Two sailors were afloat on the Pacific Ocean when they came across the most bizarre phenomenon – a sea made of rocks.

The last rays of the setting sun light the sky above the Pacific as an Australian couple, Michael and Larissa Hoult, skim across the waves aboard their catamaran, ROAM. But before they know it, they find themselves in the most extraordinary sea they’ve ever encountered. Astonishingly, its surface appears to be composed of a blanket of rocks stretching as far as the eye can see.

The Hoults are sailing in the South Pacific Ocean. The nearest land mass of any size is New Zealand’s North Island, around 1,300 miles to the south-west. The closest land of any kind is an uninhabited volcanic speck some 45 miles to the east of ROAM’s position. Late Island is part of the Kingdom of Tonga and its main island, Tonga, is about 150 miles south of the Hoults.

Michael and Larissa had set off aboard their catamaran on August 7, 2019. Their departure point was Bora Bora, an idyllic tropical island that’s part of French Polynesia. Their first destination was the Tongan islands of Vavaʻu. In fact this footloose pair had only been on Bora Bora for a couple of days.

The Hoult couple spend much of their time sailing around the Pacific aboard their state-of-the-art catamaran ROAM. The craft was built by the Hoult family at their home in Tasmania, the large Australian island off the south coast of the mainland. Every sailing season from 2016 onwards, Michael and Larissa have sailed around the Pacific, pursuing their dreams of adventure.

Although the Hoults had planned to stop off on the Vavaʻu Islands before heading on to their final destination of Fiji, by day five of their trip, August 12, they’d had a change of heart. They decided that they would sail straight on to Fiji without a stopover. Larissa was booked to work a nutrition project on Fiji, and time was getting tight.

It was on August 15, as they sailed towards their destination of Fiji that they came across the most extraordinary sight. Instead of a clear blue sea ahead of them, a vista of beige rock stretched ahead of them to the horizon. Their report of this on Facebook went viral, and the world’s press latched on to the story.

Speaking to TV network CNN, Michael said, “The rocks were kind of closing in around us, so we couldn’t see our trail or our wake at all. We could just see the edge where it went back to regular water – shiny water – at night.” Larissa had obviously found the experience unsettling. “It was quite eerie, actually,” she said. “The whole ocean was matte – we couldn’t see the water reflection of the moon.”

And the Hoults elaborated on their experience on the ROAM Facebook page. They’d actually been warned via email that there might be what was described as pumice fields ahead of them on the course they were sailing. However, their Facebook post said, “We saw none as we rounded north of Vavaʻu earlier in the day on our route [from]… Bora Bora.”

But the situation soon began to change, as the Facebook logdetailed. “At position 18 50′ S 175 05′ we had faint but distinct smell of sulfur.” And there was more to come. “Sailing on…we started seeing some floating rocks of random sizes (marbles to tennis balls)…” The sea around ROAM was growing more freakish by the minute.

The Facebook post continued, “We started to see and strike larger floating rocks. We took down all sail. Allowing the boat to continue on bare poles at two or three knots. As we could no longer smell the sulfur we assumed we would be soon clear of the rubble so elected to continue at slowest speed.” But their hopes that they would shortly be free of the “rubble” were soon dashed.

As the evening drew on to 7 o’clock the situation became positively outlandish. The Facebook post continued, “We entered a total rock rubble slick made up of pumice stones from marble to basketball size. The waves were knocked back to almost calm and the boat was slowed to one knot. The rubble slick went as far as we could see in the moonlight and with our spotlight.”

Now the Hoults were right in the middle of this extraordinary stone sea. Their Facebook entry described their attempts to take evasive action. “We made a turn to starboard and managed to sail clear of the rubble slick under staysail… the edge could be made out in the partial moonlight back to the north-east. It was extensive in all other directions.”

Once the two sailors had escaped from the rocky sea, they were able to continue on their journey to Fiji. While they’d been surrounded by the floating boulders, their rudders had become fouled, but happily this didn’t cause them any longer-term problems. It had been an intensely weird experience, but the Hoults were none the worse for it.

