Waves are beginning to reach statues and platforms built by an ancient civilization.

HANGA ROA, Easter Island — The human bones lay baking in the sun. It wasn’t the first time Hetereki Huke had stumbled upon an open grave like this one.

For years, the swelling waves had broken open platform after platform containing ancient remains. Inside the tombs were old obsidian spearheads, pieces of cremated bone and, sometimes, parts of the haunting statues that have made this island famous.

But this time was different for Mr. Huke. The crumbling site was where generations of his own ancestors had been buried.

“Those bones were related to my family,” said Mr. Huke, an architect, recalling that day last year.

Centuries ago, Easter Island’s civilization collapsed, but the statues left behind here are a reminder of how powerful it must have been. And now, many of the remains of that civilization may be erased, the United Nations warns, by the rising sea levels rapidly eroding Easter Island’s coasts.

The island is about 15 miles across at its widest. Ringing it are scores of moai statues and their platforms, called ahu.Dots show locations of ahu and moai. Archaeologists believe the moai represent the ancestors of the islanders. Polynesians discovered the island 1,000 years ago. It is one of the most remote inhabited islands on Earth. Now it is part of Chile, 2,200 miles away across the Pacific.

Many of the moai statues and nearly all of the ahu, the platforms that in many cases also serve as tombs for the dead, ring the island. With some climate models predicting that sea levels will rise by five to six feet by 2100, residents and scientists fear that storms and waves now pose a threat like never before.

“You feel an impotency in this, to not be able to protect the bones of your own ancestors,” said Camilo Rapu, the head of Ma’u Henua, the indigenous organization that controls Rapa Nui National Park, which covers most of the island, and its archaeological sites. “It hurts immensely.”

Ahu Akahanga

Similar fates are faced by islanders throughout the Pacific Ocean and along its margins, in places like the tiny Marshall Islands that are disappearing under the sea and the sinking megacity of Jakarta, where streets become rivers after storms hit. Kiribati, a republic of coral atolls north of Fiji, may be uninhabitable in a generation. Their residents may become refugees.

On Rapa Nui, the Polynesian name of this island, much of which has been recognized as a Unesco world heritage site, both the future and the past are threatened.

The island’s economy hangs in the balance. The archaeological sites are the backbone of the main industry: tourism. Last year, this island with only 6,000 residents attracted more than 100,000 visitors. Easter Island’s hotels, restaurants and tour businesses take in more than $70 million every year.

Ahu Tongariki

Tourists usually begin their days in Tongariki, where they gather to watch the sunrise from behind a line of monoliths facing inland. Groups split off to Anakena, the island’s one sandy beach, or to the ancient platforms at Akahanga, a sprawling site of former villages on the shore where, tradition holds, the island’s mythical founder, Hotu Matu’a, is buried in a stone grave.

Yet all three sites now stand to be eroded by rising waters, scientists say.

“We don’t want people seeing these places through old photos,” Mr. Rapu said.

Ahu Akahanga This moai statue, toppled years ago, faces many dangers. Residents surrounded it with stones to protect it from tourists. But the sea is the larger threat. The statue lies only yards from a sea cliff that is rapidly eroding.

Archaeologists fear the rising waves could erase clues to one of the greatest mysteries of the island: What caused the collapse of the civilization that built the stone statues?

Perhaps a thousand years ago, Polynesians discovered this island in the middle of a vast, empty sea. They created a civilization that constructed more than 1,100 moai statues, many of which were raised miles from their quarries using methods that still captivate scientists.

Less mysterious is what happened next. As the population grew, the island went from forested to barren. Europeans arrived with new diseases.

The island’s vast quarry at Rano Raraku was deserted, with dozens of moai left unfinished and abandoned. By the 1870s, the population was just over a hundred, down from thousands at its peak.

Archaeologists hotly debate whether it was resource depletion, disease, civil war, or perhaps rats that came with the islanders and ravaged forests, that was ultimately to blame. And the clues may lie inside the funeral platforms, which hold some of the few remains that can be dated to establish a timeline.

