Miami, FL

A day at the beach always comes with risks: jellyfish, sunburn, cellulite, old men in bikinis, sharks, and now another one - sink holes. The Globe investigates.

While some might see them as freak accidents, Dr. Bradley Maron has spent years studying the phenomena, after twice seeing children almost suffocate to death on a Martha’s Vineyard beach. In a letter in this week’s New England Journal of Medicine, he warns that a pastime as innocent as building a sandcastle could lead to a family tragedy.

Maron was a 23-year-old lab technician with dreams of a medical career when he came across a scene of "total chaos" during an afternoon walk on Edgartown’s South Beach in 1998, he said in an interview. Kids at a birthday party had dug a seven-foot-deep cavity in the sand and were trying to jump over it when one fell in. The walls of the hole caved, obliterating any sign of the 8-year-old girl.

Digging frantically, a lifeguard located the child’s mouth and cupped his hand over it, creating an air pocket. She survived, but the accident made an impression on the young Maron, who had witnessed a similar incident as a student lifeguard three years earlier. "I was probably at that moment of the opinion that most people are, that this must be an isolated, extremely uncommon problem," he said. "In medicine we call it a case report — something you might see once in your whole life."

But as Maron began to investigate, urged on by his father, a cardiologist who researches sudden death in athletes, he quickly uncovered similar sand cave-ins around the country. Though the accidents are rare — you’re about as likely to die from a shark attack in the United States as from falling into a beach hole – they fit a tragic pattern, according to Maron’s research: A buildup of pressure causes the sides of a hole to crumble suddenly, burying alive a child or teenager playing inside. The victim, usually a boy, remains submerged for several minutes as bystanders panic and rescuers, afraid to use a shovel because they might hit the person, struggle to reach them by hand.

Wow, we are always learning of unusual ways to die. Add this to the list.