3D model of Easter Island quarry offers new clues on how giant stone heads were made

The average statue was 4 meters (13 feet) tall and weighed 12.5 tons. (Credit: Carl P. Lipo/Binghamton University; Terry L. Hunt/University of Arizona via CNN Newsource)

Archaeologists say a 3D model of a centuries-old quarry of unfinished stone head statues on Easter Island offers new clues about how these monuments were made and the Polynesian society that brought them into being.

Also known as Rapa Nui, the remote island is famed for the gargantuan sculptures that look out over the Pacific Ocean, but its inhabitants never erected what would have been the community’s largest statue. The giant head, along with hundreds of others, remains embedded in rock in the quarry, a volcanic crater.

Individual clans, and not a single entity with an island-wide workforce as once believed, likely organized construction of the fascinating stone heads, known as moai, according to research published Wednesday in the journal PLOS One.

“The sheer scale seemed to demand centralized coordination,” said study coauthor Carl Lipo, a professor at Binghamton University’s department of anthropology in New York. “The presence of monuments became circular evidence for hierarchy. Monuments meant chiefs because chiefs built monuments.”

For the site analysis, researchers built what they described as the first high-resolution 3D model of the Rano Raraku moai quarry from 11,000 overlapping images taken by a drone in a process known as photogrammetry.

The scientists identified 30 distinct sites of quarrying activity, which they said suggested multiple independent work areas. The team also found evidence of transport of moai out of the quarry in different directions before being erected on enormous platforms dotted around the island. This approach, the authors argued, also indicated that the manufacture of megalithic figures was not under centralized management.

“This means the entire production chain — from first cutting into bedrock to final statue details — stayed within individual zones, rather than having statues move between areas for different production phases,” as would be the case in an industrial quarry, Lipo said via email.

He added that the different zones showed variability in extraction methods and finishing techniques. The pattern adds to evidence that Rapa Nui was not a politically unified society and instead consisted of small and independent family groups.

Massive scale of Easter Island’s head statues

The model gives fresh perspective to the monumental endeavor that took place on the tiny island, where around 1,000 stone statues were erected from the 13th to 17th centuries. The average statue was 4 metres (13 feet) tall and weighed 12.5 tons, with some exceeding 20 tons, Lipo said.

The model of the quarry revealed 426 moai in various stages of completion, 341 trenches cut to outline blocks for carving, and 133 voids in the rock where statues were successfully removed, plus five bollards that acted as anchor points for lowering moai down slopes. Artisans quarried and carved most of the statues in supine position, with the majority carved from the top down, although others were extracted from the side. The most common method involved defining facial details before outlining the head and body in the rock.

The unfinished statues include what would have been the largest moai if it had been finished and erected, Lipo said. Known as Te Tokanga, it is about 21 meters (69 feet) tall and would have weighed around 270 tons if completed, he said.

“Some statues exceeded practical transport limits,” Lipo said. “This would be the case if, as we suspect, competitive escalation drove communities to attempt ever-larger moai. These oversized attempts represent communities testing limits and recognizing constraints.”

The numerous statues remaining at Rano Raraku represent normal quarry operations, not abandonment, Lipo added. A 2019 study suggested that production of statues had continued until the arrival of Europeans, he noted.

“The quarry didn’t fail catastrophically but was likely deactivated by the European-introduced disruption that came with the introduction of diseases,” he said.

The latest research was the first time photogrammetry techniques had been used on the site, but the results didn’t really show anything dramatically new about Rapa Nui society, according to Helene Martinsson-Wallin, a professor in the department of archaeology at Uppsala University in Sweden. Martinsson-Wallin, who was not involved in the research, said scholars such as English archaeologist and anthropologist Katherine Routledge had identified a clan-based system 100 years ago.

“It has later been defined as a so-called open society, meaning there is no paramount chief who rules the society, and several studies have shown that this type of social structure can also exhibit megalith building structures,” Martinsson-Wallin said via email.

The study took an “innovative approach,” said Christopher Stevenson, an archaeologist and professor in the School of World Studies at Virginia Commonwealth University, who also wasn’t involved in the research. He added that the team’s hypothesis that the activities at the quarry represent decentralized moai production by different kin groups was “an important one that needs to be evaluated.”

However, Stevenson said the researchers’ evaluation was not backed up with sufficient data. For example, he said there was a style of house near the quarry not mentioned in the study that was different from less-elaborate residential dwellings and therefore could reflect some kind of social division or distinction.

Fierce debate over Rapa Nui’s society

Settled by a small group of Polynesian seafarers about 900 years ago, Easter Island, today part of Chile, has long been a source of fascination as well as fierce debate about how complex societies can sometimes ruinously fail.

Some writers, such as geographer Jared Diamond in his 2005 book, “Collapse: How Societies Choose to Fail or Succeed,” used Easter Island as a cautionary example of how the exploitation of limited resources can result in catastrophic population decline, ecological devastation and destruction of a culture through infighting.

That theory remains contentious. More recent research has suggested the opposite: that Rapa Nui was in fact home to a small but sustainable society.

The latest findings contribute to that reinterpretation, adding to a picture of a resilient community that adapted to one of Earth’s most isolated environments, Lipo said.

“The traditional story, popularized by Diamond and others, assumes that powerful chiefs drove unsustainable monument-building, causing deforestation, agricultural failure, and a population crash,” Lipo said.

“But if monument production were decentralized, with autonomous communities making independent decisions, there would be no central authority to drive the island over an ecological cliff.”