Obviously there had to be an explanation for this outlandish phenomenon. But before we find out what the scientists had to say about the rock-covered sea, let’s find out about other occasions when this bizarre anomaly has manifested itself. And it does turn out that the Hoults were far from the first to witness this strange apparition.

Image: Mike Korostelev www.mkorostelev.com/Getty Images

These rock-strewn seas are known as pumice rafts. A series of large rafts had previously appeared near Fiji in 1984, and a further five years before that as well. Some of these rafts were reportedly nearly 20 miles across. Furthermore, in August 2006, so much pumice had emerged in the Pacific Ocean near Tonga that a temporary new island was actually formed, dubbed Home Reef. This was witnessed by sailors aboard the yacht Maiken.

One of the crew wrote about the experience on the Maiken blog in an entry dated August 12, 2006 and titled “An amazing last few days – weird but amazing.” The entry read, “Early afternoon, somewhere east of the Lau Group in Fiji. We are sailing south of the island group to avoid having to pass through it during night.”

Written in deadpan, matter-of-fact style, the killer sentence came next. “Yesterday we saw the birth of an island, most likely we were the first humans to see the new creation,” it read. The blog post continued. “So you might have heard about the sailor superstition that you should ‘never leave on a Friday.’”

The blog writer described what happened when the sailors broke that Friday taboo. “Well, we did and the sea turned to stone, it is hard to get a stronger sign than that. It sounds like a bad joke, but just wait until you see the pictures. Floating stones no less.” And this amazing event attracted the attention of the press.

One of the Maiken’s crew, Swedish sailor Fredrik Fransson, spoke to Discover magazine. He described how the Maiken had embarked from Tonga’s Vavaʻu Islands. The first thing that he had noticed amiss was the color of the seawater – it just wasn’t right. Rather than the usual blue of the open ocean, the sea had a strange greenish hue, akin to the water in a lagoon.

Fransson described the scene as the Maiken sailed a westerly course. “We looked out, and in front of us it was as if there was no more sea,” Fransson told Discover. “It was like the Sahara, with rolling hills of sand as far as the eye could see.” In truth the yacht was amid a huge raft of pumice floating on the surface of the ocean.

Image: Facebook/National Oceanography Centre

The Discover article also quoted the reaction of a NASA geologist, Greg Vaughn. He was tremendously excited by the phenomenon. “We decided right then that we needed to get in there and get some satellite data,” Vaughn recalled. So NASA took aerial images of the area, capturing for the first time pictures of a new, short-lived pumice island being formed in the ocean.

But of course this new piece of real estate, Home Reef, proved to be a flash in the pan. When another scientist, Scott Bryan of London’s Kingston University traveled to the site of the island, he was to be sadly disappointed. In February 2007 he arrived at the spot in the Pacific where the island had formed. But there was nothing to be seen. It had disappeared.

But Home Reef had made its own contribution to the ecology of the Pacific. Specifically, it had enhanced the biodiversity of the ocean. Pieces of pumice, remnants of the island, had floated all the way to Australia’s Great Barrier Reef. Lying off the east coast of Australia, this reef is the largest coral formation in the world.

By the time the pumice raft pieces had made it 2,000 miles across the ocean to the Great Barrier Reef, they’d picked up a whole host of passengers. Species hitching a ride included corals, barnacles and tube worms. Anemones, oysters and algae also clung on to the pumice. And this variety of species subsequently made the Great Barrier Reef their home.

Indeed, scientists believe that pumice rafts, with their cargo of sea creatures, can play an important part in keeping the Great Barrier Reef fully stocked with a wide diversity of species. Bryan, who was studying pumice rafts and their role in the ocean ecology said, “It’s an amazing interaction of all these different aspects of Earth and surface processes, which are so dependent on one another.”

Another one of those bizarre pumice rafts appeared in 2012 in the South Pacific, 1,000 miles from New Zealand. This one was reckoned to be nearly 290 miles long and some 35 miles across, covering an area of 10,000 square miles. And it was big enough to force a Royal New Zealand Navy ship, HMNZS Canterbury, to change course.

