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A 38,000-year record of floods and debris flows in the IIo region of southern Peru and its relation to El Niño events and great earthquakes

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A 38,000-year record of floods and debris flows in the IIo region of southern Peru and its relation to El Niño events and great earthquakes

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Abstract

Previous work throughout the Ilo region of south coastal Peru has documented the existence of flood and debris-flow deposits produced by two El Niño events evidently much more severe than any in recent history. These two events have been dated to ca. AD 1300–1400 and AD 1607–08. The Late Pleistocene to Holocene record of older sedimentary deposits in this region is dominated by flood and debris-flow deposits of similar scale. These older deposits have been described and dated from three coastal, alluvial-fan sites. These deposits, which are as old as 38 200 years, are dominated by massive debris-flow deposits, several tens of cm thick, typically composed of cobble- and boulder-sized clasts in a matrix of silty sand, with characteristics indicating generation by heavy rainfall in an arid environment. Twenty-two radiocarbon dates and a single infrared-stimulated luminescence date show that particularly severe El Niño events occurred throughout the Late Pleistocene and two of three divisions of the Holocene with significantly different frequencies. The period of greatest activity was during the Early Holocene when at least six such events took place during a period of ca. 3600 years, beginning near the end of the Younger Dryas ca. 12 000 years ago. One of these events produced a debris flow that may have caused abandonment of the Paleo-Indian site at Quebrada Tacahuay, one of the oldest on the Andean coast. No severe events took place during the Middle Holocene between ca. 8400 and 5300 years ago, when a wide variety of other paleoclimate proxy records indicate that the El Niño–Southern Oscillation regime was particularly weak. Since ca. 5300 years ago, four of these severe events have taken place. The Late Pleistocene sequence is constrained by only two dates, which indicate that at least ten severe events took place between ca. 38 200 and 12 900 years ago. Mechanisms probably responsible for generating these large-scale deposits include: (1) ‘Mega-Niños’ that produced anomalously heavy rainfall along most or all of the central Andean coast; (2) El Niños that occurred shortly after great earthquakes that produced large amounts of sediment; or (3) El Niños that produced anomalously heavy local rainfall. The existence of these large-scale deposits in the Ilo region implies a level of hazard much higher than indicated by the historical record alone.

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... Interestingly, Keefer et al. (2003) inferred a similar timing of mass movements along the opposite slope of the Andes, specifically, the hyper-arid coastal region of southern Peru (Ilo region). Herein, debrisflow deposits that were dated to~38.2-12.9 ...
... Herein, debrisflow deposits that were dated to~38.2-12.9 ka, and mainly postdating 5.3 ka, are related to short-term periods of heavy rainfall from ENSO activity (Keefer et al., 2003). Additionally, other dated large-scale mass movements in the western Andes of Peru might have been related to humid climate periods, such as the~40-km 3 Chuquibamba landslide complex, which coincided with the Ouki wet climatic event (~100 ka), or the giant (~15 km 3 ) polyphase Cerro Caquilluco rock avalanche, which sequentially originated since~600 ka (Zerathe et al., 2015. ...
... Although all these discussed mass movement phases in the Andes might also reflect seismic triggering (McPhillips et al., 2014), most authors attributed slope instabilities to i) higher runoff from the scouring and undercutting of structurally preconditioned mountain slopes and ii) enhanced seasonality and the occurrence of extreme rainfall, which reduced the slope-stability threshold and increased the susceptibility of rock slopes to even low-magnitude earthquakes (Trauth and Strecker, 1999;Keefer et al., 2003). A similar interpretation was used for the occurrence of large rotational landslides in the Rio Grande canyon (New Mexico, USA) by Reneau and Dethier and Reneau (1996). ...
Article
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Climatic factors are considered major causes and triggers of slope instability, but the palaeoclimatic implications of landslides have not yet been systematically reviewed. As inferred from landslides dated to the Late Glacial and Holocene, glacial-interglacial transitions are the major intervals of enhanced landsliding, but the length of this interval varies between distinct types of landscapes. Mass movements in non-glaciated temperate mountain ranges, arid and tropical regions, and coastal areas intensified soon after the onset of the Holocene alongside the warming and wetting of the climate, whereas large rock slides in areas within the limits of Pleistocene glaciations mostly show a millennial-scale time lag with respect to glacier withdrawal. Although the incidence of landslides was ubiquitous throughout the Holocene, the mid- to late-Holocene transition (~5–4 ka) was especially favourable for the origin of landslides across distinct types of landscapes, indicating a strengthened role of mass movements during the culmination phases of interglacial climate optima. In addition, growing evidence suggests that the enhanced activity of landslides occurred during warmer interstadial conditions, which is best demonstrated in the temporal coincidence of arid-zone landslides with Quaternary “pluvials”. Future progress in the understanding of the relationships between landslides and Quaternary climate changes should benefit from the i) extension of datasets of dated landslides, ii) geographical expansion of dating studies to regions with a lack of chronologically determined landslides (e.g., tropics), iii) improvement of landslide-dating strategies involving the incorporation of independent palaeoclimatic proxies and iv) wider incorporation of numerical modeling within landslide-dating studies.
... Even less is known about the Holocene period, and what is known about fluvial sedimentation is generally explained by mechanisms involving El Niño Southern Oscillation (ENSO), e.g. Wells (1990), Keefer et al. (2003), Magilligan et al. (2008), Sandweiss et al. (2009), Abbühl et al. (2010). ENSO is characterised by interannual variations in air temperature and discharge, yet in the instrumental record there is no clear correlation between flooding, precipitation and ENSO events (Garreaud et al., 2009;Baker and Fritz, 2015). ...
... It is striking that the two youngest terraces were formed at the two key times recorded in the Cunas-Mantaro valley: the moment of renewed valley formation dated at 4418 ± 500 years ago and the moment of accelerated incision and terrace formation dated at 2245 ± 217 years ago. Similarly, in the Ilo valley (18°S latitude), bordering Chile, three debris-flow deposits were dated at the same time as terrace formation in the Cunas valley (Keefer et al., 2003; Table 7). Strong parallels also exist between our study area and the Moquegua River valley (18°S latitude; Table 7). ...
... A statistically significant correlation was also found between rainfall in the Mantaro basin and the Tropical Atlantic SST for the past decades (IGP, 2005;Silva et al., 2008). The similarities between our fluvial record and those of Wells (1990), Keefer et al. (2003) and Magilligan et al. (2008) therefore suggest that it is not ENSO that is responsible for the observed centennial-scale pattern in deposition of fluvial sediments, but rather oscillations in the SASM, modulated by a southward shift of the ITCZ, which in turn is linked to changes in North Fig. 15. Paleoclimatological reconstructions of the central Peruvian Andes. ...
Article
The occurrence of Holocene changes in the South American Summer Monsoon (SASM) in the Peruvian Andes has been well established in paleoclimatological records such as speleothem, lake and glacier records. How river systems responded to these events has, however, hardly been investigated. Here, we present evidence based on sedimentological, stratigraphical and geomorphological data as well as radiometric (optically stimulated luminescence and radiocarbon) dating that rivers from the Peruvian Andes are extremely sensitive to changes in SASM activity. The presence of lake sediments shows that from at least 12,000 years ago until 4153 ± 988 years ago a lake was present in the Mantaro River valley, possibly due to damming by a glacier or glacial landforms. A reconstruction of fluvial terrace profiles shows that 4418 ± 500 years ago the Mantaro and its tributary, the Cunas River, incised and laid down sediments simultaneously as a response to changes in regional base-level and increased SASM activity. The latter was largely subdued during a large part of the Holocene as evidenced by paleoclimatological records in the region. Between 2245 ± 217 years ago and the present, the frequency of SASM events increased drastically and both rivers formed the majority of their fluvial terraces. In total, over the past ~4000 years, the Mantaro River formed five terrace levels and the Cunas River formed seven main terraces. Locally, 11 terrace levels were recognised. Terrace formation occurred at intervals of approximately 250 to 300 years between 2245 ± 217 and 1188 ± 60 years ago and approximately every 150 years after 824 ± 66 years ago until the present. A comparison with paleoclimatological data shows that sedimentation events correlate to periods of increased precipitation and glacier retreat in the Peruvian Andes, whereas phases of incision are attributed to continuous adjustments in base-level fall. Thirty-four metres of incision has occurred since 4418 ± 500 years ago averaging 7.7 mm yr ⁻¹ . A comparison with data from other river systems in the Peruvian Andes shows that many rivers responded in a similar way to centennial-scale variations in SASM activity. Fluvial activity is thus not related to interannual variations in the El Niño Southern Oscillation (ENSO) contrary to previous proposals.
... In archaeology, disaster studies have intensified over the past decade with a focus on the role of rapid environmental change or catastrophe in societal collapse or reorganization (Anderson et al. 2007;Bawden and Reycraft 2000;Cooper and Sheets 2012;Diamond 2005;Fisher et al. 2009;Mc Anany and Yoffee 2010;Redman 2004;Sandweiss and Quilter 2008a;Schwartz and Nichols 2010). Along the arid Andean coast, such studies have tended to focus on the impact of El Niño and catastrophic flooding on culture and landscape change (e.g., Beresford-Jones 2011; Fontugne et al. 1999;Keefer et al. 1998;Keefer et al. 2003;Magilligan and Goldstein 2001;Magilligan et al. 2008;Moore 1991;Moseley and Keefer 2008;Nials et al. 1979;Rein et al. 2004;Richardson and Sandweiss 2008;Sandweiss et al. 2007;Wells 1987), though some also emphasize volcanic eruption, tectonic activity, and drought as other potential environmental catalysts to change (Keefer and Moseley 2004;Moseley 1983;Moseley et al. 1992;Pearsall 2004;Satterlee et al. 2000). ...
... In the Ilo region of far southern Peru ( Figure 1), several large punctuated environmental events have received a fair amount of archaeological and historical attention. A major El Niño termed the Miraflores event is thought to have caused widespread catastrophic destruction to late fourteenth century habitation areas, irrigation systems, and agricultural fields (Clement and Moseley 1991;Keefer and Moseley 2004;Keefer et al. 2003;Moseley and Keefer 2008; Reycraft 1998Reycraft , 2000Satterlee 1993;Zaro 2007;Zaro and Umire 2005), while the convergence of this incident with a prolonged drought is argued to have catalyzed the disappearance of Late Intermediate Period (LIP) Chiribaya culture altogether (Satterlee et al. 2000). Approximately two centuries later, the Huaynaputina volcano, in the neighboring Moquegua highlands, erupted over the course of several weeks early in the year A.D. 1600, causing widespread devastation in the upper reaches of Arequipa and Moquegua (de Silva et al. 2000;de Silva ANDEAN PAST 11 (2013): 233-262. ...
... Historic travelers in the area report that highland populations emigrated from severely impacted regions, though little mention was made of the coastal areas (de Silva et al. 2000;Vázquez de Espinosa 1942[1628). Sometime later, and potentially within only a few years or decades, another El Niño-related flood, termed the Chuza event, left a significant amount of flood and debris flow sediment among lower and coastal landscapes of the Tambo-Ilo region (Keefer et al. 2003;Moseley and Keefer 2008;Satterlee 1993;Satterlee et al. 2000). These three punctuated events are wellrepresented in the geomorphic records along the Peruvian south coast, though only the Miraflores flood and Huaynaputina eruption have received significant archaeological and historical attention, respectively, and much of this attention has emphasized the destructive nature of such occurrences. ...
... cit.) registran un pico de actividad de El Niño que decae a ~10.000 a.p. y vuelve a aumentar alrededor de ~9,000 a.p. En la Quebrada de Tacahuay, sur de Ilo (Fig. 1), Keefer et al. (1998Keefer et al. ( , 2003, registran eventos de El Niño en sedimentos aluviales que fechan entre cal. 12,500 y cal. ...
... 5700 a.p. Keefer et al. (1998Keefer et al. ( , 2003 registran una disminución signi cativa en la ocurrencia de eventos El Niño, hallando luego un gran evento fechado en cal. 5300 a.p. ...
... Moore (1991) registra la construcción de campos elevados de cultivo como respuesta del Estado Chimú a un evento de El Niño en la Quebrada de Santa Cristina, Casma, el cual fecha indirectamente en la primera mitad del siglo XIV, relacionándolo con el evento registrado por Wells (1990) para este siglo. Keefer et al. (2003) registran este mismo evento a través de depósitos aluviales en la Quebrada Mira ores, Ilo, alrededor de cal. 1330 d.C., a este evento se le conoce como «Mira ores event» o «Mira ores ood» y se le asocia a la caída de la cultura Chiribaya en la costa sur. ...
Article
Full-text available
Resumen Este artículo presenta evidencia de un mega El Niño ocurrido alrededor de ca. 600 d.C. registrada en el sitio arqueo-lógico Huaca 20-Complejo Maranga. Se discute las dinámicas hombre-medio ambiente (ecodinámicas humanas), que pudieron haber sucedido a nes del Periodo Intermedio Temprano en este sitio y en otros asentamientos de los valles de Lima. Se compara también estos datos con información contemporánea procedente de la Costa Norte y se propone que este periodo de stress ambiental pudo haber signiicado un momento de oportunidad para las sociedades del Periodo Intermedio Temprano. Palavras clave: cultura Lima, El Niño, ecodinámicas humanas, Periodo Intermedio Temprano, Costa Central, Andes. Abstract HUMAN ECO-DYNAMICS IN HUACA 20: REASSESING THE IMPACT OF EL NIÑO AT THE END OF THE EARLY INTERMEDIATE PERIOD is article presents evidence of a mega Niño event that transpired around ca. 600 d.C. recovered at the archaeological site of Huaca 20-Complejo Maranga and discusses the human eco-dynamics that could have happened at the end of the Early Intermediate Period in this site and other settlements of the Lima Valleys. is information is compared with contemporary data from the North Coast. I propose that this period of environmental stress could have signiied a time of opportunities for some societies of the Early Intermediate Period.
... On the north side of the deeply incised channel is an occupation dating to 13,120-11,380 cal BP. The earliest occupation was buried and preserved when an ancient El Niño event triggered a massive debris flow (Keefer et al. 1998;Keefer, Moseley, and deFrance 2003). The site was reoccupied ca. ...
... Quebrada Miraflores (17 26 0 S 71 22 0 W) Quebrada Miraflores, located roughly 20 km north of Ilo, contains both a late prehispanic village (Late Intermediate Period, Chiribaya culture, CE 1100-1300; Satterlee et al. 2000) as well as an exposed profile containing three thin cultural middens separated by sheet flood deposits (Keefer, Moseley, and deFrance 2003) (see Figure 3). The three thin middens all date to the Early Holocene. ...
... The three thin middens all date to the Early Holocene. The deepest midden, a deposit of organic material without shell, dates to 10,810-10,350 cal BP, while the upper shell middens indicate that coastal inhabitants occupied the site from 9940 to 8410 cal BP (deFrance, Grayson, and Wise 2009;Keefer, Moseley, and deFrance 2003). Thus far, the only Early Holocene archaeological evidence documented at Miraflores are the deep, thin midden deposits. ...
