The quantity of archaeological data for the fortified hilltop settlements of the Late Intermediate period on the Andean altiplano, called pucaras, varies greatly. Some areas, such as the territory of the Colla Aymara chieftaincy east of Lake Titicaca, are well documented thanks to recent and exhaustive research. Other areas, such as the territories of the Lupacas and the Pacajes, are much less documented. From comparative spatial analyses of satellite images from these two territories, we obtained new data on pucaras, whose characteristics seem to differ from those proposed in the archaeological literature. Through a combination of fieldwork and spatial analysis of 295 pucaras, we identified 252 unpublished sites and propose a new typology comprising four categories. Based on ethnohistoric data and the results of the architectural and geographical analyses, we discuss the possible motivations for building so many pucaras; we suggest that some reasons are of a symbolic nature.

In the Lake Titicaca Basin during the Late Intermediate period (LIP; AD 1100–1450), people's lives were overwhelmingly structured by warfare. Previous research in the region has shed light on how martial conflict between and possibly among competing ethnic groups motivated people to live in fortified villages on defensive hilltops. At the same time, there was a centuries-long drought that threatened agricultural production. Little is known about the plant use of people living in hillforts during this arduous time. Drawing on macrobotanical information collected from Ayawiri, one of the largest hillforts in the northern Titicaca Basin, I argue that the food stuffs and plants used were locally grown. Additionally, these findings indicate a possible departure from earlier symbolically charged and ritually important plant consumption practices based on the lack of imported maize. This research sheds light on how people adapted their domestic and agricultural strategies to warfare and climate change during the LIP.

Various paleoclimatic records have been used to reconstruct the hydrologic history of the Altiplano, relating this history to past variability of the South American summer monsoon. Prior studies of the southern Altiplano, the location of the world’s largest salt flat, the Salar de Uyuni, and its neighbor, the Salar de Coipasa, generally agree in their reconstructions of the climate history of the past ∼24 ka. Some studies, however, have highly divergent climatic records and interpretations of earlier periods. In this study, lake-level variation was reconstructed from a ∼14-m-long sediment core from the Salar de Coipasa. These sediments span the last ∼40 ka. Lacustrine sediment accumulation was apparently continuous in the basin from ∼40 to 6 ka, with dry or very shallow conditions afterward. The fossil diatom stratigraphy and geochemical data (δ13C, δ15N, %Ca, C/N) indicate fluctuations in lake level from shallow to moderately deep, with the deepest conditions correlative with the Heinrich-1 and Younger Dryas events. The stratigraphy shows a continuous lake of variable depth and salinity during the last glacial maximum and latter stages of Marine Oxygen Isotope Stage 3 and is consistent with environmental inferences and the original chronology of a drill core from Salar de Uyuni.

A 136-m-long drill core of sediments was recovered from tropical high-altitude Lake Titicaca, Bolivia-Peru, enabling a reconstruction of past climate that spans four cycles of regional glacial advance and retreat and that is estimated to extend continuously over the last 370,000 yr. Within the errors of the age model, the periods of regional glacial advance and retreat are concordant respectively with global glacial and interglacial stages. Periods of ice advance in the southern tropical Andes generally were periods of positive water balance, as evidenced by deeper and fresher conditions in Lake Titicaca. Conversely, reduced glaciation occurred during periods of negative water balance and shallow closed-basin conditions in the lake. The apparent coincidence of positive water balance of Lake Titicaca and glacial growth in the adjacent Andes with Northern Hemisphere ice sheet expansion implies that regional water balance and glacial mass balance are strongly influenced by global-scale temperature changes, as well as by precessional forcing of the South American summer monsoon.

Despite the hypothesized importance of the tropics in the global climate system, few tropical paleoclimatic records extend to periods earlier than the last glacial maximum (LGM), about 20,000 years before present. We present a well-dated 170,000-year time series of hydrologic variation from the southern hemisphere tropics of South America that extends from modern times through most of the penultimate glacial period. Alternating mud and salt units in a core from Salar de Uyuni, Bolivia reflect alternations between wet and dry periods. The most striking feature of the sequence is that the duration of paleolakes increased in the late Quaternary. This change may reflect increased precipitation, geomorphic or tectonic processes that affected basin hydrology, or some combination of both. The dominance of salt between 170,000 and 140,000 yr ago indicates that much of the penultimate glacial period was dry, in contrast to wet conditions in the LGM. Our analyses also suggest that the relative influence of insolation forcing on regional moisture budgets may have been stronger during the past 50,000 years than in earlier times.

