Geological Setting
Lying at the eastern edge of the Andean cordillera, Sangay was formed by volcanic processes associated with the subduction of the Nazca Plate under the South American Plate at the Peru-Chile Trench. It is the southernmost volcano in the Northern Volcanic Zone, a subgroup of Andean volcanoes whose northern limit is Nevado del Ruiz in Colombia.
The next active volcano in the chain, Sabancaya, is in Peru, a distant 1,600 km (990 mi) to the south. Sangay lies above a seismogenic tectonic slab located about 130 km (80 mi) beneath Sabancaya, reflecting a sharp difference in the thermal character of the subducted oceanic crust, between older rock beneath southern Ecuador and Peru (dated more than 32 million years old), and younger rock under northern Ecuador and Colombia (dated less than 22 million years old). The older southern rock is more thermally stable than the northern crust, and to this is attributed the long break in volcanic activity in the Andes; Sangay occupies a position at the boundary between these two bodies, accounting for its high level of activity.
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