... Strong El Niño events may have created inhospitable conditions for the inhabitants of the site, pressuring them to leave. Tacahuay is believed to have been a logistical station used to process seabirds (Keefer et al. 1998, deFrance et al. 2001, Keefer at al. 2003. Perhaps the prolonged absence of humans at the site is indicative of an absence of seabirds at Tacahuay rather than of hazardous coastal conditions. ...
... Flooding events are therefore attributed to strong El Niño events. Thick clastic debris-flow deposits from the site suggest that there were at least six separate severe flooding events from 12,900-8,500 year BP (Keefer et al. 2003). Subsequently, there were no major flooding events for ~3,000 years, until ~5,400 cal yr BP, which was preceded by a major earthquake (Keefer et al. 2003, deFrance andKeefer 2005). ...
... Thick clastic debris-flow deposits from the site suggest that there were at least six separate severe flooding events from 12,900-8,500 year BP (Keefer et al. 2003). Subsequently, there were no major flooding events for ~3,000 years, until ~5,400 cal yr BP, which was preceded by a major earthquake (Keefer et al. 2003, deFrance andKeefer 2005). ...
Thesis
Quebrada Jaguay 280 (QJ-280) is one of the oldest maritime archaeological sites in the New World. Previous excavations of the southern Peruvian coastal site have dated occupation from ~13,000-8,000 cal yr BP. These excavations also determined that the occupants of the site used preferential maritime resource procurement strategies and had an interzonal connection to the highlands. In 2017 a new excavation was conducted at QJ-280 and the remains of the marine mollusk Mesodesma donacium were recovered. Geochemical examinations on the shell remains informed on the occupational seasonality of the site and reconstructed sea surface temperatures experienced off the coast of southern Peru. The study determined that QJ-280 was seasonally occupied during the austral summer. There was a notable expansion in occupation from the Terminal Pleistocene, when the site was primarily occupied during the month of March, to the Early Holocene, when occupation occurred during the months of February and March. The impetus for the change was likely either cultural or environmental. The sea surface temperature reconstruction determined that the Pacific off the coast of QJ-280 experienced cooler than modern temperatures from ~12,000-11,000 cal yr BP during the months of March, April, and May. The reconstruction also allowed for the identification of a Terminal Pleistocene El Niño event. Occupation at QJ-280 was seasonal and likely influenced by patterns of freshwater availability during the Terminal Pleistocene and Early Holocene.
... In general, such reworking seems plausible, as pointed out in Lamb and Fonstad [2010] or in Storz-Peretz et al. [2011], who have shown that the incision/erosion of tectonically uplifted zones in river beds can be extremely rapid, up to~1 m/yr or even higher during a single large flood event. However, the river networks in the hyperarid Precordillera region are dry most of the time, except during exceptional El Niño events [e.g., Keefer and Moseley, 2003]. Thus, an important question is whether the young age for the channel deposits, implied by our data, is reasonable. ...
... Throughout the hyperarid forearc region, evidence is found for large floods and debris flows that occurred during the Pleistocene-Holocene and were associated with El Niño events. This evidence includes preserved fluvial terraces and buried archeological sites [e.g., Goldstein and Magilligan, 2011;Keefer and Moseley, 2003;Manners et al., 2007;Goldstein and Magilligan, 2011]. Radiocarbon chronologies from both coastal and Precordilleran sites suggest recurrence intervals for large El Niño-driven floods of <2500 years for the late Pleistocene, <600 years for the early Holocene, and <1500 years for the late Holocene [Keefer and Moseley, 2003]. ...
... This evidence includes preserved fluvial terraces and buried archeological sites [e.g., Goldstein and Magilligan, 2011;Keefer and Moseley, 2003;Manners et al., 2007;Goldstein and Magilligan, 2011]. Radiocarbon chronologies from both coastal and Precordilleran sites suggest recurrence intervals for large El Niño-driven floods of <2500 years for the late Pleistocene, <600 years for the early Holocene, and <1500 years for the late Holocene [Keefer and Moseley, 2003]. Goldstein and Magilligan [2011] and Manners et al. [2007] found evidence of large floods along Rio Moquegua, such as the one associated with the 1997-1998 El Niño. ...
Article
Our understanding of the style and rate of Quaternary tectonic deformation in the forearc of the Central Andes is hampered by a lack of field observations and constraints on neotectonic structures. Here, we present a detailed analysis of the Purgatorio fault, a recently recognized active fault located in the forearc of southern Peru. Based on field and remote sensing analysis (Pléiades DEM), we define the Purgatorio fault as a subvertical structure trending NW-SE to W-E along its 60 km length, connecting, on its eastern end, to the crustal Incapuquio Fault System. The Purgatorio fault accommodates right lateral transpressional deformation, as shown by the numerous lateral and vertical plurimetric offsets recorded along strike. In particular, scarp with a 5-m cumulative throw is preserved and displays cobbles that are cut and covered by slickensides. Cosmogenic radionuclide exposure dating (10Be) of quartzite cobbles along the vertical fault scarp yield young exposure ages that can be bracketed between 0 to 6 ka, depending on the inheritance model that is applied. Our preferred scenario, which takes in account our geomorphic observations, implies at least two distinct rupture events, each associated with ~3 and ~2 m of vertical offset. These two events plausibly occurred during the last thousand years. Nevertheless, an interpretation invoking more tectonic events along the fault cannot be ruled out. This work affirms crustal deformation along active faults in the Andean forearc of southern Peru during the last thousand years.
... Los depósitos aluviales y coluviales muestran superficies bien conservadas (figura 3.6) y podrían estar relacionadas con precipitaciones extraordinarias o asociadas a fenómenos de El Niño (Keefer y Moseley, 2004;Keefer et al., 2003). Del mismo modo, se demostró en los Andes que este tipo de depósitos están asociados a glaciaciones (Ratnayaka et al., 2019;Rutter et al., 2012). ...
... Los depósitos aluviales y coluviales muestran superficies poco preservadas en comparación con el sector donde aflora la Falla Cerro Carnaval, pero de igual forma podrían estar relacionadas con precipitaciones extraordinarias o asociadas a fenómenos de El Niño (Keefer y Moseley, 2004;Keefer et al., 2003). También, debemos tener en cuenta que los depósitos aluviales y coluviales en los Andes están asociados a glaciaciones (Ratnayaka et al., 2019;Rutter et al., 2012). ...
... Esta falla afecta depósitos aluviales y rocas jurásicas de la Formación Guaneros con movimientos de tipo normal. Los depósitos aluviales muestran superficies poco preservadas al igual que en el sector donde aflora la Falla Alto Los Chilenos, que podrían estar relacionadas con precipitaciones extraordinarias o asociadas a fenómenos de El Niño (Keefer y Moseley, 2004;Keefer et al., 2003) o asociadas a glaciaciones (Ratnayaka et al., 2019;Rutter et al., 2012). ...
Technical Report
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En el presente trabajo ponemos en evidencias fallas geológicas activas y cuaternarias, que se emplazan a lo largo de las pampas costeras, la Cordillera Occidental y el Altiplano. Para determinar esta relación de morfología y cinemática de fallas con la msagnitud del sismo, utilizamos un conjunto de metodologías, que incluyen las geología estructural, estratigrafía, geomorfología, sensores remotos y la paleosismología. Todas estas metodologías, contribuyeron a realizar análisis e identificar fallas geológicas activas a la región de Tacna. De acuerdo a la morfología y cinemática de las fallas Purgatorio-Mirave y Sama-Calientes, deducimos que estas fallas pueden generar sismos M>7. Además, en este trabajo, ponemos en evidencia por primera vez, una ruptura superficial de ~100 km asociada al Sistema de Falla Incapuquio. Entonces, con base a estudios neotectónicos y paleosismológicos, ponemos en evidencia de que ~100 km de escarpas de fallas de 2-4 m de altura fueron formadas por un terremoto de cinemática transpresional a lo largo de 100 km del segmento sur de la Falla de Incapuquio a principios del siglo XV (~AD 1400-1440). Las Las relaciones de escala empíricas sugieren que la magnitud de este terremoto habría sido de Mw 7,4-7,7 con al menos 2-3 m de deslizamiento neto. Eventos similares plantean un peligro significativo para las poblaciones asentadas en la región del antearco peruano. La fecha de este terremoto coincide con el colapso de la población de la civilización Chiribaya entre los años 1360 y 1400 d.C., presentamos evidencia de edificios dañados y desviados. Hacia los altos Andes, se ubican los volcanes activos de los Andes Centrales, adyacentes a ellos identificamos fallas de tipo normal, que generaron desplazamientos verticales de hasta ~20 m. Las fallas en el sector de Purupuruni, Paucarani, Vilacota, entre otros, son fallas que afectan morrenas glaciares y depósitos aluviales. De acuerdo a la longitud y desplazamiento vertical, sugerimos que estas fallas pueden generar sismos M>6.0. Los análisis neotectónicos y morfotectónicos sirven para caracterizar el potencial sismogénico de las estructuras tectónicas, lo que permite elaborar mapas de aceleración sísmica (peligro sísmico) deducido de la magnitud máxima posible que una falla activa podría generar. Asimismo, el movimiento del terreno por efectos del sismo genera procesos geológicos asociados, como por ejemplo movimientos en masa, procesos de licuación de suelos, asentamientos y grietas en el terreno, que afectan o podrían afectar ciudades, infraestructura y obras de gran envergadura. Con esta finalidad, generamos mapas de amenaza sísmica a partir de la interacción entre los mapas de susceptibilidad y el mapa de aceleración sísmica, que una falla activa podría generar. Se obtuvieron mapas de peligrosidad por movimientos en masa y los mapas de peligrosidad por procesos de licuefacción de suelos y/o asentamientos para las fallas más importantes de la región Tacna, mostrandosé que las fallas activas pueden generar aceleraciones locales altas y detonar procesos de movimentos en masa. Para poder identificar las zonas que se encuentran en riesgo o que serían afectadas por la reactivación de las fallas geológicas activas, elaboramos mapas de riesgo, treinta y uno (31) escenarios, para la región Tacna tomando como base los mapas de peligrosidad detonados por sismo, donde se superponen las capas de áreas restringidas y la capa de infraestructuras de la región (ciudades, población, hidroeléctricas, aeropuertos, represas, futuras obras de gran envergadura, etc.) De esta forma, obtenemos un mapa de riesgo donde se pueden identificar las ciudades u obras de gran envergadura que se verán afectadas por la reactivación de las fallas antes mencionadas. Estos mapas se consideran una herramienta importante para los Planes de Ordenamiento Territorial y son de gran ayuda para la toma de decisiones en planes de prevención en el marco de la gestión del riesgo de desastres. Se recomienda realizar trabajos paleosismológicos detallados en las fallas Purgatorio, Incapuquio, Sama-Calientes, Paucarani, Vilacota entre otros, con la finalidad de determinar la máxima magnitud posible y la recurrencia de estos eventos, debido a que adyacentes a estas zonas se ubican infraestructura privada y pública que podría ser afectada; en este sentido, esta información contribuirá a la Planificación del Territorio y crecimiento socio-económico del país.
... The greatest differences, as noted, take place in two defined intervals within the Middle Holocene chron, a critical phase of transition in terms of both climate and culture in the study region (Sandweiss et al. 1999;Keefer et al. 2003;Gayo et al. 2015). Nonetheless, it is possible that the regional divisions implemented here are masking potentially more profound variation between different sets of subregions. ...
... Recent studies have marshalled population genetics, geoarchaeology, and importantly, climate archives to contextualise the wealth of data on pre-Columbian demographic processes (Keefer et al. 2003;Dillehay and Kolata et al. 2004;Fehren-Schmitz et al. 2014;Perez et al. 2017). Figure 5a-c presents three palaeoclimatic archives for the Holocene that are of especial importance to contextualising millennial-scale demographic patterns illustrated by the model and permutation ...
... Third, and complementary to this, the 106KL marine sediment core records the concentration and accumulation rate (flux) of terrestrial lithic input from a continental shelf site (Rein et al. 2005). This provides a proxy for the frequency and intensity of ENSO events, as a driver of coastal flooding, highland aridity, sea temperature inversions, and resulting reconfigurations of coastal aquatic ecosystems (Moy et al. 2002;Keefer et al. 2003;Chavez et al. 2003;Sandweiss et al. 2004;Williams et al. 2008). Both concentration and flux are rendered as a percentage of the maximum recorded value in the core and must be interpreted together, as very low flux rates for the mid-Holocene could in part be due to erosional processes as well as a suppressed ENSO (Rein et al. 2005). ...
Article
This paper adopts a formal model-testing approach to the Peruvian radiocarbon (14C) record, the site of the first aggregate analysis of this type of archaeological data. Using a large and improved regional dataset of radiometric determinations (n = 1180) from the period 14000–3000 14C years before present, the study performs a comparative analysis of the demographic trajectories of two sub-regions, the desert coast and Andean highlands. Against the backdrop of theoretical models of population growth, and controlling for taphonomic factors and sampling biases, the study performs global significance and permutation tests on the data. These provide a necessary measure of statistical confidence that have hereto been absent from the discussion of pre-Columbian demography. Contrary to the findings of prior work, this study of radiocarbon data in Peru reveals that regional trends in the data are statistically indistinguishable. Further testing and comparison to climate archives is able to illustrate sustained population growth over the entire Holocene epoch in this region, with only a few notable exceptions at the end of the mid-Holocene (5000 cal BP). The findings of the analysis are viewed in relation to the cultural and technological changes that indigenous societies experienced in the timeframe in question, and some directions for methodological advances are suggested.
... Very little research, however, deals with coastal alluvial fans (CAF) additionally influenced by marine base-level change; in particular, in hyperarid settings. Such northern Chile but can also be found along coastal mountain ranges in several other hyperarid regions on earth; for instance, southern Peru (Keefer et al., 2003), northeastern Baja California (Spelz et al., 2008), the Sceleton Coast in northern Namibia (Krapf et al., 2005;Stollhofen et al., 2014), northern Somalia (Brook et al., 1996), and the Arabian Peninsula (Abrams and Chadwick, 1994;Hayward, 1985). Due to the diversity of influences on their evolution, CAF may serve as valuable geomorphological and sedimentological archives. ...
... Tectonic control, however, should be further discussed. At the coast of the Atacama Desert in southern Peru, Keefer et al. (2003) could also detect a climatic control on the alluvial fan formation by debris flows and floods. Comparing our study area to other hyperarid coastal regions of the world, shows that CAF morphology and stratigraphy mainly differs between varying large-scale tectonic regimes. ...
