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Sierra Negra (Galápagos)
Encyclopedia
Sierra Negra is a large shield volcano
at the South eastern end of Isabela Island
in the Galapagos that rises to an altitude of 1124m. 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.
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.
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. 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. 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. This fumarolic area is one of the locations where terrestrial sulfur flows have been identified, this is associated with the melting of sulfur deposits.
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. 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.
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.
on the southern shore of the volcano and it is from here that tours of the volcano start. The initial activities of the population were agriculture and fishing. 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.
The habitat for the Sierra Negra giant tortoise
, Geochelone nigra gunther which has a saddleback shell is on the southern and south eastern slopes of the volcano. This species is under threat from illegal hunting and as a result is part of the captive breeding program to try to increase its numbers.
Shield volcano
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...
at the South eastern end of Isabela Island
Isabela Island
Isabela Island may refer to:*Isabela Island *Isabela Island...
in the Galapagos that rises to an altitude of 1124m. It coalesces with the volcanoes Cerro Azul
Cerro Azul (Ecuador volcano)
Cerro Azul is a shield volcano on the south western part of Isabela Island in the Galápagos Islands, the name translates from Spanish as blue mountain...
to the west and Alcedo
Alcedo Volcano
Alcedo Volcano is one of the six coalescing shield volcanoes that make up Isabela Island in the Galapagos. The remote location of the volcano has meant that even the most recent eruption in 1993 was not recorded until two years later...
to the north. It is one of the most active of the Galapagos volcanoes with the most recent historic eruption in October 2005.
Geology
The Sierra Negra like the other volcanoes on Isabela is believed to have been created from a mantle plumeMantle plume
A mantle plume is a hypothetical thermal diapir of abnormally hot rock that nucleates at the core-mantle boundary and rises through the Earth's mantle. Such plumes were invoked in 1971 to explain volcanic regions that were not thought to be explicable by the then-new theory of plate tectonics. Some...
which has created the hotspot
Galápagos hotspot
The Galápagos hotspot is a volcanic hotspot in the East Pacific Ocean responsible for the creation of the Galapagos Islands as well as three major aseismic ridge systems, Carnegie, Cocos and Malpelso which are on two tectonic plates. The hotspot is located near the Equator on the Nazca Plate not...
. 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
Fernandina
Fernandina may refer to:*Fernandina Beach, Florida*Fernandina Island, Galapagos Islands*Fernandina , a citrus fruit...
volcano, and the Nazca plate
Nazca Plate
]The Nazca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction along the Peru-Chile Trench of the Nazca Plate under the South American Plate is largely responsible for the...
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.
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. The volcano has the largest caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...
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. 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. This fumarolic area is one of the locations where terrestrial sulfur flows have been identified, this is associated with the melting of sulfur deposits.
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 VillamilPuerto Villamil
Puerto Villamil is a small port village located on the southeastern edge of Isla Isabela in the Galapagos Islands. Of the 2,200 people who live on Isabela, the majority live in Puerto Villamil...
on the southern shore of the volcano and it is from here that tours of the volcano start. The initial activities of the population were agriculture and fishing. 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.
The habitat for the Sierra Negra giant tortoise
Galápagos tortoise
The Galápagos tortoise or Galápagos giant tortoise is the largest living species of tortoise, reaching weights of over and lengths of over . With life spans in the wild of over 100 years, it is one of the longest-lived vertebrates...
, Geochelone nigra gunther which has a saddleback shell is on the southern and south eastern slopes of the volcano. This species is under threat from illegal hunting and as a result is part of the captive breeding program to try to increase its numbers.