Those remains “could add more data to show it’s not a simple or straightforward answer to what happened,” said Jane Downes, a professor of archaeology at the University of the Highlands and Islands in Scotland, who has spent many summers in Easter Island working to document the damage.

The highway circuit that runs much of the triangular island shows a landscape that is changing.

Ovahe

The damage has been swift on Ovahe Beach, near where Mr. Huke came across bones in the sun. For generations, there had been a sandy beach here that was popular with tourists and locals. Nearby, a number of unmarked burial sites were covered with stones.

Now the waves have carried off almost all of the sand, leaving jagged volcanic stone. The burial sites have been damaged and it’s not clear how long they will survive the waves.

“I once swam in Ovahe and the sand seemed to go on for miles,” said Pedro Pablo Edmunds, the Hanga Roa mayor, in his office as he flipped through a coffee-table book with images of the beach. “Now, it’s all stone.”

Two years ago officials buried a time capsule, to be opened by islanders in 2066, near the town hall. Among the items inside were pictures of Ovahe Beach before it lost all of its sand.

“They will dig it up in 50 years and see us standing there, where there is no beach,” Mr. Edmunds said.

At a site called Ura Uranga Te Mahina on the island’s southern coast, park officials were alarmed last year when blocks of a stone wall perched about 10 feet above a rocky coast collapsed after being battered by waves.

Ahu Runga Va'e

“Now, all of this will fall next,” said Rafael Rapu Rapu, the chief archaeologist of Ma’u Henua, pointing to a map showing the platforms behind the collapsed wall.

Mr. Rapu has used a nearby site, called Runga Va’e, to experiment with measures to mitigate the damage. Using part of a $400,000 grant from the Japanese government, officials built a sea wall for protection against the waves. But it remains unclear whether the wall will be enough to stop the erosion, or if the island leaders will have to consider moving platforms and statues away from the coast in order to save them.

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Other vulnerable areas present an even tougher challenge to conservationists. One of them is the volcanic crater at Orongo, the center of the civilization’s activity around 1600, the last years before European contact. Island residents gathered for an annual swimming competition in which young men raced through open water to a nearby island, Motu Nui, to fetch bird eggs. The winner determined which clan would rule the island for the following year.

The stories of those races are told in a half-dozen large petroglyphs carved in stone perched over the edge of the caldera, vulnerable to storms and gravity.

Orongo The petroglyphs portray the competitors as they race for the birds’ eggs. But the position of the rocks on the rapidly eroding cliff has put them in danger. A major landslide hit the area in 2007.

Park officials say they are exploring the possibility of anchoring the carvings onto more stable stone, or even moving them into a museum.

“Can we take them somewhere else?” said Mr. Rapu, the archaeologist. “Yes, but you lose their context, you lose their history when doing that.”

Mr. Rapu, who grew up on the island, said he regretted the environmental changes that had befallen the area. Few birds nest on Motu Nui anymore, he said, a consequence of what he suspects is changing weather patterns. He looked over the water and recalled his father’s stories of big migrations that used to arrive at the island regularly, much like they did during the days of the competitions.

“He would tell me you could see dark clouds of them and you could hear the birds everywhere,” he said, walking back from the crater.

Sebastián Paoa, the head of planning at Ma’u Henua, said he was sure that, ultimately, the island’s inhabitants would find their way through the challenge of the rising sea levels just as they had survived the collapse in ancient times.

“They knew their environment was coming apart, but that didn’t stop them from persisting here,” he said. “It’s the same with climate change today.”

Hanga Roa

Mr. Huke, the architect, said he feels the same way.

Finding the bones of his ancestors on the beach wasn’t cause for despair, he said, but a call to action. In recent months, he’s been gathering information for a climate change assessment to be presented to officials tallying everything from erosion to the groundwater supply.

“Islands like us are always the first to face climate change,” he said. “We have been here 1,000 years. We have gotten through things like this. The world isn’t ending. And believe me, we’ve suffered through an ecological disaster before.”