Article
Along the coast of the hyperarid Atacama Desert, late Quaternary alluvial fans emerge from the Coastal Cordillera to the Pacific Ocean between 20.5°S and 25.5°S. Coastal alluvial fans (CAF) show, in comparison to the interior fans of the Atacama Desert, pronounced recent activity. However, the complex interplay between climate, lithology, and tectonics affecting the CAF morphodynamics in such hyperarid coastal settings needs to be better understood. We therefore aim at assessing the major factors driving CAF activity and evaluate their effects along gradients. We conducted an extensive study relating climatic, lithologic, and tectonic characteristics to fan and catchment geomorphology of 123 CAF. Geomorphometric analyses are based on the 12.5 m TanDEM-X WorldDEM™, catchment lithology and faults are extracted from 13 regional geological maps, and the frequency of heavy rainfall events capable of activating CAF is derived from a Weather Research and Forecasting (WRF) regional climate model. Our results point to a primary climatic control on CAF morphodynamics shown in functional relationships with catchment hydromorphometric characteristics reflecting a high susceptibility to debris flows – the main CAF-constructing process. Catchment properties along the latitudinal gradient reflect the source of significant precipitation events: frontal systems and cut-off lows which mainly originate in the extratropics and become increasingly rare towards the north. The frequency of precipitation extremes can only be correlated to the hydromorphometry and geomorphic maturity of catchments that feature a high degree of sediment transport potential and generally do not cut back far into the Coastal Cordillera. Related to the strongly reduced influence of the Pacific precipitation source towards the east, this additional climatic transition is governed by the orographic effect of the steep W-E gradient in topography. In contrast, source-area lithology is of negligible relevance for CAF catchment morphometry and fan activity. An important indirect influence of tectonics, however, can be seen in the long-term (neo)tectonic activity within the Coastal Cordillera, which in turn shapes catchments and controls the topography.
... During the middle Holocene, from 8,000 to 5,000 years before present, a strengthening of the Chilean-Peruvian Current and of the subtropical Southeast Pacific anticyclone would have intensified coastal upwellings, lowering the sea surface temperature by approximately 3°C. As a result, EN events would have been much weaker during this period and general LN-type conditions would have prevailed (Keefer & Moseley, 2003;Ortlieb et al., 2011;Carré et al., 2012Carré et al., , 2014. These environmental conditions would have been unfavorable for A. purpuratus populations, as currently observed during LN events (Valle et al., 2002;Tarazona et al., 2007). ...
... These environmental conditions would have been unfavorable for A. purpuratus populations, as currently observed during LN events (Valle et al., 2002;Tarazona et al., 2007). About 5,000 to 4,000 years ago (beginning of the late Holocene), these conditions began to revert, determining increasingly stronger and more frequent EN events toward recent times (Keefer & Moseley, 2003), which would have determined a demographic expansion of the species. In fact, very high abundances of A. purpuratus were reported in two paleolagoons from Peru: Otuma, 3,600 years before present, and Asia, 2,000 years before present. ...
Article
Full-text available
The scallop Argopecten purpuratus is a heavily exploited resource along the coasts of Peru and north-central Chile, especially after El Niño events, when the species undergoes high increases in abundance. Little is known about its genetic structure or demographic history, two important factors to ensure sustainable exploitation. We sequenced the cytochrome oxidase I and cytochrome b genes of 116 individuals from six localities (between 05°44′S 80°53′W and 23°31′S 70°33′W). We found high levels of genetic diversity in the analyzed populations. No geographical structuring was observed in the haplotype network, which consisted of a few central, widely distributed haplotypes, and many derived population-specific haplotypes separated by few mutations. This pattern suggests a recent population expansion and moderate to low current gene flow among populations. Mismatch analysis, neutrality tests, and a Bayesian skyline analysis confirmed the occurrence of a past event of population expansion approximately 5,000 years ago, which coincides with increasingly stronger and more frequent El Niño events.
... Very little research, however, deals with coastal alluvial fans (CAF) additionally influenced by marine base-level change; in particular, in hyperarid settings. Such northern Chile but can also be found along coastal mountain ranges in several other hyperarid regions on earth; for instance, southern Peru (Keefer et al., 2003), northeastern Baja California (Spelz et al., 2008), the Sceleton Coast in northern Namibia (Krapf et al., 2005;Stollhofen et al., 2014), northern Somalia (Brook et al., 1996), and the Arabian Peninsula (Abrams and Chadwick, 1994;Hayward, 1985). Due to the diversity of influences on their evolution, CAF may serve as valuable geomorphological and sedimentological archives. ...
... Tectonic control, however, should be further discussed. At the coast of the Atacama Desert in southern Peru, Keefer et al. (2003) could also detect a climatic control on the alluvial fan formation by debris flows and floods. Comparing our study area to other hyperarid coastal regions of the world, shows that CAF morphology and stratigraphy mainly differs between varying large-scale tectonic regimes. ...
Article
Due to their sensitivity to both tectonic activity and climatic variations, coastal alluvial fans (CAF) along the western flank of the Coastal Cordillera in the Atacama Desert (northern Chile) are important geo-archives for unravelling Quaternary environmental change. Our study focuses on terrestrial and marine deposits of five CAF complexes between 20° and 25°S along the coastal zone of the Atacama to identify phases of alluvial fan activity during the Late Quaternary. Based on a combination of luminescence dating and ¹⁰Be cosmogenic nuclide exposure dating as well as existing chronological data in the area, insights into climatic variations along the hyper-arid coast are presented for the Late Pleistocene derived from CAF morphodynamics. Activity of alluvial fans could be documented during time spans 95–80 ka, 60–45 ka, 35–20 ka, as well as the Holocene. Numerical dating of marine terrace deposits gives insights into the tectonic uplift of the Coastal Plain in northern Chile during the Late Quaternary period, for which estimated uplift rates between ~0.06 and ~0.57 m/ka were derived. While tectonic activity induces base-level changes, long-term tectonic activity rather indirectly controls alluvial fan activity. We suggest that alluvial fan activity is mainly controlled by atmospheric changes from the Pacific Ocean. Based on our observations, CAF in the hyper-arid Atacama Desert serve as suitable geo-archives for reconstructing climate changes during the Quaternary. In particular, the usefulness of alluvial fan systems in a water-limited environment is important for understanding the palaeoenvironmental evolution in a coastal desert.
... Very little research, however, deals with coastal alluvial fans (CAF) additionally influenced by marine base-level change; in particular, in hyperarid settings. Such an environment stretches along the coast of the Atacama Desert in northern Chile but can also be found along coastal mountain ranges in several other hyperarid regions on Earth; for instance, southern Peru (Keefer et al., 2003), northeastern Baja California (Spelz et al., 2008), the Skeleton Coast in northern Namibia (Krapf et al., 2005;Stollhofen et al., 2014), northern Somalia (Brook et al., 1996), and the Arabian Peninsula (Hayward, 1985;Abrams and Chadwick, 1994). Due to the diversity of influences on their evolution, CAF may serve as valuable geomorphological and sedimentological archives. ...
... At the coast of the Atacama Desert in southern Peru, Keefer et al. (2003) could also detect a climatic control on the alluvial fan formation by debris flows and floods. Comparing our study area to other hyperarid coastal regions of the world, shows that CAF morphology and stratigraphy mainly differ between varying large-scale tectonic regimes. ...
Thesis
Alluvial fans represent the dominant sedimentary systems within and along the margins of mountain regions where laterally confined, sediment-rich flows enter open plains or broader valleys. Successive aggradation creates a fan-shaped depositional landform featuring a complex internal architecture. Due to the direct coupling of alluvial fans to the source area, they are principally simple sediment routing systems and ideal archives to study local fluvial morphodynamics but also long-term landscape responses to (palaeo) climatic variability, tectonic activity, and base level changes. In most settings, however, it remained challenging to decipher these allogenic environmental controls. Along the coast of the hyperarid Atacama Desert in northern Chile (20.5°S-25.5°S), alluvial fans radiate from the steep western flank of the Coastal Cordillera, presenting the source area, over the narrow Coastal Plain, the sink. In the distal part, the coastal alluvial fans (CAF) interact with the marine environment, which forms an additional external control. In contrast to the last major alluvial activity in the interior Atacama Desert, dating back to the Miocene to Pliocene, the onset of CAF formation is much younger and CAF show a higher recent activity. However, the timing of their activity beyond the Holocene has barely received any attention yet. A major influence of climate on CAF formation has been proposed for a small part of the coastal Atacama; however, the interplay of climate, lithology, and tectonics in conjunction with strong, marine-driven base-level changes is still insufficiently explored. Hence, the CAF of the Atacama Desert are investigated in this comprehensive study as archives for recent to past sediment transport dynamics under coupled allogenic forcing. For this purpose, the CAF morphology as well as sedimentology, primary processes constructing the alluvial fans, relationships between the CAF systems’ hydromorphometry and the prevailing environmental characteristics (climate, tectonics, and source-area lithology), and the timing of their Quaternary evolution were assessed. While detailed field studies were concentrated on five key sites, overarching large-scale analyses of regional climatic and geologic geodata as well as geomorphometric analyses included 123 CAF systems. Results reveal that alluvial fans along the coastal Atacama Desert are in an overall advanced evolutionary state featuring voluminous aggradation and in approximately half of all cases also significant to deep entrenchment. Detailed geomorphological mapping and morphometric terrain analysis at the CAF complex Guanillos (21.97°S), enabled - besides the introduction of a multi-phase morphostratigraphic model comprising the fan’s prograde evolution and successive incision - to infer debris flows as the main depositional process in this hyperarid coastal setting. The morphological evidence is further supported by the CAF stratigraphy described in detail at five sites. Secondarily, hyperconcentrated flows were found to contribute to a large extent to the CAF aggradation. In contrast, sheetfloods are of negligible relevance, which is in accordance with previous sedimentological observations. Functional relationships between hydromorphometric catchment characteristics, the frequency of extreme precipitation events, fault density, and source-area lithology suggest a primarily climatic control on the CAF morphodynamics. Mostly restricted to catchments draining the western flank of the Coastal Cordillera, a higher frequency of precipitation extremes correlates positively with morphometric parameters indicating an increased susceptibility to debris flows (mean catchment gradient and basin relief ratio) as well as geomorphic catchment maturity. Spatial trends in catchment hydromorphometry and maturity reflect the major climatic source of rainfall events capable of creating effective sediment mobilization: frontal systems and cut-off lows which originate from the extratropical austral Westerlies and become increasingly rare towards the north. Furthermore, an increasing density of Loma vegetation can be observed towards higher latitudes so that possible feedback mechanisms of biota on sediment supply need to be considered for the southern CAF catchments. The relationships between climate and CAF morphodynamics are only seen in the geomorphometry of catchments characterized by a high degree of sediment connectivity and generally do not cut back far into the hinterlands of the Coastal Cordillera. Reflecting the strongly reduced influence of the Pacific precipitation source to the E, this sharp longitudinal climatic transition is governed by the orographic effect of the Coastal Cordillera’s steep topography. In contrast, source-area lithology could be excluded as a major controlling factor for CAF depositional processes along the coastal Atacama Desert. An important indirect influence of tectonics, however, can be seen in the long-term (neo)tectonic activity within the Coastal Cordillera, which in turn shapes catchments and controls the topography. CAF aggradation - those in the Late Pleistocene dated within the context of this study - shows peaks during the marine isotope stage (MIS) 5 (95-80 ka), MIS 3 (60-45 ka), Last Glacial Maximum (LGM) (35-20 ka), and Holocene (⪅7 ka). Those phases all coincide with more humid periods related to (i) warmer sea-surface temperatures (SST) of the SE Pacific provoking a southward shift of the Inter-Tropical Convergence Zone (ITCZ) in MIS 5 and parts of MIS 3, (ii) a weakening of the SE Pacific anticyclone and equatorward shift of the austral Westerlies during the LGM, and (iii) the onset of the modern El Niño-Southern Oscillation (ENSO) in the Middle Holocene characterized by positive SST during El Niño, which in turn favours convection of northward reaching atmospheric humidity and thus torrential rainfall. The coupling of CAF palaeoactivity to wetter phases implies that alluvial fan aggradation in the hyperarid Atacama Desert is primarily controlled by climate and is strongly transport-limited. At the CAF key site Botija (24.57°S), incision of the main channel occurred since the late MIS 3 to early LGM and can be interpreted as either a climate-driven effect due to the northward shift of the Southern Westerlies in MIS 2, the result of sudden base-level fall due to short-term megathrust earthquakes, or simply internal alluvial fan dynamics governed by autogenic controls. Regarding the onset of Pleistocene CAF formation, it cannot be excluded that remnants older than MIS 5 are buried under the younger, dated deposits. Further geochronological data along the coast is thus required to check, whether the widespread geomorphic changes of the CAF are a systematic response to an allogenic environmental control. Nonetheless, the CAF represent crucial archives for the Late Quaternary palaeoclimate of the hyperarid Atacama Desert, which preserve the climatic changes driven by the SE Pacific Ocean to a much higher degree than the interior alluvial fans. Besides the dominant control of climate on CAF evolution, tectonic impulses exert a significant short-term influence by sudden large-magnitude earthquakes changing the CAF base-level independently of eustatic sea-level changes. Against this background, mean Late Quaternary coastal uplift rates between ~0.06 and ~0.57 m/ka were derived from the datings of the elevated marine terraces.
... In addition, the lack of significant sediment storage along the Rio Salado upstream of reach PD would have limited the reworking of previously deposited sediments along the incised channel, and the geochemical homogenization of the sediment between flood deposits at PD. Spatial differences in metal concentrations between and within a given location may also be due to variations in the hydrologic drivers of the depositing floods. A number of studies in southern and coastal Peru have examined the linkages between flood deposits and the El Niño Southern Oscillation (ENSO) (see Keefer et al. [55] for a review). Although the hydroclimatology of the Atacama Desert is complex, there appears to be a strong correlation between flood deposits and ENSO related events [27]. ...
... However, rainfall from Pacific frontal storms can penetrate inland, and produce floods within higher elevation axial drainages, and low-to moderate-elevation ephemeral tributaries. An extreme, El Niño-related event that occurred in 1607 has been described in historical documents for the region [56], and was identified in paleoflood deposits examined along the coast of Peru [55,57] and along the northern Atacama of southern Peru [56]. Interestingly, the date of this event falls within the main mode (95% probability) of the calibrated ages for flood deposits FD9 and FD3 along reach RS, suggesting they were also deposited by this event. ...
Article
Toxic trace metals are a common and significant contaminant in riverine ecosystems, and are derived from both natural and anthropogenic sources. Determining the contributions of metals from these sources has proven difficult, in part, because physical and biogeochemical processes alter the nature (e.g., grain size, mineral composition, organic matter content) of the source materials as they are transported through the drainage network. This study examined the use of paleoflood deposits located along the hyperarid Rio Salado, a tributary to the Rio Loa of northern Chile, to construct local background functions and enrichment factors (LEFs) to differentiate between natural and anthropogenic metal sources. Significant variations in metal content occurred between river reaches and flood deposits of a given reach; these variations were primarily related to changes in sediment source that may reflect differences in El Niño and La Niña precipitation patterns. Three conservative elements (Al, Fe, Co) were examined to construct background functions for seven trace metals. Cobalt yielded the most effective background functions for As, Cd, Ni, Pb, and Zn; Fe was selected for Cr, and Al for Cu. The resulting LEFs approximated 1, illustrating that paleoflood deposits produced effective background functions, and could be applied to downstream sites contaminated by mining activity.
