Sierra Negra (Galápagos)

Sierra Negra

Eruption of Sierra Negra, 2005-10-25
Highest point
Elevation 1,124 m (3,688 ft)
Coordinates 0°50′S 91°10′W / 0.83°S 91.17°W / -0.83; -91.17
Geography
Location Isabela Island, Galápagos Islands, Ecuador
Geology
Mountain type Shield volcano
Last eruption October 2005

Sierra Negra (Spanish: Black Mountain) is a large shield volcano at the South eastern end of Isabela Island in the Galapagos that rises to an altitude of 1124m.[1] It coalesces with the volcanoes Cerro Azul to the west and Alcedo to the north. It is one of the most active of the Galapagos volcanoes with the most recent historic eruption in October 2005.

Guided tours of the volcano typically start at Puerto Villamil and traverse the rim of the caldera along its East side before heading into the fresh lava fields north east of the main crater.

Geology

The Sierra Negra like the other volcanoes on Isabela is believed to have been created from a mantle plume which has created the hotspot. The age of Sierra Negra and the other volcanoes on Isabela is hard to determine as they are in a North-South line to the east of the hotspot, which is believed to be under Fernandina volcano, and the Nazca plate is moving east. This puts the volcanoes perpendicular to the hotspot. The surface of Sierra Negra and its neighbouring volcanoes are also covered by young lavas, adding to the difficulty of aging them. An estimate based on volume (588 km3) and eruption rates suggest that Sierra Negra is approximately 535,000 years old.[2]

The morphology of Sierra Negra is the upturned soup bowl shape of the other Isabela volcanoes, however it does not have the steep sloping sides that are on others. Instead the slope goes from approximately 2 degrees at its base and although increasing averages only 5 degrees.[3] The volcano has the largest caldera of all of the Galapagos volcanoes, with dimensions of 7.2 x 9.3 km, with the long axis being south west to north east.[2] The caldera is also the shallowest of the Isabela volcanoes at only 100m. The caldera is structurally complex with a 14 km long ridge within it. A large fumarolic area, Volcan de Azufre, lies between this ridge and the western caldera wall.[3] This fumarolic area is one of the locations where terrestrial sulfur flows have been identified, this is associated with the melting of sulfur deposits.[4]

Caldera of the Sierra Negra volcano. The entire floor of the caldera is covered by lava flows from the 2005 eruption with flows emanating from the slightly elevated fissure plateau on the far right of the picture.

The volcano is one of the most active in the Galapagos, with the last eruption starting on 22 October 2005 and lasting until 30 October 2005. This eruption is estimated to have produced 1.5x108 m3 of lava.[3] Despite the GPS monitoring on Sierra Negra there was no advance warning of the eruption. There had been expansion of the caldera floor since 1992 but no short term deformational signal was noted before the eruption. Contraction continued through the nine-day eruption before starting again immediately after the eruption ended.[5][6][7]

Other eruptions in the historical record are 1911, 1948, 1953, 1954, 1957, 1963, and 1979. Eruptions in earlier years are recorded by dating lava flows but their location on the volcano and the dates of the eruption are not known precisely.

Ecology

The majority of the 2200 population on Isabela live in the town of Puerto Villamil on the southern shore of the volcano. Consequently, the eastern side of the volcano is partly used for agriculture, with fishing the initial activities of the island's population. Those involved in farming were one of the sources of non native species including cattle and goats, some of which escaped and became feral, other sources were sailors who released goats to provide a source of fresh meat on future trips. Eradication efforts of feral goats were undertaken in Northern Isabela island, north of the Perry isthmus between Sierra Negra and Alcedo volcanoes but not in the southern portion of the island.[8]

While the southern and eastern side of the volcano is covered with lush tropical forest vegetation and fertile soil at moderate altitudes, the higher reaches are more barren with bushes and grasses of modest height of 2–3 meters. The northern side of the volcano is almost entirely devoid of vegetation (with the exception of some cacti) as it has been resurfaced in more recent times by lava flows.

