The sand dune at Indiana Dunes National Lakeshore along Lake Michigan that mysteriously swallowed a 6-year-old boy in 2013 will remain closed for the summer, according to Bruce Rowe, a park spokesman.

Rowe says that scientists are still hard at work studying Mount Baldy, the 120-foot-tall dune that nearly killed the boy. The work is not expected to finish until fall, and the park will remain closed until then, although other parts of the area will remain open.

Nathan Woessner of Sterling, Ill., was trapped for more than three hours under 11 feet of sand while traversing the dune with his family and friend. While walking along the area with his 8-year-old friend Colin Karrow, he disappeared into a stovepipe sinkhole.

"When Colin came down the hill, I'll never forget the look on his face and the sound of his voice," said Faith Woessner, Nathan's mother. "I knew something was very, very wrong."

The incident is a mystery because the dune's surface showed no sign of the opening or even upturned sand - something you would expect if someone dug the hole. Ruling that out of the question, the other possibility is that the cavity was natural, but this conflicts with current science, as dunes aren't supposed to have natural cavities due to their composition.

"I felt absolutely shattered," said Erin Argyilan, a scientist who was fininshing up a study on Mounty Baldy around the time that Nathan was found. She claims that the incident completely conflicted with everything she had learned about geology over her years in the field.

Nathan was eventually discovered dozens of feet beneath the dune's surface after a three-and-a-half hour search. At first, he had no pulse or breath and his body - covered in sand - was frozen.

Most people buried in sand die of suffocation within 10 minutes, but after being hospitalized for approximately two weeks, Nathan's mother says that he recovered and is now doing well.

"He's exactly the same as he was before," she said.

Doctors believe that Nathan likely survived due to an air pocket or a mammalian diving reflex that slowed down his vital organs to conserve oxygen. However, when it comes to the mystery of how the sinkhole formed in the sand dune in the first place, scientists are still searching for an answer.