Cerro Azul ( Spanish: ''Blue Hill'') is a

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava ...

on the south western part of Isabela Island in the

Galápagos Islands The Galápagos Islands () are an archipelago of volcanic islands in the Eastern Pacific, located around the equator, west of the mainland of South America. They form the Galápagos Province of the Republic of Ecuador, with a population of sli ...

. At a height of it is the second highest peak in the Galapagos and due to its

topographic prominence In topography, prominence or relative height (also referred to as autonomous height, and shoulder drop in US English, and drop in British English) measures the height of a mountain or hill's summit relative to the lowest contour line encircling ...

of over it is categorised as an ultra. The volcano is one of the most active in the Galapagos, with the last eruption between May and June 2008.

Geology

The Galapagos Islands are believed to be formed from a

mantle plume A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic ho ...

which creates a hotspot of volcanic activity away from plate boundaries where islands then form above it, similar to process that has created the Hawaiian islands. Cerro Azul is at the edge of the upwelling with steep drop offs in the ocean to the West, while the sea is shallower to the east of Isabela Island. Cerro Azul is one of six coalescing volcanoes on Isabela Island:

Ecuador Ecuador, officially the Republic of Ecuador, is a country in northwestern South America, bordered by Colombia on the north, Peru on the east and south, and the Pacific Ocean on the west. It also includes the Galápagos Province which contain ...

Wolf The wolf (''Canis lupus''; : wolves), also known as the grey wolf or gray wolf, is a Canis, canine native to Eurasia and North America. More than thirty subspecies of Canis lupus, subspecies of ''Canis lupus'' have been recognized, includin ...

, Darwin, Alcedo, and Sierra Negra. Cerro Azul is shaped like a large upturned soup bowl and, like the other volcanoes on Isabela Island, has a large caldera. Its caldera, at 4x5 km across, is one of the smallest. The caldera shows evidence of collapse following eruptive episodes and reaches a depth of 450 m to 650 m below the rim of the caldera; only Wolf Volcano in the Galapagos is as deep. The volcano is 34 by 22 km at maximum and has a volume of 172 km3. It has steep upper slopes of between 12 and 30 degrees. The shape of the volcano is affected by the sharp ocean drop off to the west where this flank of the volcano slopes steeply to the ocean. Historical eruptions date back to 1932, but the volcano has had a number of active periods since then in 1940, 1943,1949, 1951, 1959, 1968, 1979, 1998 and most recently in 2008. It is estimated that the surface of the volcano is less than 5000 years old and that the volcano itself is about 350,000 years old. The age of Cerro Azul is similar to Sierra Negra and Alcedo, and their positioning is believed to be due to an interaction between the plume and the

lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...

rather than plate movement over the magma plume. The 2008 eruption began in May and included a fissure eruption on the southeast flank of the volcano; the eruption in 1998 had also included fissure eruptions on this part of the volcano. The fissure eruptions resulted in lava flowing from the fissure. There was also an eruption within the caldera. A second fissure opened lower down the slope in early June. Analysis of the lavas on Cerro Azul show a range of tholeiitic to alkalic basalts that are unlike the neighboring Sierra Negra or Alcedo volcanoes. A study published in 2006 showed that there was continuous expansion of the volcano prior to and after the eruption in 1998. This expansion would have been due to the emplacement of magma into the magma chamber.

Wildlife

The

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of Galapagos tortoise on the island is ''Geochelone vicina''. This subspecies is dome-shelled and has an overlapping range with the species on the neighboring Sierra Negra volcano, ''Geochelone guentheri'', which is a saddle-backed tortoise. The Cerro Azul tortoises were not affected by the 2008 eruption, although the 1998 eruption did force the National Park authorities to move the tortoises by land and helicopter. Other tortoises were killed in that eruption, either from lava or associated fires.

References

{{DEFAULTSORT:Cerro Azul (Ecuador Volcano) Azul Azul Volcanoes of the Galápagos Islands Polygenetic shield volcanoes Pleistocene shield volcanoes Holocene shield volcanoes

Geology

Wildlife

See also

References