ORONO, Maine — It happened, apparently, over the course of just a few decades — a series of major natural catastrophes which eventually forced the people of an ancient society to abandon their land and buildings.
Although modern civilization is infinitely better prepared to handle catastrophes such as earthquakes, flooding and loss of agricultural areas, the convergence of such events, as happened around 3,800 years ago in Peru, could cause damage today.
That warning is at the root of research published this week in the journal Proceedings of the National Academy of Sciences. University of Maine anthropology professor and graduate dean Dan Sandweiss, and David Keefer, a California-based geologist who is affiliated with UM’s Climate Control Institute, were among five authors of the report.
“The lesson to take is to look out for the synergic effects of these convergent catastrophes,” said Sandweiss. “Even if they’re isolated events, the effects can be much greater.”
It appears this happened to the people living in an ancient society in Peru’s Supe Valley, including a site called Caral, the largest monumental site of the Late Preceramic era in South America.
That area of Peru has a desert climate, but it was successfully inhabited, fished and farmed for more than 2,000 years. It was one of the world’s richest fisheries because the nutrient upswelling in the area’s waters made for a diversity of fish. Sandweiss said the inhabitants had access to deep-water fish because of inlets and high cliffs off which they could drop lines. The rain and glacier melt coming off the Andes allowed the inhabitants to irrigate crops and have access to drinking water.
“That led to people being able to live, and to have a complex society,” Sandweiss said.
After centuries of prosperity, however, the El Nino weather phenomenon became more frequent, bringing flooding rainwater. El Nino refers to a disruption of the ocean-atmosphere system in the tropical Pacific, which has caused intense rainfall and flooding, drought and forest fires all over the world.
At the same time, the study area in Peru is extremely seismic and prone to heavy earthquakes. Those earthquakes would shake up the landscape, leaving debris sitting on top of the ground.
Apparently, El Nino floodwaters washed the buildup of earthquake debris toward the coast and into the Pacific Ocean, where Sandweiss said two key things happened to the Peruvian sites, which went as far as 25 kilometers inland.
First, the debris created a ridge that straightened out the coastline, therefore reducing the types of maritime life, and making it hard to access the coast. Second, the constant breeze that blows inland likely picked up sand and dropped it on top of crops.
Faced with the loss of their fishing grounds and degradation of crop areas, Sandweiss said, the inhabitants left.
“We think this got into full swing about 3,800 years ago and in fairly short order this early set of sites in this area we’re studying were abandoned,” Sandweiss said. “With the convergent catastrophes, people likely had a crisis of faith, they likely did not support temples and essentially this area became a backwater. This area was really hit, and hit by something that seemed to affect them for a long time, as this ridge of sand would have done.”
Successor societies to the north also showed signs of collapse when the frequency of El Nino increased and the sand ridge moved north. It’s unclear where the people went, but Sandweiss theorized some of the inhabitants may have died of famine.
The likelihood of that happening now is low because of technology that can produce models of the effects of El Nino, as well as obvious improvements in transportation to move people and resources.
In fact, Sandweiss said, when the last El Nino phenomenon happened in 1997 and 1998, the government of Peru heeded warning and put programs into place that seemed to lessen the damage somewhat.
El Nino has been linked to global warming, although its frequency seems to have changed throughout history, Sandweiss said.
“The best thing we can do is to continue to improve the climate models to predict El Nino, so we can get ready for it,” he said.
The research that went into the article took place over the last three years, but it was built on work that has been done since the early 1980s. Peruvian archaeologist Ruth Shady, who is also listed as an author of the report, has done fieldwork in the Supe Valley since 1994.