Salty Brine Beach in Narragansett, Rhode Island, was evacuated Saturday morning after an explosion sent one woman flying onto nearby rocks, officials told BuzzFeed News.
The 50-year-old woman has been taken to a nearby hospital, Department of Environmental Management Rayna McGuire said. There were no other reports of injuries.
Officials originally said they were searching for a suspect they believe planted an item in the sand, then fled to a neighboring beach, Sgt. Thomas Silvia told the Providence Journal.
However, after investigating further authorities said they don't believe the explosion was a malicious event.
"We believed there had been an explosion, a small explosion — sub-surface– that literally erupted out of the sand and virtually caused one of our beach patrons to ultimately fall backwards and forwards," Larry Mouradjian, with the Dept. of Environmental Management, said at a news conference.
Authorities are chalking the explosion up to a "ground disturbance," though they aren't sure what exactly occurred, the Providence Journal reported.
"Something did happen but we are not sure exactly what," Mouradjian told the Providence Journal.
Authorities had been investigating a possible connection with a recent series of "suspicious" fires that sunk three fishing boats at a nearby pier on Friday, but later determined the incidents were not connected, WPIR reported.
The explosion occurred under the sand almost directly beneath the woman who was blown onto the rocks, McGuire said.
Witnesses told local news sources that they saw her lawn chair fly directly into the air before she landed on a rock wall above the beach.
One witness, Mario Lewis, told the Providence Journal that the explosion looked like an "M-80 boom, like a grenade."
He added that despite that, it sounded to him like a gas explosion.