Andean volcanism occurs within the Andean Volcanic Arc (AVA), which is the
product of subduction of the Nazca Plate and Antarctica Plates beneath the
South America Plate. The AVA is Earth's longest but discontinuous
continental-margin volcanic arc, which consists of four distinct segments:
Northern Volcanic Zone, Central Volcanic Zone, Southern Volcanic Zone, and
Austral Volcanic Zone. These segments are separated by volcanically inactive
gaps that are inferred to indicate regions where the dips of the subducting
plates are too shallow to favor the magma generation needed to sustain
volcanism. The Andes host more volcanoes that have been active during the
Holocene (past 10 000 years) than any other volcanic region in the world, as
well as giant caldera systems that have produced 6 of the 47 largest
explosive eruptions (so-called "super eruptions") recognized worldwide
that have occurred from the Ordovician to the Pleistocene.
The Andean region's most powerful historical explosive eruption occurred in
1600 at Huaynaputina Volcano (Peru). The impacts of this event, whose
eruptive volume exceeded 11 km3, were widespread, with distal ashfall
reported at distances >1000 km away. Despite the huge size of the
Huaynaputina eruption, human fatalities from hazardous processes
(pyroclastic flows, ashfalls, volcanogenic earthquakes, and lahars) were
comparatively small owing to the low population density at the time. In
contrast, lahars generated by a much smaller eruption (<0.05 km3) in
1985 of Nevado del Ruiz (Colombia) killed about 25 000 people – the worst
volcanic disaster in the Andean region as well as the second worst in the
world in the 20th century. The Ruiz tragedy has been attributed largely
to ineffective communications of hazards information and indecisiveness by
government officials, rather than any major deficiencies in scientific data.
Ruiz's disastrous outcome, however, together with responses to subsequent
hazardous eruptions in Chile, Colombia, Ecuador, and Peru has spurred
significant improvements in reducing volcano risk in the Andean region. But
much remains to be done. |