Easter Island's famous moai statues are crumbling into the sea, forcing locals to face urgent decisions about how best to protect their heritage.

In an ancient quarry on top of a volcano on a remote Pacific island, half-finished figures hewn into the rock ignore Maria Tuki as she walks by.

The rugged faces of these figures sport world-famous furrowed brows and sloping noses. This is the land of the moai, iconic human statues unique to Rapa Nui, also known as Easter Island – an isolated island around the size of Washington DC situated 3,500km (2,170 miles) off the coast of Chile.

Before my visit, I expected to see just a couple of these famous faces at designated tourist sites. But the sheer number of the moai is breathtaking; bits of them are strewn alongside roads, bordering the coast, and shouldering hills. Together, they form a real physical reminder of this land's ancient history.

Centuries ago, Tuki's ancestors carved and chiselled many hundreds of monoliths like the ones here. Evidence of that activity is everywhere, both in the heavily worked quarry itself, where some still remain deeply embedded in the mountain, and in the surrounding land, where finished statues lie abandoned, forming paths to the island's edge. It is thought that teams of workers sometimes lost their grip while transporting the statues to the stone platforms dotted around the coast.

At first glance, the imposing moai, with their stern expressions, seem hardy. But they are made from tuff, a volcanic rock largely composed of compressed ash. This type of stone is porous and unusually soft. The wind and rain do not treat it kindly.

Up close, the aging visages of the moai are riddled with signs of erosion and staining. They are gradually wearing away to dust. Tuki, who works in Rapa Nui's tourism industry, is essentially watching these stunning figures slowly disappear. "My father told me that the moai would go back into the ocean one day," she says. Tuki's father, who died in 2020, was a famed contemporary moai sculptor.

The original statues, mostly carved between 1100 and 1600AD, are increasingly the subject of conservation efforts, given that weathering – supercharged by climate change – threatens to destroy them. Community leaders in Rapa Nui are looking for ways to track and mitigate the damage, trying everything from chemical treatments to making 3D scans of the statues using drones before they are lost. All options are on the table as the community grapples with how to manage its rapidly changing heritage – from relocating them out of harm's way to allowing them to succumb to it, as some argue is part of the moai's lifecycle.

There are roughly 1,000 statues on the island in various stages of completion, with about 200 perched on their final platforms, known as ahu. The majority of these platforms are positioned along the island's coast, staring silently out to sea.

The moai were created by the first communities of Polynesian people living on the island to represent the likenesses of their ancestors and the family of chief Hotu Matu'a, who is thought to have first settled the island after canoeing to Rapa Nui from an island in East Polynesia. At some point in the late 18th and early 19th Century, the statues were all mysteriously toppled, likely because a new religious movement took hold on the island, or possibly because of some conflict – historians have yet to find definitive answers. Due to the formidable history etched in these huge stone statues, in 1995 the Rapa Nui National Park was listed as a Unesco World Heritage site.

Still, the moai aren't perfect and pristine statues, shielded from their surroundings. In fact, they began deteriorating as soon as they were carved, according to the 1997 book Death of a Moai by historian Elena Charola. The tuff was stressed as it was chipped and pecked out of the quarry, chafed by ropes, then scratched and scraped on the long journey downhill, Charola writes.

From the day they were erected, the sun, wind, rain and vagaries of temperature have also taken their toll on the moai. When moisture from sea spray evaporates, salt crystallises inside the soft volcanic tuff expands, causing the statue to flake or spall, creating hairline cracks and honeycomb-shaped cavities. I notice lichens growing on the surface of many of the statues, with the appearance of concentric rashes.

Animals interfere with the moai, too. Horses and cattle scratch their itches on the monoliths while birds claw into the tuff and deposit toxic droppings, or guano, which erodes the material yet further. In 2020, a truck accidentally crashed into one of the faces.

Crucially, though, weathering of the moai appears to have increased sharply during recent decades, Daniela Meza Marchant, lead conservator for the Ma'u Henua Indigenous community that runs the Rapa Nui National Park, has said. She noted that images and records from the past century show alteration has increased over the past 50 years compared to the previous 50.

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