... En este contexto, las condiciones paleoclimáticas corresponden al Holoceno Temprano, el cual está caracterizado por un proceso de desglaciación bajo condiciones más secas que la era anterior, lo que permitió el establecimiento de asentamientos tempranos a lo largo de los Andes (Cf. Rademaker et al. 2014;Jolie et al. 2011;Keefer et al. 2003;Lavallée y Julien, 2012;Nuñez et al. 2013). Para nuestro caso de estudio, esta ocupación representa el 18.9% (Tabla 1) y el clima presenta una variación importante en esta latitud, registrándose condiciones húmedas y frías con eventos continuos de avance glaciar (Cf. ...
... Los resultados también nos muestran un espacio temporal sin evidencia directa de algún tipo de puntas de proyectil, que correspondería desde el 10,000-5,000 AP, el cual estaría asociado con el Holoceno Medio, época en la cual el clima fl uctuó de manera inestable registrándose un evento de condiciones muy húmedas y frías con un pico máximo alrededor de los 5,000-4,000 AP en la Cordillera Central (Stansell et al. 2013) y condiciones muy secas y frías en la parte sur de los Andes (Sylvestre et al. 1999;Abbott et al. 2003). Lo anterior afectó de manera considerable a los asentamientos tempranos de esta época, tanto los situados en la costa como en la puna, a través de un hiatus arqueológico o "silencio arqueológico" (Nuñez et al. 2013;Keefer et al. 2003). ...
... After this event, none of the more recent wet climatic events identified on the Al- tiplano (e.g., Michin, 48-36 ka, and Tauca, 26-15 ka) trig- gered a large landslide or remobilized the Chuquibamba de- bris flow. Similarly, in Southern Peru, Keefer et al. (2003) identified only centimeter-scale debris flows for the last 38 kyr. These observations are consistent with the preserva- tion of the Chuquibamba debris-flow morphology since its emplacement. ...
... No relationship between a M w 8.0 subduction earthquake and a giant landslide has been previously documented in southern Peru ( Lacroix et al., 2013). However, Keefer et al. (2003) point out that a close temporal succession of subduction earthquakes and El Niño events produces debris flows in the coastal region (southern Peru). In our study area, even if the Ouki wet phase would favor triggering, we cannot exclude a contemporaneous seismic triggering event (sub- duction or crustal earthquake) for the Chuquibamba debris flows. ...
Thesis
Full-text available
Ma thèse se focalise sur l'étude des mécanismes qui ont conduit au soulèvement et à la construction du relief dans les Andes du Nord du Pérou. Dans cette région, la Cordillère Blanche forme les plus hauts sommets péruviens (> 6000 m) et constitue une anomalie à l'échelle des Andes. La morphologie de cette région des Andes est marquée par un pluton de forme atypique, allongé et à l'affleurement sur plus de 150 km. Ce pluton est bordé par une faille normale de plus de 200 km de long. La présence de cette faille normale majeure en contexte de subduction plane reste surprenante car ces zones de subduction planes semblent induire une augmentation du raccourcissement dans la plaque chevauchante. Mon travail a eu pour objectifs de caractériser les variations de l'état de contraintes régional, l'âge du soulèvement et de discuter les processus géodynamiques qui ont contribué à la formation du relief. Dans ce cadre, j'ai utilisé une approche pluridisciplinaire impliquant sur plusieurs échelles spatio-temporelles et comprenant à la fois de nouvelles données de terrain, leur analyse et leur modélisation.Mes données de microtectonique indiquent qu'il est possible de générer de l'extension au dessus d'une subduction plane à l'échelle régionale. Ces données sont en contradiction avec l'augmentation du raccourcissement classiquement attendue dans la plaque chevauchante. Mes nouvelles données de thermochronologie basse température et leur modélisation montrent une augmentation de l'exhumation induite par le soulèvement de la Cordillère Occidentale à 15 Ma. En les confrontant aux modèles précédents, je propose un soulèvement régional lié à l'aplatissement de la subduction et à la topographie dynamique associée.J'ai également étudié l'impact de l'arc Miocène sur le soulèvement à une échelle plus locale. Pour cela, j'ai compilé tous les âges de refroidissement du pluton disponibles dans la littérature. En parallèle, j'ai obtenu les premières données de profondeur de mise en place du batholite de la Cordillère Blanche. Cela m'a permis de proposer une structure du batholite en sills empilés puis basculés vers l'est. De plus, la modélisation des variations spatio-temporelle des taux d'érosion à partir des données de thermochronologie basse température indique une augmentation importante des taux d'érosion dans la Cordillère Blanche à partir de 2 Ma. L'arc Miocène ne semble donc pas contribuer significativement au soulèvement malgré sa probable contribution à l'épaississement de la lithosphère. En revanche, l'érosion glaciaire récente semble contribuer fortement à l'exhumation de la Cordillère Blanche et au basculement du batholite.Dans la dernière partie de ma thèse, pour quantifier l'importance de l'érosion dans la création du relief et le soulèvement, j'ai modélisé l'évolution du paysage de la région (FastScape). Mes modélisations numériques démontrent le rôle majeur de l'érosion et du rebond flexural associé dans la création du relief et les taux de soulèvement. Pour finir, basée sur les données de la littérature et celles apportées par mon travail de thèse, je propose un nouveau modèle pour expliquer la faille normale de la Cordillère Blanche dans son contexte régional. Ce modèle implique une faille normale d'extrado et l'érosion importante du mur de la faille.
... Kochel 1987;Wieczorek 1987;Zimmermann & Haeberli 1992;Scott 2000;Griffiths et al. 2004;Foulds et al. 2014) and in Quaternary stratigraphic records (e.g. Kochel & Johnson 1984;Grosjean et al. 1997;Keefer et al. 2003;Yafyazova 2003;Sletten & Blikra 2007;Schlunegger et al. 2013). Extreme meteorological events also trigger bedrock and colluvial landslides (Selby 1976;Starkel 1976;Crozier 1997;Trustrum et al. 1999;Beylich & Sandberg 2005), which are subject to rapid reworking in highland catchments and drastically increase sediment yield (Markham & Day 1994;Allen & Hovius 1998;Hovius et al. 2000). ...
Article
The role of climate change in driving alluvial-fan sedimentation is hard to assess in pre-Quaternary successions, for which detailed chronologies and climate-proxy records cannot be easily established. In the Teruel Basin (Spain), high-resolution (10⁴-10⁵ years) chronological and palaeoclimatic information was derived by orbital tuning of Late Miocene mudflat to ephemeral- lake deposits. The semi-arid palaeoclimate made this low-gradient, basinal environment sensitive to thresholds in the local hydrological balance. Basic facies rhythms are attributed to alternating, relatively humid/arid phases controlled by the climatic precession cycle. The lower stratigraphic interval of this reference section interfingers with distal, coarse-clastic beds from a coeval alluvial fan. The consistent interdigitation of debris-flow deposits with distal strata indicative of arid-to-humid climate transitions shows that fan sedimentation was regulated by climate cyclicity. In particular, the largest volumes of terrigenous debris were shed from the fan onto adjacent mudflats during transitions to relatively humid periods with pronounced seasonality, during precession minima. Distal to medial sections within alluvial-fan outcrops also feature prominent, laterally continuous alternations of coarse- and fine-clastic packages. This high degree of architectural organization, uncommon in fan successions, and stratigraphic relationships with the reference section suggest orbitally controlled climate change to have been the forcing mechanism.
... According to previous studies [1][2][3][4][5][6], we have known that there occur many Quaternary debris-flow deposits in the southeastern (SE) marginal area of the Tibetan Plateau (TP), especially in valleys of the upper reach of the Jinsha River and that they can provide rich information for geomorphic evolution, tectonic movement or climate change and others. In valleys of the upper reach of the Jinsha River, Zhang [7] identified one planation surface, two erosion surfaces and seven levels of alluvial terraces. ...
Article
Full-text available
Large fan shaped debris-flow deposits occur at the piedmont west of Benzilan, in the upper stream of the Jinsha River, southwest China. The accumulation is composed of alternation of debris-flow units and reddish gravel soil units, seemly showing a binary structure. The debris-flow deposit has a mean thickness of 100 m. We did analysis on particle size, major element, clay mineral, pollen and electronic spin resonance (ESR) dating for samples from the debris-flow accumulation. Our study shows that the reddish gravel soil was in fact the debris flow material and its apparent differences from the debris flow material, especially color, was due to weathering. It was a relative dryhot climate to weather the upper part of the debris flow body into the reddish gravel soil. Evident chemical difference between the soil and debris-flow units was caused essentially by carbonate dissolution from soils. The debris-flow sequences indicate that the climate of the upper Jinsha River valley during the Early Pleistocene was characterized by a remarkable wet-dry alternation and would be warmer than today. The study area would be uplifted by 1300 m since the Early Pleistocene.
... These wetter conditions in the Central Andes were responsible for severe rainstorms that apparently led to an exceptional debris flow occurrence in the Mendoza River valley. A pre-historic record of El Niño events since about 30,000 years ago has been related to storm-induced events (Rodbell et al. 1999;Moy et al. 2002;Keefer et al. 2003;Vargas et al. 2006), and increased numbers of storm-landslides during positive warm ENSO phases (El Niño) have been reported around the world (Moseley 1999;Ngecu and Mathu 1999;Gabet and Dunne 2002;Bookhagen and Strecker 2009). Regionally, for South America and the Caribbean, a significant interannual variation in the number of landslides during the El Niño/La Niña cycle has been found (Sepúlveda and Petley 2015). ...
Article
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Since Holocene time, above-mean precipitations recorded during the El Niño warm ENSO phase have been linked to the occurrence of severe debris flows in the arid Central Andes. The 2015–2016 El Niño, for its unusual strength, began driving huge and dangerous landslides in the Central Andes (32°) in the recent South Hemisphere summer. The resulting damages negatively impacted the regional economy. Despite this, causes of these dangerous events were ambiguously reported. For this reason, a multidisciplinary study was carried out in the Mendoza River valley. Firstly, a geomorphological analysis of affected basins was conducted, estimating morphometric parameters of recorded events such as velocity, stream flow, and volume. Atmospheric conditions during such events were analyzed, considering precipitations, snow cover, temperature range, and the elevation of the zero isotherm. Based on our findings, the role of El Niño on the slope instability in the Central Andes is more complex in the climate change scenario. Even though some events were effectively triggered by intense summer rainstorm following expectations, the most dangerous events were caused by the progressive uplifting of the zero isotherm in smaller basins where headwaters are occupied by debris rock glaciers. Our research findings give light to the dynamic coupled system ENSO–climate change–landslides (ECCL) at least in this particular case study of the Mendoza River valley. Landslide activity in this Andean region is driven by wetter conditions linked to the ENSO warm phase, but also to progressive warming since the twentieth century in the region. This fact emphasizes the future impact of the natural hazards on Andean mountain communities.
... The hy- drology of the drainage was not static through time. Geomorphological studies of the hydrological history of the drainage indicate that the distribution and availabil- ity of water in both rivers and springs fluctuated during the Holocene in response to past climatic conditions, an- cient El Niño flood events, seismically-induced land- slides, and the onset of the Little Ice Age in the late fifteenth century (Clement and Moseley 2001;Goldstein and Magilligan 2011;Keefer et al. 2003;Keefer and Moseley 2004;Liu et al. 2005;Magilligan and Goldstein 2001;Magilligan et al. 2008;Reycraft 1998;Satterlee 1993;Thompson et al. 1986). Volcanism has also played a role in the region, particularly in 1600 CE with the wide- spread and catastrophic eruption of the Huaynaputina volcano that buried pasture under ashfall ( Thouret et al. 1999Thouret et al. , 2002). ...
... El Niño-induced flood deposits that overlay late prehispanic cultural remains comprise the Miraflores Unit of the local Holocene geological column, which also includes earlier paleo-flood deposits (Keefer et al. 1998(Keefer et al. , 2003) (see Figure 3, shaded area). Interpreted as dating to ∼A.D. 1300 (Magillgan and Goldstein 2001), the flood is considered to have been the study area's most severe ENSO event of the last millennium (see Satterlee 1993;Satterlee et al. 2000). ...
Article
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We describe diachronic evidence of moisture reduction and its consequences for coastal irrigation, agriculture, and settlement at Quebrada Tacahuay, a large drainage south of the Osmore River in far southern Peru. These observations are the first for a drainage of this size and for one with occupation spanning over 12,000 years for southern Peru. Following several millennia of occupation by coastal foragers, farming populations settled the lower elevations of the drainage. Our analysis indicates that agricultural production was well developed in the fourteenth century prior to a previously documented, catastrophic El Niño Southern Oscillation (ENSO) flood that took place sometime during the early-fourteenth century. Later in the fifteenth century the Inca conquest of the region and establishment of a coastal tambo and village was accompanied by agricultural expansion and the creation of new terraces. Subsequent Spanish colonization took place during the Little Ice Age and a period of increased coastal moisture. The historic and modern contraction of a large olive grove document the ongoing reduction in the coastal aquifer.
... En Sudamérica, los trabajos basados en este tipo de proxys son muy escasos y básicamente centrados en las llanuras costeras y el desierto de Atacama (Chile) (Manners et al., 2007;Gayo et al., 2012, Keefer et al., 2003. En el Noroeste Argentino la aplicación de estos estudios es más difícil ya que los registros sedimentarios dominantes corresponden a grandes abanicos aluviales formados por procesos fluviales y de flujos de detritos (debris flow) donde los registros holocenos tienen escasa continuidad temporal. ...
... En Sudamérica, los trabajos basados en este tipo de proxys son muy escasos y básicamente centrados en las llanuras costeras y el desierto de Atacama (Chile) (Manners et al., 2007;Gayo et al., 2012, Keefer et al., 2003. En el Noroeste Argentino la aplicación de estos estudios es más difícil ya que los registros sedimentarios dominantes corresponden a grandes abanicos aluviales formados por procesos fluviales y de flujos de detritos (debris flow) donde los registros holocenos tienen escasa continuidad temporal. ...
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The Tafí Valley is a small basin located in the northern sector of the Sierras Pampeanas in Northwest Argentina. The geomorphological studies made in the area showed the presence of very representative Holocene morpho-sedimentary records, which are useful for regional paleoenvironmental reconstruction. The study of the main slope accumulations, fluvial terraces, and alluvial fans provided several geoarchaeological records, paleontological remains, and volcanic ash layers as well as radiocarbon and thermoluminescence datings. We used all these data to construct a paleoenvironmental sequence. This sequence was also accompanied by some previously obtained data and detailed geomorphological cartography. Four morphosedi-mentary units were identified. The oldest unit (H1) comprises the Early and Middle Holocene (ca. 13000-ca. 4200 BP). It could be divided into two sub-stages (H1a and H1b), with different environmental signs. They appear separated by a tephra layer (V0) dated ca. 10000 BP. The end of sub-stage H1b is limited by another ash layer (V1) dated ca. 4200 BP. By that time, an incision process had already started separating this sub-stage from the next one. Stage H2 spans from ca. 4200 BP to ca. 630 BP, and extends vastly throughout the valley. It was possible to identify several features of human settlements (Tafí and Santa María Cultures) corresponding to that period. The characteristics of the sediments indicate a strong anthropogenic influence during its formation. Finally, two minor units (H3 and H4) cover the last centuries of the Holocene sequence, separated by incision phases. The Holocene set was related to the regional and global paleoclimatic evolution. © 2018, Instituto Geologico y Minero de Espana. All rights reserved.
