers a surface area of about 3,500 square kilometres (1,400 sq mi)[17] and is the largest ignimbrite system in the Puna plateau.[84]
Toconquis Group
The first stage occurred between 5.60 and 4.51 million years ago and consisted of the eruption of large
The formation is fairly heterogeneous, with some ignimbrites separated by sharp contacts and the degree of welding and crystal content of
On the northern side of the Galán complex, ignimbrites extend up to 80 kilometres (50 mi) away from the caldera and may have reached even larger distances prior to erosion,[88] and they have thicknesses of 300 metres (980 ft).[91] The ignimbrites have a total volume of about 650 cubic kilometres (160 cu mi), with the Real Grande ignimbrite comprising over half of its volume.[34][92] The volume of the individual ignimbrites increases the younger they are[93] with the initial Blanco and Merihuaca ignimbrites having a volume of about 70 cubic kilometres (17 cu mi).[92]
The last eruption may have generated a caldera that was later obliterated.
Galán ignimbrite
2.08 ± 0.02 million years ago
The Galán ignimbrite is fairly homogeneous and has a high crystal content;[63] overall it appears that the eruption commenced and reached large dimensions fairly quickly without leaving time for an eruption column or distinct flow units to form, except in some places.[105][106][100] Conversely, the produced flows were relatively slow flows[107] that had little capacity to pass above topographic obstacles or to move rocks around.[108] It nevertheless spread over large distances, since the topography of the region had been flattened by the previous Toconquis ignimbrites,[109] and was still hot by the time it came to a standstill.[110] Pumice is scarce and usually present in only small fragments, and lithic fragments are also uncommon except at the bases of the deposit. Fiamme structures on the other hand are fairly common especially where the ignimbrite crossed river valleys. The ignimbrite displays varying degrees of welding but has often spectacular columnar joints.[28][111]
At first it was assumed that this ignimbrite crops out over a surface of 7,500 square kilometres (2,900 sq mi) but later it was found that it covers a surface closer to 2,400 square kilometres (930 sq mi).[88] Between the intracaldera ignimbrite, the parts of the ignimbrite that extend away from the caldera and outcrops at large distance, the volume is about 650 cubic kilometres (160 cu mi),[92] down from earlier estimated of volumes exceeding 1,000 cubic kilometres (240 cu mi)[96] but the Galán eruption is still one of the biggest known volcanic eruptions[100] and the volcano has produced almost half of the volume of ignimbrites in the southern Puna.[112] The Galán ignimbrite is the largest ignimbrite erupted by this centre;[26] there is a tendency of the volume of individual ignimbrites to increase as the volcanoes grow younger, not only at Galán but also at other Puna ignimbrite centres, and this may be a consequence of progressive changes in the crust.[113] Such giant eruptions have not been observed during historical time and are considered to be among the most dangerous volcanic phenomena known.[114]
Kay et al. proposed that the Galán ignimbrite consisted of three separate units, an intracaldera one emplaced 2.13 million years ago and two extracaldera ones 2.09 and 2.06 million years ago.[75]
Post-Galán volcanism
The main Galán caldera formed during the Galán ignimbrite eruption,[94] and it is possible that the collapse of the magma chamber roof actually started the eruption.[106] Later it was found that a trapdoor collapse is a more plausible interpretation of the caldera structure[30] and that the caldera appears to be much smaller than its present-day topographic expression.[32] Most likely a lake formed within the caldera after its eruption.[115][41]
Later volcanic activity resulted in lava flows of dacitic composition being erupted along the ring fault of the caldera, as well as the formation of the resurgent dome by about 2 kilometres (1.2 mi) uplift along the eastern caldera margin fault.
See also
Notes
- ^ Silicic volcanic rocks are volcanic rocks such as dacite and rhyolite that contain at least 63% silicon dioxide. Volcanoes erupting such rocks tend to undergo explosive eruptions.[15]
- ^ The "Altiplano Puna Magma Body" is a layer underneath the Altiplano that consists of large amounts of molten magma, with a volume of about 10,000 cubic kilometres (2,400 cu mi).[21]
- ^ A volcanic rock relatively rich in iron and magnesium, relative to silicon.[60]
References
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Further reading
- Cerro Galan Caldera Archived 2017-02-18 at the Wayback Machine Oregon State University
- Cerro Galan Caldera, Argentina, from How Volcanoes Work, by Vic Camp, Department of Geological Sciences, San Diego State University
- "Cerro Galán". Global Volcanism Program. Smithsonian Institution.
- Ben G. Mason; David M. Pyle; Clive Oppenheimer (2004). "The size and frequency of the largest explosive eruptions on Earth". Bulletin of Volcanology. 66 (8): 735–748. S2CID 129680497.