The ever-shifting sands of Cape Cod have parted to reveal a new mystery: a 50-foot-long shipwreck unearthed by erosion in shallow waters just off North Beach Island in Chatham, town and state officials said.

The wreck was spotted Nov. 29 by an airplane pilot as he and an aerial photographer flew along the coast.

“It’s not a case of pirate treasure or lots of people killed in an accident,’’ said Victor Mastone, director of the state’s Board of Underwater Archeological Resources. “It strikes me that it’s a vessel that might have run aground and sanded over.’’

At low tide, the wreckage, which appears to be made of wood, sits in 8 to 10 feet of water, but it cannot be seen from the beach, officials said. The vessel, which remains partially buried in the sand, appears to have had two or three masts. Its discovery was first reported in the Cape Cod Times. The ship’s identity remains unknown as officials take a closer look, and even then its history might be difficult to uncover, Mastone said. The best guess at the moment is that it was a cargo vessel.

“Two-masted and three-masted schooners are the most common vessel of the 19th century. They’re the 18-wheelers of their day,’’ Mastone said. “They’re so common, on one level, that it’s hard to narrow down.’’

The coastline around Chatham is constantly changing as forces of nature shift the sands, said Theodore L. Keon, director of Chatham coastal resources. Where the wreck is now buried was an inlet a century ago.

“It may well have sank in this location about 100 years or so ago,’’ Keon said.

With a possible nor’easter headed up the coast this weekend, the shipwreck is vulnerable, he said. Strong waves and winds could begin to dismantle it. That would be unfortunate, but there are probably many other wrecks waiting to be found in the area, Keon said.

“Pieces of shipwrecks are quite common to come up along the Cape Cod beaches,’’ he said. “There have been hundreds of shipwrecks on the shores because there were thousands of ships traveling along the Cape.’’

The state plans to continue to investigate the wreck, weather permitting, in January.

Officials have discovered several other shipwrecks along the Cape recently. Planks emerged last month off of Nauset Beach in Orleans of what is believed to be the Montclair, a cargo vessel and suspected rum runner from Nova Scotia that sank in 1927.

In April, the wreck of the British warship HMS Somerset III, which was guarding Boston Harbor the night Paul Revere began his gallop to Lexington in 1775 and sank three years later, appeared off the Cape Cod National Seashore in Provincetown.

L. Finch can be reached at lfinch@globe.com.

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