... Most areas in the Atacama experience no rain at all for several consecutive years; most significant precipitations are related to intense El Niño events (e.g. Vuille, 1999;Vargas et al., 2000;Keefer et al., 2003;Houston, 2006). ...
Article
The origin of topographically controlled aeolian landforms in high-relief settings is difficult to synthesize under general models, given the dependence of such accumulations on local morphology. Quaternary sand ramps have been linked to palaeoclimate, regional geomorphology and wind patterns; however, controls on the early development and preservation of such landforms are poorly known. This study describes the morphology and sedimentology of complex sedimentary aprons along steep coastal slopes in the Atacama Desert (Chile). Direct slope accessibility and continuous stratigraphic exposures enable comparisons between active processes and stratigraphic signatures. Stratigraphic facies distribution and its links with patterns of aeolian deposition show that the preservation of wind-laid sediments depends on the morphology and processes of specific slope sectors. The spatial organization of runoff depends on bedrock configuration and directly controls the permanence or erosion of aeolian sediment. The occurrence of either water or mass flows depends on the role of aeolian fines in the rheology of flash floods. In turn, the establishment of a rugged surface topography controlled by patterns of mass-flow deposition creates local accommodation for aeolian fines, sustaining the initial aggradation of a colluvial-aeolian system. By contrast, slopes subject to runoff develop a thin, extensive aeolian mantle whose featureless surface is subject mostly to sediment bypass down- and across-slope; the corresponding stratigraphic record comprises almost exclusively thin debris-flow and sheetflood deposits. Slope morphology and processes are fundamental in promoting or inhibiting aeolian aggradation in mountain settings. Long-term sand-ramp construction depends on climate and regional topography, but the initial development is probably controlled by local geomorphic factors. The observed interactions between wind and topography in the study area may also represent a process analogue for the interpretation of similar geomorphic features on Mars.
... In South America, the only studies following this approach have been conducted in the valleys and coastal plains of the Atacama Desert (i.e. Manners et al., 2007;Gayo et al., 2012;Keefer et al., 2003). The main difficulty in this type of studies is discerning whether the processes that caused the accumulations are anthropogenic or climatic (Fuchs, 2007;Zielhofer et al., 2008;Constante et al., 2011;Bellin et al., 2013;Ackermann et al., 2014). ...
Article
Available online xxxx This paper studies the changes in the geomorphological dynamics recorded in 18 ephemeral streams located on the east side of Loma Pelada (Tafi Valley), a part of the Sierras Subandinas (Northwest Argentina). The applied methodology is based on photointerpretation, field survey, and descriptions of the Holocene alluvial fillings dated by tephras, archaeological artefacts, and absolute datings. The records show a coupled system of slope-terrace -alluvial fans resulting from the environmental changes of four alternating aggradation/degradation stages. The oldest stage (1) was generated by climatic causes and covers Early to Mid-Holocene (ca. 13,000–10,000 BP to ca. 4200 BP). After the incision of these accumulations, a new aggradation stage (2) was triggered by anthro-pogenic activity occurring from right before 2500 BP to the 15th century. During that time human occupations of the Tafí Valley were intense. Two wetter events occurred around 4200 and 2800 BP in the area, related to global cooling phases. Lastly, two more recent phases (3 and 4) are associated with the climatic variability of the LIA and the Present Warm Period. The results highlight the sensitivity of headwater catchments of dry subtropical mountainous areas to climate changes, anthropogenic impact, and their relationship with global climatic data.
... En Sudamérica, los trabajos basados en este tipo de proxys son muy escasos y básicamente centrados en las llanuras costeras y el desierto de Atacama (Chile) (Manners et al., 2007;Gayo et al., 2012, Keefer et al., 2003. En el Noroeste Argentino la aplicación de estos estudios es más difícil ya que los registros sedimentarios dominantes corresponden a grandes abanicos aluviales formados por procesos fluviales y de flujos de detritos (debris flow) donde los registros holocenos tienen escasa continuidad temporal. ...
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El valle de Tafí es una pequeña cuenca intermontana de las Sierras Pampeanas del Noroeste Argentino. Los estudios geomorfológicos efectuados han permitido reconocer la existencia de registros morfosedimentarios del Holoceno de gran interés para la reconstrucción paleoambiental regional. El estudio de las principales acumulaciones de laderas, terrazas fluviales y conos aluviales aportó numerosos registros geoarqueológicos, restos paleontológicos, cenizas volcánicas, así como dataciones 14C y de termoluminiscencia, de interés para elaborar una secuencia paleoambiental. Estos datos, junto a antecedentes y la elaboración de cartografía geomorfológica permiten diferenciar 4 unidades morfosedimentarias. La etapa más antigua (H1) comprende el Holoceno inferior y medio (ca. 13000-ca. 4200 BP) subdividida en dos subunidades (H1a y H1b), de diferente signo ambiental, separadas por un evento volcánico (V0) datado en ca. 10000 BP. El final de H1b queda delimitado por otro aporte de tefras en ca. 4200 BP, cuando esta unidad comenzaba a quedar individualizada por una fase de incisión. La etapa H2 abarca desde ca. 4200 BP hasta ca. 630 BP alcanzando notable extensión en el valle. La presencia de ocupación humana durante este periodo (Culturas Tafí y Santa María) y las características de los sedimentos indican una gran influencia de la acción antrópica en su formación. Finalmente, dos unidades menores (H3 y H4) cubren los últimos siglos de la secuencia holocena, separadas por fases de incisión intermedias. Los datos del conjunto holoceno han sido puestos en relación con la evolución paleoclimática regional e integrados en los principales eventos de carácter global.
... The same process was observed more downstream in the Peruvian part of Napo basin (Guyot etal., 2007). Along different mountain ranges of the planet in general (Hovius, 1998;Leeder et al., 1998;Hsieh and Knuepfer, 2001), and in South America in particular, some works (Weng et al., 2002;Aalto et al., 2006;Keefer et al., 2003) have already put in evidence the dependence of fluvial transport with climate and tectonics. These relations complete those well-known processes of sediment transfer (erosion and/or transport and/or sedimentation) with the physiographic characteristics (climate, morphology, vegetation, pedologic coverings, geology, land usage, drainage network, etc.) of mountainside basins, as illustrated by Restrepo et al. (2006) in the Magdalena basin in Colombia. ...
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The Upstream-downstream sediment budget along the Napo River (100520 kill 2, 6300 m(3) s(-1)) was studied in the Andean foothills of Ecuador, at the west of the Amazon basin. A comparative study was made during four hydrological cycles (2001-2005) for three hydrological stations located upstream, and during one hydrological cycle (2004-2005) for the Fourth one located near the mouth of the Napo River (region of Iquitos in Peru). This analysis showed an unusual increase in the concentration of suspended sediment recorded for the western part of the Amazon plain. Like the runoff (81 l s(-1) km(2)), which is a world's maximum, the erosion rate (1160 t km(-2) year(-1), i.e. 47% of total suspended solid (TSS) export at the exit of Ecuador), one of the highest for a floodplain basin is the result of a stepper slope than in the rest of the Andean foothills, where typically sedimentation phenomena are predominant, and can be explained in part by a greater tectonic activity. Similar phenomenes were evidenced in small mountainous rivers in New Guinea (Milliman and Syvitski, 1992; Milliman, 1995). On the headwaters of the Napo River drainage basin, the tectonic uplift causes the Pastaza Megafan's existence. This progressively diverts the Course of Napo River towards north and also provokes the remobilization of fine fluvial deposits. Moreover, this geodynamic trend is completed by the impact of volcanic eruption, earthquakes and landslides. The combination of these phenomena, so common in the region, has provided a large sediment transfer, not only at present but also in the past, as can be confirmed by the presence of incised terraces, mainly formed by volcanic materials. Then, these results were compared with a similar Study carried out further south in the Madeira basin at the Bolivian foothills. These studies show the spatio-temporal variability of the relation between sediment transfer and geodynamic processes at the Andean Piedmont.
... It also would not account for the palaeotsunami deposit in New Zealand. Other more reasonable tsunamigenic sources would seem to be either the Chilean precursor to the 1575 CE (Valdivia) Chile earthquake that occurred sometime between 1280 CE and 1390 CE (Cisternas et al., 2005), or a possible event along the Peruvian coast between 1300 CE -1400 CE (see Fig. 13) although the latter suggestion seems unlikely since the proxy evidence used to tentatively identify it appears most likely to be related to El Niño activity (Magilligan and Goldstein, 2001;Keefer et al., 2003;Rein, 2007). The latter would be a better fit with the New Zealand data and numerical modelling suggests that it might also affect Ecuador. ...
Article
There is a rapidly growing number of palaeotsunami sites being reported from the Pacific region but rarely have researchers looked far beyond their immediate site to find contemporary evidence at more distal locations. However, over the past 150 years the region has experienced giant earthquakes and their associated tsunamis from several key circum-Pacific sources. The 2011 Tōhoku, 1960 Valdivia, 1946 Aleutian and 1868 Arica tsunamis have been Pacific-wide events that, together with recent modelling, serve as a guide in helping to understand those that occurred in prehistory. Extant palaeotsunami data were used in conjunction with numerical modelling to examine current evidence for the spatial extent of notable prehistoric events dating back as far as 3800 years BP. An outcome of this work was the recognition that any search for palaeotsunami evidence should be intrinsically linked with numerical modelling as a guide to identifying additional potential sites for further research in order to better understand the nature and extent of individual events. Another outcome of this study was the identification of several key island archipelagos that are worthy of focussed research because they have the potential to rapidly accelerate our understanding of the magnitude and frequency of past events. These include the centrally located Hawaiian Islands and the Marquesas archipelago that are exposed to Pacific-wide tsunamis from most circum-Pacific sources. It was also noted that there has been a dearth of research in some sectors of the Pacific Ocean, such as the western Pacific archipelagos of the Federated States of Micronesia, Palau, Guam, and Northern Mariana Islands, while conversely in other sectors a significant quantum of research is showing great promise such as in New Zealand, the Samoan archipelago, Cook Islands, and Vanuatu. The ultimate finding of this work is that while much has been achieved, much more remains to be done to better understand the magnitude and frequency of past events and the true nature of tsunami hazard and risk in the region.
... Again, several authors have emphasized the correlations of ENSOrelated deposits ("event-strata") among different archaeological Peruvian sites [9][10][11]. These correlations would support the concept of Mega or Super El Niño events [12][13][14] leading to heavier precipitation phases driven by ENSO, which would hit the central Andean coast with centennialscale periodicity. It is worth observing that the understanding of the variability of El Niño over geological time is crucial for assessing the environmental and economic consequences due to the incoming fluctuations of ENSO [15][16][17]. ...
Article
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Several central Andean pre-Columbian sites struck by hydrogeological disasters due to El Niño-Southern Oscillation (ENSO) events are reported in the literature. The mainstream explanation for the decline and demise of Cahuachi (pampa of Nazca, south Peru) implies the damage and burial of such a ceremonial center as a consequence of two catastrophic river floods, which occurred around 600 CE and 1000 CE, respectively. Therefore, geological studies at Cahuachi are mandatory with regard to both the correlations of ENSO-related deposits (“event-strata”) among different Peruvian sites and the assessment of the millennium-scale climate variability. In particular, the latter is crucial to evaluate the environmental and economic consequences due to the incoming fluctuations of ENSO. In this paper, stratigraphic, grain-size distribution, and petrographic investigations on a sedimentary section exposed close to one of the main temples of Cahuachi are reported. They represent the first test for the current mainstream explanation. The preliminary finding indicates that the studied stratigraphic interval may belong to the common regional succession of the pampa of Nazca rather than the ENSO-related deposits described in the literature. However, further geological research will be necessary to unravel this issue in more detail.
... The subsequent Moche V culture was re-established inland between AD 600 and 750, near the confluence of highland rivers draining the Andean foothills where the water supply was more reliable (de Menocal, 2001). For earlier periods in the same region, successive earthquakes, El-Niño flooding, beach ridge formation nourished by sediment eroded during earthquakes and floods, and sand dune incursion caused a series of natural disasters that contributed to the demise of local coastal settlements (Keefer et al., 2003;Sandweiss et al., 2009). ...
Chapter
A series of case studies, derived from Holocene palaeoenvironmental investigations, archaeology, and history, are used to analyze ancient natural hazards and their impact on societies. The evolution of societies is inscribed in geomorphology, as a close relationship exists between the landscape and humans. Four factors underpin disasters: time, space, type of society, and type of event. In some cases, disasters apparently caused civilization to collapse, but, in other cases, they have spawned innovations and led to more resilient societies. In the face of landscape change, our modern society should not be lured by technology and globalization, as these could become more sources of vulnerability than of prevention and mitigation. Changes always have a cost. Civilizations have always had difficulties coping with the element of surprise in a hazard; this will remain uncontrollable. If a natural hazard occurs in a restricted area of the planet, its impact may be felt worldwide due to our current great interconnectedness.
... Records of flash floods and debris flows linked to paleo-El Niño events have been reported during the late Pleistocene in Southern Peru (e.g. Keefer et al., 2003). Then evidences of more persistent humid conditions related to ENSO-like climate configuration during the last interglacial periods are recorded as paleolakes extensions (e.g. ...
Article
The western flank of the Central Andes hosts some of the largest terrestrial landslides (v > km³), which morphologies are particularly well-preserved due to low erosion rates related to the hyper-arid climate prevailing in this region since the Miocene. First-order questions are pending about the factors controlling the development and the triggering of those large-scale slope failures. Previous studies provided some geomorphological analysis and dating on individual study cases, but a regional-scale vision of landslide processes long the Central Western Andes is missing. Here we report an original inventory of large landslides (areas from 0.1 to 180 km²) established along the western flank of the Central Andes between latitudes ca. 15 and 20° S, and from the Pacific coast to the Altiplano. Based on manual mapping (using satellite images analysis, Google Earth and DEMs analysis) and a compilation of previous works, we inventoried more than a thousand large landslides in this region. We then statistically explored the database according to the landslides typology, size, abundance and relation to geologic, tectonic and climatic settings of the Central Western Andes in order to provide a first insight on their controlling factors. Landslide size-frequency distribution follows a power-law with an exponent of 2.31 ± 0.16 and a cut-off of 4.0 ± 1.9 km² showing a strong contribution of the largest landslides to the cumulated landslide area. We revealed a dominance of rockslide typology (86%) characterized by in-mass slides, the rest being rock-avalanche type (14%) marked by typical granular-flow morphologies. Combination of specific lithology and great local relief emerge as favorable conditioning factor for large landslide initiation, in particular in the case of river incisions though ignimbrites of the Paleogene-Neogene (Huaylillas Formation), concentrating >30% of the landslides. Moreover, landslide clusters tend to follow crustal faults networks suggesting a long-term control of tectonic activity. Most of the identified landslides are paleo events. We tentatively argue that their triggering could not have been possible in the current hyper-arid conditions of the Atacama Desert and its periphery. Future research providing dating on some of the landslide clusters identified in this study is needed to explore possible temporal correlations between periods of landslide activity and external seismic and/or climatic cycles.
