The Andean volcanic arc includes over 200 potentially active Quaternary volcanoes, and at least 12 giant caldera/ignimbrite systems, occurring in four separate segments referred to as the Northern, Central, Southern and Austral Volcanic Zones. Volcanism results from subduction of the Nazca and Antarctic oceanic plates below South America. Active volcanoes occur where the angle of subduction is relatively steep (25°), and active arc segments are separated by regions below which subduction angle decreases and becomes relatively flat (<10°) at depths 100 km. Segments of low angle subduction formed beginning in the Miocene in association with subduction of buoyant oceanic plateaus and ridges, and current segmentation of subduction geometry and active Andean volcanic zones is clearly a transient feature related to Neogene tectonics. A genetic relation between subduction and volcanism is confirmed by geochemical studies indicating that generation of Andean magmas is initiated by dehydration and/or melting of subducting oceanic lithosphere and interaction of these slab-derived fluids/melts with the overlying mantle wedge. Continental crust is incorporated into Andean magmas by a combination of both subduction of crust into the subarc mantle and assimilation of crust into mantle-derived magmas. Variations in the rate of subduction erosion and subduction of continental crust significantly affect not only Andean magma chemistry, but also the along-strike intraplate mechanical coupling in the subduction zone and the dynamics of mountain building in the Andes. Crustal components are most significant in magmas erupted in the Central Volcanic Zone, where the crust is extremely thick (70 km) and estimated rates of subduction erosion of the continental margin, possibly equivalent to as much as 4% of the volume of subducting oceanic crust, are also greatest due to the hyper-arid climate conditions and low sediment supply to the trench. Obvious hazards associated with Andean volcanoes include lava and pyroclastic flows, lahars, debris flows resulting from sector collapse, and tephra falls. More than 25,000 people have been killed by the 600 eruptions of these volcanoes catalogued since the year 1532, most of these by lahars generated during the eruption of Nevado del Ruiz, Colombia, in 1985. Despite the fact that 20 million people live within <100 km of an active Andean volcano, mostly in low-lying areas in the intermontane valleys of Colombia and Ecuador and the Central Valley of south-central Chile, only <25 of these volcanoes are continuously monitored for signs of activity

Tephra deposits exposed in road-cuts in both Chile and Argentina between approximately 42°30' to 45°S preserve evidence of four small (VEI <3 and volume <0.15 km³) and seven medium size (VEI = 3-5 and volume between 0.15 to 1 km³), or possibly larger, explosive Holocene eruptions of seven of the eight stratovolcanoes in this southernmost segment of the Andean Southern Volcanic Zone (SVZ). These eruptions include one from the Chaitén volcano at approximately 9,370 BP, two from the Michinmahuida volcano occurring at <6,350 BP and <3,820 BP, three from the Corcovado volcano with the oldest one occurring sometime between <9,190 and 7,980 BP and the two younger ones at <7,980 BP and <6,870 BP, one from the Yanteles volcano at <9,190, two from the Melimoyu volcano occurring at <2,740 BP and <1,750 BP, one from the Mentolat volcano at <6,960, and one from the Macá volcano at approximately <1,540 BP. The principal orientation, to the east, of the tephra plumes produced by these Holocene explosive eruptions in this arc segment, indicates a possible impact for future explosive eruptions on aeronavigation routes in Argentinean Patagonia. The total of eleven small and medium size explosive eruptions over a period of about 8,000 years implies a frequency of one eruption approximately every 725 years in this segment of the Andean SVZ, with each of the eight volcanoes having produced on the average 1.4 eruptions during the Holocene. This is about as frequent as for similar size eruptions from individual volcanic centers further north in the SVZ. In contrast, the Hudson volcano, the southernmost volcano in the SVZ, located just north of the Chile Rise-Trench triple junction at 46°S, has had three very large and nine other documented small explosive Holocene eruptions, and thus both larger and more numerous explosive Holocene eruptions than all the other centers in the southernmost SVZ combined. Hudson volcano may be significantly more active than the other centers in the southernmost SVZ because of its location close to the triple junction

El Teniente, the world’s largest Cu deposit, is hosted in Late Miocene and Pliocene plutons that intrude the older Teniente Volcanic Complex (or Farellones Fm; 14·2–6·5 Ma). The Late Miocene and Pliocene plutonic host rocks of the deposit include, sequentially, the relatively large (>50 km³) Teniente Mafic Complex laccolith (8·9 ± 1·4 Ma), the smaller (∼30 km³) Sewell equigranular tonalite complex (7·05 ± 0·14 Ma) and associated andesitic sills (8·2 ± 0·5 to 6·6 ± 0·4 Ma), small dacitic porphyry stocks (<1 km³; 6·09 ± 0·18 Ma), the unusual Cu- and S-rich ‘Porphyry A’ anhydrite-bearing granitoid stock (<1 km³; 5·67 ± 0·19 Ma), the Teniente Dacite Porphyry dike (4 km below the paleosurface. To produce the ∼100 × 10⁶ tonnes of Cu in the deposit requires a batholith-size (>600 km³) amount of magma with ∼100 ppm Cu. We suggest that both the mineralized magmatic–hydrothermal breccias and the progressively smaller volumes of more fractionated, but isotopically equivalent, Late Miocene and Pliocene felsic plutonic rocks that host the deposit were derived from the roof of a large, long-lived, thermally and chemically stratified, open-system magma chamber, or magmatic plumbing system, recharged from below by mantle-derived magmas. Only when this system fully solidified did post-mineralization mafic olivine-hornblende-lamprophyre dikes (3·85 ± 0·18 to 2·9 ± 0·6 Ma) pass through the system from the mantle to the surface. The significant progressive temporal isotopic evolution, to higher ⁸⁷Sr/⁸⁶Sr (from 0·7033 to 0·7049) and lower ε_Nd (from +6·2 to −1·1), that occurred between the Late Oligocene and Pliocene in the vicinity of El Teniente for mafic mantle-derived magmas, and by implication their sub-arc mantle-source region, was due in part to increased mantle-source region contamination by subducted crust tectonically eroded off the continental margin. The post-mineralization olivine-hornblende-lamprophyres also imply extensive hydration of the mantle below this portion of the Andean arc by the Pliocene, which may have played a role in producing oxidized volatile-rich magmas and mineralization at El Teniente.

Tierra del Fuego represents the southernmost limit of human settlement in the Americas. While people may have started to arrive there around 10 500 BP, when it was still connected to the mainland, the main wave of occupation occurred 5000 years later, by which time it had become an island. The co-existence in the area of maritime hunter-gatherers (in canoes) with previous terrestrial occupants pre-echoes the culturally distinctive groups encountered by the first European visitors in the sixteenth century. The study also provides a striking example of interaction across challenging natural barriers.