The Ecuadorian volcanic arc is part of the Northern Andean Volcanic Zone (NVZ), extending from 5 ° N (Cerro Grande volcano in Colombia) to 2 ° S (Sangay volcano in Ecuador) (Barberi et al ., 1988). South of Sangay there are no active volcanoes in the Andes to the region of Arequipa, Peru.
The volcanism in the Ecuadorian Andes is a result of the subduction of the Nazca oceanic plate under the continental plate of South America. The oceanic Nazca plate is aged between 12 and 20 million years (Ma) off the coast of Ecuador and includes underwater Carnegie Ridge. This ridge of volcanic origin, is the result of the activity of the Galápagos hotspot on the Nazca plate.
The Ecuadorian volcanic arc is characterized by very wide ( 100-120 km ) and present several parallel rows of volcanoes, what differentiates the volcanic arc of Colombia (30-50 km wide ), which consists of a single row of volcanoes. Ecuadorian volcanoes can be classified in two ways: the first classification is Hall and Beate ( 1991), who defined four rows depending on the type of foundation / substrate underlying the volcanoes Western Cordillera , the Inter-Andean Valley , the Cordillera Real and the East. Instead, the second corresponds to Monzier et al. ( 1999), who based on geochemistry volcanoes grouped in three rows of NNE ( Volcanic Front of the Main Volcanic Arc and Tras- arc ) and Riobamba volcanoes that form the southern Ecuadorian arc termination. This geochemical grouping includes the Main Arc volcanoes plus Interandean Valley of the Cordillera Real, while the separation of the volcanoes of Riobamba is made based on its restricted geochemical variability ( basic andesites to andesites ) from the rest arc ( Hall et al. 2008)