... Both approaches suggest a phase dominated by the C mode 6-7ka following a phase dominated by the E mode. The strong E mode recorded 7-8ka is consistent with an increased frequency of coastal floods in Peru (Carr e et al., 2014;Keefer et al., 2003;Rein, 2007). After 5ka, both records indicate contributions of E and C modes similar to modern. ...
Article
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Lack of constraint on spatial and long-term temporal variability of the El Niño southern Oscillation (ENSO) and its sensitivity to external forcing limit our ability to evaluate climate models and ENSO future projections. Current knowledge of Holocene ENSO variability derived from paleoclimate reconstructions does not separate the role of insolation forcing from internal climate variability. Using an updated synthesis of coral and bivalve monthly resolved records, we build composite records of seasonality and interannual variability in four regions of the tropical Pacific: Eastern Pacific (EP), Central Pacific (CP), Western Pacific (WP) and South West Pacific (SWP). An analysis of the uncertainties due to the sampling of chaotic multidecadal to centennial variability by short records allows for an objective comparison with transient simulations (mid-Holocene to present) performed using four different Earth System models. Sea surface temperature and pseudo-δ18O are used in model-data comparisons to assess the potential influence of hydroclimate change on records. We confirm the significance of the Holocene ENSO minimum (HEM) 3-6ka compared to low frequency unforced modulation of ENSO, with a reduction of ENSO variance of ∼50 % in EP and ∼80 % in CP. The approach suggests that the increasing trend of ENSO since 6ka can be attributed to insolation, while models underestimate ENSO sensitivity to orbital forcing by a factor of 4.7 compared to data, even when accounting for the large multidecadal variability. Precession-induced change in seasonal temperature range is positively linked to ENSO variance in EP and to a lesser extent in other regions, in both models and observations. Our regional approach yields insights into the past spatial expression of ENSO across the tropical Pacific. In the SWP, today under the influence of the South Pacific Convergence Zone (SPCZ), interannual variability was increased by ∼200 % during the HEM, indicating that SPCZ variability is independent from ENSO on millennial time scales.
... Consequently, it is often argued that exceptional rainfall, or destruction of the irrigation systems, was the main driver of the decline of ancient populations in the region. For example, Keefer et al. (2003) and Wells (1990) suggested that large floods associated with El Niño Southern Oscillation in ∼1330 CE (known as the Miraflores flood) may have contributed to a ∼70-80% decline in the population of the Chiribaya civilization of the Moquegua Valley (Figure 1) between 1360 and 1400 CE. However, Clement and Moseley (1991) argue that a famine in the nearby Carrizal valley around 1360-1400 CE is incompatible with a mega-Niño event. ...
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We present the results of a paleoseismic survey of the Incapuquio Fault System, a prominent transpressional fault system cutting the forearc of South Perú. High-resolution DEMs, optical satellite imagery, radiocarbon dating and paleoseismic trenching indicate that at least 2-3 m of net slip occurred on the Incapuquio Fault generating a complex, ∼100 km-long set of segmented fault scarps in the early 15th century (∼AD 1400-1440). We interpret the consistent along-strike pattern of fault scarp heights, geometries and kinematics to reflect a surface rupture generated by a single Mw 7.4-7.7 earthquake, suggesting that brittle failure of the forearc poses a significant, yet mostly overlooked, seismic hazard to the communities in coastal areas of Perú. The timing of this earthquake coincides with the collapse of the Chiribaya civilization in ∼AD 1360-1400, and we present evidence of damaged buildings along the fault trace that may be of Chirabayas age. Our surface faulting observations, when combined with observations of deformation in the forearc from geodesy and seismology, also demonstrate that the forearc in South Perú experiences a complex, time-varying pattern of permanent strain, with evidence for trench-parallel shortening, trench-parallel extension and trench-perpendicular shortening all in close proximinty but in different periods of the megathrust earthquake cycle. The kinematics of recent slip on the Incapuquio Fault are consistent with the sense of interseismic strain within the forearc measured by GPS, suggesting the fault is loaded towards failure between megathrust earthquakes.
... It is still unclear how the El Niño event played a role in the algarrobo evolution. The oldest El Niño event is dated back to 38000 years ago during the late Pleistocene (millions of years after the arrival of Algarrobo to the South American coast, Keefer et al., 2003). The survival and reproduction of drought-adapted genotypes might have been perpetuated during the El Niño events, which probably provided enough fresh water to keep populations alive, just as it does now . ...
Article
Prosopis pallida (algarrobo) is a highly adapted species to extremely dry and wet conditions. Its geographic distribution at both sides of the Pacific Ocean is associated with its plastic response to El Niño event, an extreme climate event that changes precipitation regimes. In this review, we summarized the current knowledge of this versatile species based on scientific literature. Our analysis conducted identify three main research topics: geographical distribution, ecophysiology and population plasticity, and ecosystem services provision to guide the review in a methodological and unbiased way. In the geographical distribution section, we describe the origin, history, and native distribution of algarrobo, as well as the current distribution and the degree of invasiveness in some countries. In the ecophysiology and population plasticity section, we focus on the mechanisms used by algarrobo to avoid water stress during drought and maximize plant growth during El Niño. We discuss how this is reflected in the most important leaf functional traits, such as leaf mass per area (LMA) or gas exchange-related traits. We analyse the importance of phenotypic plasticity and intraspecific variability as adaptive ways to resist extreme rainfall and prolonged droughts on P. pallida growth during the last 50 years. Finally, we summarized the main ecosystem services and ecological benefits provided by P. pallida as well as its potential industrial uses. With this review, we wish to consolidate the current scientific knowledge of this species, to point out gaps of knowledge and suggest future research directions. As the world becomes a warmer place, P. pallida can be a key species to understand plant resilience to extreme events in dryland ecosystems.
... Due to the heterogeneity of alluvial fan deposits (e.g., coarse-grained structure) and their usually long chronologies, difficulties remain in accurate dating (Bowman, 2019;Mather et al., 2017). Previous attempts have used dating with cosmogenic nuclides, radiocarbon dating, Ar-Ar dating (volcanic ash beds) and U-series dating methods (e.g., Bowman, 2019;Cerling et al., 1999;Clarke, 1994;Hooke and Dorn, 1992;Keefer et al., 2003;Lee et al., 2010;Robinson et al., 2005;Vargas et al., 2006). But these applications are limited by the non-systematic availability of suitable dating material, which may also sometimes lie beyond the dating range of a given method. ...
Article
Coastal alluvial fans (CAF) are important geo-archives due to their sensitivity to both tectonic activity and climatic changes and they may give key insights for geomorphic and sedimentary processes. In this study we test the potential of K-feldspar post infrared-infrared stimulated luminescence (pIR-IRSL) and quartz electron spin resonance (ESR) methods for dating alluvial fan complexes in arid environments. The existing chronological data from marine terraces that interact with CAF make the Atacama Desert in northern Chile an excellent setting for this research. Samples have been collected from alluvial, marine and aeolian sediments embedded in the CAF complexes, allowing evaluation of the different signal properties and bleaching characteristics of the pIR-IRSL and ESR signals (Al and Ti centres) over Late Pleistocene time scales. pIR-IRSL dose distributions of clast-rich alluvial fan samples are characterised by higher scatter and demonstrate heterogeneous bleaching, while matrix-rich alluvial fan deposits show rather homogeneous poor bleaching in the dose dispersion as indicated by modern analogue samples. In contrast, marine and aeolian deposits are homogeneously well bleached, supported by modern littoral samples. Following the quartz multiple centre (MC) ESR dating approach (Al and Ti centres), bleaching of the different centres prior to deposition has been achieved. While the Ti–H centre provides mostly lower doses than the Ti–Li centres, in most cases the Al centre provides the highest dose values. This pattern is consistent with their respective bleaching kinetics and suggests that the Ti centre signals most likely provide the closest estimate to the true burial dose for samples with doses >200 Gy. ESR and pIR-IRSL ages are consistent at 2σ for the marine, aeolian and clast-rich debris-flow deposits, which is in agreement with existing chronological data in this area. It appears that the mode of sediment transport on alluvial fans, either as matrix- or clast-rich flows, plays an important role in sediment bleaching. While clast-rich alluvial fan deposits are likely better bleached, we cannot exclude insufficient bleaching during matrix-rich alluvial fan flows; our dating results suggest that both pIR-IRSL and ESR dating overestimate the true burial age. The combination of pIR-IRSL and MC ESR dating can be considered a promising tool for deciphering alluvial fan formation over (Late) Pleistocene timescales.
... For instance, in the Majes river, located at about 300 km northwest to the Locumba valley, Steffen et al. (2010) pointed to the occurrence of major periods of aggradation at ca. 20 ka and between 12-8 ka. In the Moquegua valley (50 km northwest to Aricota), Keefer et al. (2003) reported the existence of extensive flood and debris flow deposits dated between 12 and 8.4 ka, and at least ten severe events that took place between 38 and 13 ka. At a larger scale along the western margin of the Andes in Peru, Litty et al. (2017) highlighted changes in precipitations patterns during the last 100 ka through shifts of the sediment provenance. ...
Article
The central part of the Western Andes holds an exceptional concentration of giant paleolandslides involving very large volumes of rock material (v > km3). While those gravitational slope failures are interpreted consensually as an erosional response to the geodynamic activity of the Andes (relief formation and tectonic activity), the question of their triggering mechanisms remains enigmatic. To clarify the respective roles of climatic versus seismic forcing on the Andean landslides, new temporal constraints on paleo movements are essential. Here, we focus on one of those giant slope failures, the Aricota giant landslide that damned the Locumba valley in southern Peru. We conducted fieldwork, high-resolution DEM analysis and cosmogenic nuclide dating to decipher its development history and failure mechanisms. Our results point to the occurrence of two successive rockslide events. A giant failure mobilizing a rock volume of ca. 2 km3 first produced a dam at 17.9 ± 0.7 ka. Considering its height of ca. 600 m, the Aricota rockslide dam is one of the five largest landslide dams. At 12.1 ± 0.2 ka, a second event produced ca. 0.2 km3 of material, and the rock-avalanche debris spread out over the dam. As the chronology of those two events is pointing to the two main paleoclimatic pluvial periods in this region (Heinrich Stadial 1a and Younger Dryas), we favor the interpretation of a climatic forcing. At a regional scale, the concomitant aggradation of alluvial terraces and fan systems along the nearby valleys highlights higher regional erosion, sediments supply and mass-wasting events during those paleoprecipitation events and strengthens this conclusion.
... Se puede hacer una reflexión análoga para otro tipo de catástrofes similares: aludes, inundaciones súbitas... Aunque algunas pudieron tener una magnitud absolutamente sin paralelos en la actualidad. Las citadas rupturas de los diques de los lagos de deshielo de las grandes masas glaciares en el hemisferio norte (lago Agassiz, Báltico y probablemente los de los glaciares asio-siberianos) o grandes episodios que combinaron terremotos con grandes manifestaciones del El Niño [201] fueron acontecimientos súbitos difíciles de imaginar hoy día. Y todo ello pudo ocurrir delante de los ojos de grupos humanos, que vieron cortado de forma súbita y prolongada su paisaje. ...
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We need to integrate the analysis of sudden changes as well as gradual changes in Prehistory. Sudden changes in nature sometimes let to catastrophes. It depends just on the magnitude, speed of change and specially on the state of the society affected by the change. I have chosen 10+1 example of sudden changes in the oldest prehistory to illustrate this thesis.
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Pre-Columbian Andean cultures have generally been characterized as having strong cultural and religious ties to their surrounding landscape and the natural world. Plants and animals associated with this sacred landscape have had, and in some societies continue to have, a particular cultural and religious meaning. Food crops and cultigens that sustained life and their associated preparation were often seen as a sacred act, with strong cultural associations to ethnic identity. Other plants have had direct associations to ritual and religious practices and were seen as sacred, reaffirming the diversity and complexity of Andean foodways and local cuisines. Anthropologists and archaeologists have documented the symbolic complexity of the natural world and the social importance of feasting, rituals and rites in contemporary and historical societies. Cultural perceptions and beliefs regarding the natural world and their associated plants and cuisines were subsequently modified to varying degrees by the Spanish conquest and introduction of foreign plants and animals. Contributions in this volume explore the art history and history to examine the roles of food through particular interdisciplinary lenses. Research from diverse regions of the cordillera further emphasize the diversity of Andean cultures. Contributions explore and analyze these topics in the context of historic and contemporary Andean culture, with examples of how domesticates, cuisines, their preparations, and basic ingredients continue to influence present day foodways and regional tastes.
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The Osmore Drainage of southern Peru has a long and rich history of human occupation. While the utility of stable oxygen and radiogenic strontium isotope values in identifying paleomobility between this region and population centers in the Bolivian altiplano has been well established, many questions about intra-regional mobility remain. To better understand how these methods can be used to detect localized residential mobility, we present new δ¹⁸Omw(VSMOW) and ⁸⁷Sr/⁸⁶Sr values from water, soil, plant, and faunal samples. Samples were collected primarily from traditionally farmed agricultural fields in the upper, middle, and lower Osmore Drainage. Results are indiscernible between the upper and middle drainage, while marine contribution to the lower drainage produces distinct values. We discuss the methodological limitations and implications of our results for the use of stable oxygen and radiogenic strontium isotope analyses for intra-regional paleomobility studies in the Osmore Drainage.
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The Ocoña River Valley, in the Arequipa Department in southern Peru, extends over 150 km from the Pacific coast to its headwaters in the Andes Mountains. While traditionally sparsely populated with farmers and crawfish fishermen, the valley has seen a large population growth in the last 20 years as small gold mines have developed. This change poses the opportunity to evaluate three research questions: How do geologic hazards and risks increase from mining activity? How does unplanned urban development affect risks? How do landforms restrict development and thereby increase risks? The combination of climate, topographic, and hydrologic conditions result in widespread hazards from debris flows, collapsible soils, erosion, rockfall, flooding, and liquefaction. We have developed maps of these hazards for three communities where mines have recently developed, Secocha, Alto Molino, and San Juan de Chorunga, and then we conducted a risk analysis for changing conditions, termed “Risk–Risk” analysis. Because of the lack of vegetation on mountain slopes, mining operations typically only affect rockfall hazards, mostly in the immediate vicinity of the mines and in the nearby runout zones. However, increased population and associated settlement infrastructure is constrained by steep slopes and regularly-flooded valleys, so residents live in fan and terrace areas with substantially increased risks from debris flows and collapsible soils and moderately increased risks from flooding and rockfall.
