This photo from the New Zealand Defense Force shows some of the pumice found in a vast volcanic "raft" floating off the coast of New Zealand.
Credit: New Zealand Defense Force

A massive "raft" of volcanic rocks covering more than 7,500 square miles has been spotted off the coast of New Zealand, puzzling scientists.

Royal Australian Navy Lt. Tim Oscar called it "the weirdest thing I've seen in 18 years at sea," according to National Public Radio.

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"As far ahead as I could observe was a raft of pumice moving up and down with the swell," he said in a New Zealand Defense Force press release. "The rock looked to be sitting two feet above the surface of the waves, and lit up a brilliant white colour in the spotlight. It looked exactly like the edge of an ice shelf."

Oscar was aboard the Royal New Zealand Navy's HMNZS Canterbury on Thursday when the ship investigated the phenomenon.

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Experts told BBC News it's likely the result of an eruption of the underwater volcano known as Monowai, located to the north of New Zealand.

Pumice can form when lava from an underwater volcano comes into contact with seawater. Since it's less dense than water, it quickly rises to the surface of the ocean, according to BBC News.

At 7,500 square miles, the pumice raft is about 200 square miles larger than New Jersey, NPR reported.

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