At 2,500 miles off the coast of Chile, the island is one of the world's most remote places inhabited by people.
Up to 1,000 years ago, the islanders started putting giant red hats on the statues.
The research team, from the University of Manchester and University College London, think the hats were rolled down from an ancient volcano.
Dr Colin Richards and Dr Sue Hamilton are the first British archaeologists to work on the island since 1914.
They pieced together a series of clues to discover how the statues got their red hats. An adze, a road, and an ancient volcano led to their findings.
Dr Richards said: "We know the hats were rolled along the road made from a cement of compressed red scoria dust."
Each hat, weighing several tonnes, was carved from volcanic rock. They were placed on the heads of the famous statues all around the coast of the island.
However, precisely how and why the hats were attached is unknown.
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Originally posted by bigern
Amazing, I had no clue they were that big. I knew they sank but assumed it was no more than a few feet at most. Maybe they really are a lot older than we realize. Is it possible that the island could have been submerged at one point after their creation softening the soil and that caused them to sink so much?