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The ephemeral and fragmented nature of plant communities in the desert region of Ica, Peru have contributed to the poor documentation of its flora. This study provides the first comprehensive checklist and analysis of the vascular plants and habitats of the region, based on over 1800 herbarium collections, site-specific vegetation surveys and monitoring (2001–2017). Here, we report 501 taxa belonging to 283 genera in 68 families, with an outstanding number of taxa (297) representing new records for the region; over 10% of the flora (52 taxa) is categorised as threatened (CR, EN, VU). Asteraceae is the largest family in the checklist, followed by Poaceae, Fabaceae and Solanaceae. The highest species richness is found in quebradas and huaycos (170 taxa), followed by lomas (137 taxa) and huertas (115). Of the lomas taxa, 28% are assessed nationally as threatened, and 95 taxa (68%) are endemic to Peru. Across all habitats five species are restricted to the Ica region (Cleistocactus clavispinus, Haageocereus icensis, Onoseris humboldtiana, Nolana willeana, Tecoma fulva subsp. guarume). Nolana willeana, not collected since 1956, was rediscovered in 2006. We provide insights into habitat and taxonomic delimitation of enigmatic species in the following genera: Bulnesia, Capparis, Eremocharis, Hoffmannseggia, Leptoglossis, Lomanthus Maytenus, Poissonia and Weberbauerella, among others. We support the reinstatement of Prosopis limensis as a valid species and provide information for its identification in the field. Analysis of Inga feuillei as an ancient domestication vital to agriculture, is provided, and we report an additional 127 cultivated species associated with traditional agriculture, assessing origins and conservation priority. We present climatic and geological observations for the region with spatial and ENSO-related research from data, plots and transects. A vegetation map and niche model are provided. Threatened lomas species are detailed to support conservation and policy. To aid identification we provide photographs of 155 plant species and all key habitats. The sustainable wellbeing of the Ica region depends on concerted collaboration to monitor, conserve and restore native plants wisely for the natural resources they provide to people and agriculture.
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El Indio, an Au-Cu-As deposit with outstanding gold grades, was mined in the Andes of the Coquimbo region, Chile, between 1975 and 2002. Sediment and water sampling of the rivers in the 2000 s found exceptional As and metal levels in modern and old sediments. The studies also revealed that acid rock drainage (ARD) has been present in the district for nearly 10,000 years and the effect that the mining of the district had in terms of geochemical anomalies. The convergence of mineralogical, structural, and hydrologic conditions has generated a metal-rich ARD, a process followed by transference of metals to the fine sediments. In this context, the study also deals with the risk of metal and metalloid transfers from the sediments to the river waters as a consequence of eventual physical-chemical changes, due for example, to climatic-driven conditions. Water and sediment samplings were carried out to provide materials for selective extraction tests under acidic, acid-reducing, and acid-oxidizing conditions. The different behavior of metals and metalloids was revealed and highlighted the refractory character of As. Additionally, the study included the characterization of the sediment’s mineralogy, and allowed the detection of new geochemical anomalies of Cu, Zn, Co, and Y in the Incaguaz River, along with high dissolved Li concentrations in the Toro and Turbio rivers.
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Evidence for a link between a changing climate and the promotion, adjustment, modulation or triggering of earthquake and volcanic activity is robust and many of the mechanisms well established. Tectonic geomorphology sheds light on this relationship, which is abundantly recorded and preserved in the form of geomorphological signatures that include fault scarps, displaced landscape features and volcanic and mass-movement related landforms. The tie-in between a changing climate and tectonic activity is best defined during the period of rapid and dramatic environmental change that involved the transformation from ‘ice world’ to ‘water world’ between the end of the last glacial maximum - variously dated at between 24 and 18 ka, 26 and 19 ka and 28 and 23 ka - and the Mid-Holocene (8.2–4.2 ka). Looking ahead, anthropogenic global heating and climate breakdown bring the prospect of a renewed response from the solid Earth, promoting an elevated threat from earthquake and volcanic activity driven by wholesale cryosphere retreat, accelerating sea-level rise, and extreme precipitation.
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The biodiverse montane forests of the tropical Andes are today frequently disturbed by rainfall-driven mass movements which occur mostly during extreme El Niño events. Over the coming decades these events are projected to double under the 1.5 °C global warming scenario. The consequent increased rainfall and mass movement events likely present an elevated risk to millions of people living in the Andes. However, the impact of more frequent rainfall extremes remains unclear due to a lack of studies that directly link past changes in El Niño-Southern Oscillation (ENSO) frequency to forest and landscape disturbance patterns. Here, we present the first Holocene palaeoecological record from Laguna Pallcacocha, southern Ecuador, a key site for El Niño reconstructions. We demonstrate that for the past 10,000 years plant taxa indicative of recolonization – such as Alnus acuminata – covary with El Niño-induced flood layers in the lake. An amplified forest disturbance pattern is observed in the late Holocene, suggesting enhanced slope instability following deforestation. The temporal pattern is not explained by tree line fluctuations or human impact, while the latter does amplify the impact of ENSO on landscape disturbance. Spatial correlations between modern ENSO and precipitation are consistent with a regional comparison of Holocene records of landscape disturbance. Our results indicate that climate extremes, such as those associated with future intensification of El Niño, combined with ongoing land use change will increase the frequency of mass movements elevating risks for millions of people in the Andes.
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PurposeArid and hyper-arid zones worldwide are reservoirs of chemical compounds, among them are various trace elements. With climate change, abnormal precipitation is occurring in arid and hyper-arid mountainous zones, which in turn is increasing the displacement of trace elements from mountainous to populated areas. The objective of this study was to evaluate trace element displacement of a sediment-laden flood in the Copiapó River Basin on March 24–25, 2015. Materials and methodsSixty topsoil samples were taken from 20 agricultural fields. Soil organic matter content, pH, electrical conductivity, and particle size were determined according to accepted procedures in Chile. Samples were acid-digested to determine total Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Se, and Zn content by flame atomic absorption spectroscopy. Hydride generation AAS was used for As and Se determination, and Hg was quantified by cold vapor AAS. Detection limits were 0.2, 0.05, 0.1, and 5.0 mg kg−1 for Cd, Hg, Se, and Mo, respectively. Correlation and principal component analyses were made, and theoretical distribution functions were fitted to each element. Results and discussionMetal concentration showed a strong correlation between SOM and particle size, explaining the first component from the principal component analysis. All trace elements correlated well between each other except for Mo and Se. Mo values were consistently below detection levels (<5.0 mg kg−1). Expected values for the elements were (95% of probability): 13–37 g Al kg−1, 10–50 mg As kg−1, <0.2–0.6 mg Cd kg−1, 13–25 mg Cr kg−1, 27–281 mg Cu kg−1, 27–40 g Fe kg−1, <0.05–6.5 mg Hg kg−1, 516–1.080 mg Mn kg−1, 7–24 mg Ni kg−1, 13–50 mg Pb kg−1, 0.2–0.6 mg Se kg−1, and 61–172 mg Zn kg−1. Concentrations of As, Cu, and Hg were consistently above national standards. Conclusions The authors conclude that the trace element contents in sediments deposited by the event are within expected values based on soil data in Chile.
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Much of the early prehistory of the Americas lies underwater along its coastlines and in the submerged caves and cenotes of Florida and Central America. A cenote (from Yucatan Maya dzoonot ‘well’) is a deep natural pit, or sinkhole, resulting from the collapse of a doline or limestone bedrock that exposes groundwater underneath. Cenotes are a unique resource in a dry land, especially associated with the Yucatan Peninsula and some nearby Caribbean islands, and were sometimes used by the ancient Maya for sacrificial offerings. In times of lowered sea level and drier climate, as prevailed in the terminal Pleistocene, they were rare sources of freshwater for people and animals. Cenotes and the extensive cave systems to which they are linked have become the focus of palaeontological and palaeoanthropological studies by North American and Mexican Prehistorians, with the Vice-Directorate for Underwater Archaeology, National Institute of Anthropology and History (INAH) commanding several of these efforts. The search for early humans in the Yucatan Peninsula started more than a century ago when Henry Mercer arrived in search of early Americans; however, only in the last fifteen years have systematic efforts been undertaken. Efforts by archaeologists and cave-diving explorers have already resulted in the discovery of numerous assemblages of Pleistocene megafauna and pre-Maya humans. Finds near Tulum, Quintana Roo state, include some of the most complete early Americans skeletons, as well as a largely varied faunal complex including numerous examples of extinct megafauna. Some of the human skeletons are thought to be among the oldest in the hemisphere and they are so well preserved that now they are providing enough organic material for ancient DNA analysis and stable isotope studies. Associated concentrations of bat guano, wood, wood charcoal and calcite formations hold promise for advances in palaeoecology and sea-level history. Despite their great scientific value, these deposits are increasingly at risk from water pollution, salinization, tourism and urban development. As such dangers threaten inundated caves and cenotes all over the world, a major concern for UNESCO and other international and national agencies has been to set minimal standards for protecting this important heritage, which includes detailed recording at the sites and maintaining the materials in situ whenever possible.
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The Pampean loess is the most extensive continental paleo-record of aeolian material in the Southern Hemisphere, recording the deposition of dust transported by two major zonal wind systems: the southern westerly winds and the subtropical jets. In order to increase the understanding on paleo-atmospheric circulation over the Southern Hemisphere, we evaluate dust provenance through REE, Nd, Sr and Pb isotopes in three sections deposited during late Pleistocene-early Holocene across 700 km in the loess belt of the Pampean region in central Argentina. The isotopic comparison of loess from the three sections with southern South American (SSA) potential dust sources show that (1) sources from the southern Altiplano to latitudes of northern Patagonia supplied dust to the Pampas, (2) the slight Sr-Nd isotopic difference between fine and coarse loess may be attributable to grain size effects rather than to differences in provenance, and (3) higher mass accumulation rates in the Pampas are associated with an increased presence of dust originated in the southern Altiplano and southern Puna during the spans of 43-41 ka BP, 20-18 ka BP, 14.6-12.6 ka BP and 11.4-8.9 ka BP. We associate these rises in continental dust fluxes with climatic transitions from wetter to drier periods in the Puna-Altiplano Plateau related to synchronous climatic shifts to humid conditions at the Pampean Plain, probably triggered by El Niño-like conditions. The isotopic comparison with modern SSA dust indicates similar provenance compared to paleo-dust records, suggesting almost constant dust sources from MIS 3 to modern times and/or modest changes in the geochemical signature under the activation/deactivation of the different dust sources. Moreover, contrasting the isotopic signature of the loess sections with more distal palaeoarchives (i.e., South Atlantic Ocean marine sediment cores and Antarctic ice cores), the new data suggest that contrary to previous ideas, the Pampean Loess was not an important source of dust to these regions. Also, a common dust provenance during cold periods (e.g., Last Glacial Maximum and Antarctic Cold Reversal) supports the idea that changes in atmospheric transport efficiency can better explain dust flux variations observed over glacial/interglacial periods in distant palaeoarchives than changes in provenance.
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The arid desert coast of northern Peru has traditionally been viewed either as existing in stasis, or as experiencing punctuated change from sudden flood events, followed by a return to system equilibrium. Despite these environmental extremes, the region was home to agriculture-based societies for millennia, and the success of these farming systems is considered an early example of irrigation technology transforming marginal landscapes. However, a closer examination of the long-term human-environment history of the Chicama Valley, one of the largest valleys in the coastal region, demonstrates that this landscape is the product of protracted interactions across at least three systems: the local environment, El Niño Southern Oscillation (ENSO), and farming. Here, El Niño floods, typically considered high-risk events, are fundamental to local biodiversity and renewal, resulting in a desert ecosystem that is both robust and elastic. The prehispanic farmland known as the Pampa de Mocan (1100BC–AD1460), is presented as a case study to observe the co-evolution of agricultural technology and an ENSO-hyper-arid environment. This ancient farming system developed the capacity to toggle between sudden floodwater inputs and periods of water scarcity. Alongside water and soil conservation practices, prehispanic agriculturalists implemented technologies that were designed to mitigate El Niño flooding and incorporate its byproducts to supplement available resources. The convergence of these interacting systems on the Pampa de Mocan offers new insights into the role of risk in building resilience.
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A modern analogue for past convergent disasters.
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It has long been estabished that gas and fine ash from large equatorial explosive eruptions can spread globally, and that the sulphuric acid that is consequently produced in the stratosphere can cause a small, but statistically significant, cooling of global temperatures,. Central to revealing the ancient volcano-climate connection have been studies linking single eruptions to features of climate-proxy records such as found in ice-core and tree-ring chronologies. Such records also suggest that the known inventory of eruptions is incomplete, and that the climatic significance of unreported or poorly understood eruptions remains to be revealed. The AD 1600 eruption of Huaynaputina, in southern Peru, has been speculated to be one of the largest eruptions of the past 500 years; acidity spikes from Greenland and Antarctica ice, tree-ring chronologies, along with records of atmospheric perturbations in early seventeenth-century Europe and China,, implicate an eruption of similar or greater magnitude than that of Krakatau in 1883. Here we use tephra deposits to estimate the volume of the AD 1600 Huaynaputina eruption, revealing that it was indeed one of the largest eruptions in historic times. The chemical characteristics of the glass from juvenile tephra allow a firm cause-effect link to be established with glass from the Antarctic ice, and thus improve on estimates of the stratospheric loading of the eruption.
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Ice cores that were recovered from the summit of Sajama mountain in Bolivia provide carbon-14-dated tropical records and extend to the Late Glacial State (LGS). Oxygen isotopic ratios of the ice decreased 5.4 per mil between the early Holocene and the Last Glacial Maximum, which is consistent with values from other ice cores. The abrupt onset and termination of a Younger Dryas-type event suggest atmospheric processes' as the probable drivers. Regional accumulation increased during the LGS, during deglaciation, and over the past 3000 years, which is concurrent with higher water levels in regional paleolakes. Unlike polar cores, Sajama glacial ice contains eight times less dust than the Holocene ice, which reflects wetter conditions and extensive snow cover. (Résumé d'auteur)
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Classifications of flowing sediment-water mixtures have, in the past, been based primarily on relative, qualitative differences in the style and rate of movement as well as on morphology and sedimentology of deposits. A more quantitative and physically relevant classification is presented here, based on thresholds in rhéologie behavior. The classification is constructed on a two-dimensional matrix in which flows are located according to deformation rate (mean velocity) and sediment concentration, with composition of the mixture constant. Three major rhéologie boundaries are crossed as sediment concentration increases from 0 (clear water) to 100 percent (dry sediment): (1) the acquisition of a yield strength-the transition from liquid "normal streamflow" to plastic "hyperconcentrated streamflow"; (2) an abrupt increase in yield strength coinciding with the onset of liquefaction behavior-the transition to "slurry flow"; and (3) the loss of the ability to liquefy-the transition of "granular flow." These three rhéologie boundaries shift according to particle-size distribution and composition of the mixture. Processes controlling flow behavior depend on deformation rate (velocity). Rateindependent frictional and viscous forces dominate at lower velocities and in finer grained mixtures; rate-dependent inertial forces dominate at higher velocities and in coarser grained mixtures. As velocity increases, grain-support mechanisms change from low-energy varieties (buoyancy, cohesion, structural support) to progressively higher energy mechanisms (turbulence, dispersive stress, fluidization). Existing nomenclatures of geologic flow phenomena can fit within this rhéologie classification. The morphology and sedimentology of flow deposits commonly can be used to deduce rhéologie behavior, but caution needs to be exercised in inferring processes from deposits.
