Beach erosion on a remote island in Tonga has revealed a trove of petroglyphs that archaeologists say are similar to those found in Hawai'i, hinting at the possibility of early travel between the two archipelagos.

More than 50 petroglyphs were found late last year on several slabs of beach rock at the northern end of Foa Island, in Ha'apai. The rocks apparently were buried for centuries under several feet of sand until heavy seas exposed them.

The carvings were spotted by two Australian visitors who notified Tonga artist and amateur archaeologist Shane Egan, who in turn contacted archaeologist and ethnohistorian David Burley, a professor at Simon Fraser University in Canada. Burley has conducted a number of field surveys and excavations in Tonga, which is about 3,000 miles southwest of Hawai'i.

"Initially I was a bit stunned, knowing the distance and difficulty of travel between the two groups of islands," Burley said in an e-mail to The Advertiser. "The evidence, however, is visual and difficult to ignore or explain in ways other than direct contact."

Burley and Egan mapped the petroglyphs in December. The carvings, averaging 8 to 12 inches, appear on two major panels and a number of smaller ones. Burley said the outlines of feet and male and female stick figures are the most abundant forms. Other images include cup shapes, dogs, turtles, a lizard and a turtlelike man and a fish with arms.

Burley said the designs "are pretty much identical" to those catalogued in Hawai'i. "Notably, while aspects of form or features can be found in several of the images elsewhere in east Polynesian rock art, the Tongan and Hawaiian ones are clearly of the same ilk and a considerable degree different from the rest," he said.

The stick figures have open body forms, but one has a closed triangular body not identified anywhere outside of Hawai'i, according to Burley. One human form appears with a headdress that is also similar to a Hawaiian form.

Another image resembles a kapu stick, a tapa-covered ball on a stick carried as a sign of approaching royalty, indicating it was created by someone knowledgeable in Hawaiian cultural protocols, he said.

Because the Tonga images are carved in beach rock within a tidal zone, any sheen typical of rock art is gone, making it impossible to radiocarbon-date the petroglyphs, Burley said.

However, the style corresponds to Hawaiian petroglyphs dating from A.D. 1200 to A.D. 1500. Burley said that if the Tonga carvings also originate from that period, they would correspond with two adjacent archaeological sites, a prehistoric village and a mound used for the chiefly sport of pigeon snaring.

Tianlong Jiao, head of the Anthropology Department at Bishop Museum, called the Tonga rock carvings "a very intriguing discovery." Although they appear "very similar" to images on Hawaiian petroglyphs, Jiao said he wouldn't necessarily "jump to the conclusion" that Hawaiians visited Foa Island, especially since the age of the carvings is unknown.

"Without a chronological context, it's very hard to argue that there was direct population contact between the two archipelagos," Jiao said.

More than 150 petroglyph sites have been identified in Hawai'i. Jiao said rock carvings are a part of Polynesian culture and it should be no surprise to find them on the islands of the South Pacific.

Petroglyphs are more common in eastern Polynesia, especially in the Marquesas, Tahiti and Hawai'i, and less so in Samoa and Tonga, in western Polynesia. Previously reported rock art in Tonga has been limited to simple geometric engravings at royal burial structures.

The outline of a foot on a stone at a royal tomb on 'Uiha was recorded in 1991 by Burley. There has since been evidence the stone may have been quarried from Foa Island, near the site of the newly discovered carvings.

Burley said he's convinced the Foa petroglyphs pre-date the arrival of British explorer Capt. James Cook, who made several visits to Tonga in the 1770s. He discounts any speculation the images may have been done by a Hawaiian who visited Tonga on a European ship during the 19th-century period of whaling and trade, because Hawaiian petroglyphs of that period typically featured muscled images, ships, horses and other figures contemporary to the times.

Burley also cited a historical account from 1806, when the British vessel Port au Prince was captured by Tongans not far from the petroglyph site. One of the crew was reported to be a "Sandwich Islander," a reference to someone from Hawai'i.

"This seems too late for the images at Foa," he said.

Although the designs indicate they were carved by a Hawaiian, Burley remains cautious about what that might mean.

"If this is true, then how a Hawaiian got to Tonga is the serious question," he said.

The position of Ha'apai, the island group where the site is located, was known by the Tahitian navigator Tupaia, who drew a map for Capt. Cook, according to Burley. Islanders from French Polynesia are believed to have voyaged to Hawai'i and back, and Tongans traveled widely through Oceania from the 12th to 18th centuries during the height of the Tu'i Tonga dynasty, "so anything is possible, including a chance encounter with and the bringing back of a Hawaiian," he said.

"I am not sure we will ever be able to answer the specific scenario, but the fact that the link exists is truly significant in its own right. East and West Polynesia had some degree of connection and relationship long before Europeans arrived with sailing ships."

Regardless of who created the petroglyphs, Egan said they are in danger of disappearing again, either from further erosion or reburial under new layers of sand and gravel.

Egan said there are plans to preserve them.