The emergence off Elbow Beach of a marine feature seemingly from nowhere is a “testament to the incredible power of the ocean”, according to a conservationist at the Bermuda Institute of Ocean Sciences.

Chris Flook, the boat and dock supervisor at BIOS, identified the rock mass that has puzzled beachgoers as a boiler reef that was overturned by the force of the sea.

“I saw it from the shore and thought, I don’t remember that being there,” Mr Flook said. “There was a new rock sticking way out of the water.

“My son and I swam out to check it out. It’s a boiler reef that just fell from the wave and swell pressure. But the force to make that happen has to be incredible.”

Boiler reefs, a common sight along the South Shore, are so called because their tops, which reach the surface, churn with breaking waves.

Mr Flook, who has spent much of his life on the water, spotted last October that something new had appeared off the Paget beach.

“It’s quite impressive — it’s a huge piece of rock, the whole boiler.”

He said he had not seen anything like it before.

“It wouldn’t have happened on its own. A passing storm would probably have been the catalyst. It just goes to show how much those boilers protect the mainland. They’re critical for stopping us from just eroding away under the power of the waves.

“To put it in context, when you see those big ocean swells and the waves smashing the shoreline, a single cubic foot of salt water weighs about 64lb.”

Mr Flook said it was possible that two near-miss hurricanes last September could have delivered the force to upend the reef: Earl, which brushed past the island as a Category 2 storm, followed by Fiona, another close call as a Category 4 hurricane.

Elbow Beach was worst hit among several South Shore beaches heavily eroded by Fiona.

As well as protecting Bermuda’s shores from the sea, the island’s network of reefs provide a critical habitat for sea life — and have presented a hazard for mariners throughout the island’s history.

They are susceptible to storm damage as well as climate change, which is thought to increase the intensity and range of hurricanes.

The storms can also prove beneficial to reefs, by dredging cooler water up to the surface and taking the edge off high sea temperatures.