A newly identified drought on the Pacific island of Rapa Nui, also known as Easter Island, could have spurred islanders to invest fewer resources in building their legendary stone monuments. But some archaeologists dispute this interpretation.
The island of Rapa Nui has become central to a cautionary tale of disaster caused by unsustainable use of resources. The standard narrative is that the arrival of the first Polynesians on the tiny island in the 1200s led to rapid deforestation, in part to support the building of the giant stone moai statues and monumental platforms, called ahus. In this version of events, swift environmental degradation then led to a population collapse before the arrival of Europeans in the 1700s. The statues remain as an eerie warning against overexploitation of the natural world.
More recently, however, archaeologists have challenged this picture of social collapse on Rapa Nui prior to contact with Europeans. Environmental changes, such as drought, have been proposed as an alternative way to understand shifts in Rapa Nui society, including a departure from statue-building. But direct evidence for drought during key periods has been lacking until now.
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at Columbia University in New York and his colleagues analysed hydrogen isotopes in the waxy coating of ancient leaves preserved in lake sediments spanning the history of the island’s inhabitation. The amount of such isotopes in leaf wax is strongly correlated with changes in local precipitation, which gave the researchers a tool for assessing past changes in rainfall on the island.
The leaf wax record suggests the island saw a substantial deficit in annual precipitation between 1550 and the early 1700s, with rainfall reduced by as much as 900 millimetres per year. For context, a drought on Rapa Nui between 2010 and 2017 that severely stressed freshwater reserves was associated with a reduction in annual precipitation of just 370 millimetres.
D’Andrea and his colleagues declined to comment on their research before it has been published in a peer-reviewed journal. However, in the draft of their paper posted online, they point out that these extended dry conditions coincided with, and may have spurred, major shifts in Rapa Nui society, including a reduction in monumental sculpture projects.
“Our hypothesis does not necessitate violent war or demographic collapse at 1600 CE, but provides a reasonable explanation for possible drivers of intercommunity conflict, a need for spatial reorganisation, and an impetus for cultural development on the island,” they write.
“Droughts do occur on Rapa Nui and they can be really dramatic,” says a geologist at the University of Alaska Fairbanks, who was not involved with the study. In 2008, he and his colleagues reported evidence for prior to the arrival of people. “All these years I’ve been waiting for someone to follow up on that. And they did it,” he says.
However, archaeologists are sceptical that the drought was a major source of conflict or decline. “This dials in when this drought could have hit the island. Their evidence is pretty substantial,” says at the University of Illinois Urbana-Champaign. “What I’m tentative about are the cultural conclusions they make.”
While such a change in precipitation would have had an effect, “it’s unclear to me what impact it actually had”, says , an archaeologist at Binghamton University in New York, who points out that there is a lack of evidence of dietary stress in skeletons from the drought period – and evidence of continued activity in the quarries used to build the moai and ahu afterwards.
Rather, the fact that islanders dealt with such severe drought “adds more evidence that Rapa Nui people had to manage the fact that the island was changing, both due to people and natural changes”, he says.
“We’re so focused on this environmental collapse when it could have been these other things that stopped statue making,” says Simpson.
EarthArXiv