This work presents the first reconstruction of late Pleistocene glacier fluctuations on Uturuncu volcano, in the Southern Tropical Andes. Cosmogenic 3He dating of glacial landforms provides constraints on ancient glacier position between 65 and 14 ka. Despite important scatter in the exposure ages on the oldest moraines, probably resulting from pre-exposure, these 3He data constrain the timing of the moraine deposits and subsequent glacier recessions: the Uturuncu glacier may have reached its maximum extent much before the global LGM, maybe as early as 65 ka, with an equilibrium line altitude (ELA) at 5280 m. Then, the glacier remained close to its maximum position, with a main stillstand identified around 40 ka, and another one between 35 and 17 ka, followed by a limited recession at 17 ka. Then, another glacial stillstand is identified upstream during the late glacial period, probably between 16 and 14 ka, with an ELA standing at 5350 m. This stillstand is synchronous with the paleolake Tauca highstand. This result indicates that this regionally wet and cold episode, during the Heinrich 1 event, also impacted the Southern Altiplano. The ELA rose above 5450 m after 14 ka, synchronously with the Bolling–Allerod.

We revise substantially the regional chronology of lake-level fluctuations from the late-glacial/early Holocene humid phase along a high altitude transect (3500 to 4500 m) between 18°S and 28°S in the Southwestern Altiplano of Northern Chile. Radiocarbon dates and 210Pb profiles for limnic and terrestrial materials allow us to estimate and justify reservoir correction values for conventional 14C dates. Our chronology suggests that the latest Pleistocene/early Holocene humid phase started between 13,000 and 12,000 14C yr B.P., and that maximum lake levels were reached between 10,800 and 9200 14C yr B.P. This is significantly younger than what has been established so far for the Titicaca–Uyuni Basin in Bolivia. The paleolakes disappeared sometime between 8400 and 8000 14C yr B.P. Our revised chronology agrees with the regional history of human occupation, and is broadly synchronous with vegetation changes in subtropical continental South America, and with the onset of wetland expansion in the northern hemisphere tropics.

We have developed an 87Sr/86Sr, 234U/238U, and δ18O data set from carbonates associated with late Quaternary paleolake cycles on the southern Bolivian Altiplano as a tool for tracking and understanding the causes of lake-level fluctuations. Distinctive groupings of 87Sr/86Sr ratios are observed. Ratios are highest for the Ouki lake cycle (120–95 ka) at 0.70932, lowest for Coipasa lake cycle (12.8–11.4 ka) at 0.70853, and intermediate at 0.70881 to 0.70884 for the Salinas (95–80 ka), Inca Huasi (~ 45 ka), Sajsi (24–20.5 ka), and Tauca (18.1–14.1 ka) lake cycles. These Sr ratios reflect variable contributions from the eastern and western Cordilleras. The Laca hydrologic divide exerts a primary influence on modern and paleolake 87Sr/86Sr ratios; waters show higher 87Sr/86Sr ratios north of this divide. Most lake cycles were sustained by slightly more rainfall north of this divide but with minimal input from Lake Titicaca. The Coipasa lake cycle appears to have been sustained mainly by rainfall south of this divide. In contrast, the Ouki lake cycle was an expansive lake, deepest in the northern (Poópo) basin, and spilling southward. These results indicate that regional variability in central Andean wet events can be reconstructed using geochemical patterns from this lake system.

On June 23, 2001, an M8.4 earthquake that originated in southern Peru triggered the partial collapse of the Chislluma bofedal (water meadows) in the Altiplano (high-altitude plateau) of northern Chile. The seismic waves evidently produced the liquefaction of the bofedal and caused its partial collapse generating a flow. The flow deposit was mainly made of long-fiber grass and water, with minor amounts of clastic material. It traveled more than 14 km downstream at a peak velocity of 50 km/h. It destroyed the water meadows and killed more than 20 llamas. Slurry flows caused by meadow liquefaction are a previously unrecognized seismic-induced geological hazard for high-altitude plateau areas such as the Altiplano.

A simple mass balance model provides insight into the hydrologic, isotopic, and chemical responses of Lake Titicaca to past climatic changes. Latest Pleistocene climate of the Altiplano is assumed to have been 20% wetter and 5°C colder than today, based on previous modeling. Our simulation of lacustrine change since 15,000 cal yr B.P. is forced by these modeled climate changes. The latest Pleistocene Lake Titicaca was deep, fresh, and overflowing. The latest Pleistocene riverine discharge from the lake was about 8 times greater than the modern average, sufficient to allow the expansion of the great paleolake Tauca on the central Altiplano. The lake δ18O value averaged about −13‰ SMOW (the modern value is about −4.2‰). The early Holocene decrease in precipitation caused Lake Titicaca to fall below its outlet and contributed to a rapid desiccation of paleolake Tauca. Continued evaporation caused the 100-m drop in lake level, but only a slight (1–2‰) increase (relative to modern) in δ18O of early Holocene lake waters. This Holocene lowstand level of nearly 100 m was most likely produced by a precipitation decrease, relative to modern, of about 40%. The lake was saline as recently as 2000 cal yr B.P. The timing of these hydrologic changes is in general agreement with calculated changes of insolation forcing of the South American summer monsoon.

