El Nino has been a major driver of societal collapse, various catastrophes and cultural change in coastal Peru for millennia, but it isn't the only culprit.
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In a new study, University of Maine researchers warn against over-interpreting the role climatic change, like an El Nino event, plays in societal and cultural transition.
Dan Sandweiss, a professor in the Anthropology Department and Climate Change Institute, and Kirk Maasch, a professor in the School of Earth and Climate Sciences and the Climate Change Institute, investigated whether climate influenced the abandonment of three sites in the Lambayeque Valley in northern Peru: Pampa Grande not long after 750 A.D., Batán Grande in 1100 A.D. and Túcume, America's largest pyramid center, between 1532 and 1547 A.D. Sandweiss excavated Túcume in collaboration with Norwegian explorer Thor Heyerdahl in the 1990s.
All three sites were major centers of Andean society at their time, and large adobe and fill mounds in each site were burned when they were abandoned. Pampa Grande covered 600 acres and centered around the mound Huaca Fortaleza. Batán Grande had eight large mounds. Túcume spanned 200 hectares with 13 major mounds and several dozen smaller structures, according to researchers.
Sandweiss and Maasch analyzed data from three proxy records for climate change and El Nino activity to determine whether they occurred around the same time as the abandonment of these sites. Those records included an ice core from the Quelccaya ice cap in southern Peru, a marine sediment core from the coast and a lake sediment record from Pallcacocha in highland Ecuador.
The data showed that climate contributed to the abandonment of Pampa Grande and Batán Grande, but not Túcume, which resulted from the Spanish conquest. The new study also revealed associations between the abandonment of Pampa Grande and Batán Grande and El Nino, albeit at different degrees of intensity.
"Our study shows that equifinality—similar outcomes from different causes—likely happened in Peruvian prehistory," says Maasch. "This urges caution in seeing a single process such as climate change as the prime driver of all abrupt change."
Ice core and marine and lake sediment core records showed that the abandonment of Pampa Grande occurred during the onset of the Medieval Warm Period, a time of extreme drought and a strong peak in El Nino intensity, according to researchers. The abandonment of Batán Grande happened at the latter end of the Medieval Warm Period during a drought and when there was a small peak in El Nino intensity. After both sites were abandoned, El Nino intensity diminished and new mound centers were built, researchers say.
Civilizations along the Peruvian Coast experience several different types of El Nino. Researchers theorize that the abandonment of Pampa Grande and Batán Grande occurred during a Central Pacific El Nino, which is known for causing drought in areas of the Andean Highlands like the Lambayeque Valley.
Sandweiss and Maasch previously found connections between climate and cultural change in early Peruvian civilizations, particularly during initial monument construction in 5800 B.P., at the end of the Late Preceramic Period around 3800–3600 B.P., and at the conclusion of the Initial Period temple tradition at 2850 B.P. The climatic pattern has brought extreme weather conditions that decimate agricultural infrastructure, depress fisheries, usher in disease and damage archaeological resources in northern Peru, and it continues to threaten the region's economy and culture.
"When we began working on the Peruvian coast, we saw El Nino events as unmitigated disasters," says Sandweiss. "Thanks to more recent work by many colleagues and studies like this one, we now have a better understanding of the resilience of ancient Peruvians in the face of climatic and other catastrophes. Along with technological responses, ideological changes such as site abandonment were part of the cultural repertoire for dealing with disaster."
Sandweiss has spent decades conducting pioneering research on the origins of El Nino and fluctuations of its frequency and intensity over time. He also is credited with discovering variation in the frequency of El Nino events during the Holocene (the last 11,400 years) and, in the process, demonstrating the value of archaeological remains as records of past climates and early maritime adaptations.
His work on El Nino has provided seminal contributions to the field and provided a scientific foundation for exploring the impact of climatic disasters on cultural change in the Andes. ■