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The archaeological site of Quebrada Tacahuay, Peru, dates to 12,700 to 12,500 calibrated years before the present (10,770 to 10,530 carbon-14 years before the present). It contains some of the oldest evidence of maritime-based economic activity in the New World. Recovered materials include a hearth, lithic cutting tools and flakes, and abundant processed marine fauna, primarily seabirds and fish. Sediments below and above the occupation layer were probably generated by El Niño events, indicating that El Niño was active during the Pleistocene as well as during the early and middle Holocene.
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Recent construction of a 10 × 3 irrigation canal across the Batán Grande–Poma archaeological complex of northern Peru provided an opportunity for inspection of soil profiles and detailed sampling along a five km transect bisecting an important concentration of ceremonial structures built during the past 3000+ years. From laboratory analysis of 80 soil samples we conclude no long-term irrigation agriculture was practiced in this area and it was unimportant as a resource base. Stratigraphic studies indicate few sediments survive from the 1925 El Niño event, but a massive bed attributable to prehistoric slack-water flood sediments has been identified and can be bracketed between ca. A. D. 650–1000 by associated diagnostic funerary ceramics. Other flood deposits representing the same or different events are described, but we conclude intervalley correlations will be difficult until more precise dating methods are available.
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Lithostratigrahic and mineralogic analyses of sediments from hypersaline Bainbridge Crater Lake, Galpagos Islands, provide evidence of past El Nio frequency and intensity. Laminated sediments indicate that at least 435 moderate to very strong El Nio events have occurred since 6100 14C yr BP (7130 cal yr BP), and that frequency and intensity of events increased at about 3000 14C yr BP (3100 cal yr BP). El Nio activity was present between 6100 and 4000 14C yr BP (4600 cal yr BP) but infrequent. The Bainbridge record indicates that there has been considerable millennial-scale variability in El Nio since the mid-Holocene.
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Sedimentological, mineralogical and geochemical analyses of sediment cores from 9 m-deep, saline Laguna Miscanti, Chile (23 44S, 67 46W, 4140 m a.s.l.) together with high-resolution seismic profiles provide a mid to late Holocene time series of regional environmental change in the Atacama Altiplano constrained by 210Pb and conventional 14C dating. The mid Holocene was the most arid interval since the last glacial maximum, as documented by subaerial exposure and formation of hardgrounds on a playa surface. Extremely low lake levels during the mid Holocene appear consistent with lower effective moisture recorded at other sites along the Altiplano and in the Amazon Basin. Termination of this arid period represented a major shift in the regional environmental dynamics and inaugurated modern atmospheric conditions. The cores show a progressive upward increase in effective moisture interrupted by numerous century-scale drier periods of various intensities and durations that characterize a fluctuating late Holocene climate. In spite of chronological uncertainties, the major environmental changes seem to correlate with the available paleorecords from the region providing a coherent account of effective moisture variability in the tropical highlands of South America.
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Precipitation rates in the Atacama Altiplano 22–24S were 400–500 mm yr–1 during late glacial and early Holocene times as opposed to 200 mm yr–1 today. This humid phase (Tauca phase) was likely due to strengthened tropical (monsoonal) circulation, which brought continental moisture to the Atacama Altiplano. The lake level of Laguna Leja (2330S, 4350 m) at that time was up to 25 m higher than it is today. Mg/Ca and Sr/Ca data from lake sediments show that, what today is a highly saline lake was a freshwater lake at that time. Seasonally-laminated calcareous sediments were deposited between 13 500 and 14C and3H data from lake-, ground- and well water suggest that modern groundwater formation (i.e. water
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The oceanographic phenomenon known as El Niño is the subject of intensive recent study. Any hypotheses regarding physical causes and predictability of El Niño should consider its geological history. New geoarchaeological evidence suggests that the El Niño phenomenon did not exist along the northern and central coasts of Peru before about 5000 years B.P. Molluscan faunas from archaeological sites at Pampa las Salinas and Salinas de Chao permit temporal bracketing of a major structural change in the East Pacific water mass. The boundary between the warm Panamic Province and the cold Peruvian Province, which today occurs at about 5 degrees south latitude, was some 500 km further south from at least 11,000 years B.P. to about 5000 years B.P. This conclusion is corroborated by many other lines of evidence including phosphorite distribution, timing of glacial retreat, sea level change, radiolarian, diatom and fish scale distributions, and beach ridge patterns. The present day arid coastal climate of north central Peru is probably a post-5000 year B.P. development. Hunter–gatherer populations of the area would most likely have exploited more land-based seasonal resources from grasslands and forests before 5000 years B.P., and relied less upon the diminished productivity of warm water maritime resources.
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Analyses the decades to millennial cycles in climate and the possible mechanisms involved in the solar and Milankovitch cycles. -from Author
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Geological effects of the destructive May 31, 1970, Perú earthquake (Ms = 7.7) extended over roughly 65,000 km2 of west-central Perú. Earthquake-triggered slope failures of all types that occurred throughout the mountainous parts of the region extensively damaged transportation routes and irrigation canals and temporarily dammed some rivers and lakes. The geologically most important and spectacular of these, a cataclysmic debris avalanche from between 5,500 and 6,400 m altitude on the north peak of Huascarán Mountain, buried the city of Yungay and part of Ranrahirca (elevation about 2,500 m) with a loss of more than about 18,000 lives. The debris avalanche involved 50-100 million m3 of rock, ice, snow, and soil that traveled 14.5 km from the source to Yungay at an average velocity of between 280 and 335 km/hr. Exceptionally rapid movement of the avalanche is indicated by eyewitness accounts, by topographic irregularities as high as 140 m that were overridden, and locally by boulders weighing several tons that were hurled as much as 1,000 m beyond its margins. A pulse of muddy water from the debris avalanche that swept down the Río Santa 160 km to the sea inundated farms and small settlements, buried highway and railroad routes, and destroyed the diversion dam and access bridge to a major hydroelectric plant. The extensive destruction to communities and an additional estimated 20,000 casualties resulted primarily from failure of adobe and masonry structures which had little shear resistance to lateral forces imposed by seismic shaking. The degree of damage to buildings and to transportation routes was aggravated in some areas of saturated unconsolidated deposits by differential compaction, downslope slumping or sliding, lateral spreading of liquefied sediments toward free faces, and possibly amplification of seismic vibrations. The absence of surface tectonic displacements or of a significant tsunami and the spatial distribution of the main shock and aftershocks suggest that the earthquake originated by movement on a fault, or faults, beneath the continental shelf at depths between 45 and 65 km.
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Over 4 km of coastal progradation produced the Santa beach ridge complex in central Peru. The complex is comprised of more than 15 individual beach ridges that can be divided into four morphostratigraphic groups on the basis of ridge spacing and geometry. Each morphostratigraphic group accreted during periods of glacial contraction and increased meltwater discharge in the headwaters of the drainage basin. The cross-sectional morphology of individual ridges is a result of oceanographic conditions at the time of ridge accretion. Ridge crest height reflects the wave energy of the last storm event before the accretion of the subsequent ridge. The earliest ridges have subdued morphology indicating frequent overtopping and deposition during a period of rising sea-level. Ridge height peaks subsequent to sea-level stabilization and drops off gradually indicating a relative decrease in wave height through time. A zone of lower slope at the base of the beach face of individual ridges indicates the apparent tidal range during ridge formation. Apparent tidal range varies from 1.00 to 2.12 m during ridge accretion. A sea-level curve was created using apparent tidal range elevations through the complex and radiocarbon age estimates on in situ and detrital shell debris and driftwood. This model produces a sea-level curve that peaks between 7.0 and 6.0 ka at about 1 m above present mean sea-level and then remains relatively stable falling to the present level sometime within the past 0.5 ka.
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Quebrada Tacahuay, located on the south coast of Peru, is one of the oldest expressions of maritime adaptations in the Western Hemisphere. Excavations conducted in 1997 and 1998 indicate that humans focused their activities on the collection and butchering of marine birds, particularly cormorants and boobies, and other marine resources more than 10,290 years ago (uncalibrated radiocarbon years B. P.). In addition to abundant zooarchaeological remains, cultural material includes unifacial lithic tools and one worked marine mammal rib. We report on the use of marine resources at the site in conjunction with the taphonomic history of site formation. Geological data indicate that El Niño flood events initially occurred during the Pleistocene and at various times during the Holocence. The abundant use of seafood indicates that Quebrada Tacahuay represents a specialized coastal extraction station used by Late Paleo-Indian populations with a well-developed littoral adaptation.
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This paper describes a general method for determining the amount of earthquake-induced landsliding that occurs in a seismically active region over time; this determination can be used as a quantitative measure of the long-term hazard from seismically triggered landslides as well as a measure of the importance of this process to regional slope-erosion rates and landscape evolution. The method uses data from historical earthquakes to relate total volume of landslide material dislodged by an earthquake to the magnitude, M, and seismic moment, Mo, of the earthquake. From worldwide data, a linear-regression relation between landslide volume, V, and Mo is determined as: V = Mo/1018.9(±0.13), where Vis measured in m3 and Mo is in dyn-cm.
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The eastern tropical Pacific and areas along its fringe in South America experienced the most intense El Nino occurrence of the twentieth century between June 1982 and July 1983. At least twenty-five spells of bad weather caused extensive damage to agriculture, structures, and transportation in southern Ecuador, Peru, the Galapagos Islands, and eastern Polynesia. The basins of the Tumbes, Chira, Piura, Lambayeque, Zana, Reque, Jequetepeque, Chicama, Moche, and Viru rivers in Peru were the most affected areas. In the ocean reduced fish stocks caused starvation among seabirds and mammals. The altiplano highlands suffered severe drought. There is a coincidence between past El Nino occurrences and tropical volcanic activity. The eruption of El Chinchon in April 1982 appears to be closely related to El Nino 1982-83.
Article
Recent debate about the development of complex societies on the north coast of Peru has turned on the relative importance of marine vs. terrestrial resources and the extent to which different resource zones are upset by El Niño/Southern Oscillation (ENSO) events. While ENSO events are cited frequently as having important consequences for Prehispanic Andean societies, in fact there are few archaeological data about the nature of cultural responses to a specific ENSO event. Archaeological data from two Chimu settlements in the Casma Valley, Peru—Quebrada Sta. Cristina and Manchan—document the occurrence of a fourteenth-century A.D. ENSO event and some of the cultural responses to that prehistoric El Niño.
Article
Electrical conductivity measurements from a new Greenland ice core are reported which confirm previous findings of relatively warm 'interstadial' periods during the last glaciation and short returns to colder conditions during the glacial to interglacial warming. The measurements also reveal a hitherto unrecognized mode of rapid climate variation. Fluctuations in ice conductivity on scales of less than five up to 20 years reflect rapid oscillations in the dust content of the atmosphere. The 'flickering' between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation.
Article
Significant precipitation along the north-central coast of Peru (lat 5°-10°S) occurs exclusively during El Niño incursions of warm water into the Peruvian littoral. Flood deposits from this region therefore provide a proxy record of extreme El Niño events. I present a 3500 yr chronology of the extreme events based on radiocarbon dating of overbank flood sediments from the Rio Casma (lat 9.2°S).The flood-plain stratigraphy suggests that the El Niño phenomenon has occurred throughout the Holocene and that flood events much larger than that which occurred during 1982-1983 occur here at least once every 1000 yr.
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We measured stable oxygen isotope ratios and skeletal growth rates in the massive corals Pavona clavus and P. gigantea from the west coast of Isabela Island, Galapagos, to assess interannual to decadal climate variability in the eastern Pacific. Comparisons of instrumental data sets show that sea surface temperatures (SST) in the Galapagos region are representative of a broad portion of the eastern equatorial Pacific. The P. gigantea isotope record is nearly monthly in resolution, spans the period 1961-1982, and shows strong correlation with a Galapagos instrumental SST record. Cross-spectral analysis shows that SST can explain greater than 80% of the variance in δ18O at both the annual cycle and within the high-frequency portion of the ENSO band (3-5 years). The P. clavus record is annual in resolution, extends from 1587 to 1953 A.D., and was obtained from a 10-m diameter colony preserved within the Urvina Bay uplift. The isotopic record appears to be a very good, but not perfect, indicator of ENSO events. The dominant oscillatory modes, both within the ENSO and interdecadal frequency bands, shift to shorter periods from the early to middle 1700s and again from the middle to late 1800s. This may reflect major reorganizations within the tropical ocean-atmosphere system and suggests that tropical Pacific climate variability is linked across timescales ranging from years to decades. -from Authors
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Data from 40 historical world-wide earthquakes were studied to determine the characteristics, geologic environments, and hazards of landslides caused by seismic events. This sample of 40 events was supplemented with intensity data from several hundred United States earthquakes to study relations between landslide distribution and seismic parameters. Fourteen types of landslides were identified in the earthquakes studied. The most abundant of these were rock falls, disrupted soil slides, and rock slides. The greatest losses of human life were due to rock avalanches, rapid soil flows, and rock falls. Correlations between magnitude (M) and landslide distribution show that the maximum area likely to be affected by landslides in a seismic event increases from approximately 0 at M ≅ 4.0 to 500,000 km2 at M = 9.2. Threshold magnitudes, minimum shaking intensities, and relations between M and distance from epicenter or fault rupture were used to define relative levels of shaking that trigger landslides in susceptible materials. Four types of internally disrupted landslides—rock falls, rock slides, soil falls, and disrupted soil slides—are initiated by the weakest shaking. More coherent, deeper-seated slides require stronger shaking; lateral spreads and flows require shaking that is stronger still; and the strongest shaking is probably required for very highly disrupted rock avalanches and soil avalanches. Each type of earthquake-induced landslide occurs in a particular suite of geologic environments. These range from overhanging slopes of well-indurated rock to slopes of less than 1° underlain by soft, unconsolidated sediments. Materials most susceptible to earthquake-induced landslides include weakly cemented rocks, more-indurated rocks with prominent or pervasive discontinuities, residual and colluvial sand, volcanic soils containing sensitive clay, loess, cemented soils, granular alluvium, granular deltaic deposits, and granular man-made fill. Few earthquake-induced landslides reactivate older landslides; most are in materials that have not previously failed.
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The largest explosive eruption (volcanic explosivity index of 6) in historical times in the Andes took place in a.d. 1600 at Huaynaputina volcano in southern Peru. According to chronicles, the eruption began on February 19 with a Plinian phase and lasted until March 6. Repeated tephra falls, pyroclastic flows, and surges devastated an area 70 × 40 km2 west of the vent and affected all of southern Peru, and earthquakes shook the city of Arequipa 75 km away. Eight deposits, totaling 10.2 13.1 km3 in bulk volume, are attributed to this eruption: (1) a widespread, ˜8.1 km3 pumice-fall deposit; (2) channeled ignimbrites (1.6 2 km3) with (3) ground-surge and ash-cloud-surge deposits; (4) widespread co-ignimbrite ash layers; (5) base-surge deposits; (6) unconfined ash-flow deposits; (7) crystal-rich deposits; and (8) late ash-fall and surge deposits. Disruption of a hydrothermal system and hydromagmatic interactions are thought to have fueled the large-volume explosive eruption. Although the event triggered no caldera collapse, ring fractures that cut the vent area point to the onset of a funnel-type caldera collapse.