Easter Island Heads Mystery Solved? Rapa Nui Civilization Built Moai by Freshwater Locations

Moai represent the ancestors of the Rapa Nui people. iStock

The lost civilization of Easter Island may have chosen the location of the iconic moai heads to signal where fresh water was available, a study has suggested.

Carl Lipo, an anthropologist who has spent almost 20 years studying the Rapa Nui people and their disappearance from Easter Island, was looking at how the population was able to survive with such limited access to drinking water. Across the island, there is very little access to freshwater—springs and streams are almost completely absent and there is very little rainfall (approximately 48.8 inches per year). So how did a civilization of an estimated 15,000-20,000 at its peak manage to survive?

To find out, Lipo and his colleagues Matt Becker and Tanya Bronson, from California State University Long Beach, carried out field studies looking at how the islanders might have used brackish groundwater discharge that surfaces along coastlines. Brackish water is saltier than normal water, but not as salty as seawater. Previous accounts from European explorers indicated the Rapa Nui people drank brackish water, but where they accessed it was not known.

Lipo's research, published in the Hydrogeology Journal, finds the islanders could have survived by drinking the brackish groundwater discharge that becomes ponded in trenches along the coast, or that floats on the coastal waters of the island. "Two field surveys indicate abundant locations of brackish but potable water along the coastline… Although coastal groundwater sources are of poor quality, they were apparently sufficient to support the population and allow them to build the magnificent statues for which Easter Island is famous," the study concludes.

Easter Island heads might have been located by drinking water sources. iStock

What is more intriguing, however, is the location of the water sources and the position of the Easter Island statues. The moai appear to have been placed at spots where drinking water was available.

The statutes—which can reach up to 30 feet in height—are carved from compressed volcanic ash. In total, there are almost 900 statues. They were built at some point between 1200 and 1600. After the Europeans arrived in the 1700s, they were toppled over, which has been attributed to tribal warfare and an earthquake.

Why the Rapa Nui built these statues and what purpose they served is not entirely understood. It is thought they were symbols of religious and political power, representing the ancient ancestors of Polynesians. Most of the statues are located on the coasts of Easter Island—Lipo suggests this could have been done for practical purposes.

"Now that we know more about the location of freshwater, however, the location of these monuments and other features makes tremendous sense: they are positioned where freshwater is immediately available," he said in a statement.

The team will now try to better understand how closely the location of the moai and the availability of drinking water are tied. This could eventually provide answers about one of the world's most enduring archaeological mysteries.

Lipo told Newsweek: "The issue of water availability—or the lack of it—has often been mentioned by researchers who work on Rapa Nui/Easter Island. When there were clear 'wells'—i.e., holes that provide access to fresh water—it was noted that the archaeological remains tended to be relatively dense. Yet it wasn't until Becker and Brosnan started to examine the details of the hydrology that we saw that fresh water access and statue location were so tightly linked together.

"The more we looked the more consistently we saw this pattern. Places without ahu/moai showed no fresh water. The pattern was striking and surprising in how consistent it was. Even when we find ahu/moai in the interior of the island, we find nearby sources of drinking water. That was a real surprise."

He said the question of why the heads were built where they were is one of the key mysteries of this civilization. You would think that such huge monuments would be placed in spots where they could be visible to outsiders—yet often they are often found in shallow hollows or in places generally not visible to outsiders. This, Lipo said, doesn't make sense.

"Linking the location of statues with key natural resources offers us the opportunity to learn about some of the functional reasons communities went through such great extents to establish monuments," he said. "Knowing the details of the island's hydrology and understanding that fresh water was a key ingredient in monument location now allows us to start generating hypotheses about the role that statues/monuments played in the community … This may well help unravel the secret to why this island boasts so many massive statues."

The Rapa Nui civilization collapsed after the arrival of European explorers. Foreign disease is thought to have played a huge role in their demise—along with the slave raiding expeditions in the 1860s.

Lipo said they are now "tantalizingly close" to putting all the pieces of the Easter Island puzzle together. Understanding the hydrology should, he says, provide an important step towards working out what island life was like for the Rapa Nui. "They were ingenious in their ability to transform this remote and isolated place—one that was plagued by remarkably constrained natural resources—into a place that could support the islands communities over at least five centuries," he said. "What they did was an incredible feat—but one that has been misinterpreted by outsiders who make European assumptions about what the island 'should look like.'

"The ancestors of Rapa Nui were indeed wise—and it is our job to learn as much of this wisdom as possible."

This story has been updated to include quotes from Carl Lipo.