An unexpended U.S. Navy flare was found and detonated on a Chappaquiddick beach Sunday, with help from a bomb squad on Island for the Presidential visit.

Trustees of Reservations Vineyard Superintendent Chris Kennedy told the Gazette Monday morning that a Trustees ranger found an unexpended flare on East Beach Sunday afternoon.

The phosphorus flare was fairly new and had various warning labels on it, Mr. Kennedy said.

He said the silver canister posed a risk to beachgoers. “It contains white phosphorus, which burns incredibly hot and is very unstable,” he said.

The Trustees snapped a photo and sent it to the Edgartown police, Mr. Kennedy said. Coincidentally, an explosive ordnance disposal team was on the Island for President Obama’s vacation. This team was contacted and came to take a look.

After some consideration, they decided the safest thing to do was to blow up the device where it was found, Mr. Kennedy said. C-4 plastic explosives were used, and the process left a crater four feet in diameter, Mr. Kennedy said. They also cleared all the shrapnel surrounding where the bomb was detonated.

The beach was closed for about an hour, and was reopened to the public by 5:30 p.m. Sunday.

The Trustees are somewhat accustomed to finding World War II debris on their beaches, but it is more unusual for a modern device to appear. “We have had torpedoes that have occasionally washed ashore,” Mr. Kennedy said.

“All they told us is don’t be surprised to find more,” Mr. Kennedy said.

There are naval stations nearby, including one in Newport, R.I.

Had the bomb squad not been present, Mr. Kennedy said, there would have been a longer wait for a team to reach the Vineyard.

“It worked out very well as far as timing goes and their availability,” he said. “It was very fortunate that they were here,”