According to TV news network CNN in August 2012, one mariner who saw the raft said that it was “the weirdest thing I’ve seen in 18 years at sea.” And Lieutenant Tim Oscar of the Canterbury said, “The lookout reported a shadow on the ocean ahead of us, so I ordered the ship’s spotlight to be trained on the area.”

“As far ahead as I could observe was a raft of pumice moving up and down with the swell,” Oscar recalled. And he continued, “As we moved through the raft of pumice we used the spotlights to try and find the edge – but it extended as far as we could see.”

Oscar described to CNN what this pumice raft had looked like. “The rock looked to be sitting two feet above the surface of the waves, and lit up a brilliant white color in the spotlight. It looked exactly like the edge of an ice shelf,” Oscar said. And that brings us back to our earlier question: what on Earth causes these other-worldly pumice rafts?

What is it that can turn the surface of the ocean into a landscape of floating rocks? As we’ve already seen, the rocks are in fact pumice. You might be familiar with pumice as something you have in your bathroom. The stone is used to get rid of dead skin, and it’s been put to that purpose since at least the time of the ancient Egyptians.

Pumice stone can also be used to banish unwanted body hair by vigorous rubbing. And in powder form the Romans used it as a kind of toothpaste. Even today, there are toothpastes on the market that have an element of ground pumice in their ingredients to act as a tooth whitener.

But what about these pumice rafts floating on the open ocean? We met Scott Bryan earlier when he was working at Britain’s Kingston University. Now he’s an associate professor at Australia’s Queensland University of Technology. Bryan gave an overview of the pumice raft phenomenon in an August 2019 interview with U.K. news broadcaster the BBC.

Bryan said that these pumice mats appeared about very five years in the region of the Pacific where the Hoults saw their rock-strewn sea. “It is a phenomenon reported over time, usually as islands in the middle of the ocean that people encounter but then can’t find again. It can be as if the whole surface [of the ocean] has turned to land,” Bryan explained.

And the BBC reported that although a type of rock, pumice has so many bubbles in its make-up that it can easily float on the surface of the sea. So now we know why it floats, but where does it appear from every five years or so? In a word, the answer is: volcanoes. Specifically undersea volcanoes, or ones near the coast.

When a volcano erupts beneath the waves, it spews out a mixture of gases and rubble. Some of that debris is in the form of pumice stone which as we’ve seen has enough bubbles in it to float. However, what can be seen on the surface of the sea is only around 10 percent of the pumice. Like an iceberg, the majority of the structure sits beneath the surface.

And NASA tracked the progress of the pumice raft that the Hoults stumbled across. Scientists there even identified an underwater eruption that might have been the source of this particular pumice raft. It came, the boffins believed, from a volcano with no name not far from the island of Tonga. This volcano was last active in 2001 before its latest eruption.

The NASA Earth Observatory website quoted the words of Erik Klemetti, a volcanologist at Denison University. “Pumice rafts can drift for weeks to years, slowly dispersing into the ocean currents. These chunks of pumice end up making excellent, drifting homes for sea organisms, helping them spread.” Earlier we heard Scott Bryan discussing the ability of pumice rafts to spread life forms around the ocean.

Speaking to the Australian Broadcasting Corporation (ABC), Bryan spoke in particular about this most recent pumice mat floating across the Pacific. “In this 150-odd square kilometers [60 square miles] of pumice out there right now, there’s probably billions to trillions of pieces of pumice all floating together, and each piece of pumice is a vehicle for some marine organism,” Bryan told ABC.

Bryan reckoned that pieces of this pumice raft, borne by ocean currents, would reach the coast of Australia in around a year’s time. He observed, “When it gets here, [the pumice raft will be] covered in a whole range of organisms of algae and barnacles and corals and crabs and snails and worms.”

Image: JoshuaWells_Photography/Getty Images

Climate change and other environmental factors already threaten the health of the 1,400 miles of the Great Barrier Reef. So it’s good to hear that pumice rafts have the potential to actually enhance the area. As Bryan said, “We’re going to have millions of individual corals and lots of other organisms all coming in together with the potential of finding new homes along our coastline.”