The habitat for the Sierra Negra giant tortoise, Chelonoidis nigra guentheri, which has a saddleback shell, is on the southern and south eastern slopes of the volcano.[9] This species is endangered due to population pressure brought on by hunting, habitat alteration, and predation by feral mammals.[9][10] C. n. guentheri is part of an ecosystem restoration program in order to recover the population of the tortoises in their natural habitat.[11][12]

See also

References

  1. ↑ Mouginis-Mark, P. J.; Rowland, S. K.; Garbeil, H. (1996). "Slopes of western Galapagos volcanoes from airborne interferometric radar". Geophysical Research Letters. Washington,DC, U.S.A.: American Geophysical Union. 23 (25): 3767–3770. doi:10.1029/96gl03280. ISSN 0094-8276. Retrieved June 16, 2013.
  2. 1 2 Naumann, Terry; Geist, Dennis; Kurz, Mark (May 2002). "Petrology and Geochemistry of the Volcán Cerro Azul: Petrologic Diversity among the Western Galápagos Volcanoes" (PDF). Journal of Petrology. Oxford University Press. 43 (5): 859–883. doi:10.1093/petrology/43.5.859. Retrieved June 16, 2013.
  3. 1 2 3 "Sierra Negra". Global Volcanism Program. Smithsonian Institution.
  4. ↑ NASA A Primer on Sulfer
  5. ↑ Naumann, T. R.; Harpp, K. S.; Geist, D. J.; Chadwick, W. W. (December 2006). "Chronology of the 2005 Sierra Negra Eruption, Galapagos, Ecuador (Abstract)". Eos Trans. Fall Meet. Suppl., Abstract V23A-0585. San Francisco, U.S.A.: American Geophysical Union. 87 (52). Retrieved June 17, 2013.
  6. ↑ Geist, Dennis, J.; Harpp, Karen S.; Naumann, Terry R.; Poland, M.; Chadwick, William W.; Hall, Minard; Rader, Erika (2008). "The 2005 eruption of Sierra Negra volcano, Galápagos, Ecuador". Bulletin of Volcanology. Springer-Verlag. 70 (6): 655–673. doi:10.1007/s00445-007-0160-3. ISSN 1432-0819. Retrieved June 17, 2013.
  7. ↑ Amelung, Falk; Jónsson, Sigurjón; Zebker, Howard; Segall, Paul (October 26, 2000). "Widespread uplift and 'trapdoor' faulting on Galápagos volcanoes observed with radar interferometry". Nature. Nature Publishing Group. 407: 993–996. doi:10.1038/35039604. ISSN 0028-0836. Retrieved June 17, 2013.
  8. ↑ Darwin Foundation
  9. 1 2 Swingland, Ian R.; Klemens, Michael W.; The Durrell Institute of Conservation and Ecology, eds. (1989), "The Conservation Biology of Tortoises" (PDF), Occasional Papers of the IUCN Species Survival Commission (SSC) No. 5, Switzerland: International Union for Conservation of Nature and Natural Resources, pp. 24–28, ISBN 2880329868, retrieved June 17, 2013 Missing or empty |title= (help)
  10. ↑ "Tortoise & Freshwater Turtle Specialist Group. Chelonoidis nigra spp. guentheri". IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. International Union for Conservation of Nature and Natural Resources. 1996. Archived from the original on June 27, 2014. Retrieved June 17, 2013.
  11. ↑ "Ecosystem Restoration: Giant Tortoise Recovery". Galapagos Conservancy: Conservation: Project Areas. Galapagos Conservancy. Retrieved June 17, 2013.
  12. ↑ "The Galapagos National Park Service will repatriate 150 juvenile tortoises from the Isabela Island Breeding Center". Galapagos Conservancy: Newsroom. Galapagos Conservancy. April 10, 2013. Retrieved June 17, 2013.
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