Stratigraphic relationships, radiocarbon dating, sediment and peat characteristics, and rates of peat and carbon accumulation from a soligenous peatland, or “bofedal,” in the Chilean Altiplano shows the peatland to be unusually young, dynamic, and sensitive to environmental changes. The site lies in the National Park Nevado de Tres Cruces in the puna desert grassland at an elevation of 4300 m a.s.l. Eight peat cores were extracted from a 1.75-km transect yielding a maximum of 3.6 m of organic sediment. Organic matter began to accumulate 1700–1100 cal yr B.P. under a progressively arid local climate, after a period when regional climate is believed to have been more humid than at present. Areas of greater relief and better drainage in the valley bottom eventually fostered the growth of a riparian cushion plant community after water flowing down the valley began to diminish. This led to rapid lateral expansion of the riparian peatland communities over open water in topographic depressions at a rate heretofore unprecedented in the peatland literature. It appears that development of the peatland has been encouraged by autoregulation of internal hydrology. The drainage impediment created by organic mass accumulation in lower-relief areas probably reduced the amount of water arriving at the lower reaches of the peatland. These areas have become progressively drier and have since died and oxidized. Through endogenous peat accumulation and a concomitant drainage impediment, the ecosystem has been migrating upstream over the past 50 years.

This paper presents a high-resolution ice-core pollen record from the Sajama Ice Cap, Bolivia, that spans the last 400 yr. The pollen record corroborates the oxygen isotopic and ice accumulation records from the Quelccaya Ice Cap and supports the scenario that the Little Ice Age (LIA) consisted of two distinct phases�"a wet period from AD 1500 to 1700, and a dry period from AD 1700 to 1880. During the dry period xerophytic shrubs expanded to replace puna grasses on the Altiplano, as suggested by a dramatic drop in the Poaceae/Asteraceae (P/A) pollen ratio. The environment around Sajama was probably similar to the desert-like shrublands of the Southern Bolivian Highlands and western Andean slopes today. The striking similarity between the Sajama and Quelccaya proxy records suggests that climatic changes during the Little Ice Age occurred synchronously across the Altiplano.

A balanced cross-section spanning the Eastern Cordillera and Subandean Zone of southern Peru (13–15°S) constrains ~130 km (38%) of Cenozoic orogen-normal SW–NE Andean deformation accommodated by thick- and thin-skinned retro–arc fold–thrust belt shortening that overprinted pre-Andean Triassic normal faults. Zircon and apatite (U–Th)/He ages demonstrate continuous Oligocene to Miocene cooling of the Permo-Triassic Coasa pluton in the Eastern Cordillera. Zircon (U–Th)/He ages (~34–18 Ma) are reset and define a steep age versus elevation relationship. Apatite (U–Th)/He results reveal reset ages that define two spatially separated groups with ages of ~30–26 Ma and ~17–11 Ma. Detrital zircon U–Pb geochronologic results from Cretaceous–Cenozoic siliciclastic rocks from the Altiplano/Eastern Cordillera record Andean fold–thrust belt and magmatic-arc sediment sources. Correlative Subandean Zone rocks preserve a cratonic sediment contribution, with minor Andean sediment appearing in some Cenozoic rocks. We propose that earliest Andean deformation and structural compartmentalization of the Eastern Cordillera was linked to selective inversion of inherited Permo-Triassic basement-involved normal faults that guided subsequent thick- and thin-skinned deformation. Provenance variations between the hinterland and foreland depocentres reveal competing eastern and western sediment sources, reflecting an axial zone in the Eastern Cordillera that coincided with the inherited Triassic graben and impeded sediment source mixing. Our zircon and apatite (U–Th)/He ages are consistent with published constraints along strike and support pulses of Eocene to late Miocene exhumation that were likely driven by normal fault reactivation and protracted Eastern Cordillera deformation.

Rural depopulation has different effects on biodiversity and ecosystems in many regions of the world. For large carnivores such as pumas (Puma concolor) the effects are uncertain. An analysis of relationships between patterns of rural depopulation and perceptions of the risk posed by pumas among Aymara people in the altiplano region of Chile examined perceived risk, as well as self-reported losses, in relation to livestock husbandry, sociodemographic variables (age, household size, and residency status), and reported self-sufficiency. There was no evidence that rural depopulation elevated perceived risk, or the level of self-reported losses of livestock blamed on pumas. Indeed, many respondents, including older respondents and those with smaller households, reported a decline in perceived risk over the preceding five years. These perceptions of risk were not associated with self-reported losses to pumas in the previous year. An increase in perceived risk was associated with the use of guards for livestock, suggesting livestock owners accommodated their absences from herds by using guards. Absolute numbers of livestock lost increased with the distance from households to where livestock were grazed or gave birth. A cost-effective verification system for puma attacks is recommended, and further human dimensions research is required to identify the owners who complained and the costs and benefits of different wildlife species. Further interventions to prevent either livestock losses or retaliation against pumas can then be targeted more precisely.

Researchers in the High Andes in northern Chile report the study of a fine cave sequence, supported by 19 radiocarbon dates. The initial occupation at c. 11 500 cal BP represents the earliest human occupation known at this altitude. The toolkit suggests a hunting (logistical) camp used to take advantage of the animals gathering in the rich wetland of the neighbourhood.