SOUTH BEND, Ind. (AP) — A park spokesman says a popular sand dune along Lake Michigan will remain closed this summer as scientists work to determine why a 6-year-old boy was nearly buried alive in 2013.

Indiana Dunes National Lakeshore spokesman Bruce Rowe says scientists have been studying Mount Baldy, a dune near Michigan City that is more than 120 feet tall. He says their work isn’t expected to finish until fall, so the dune cannot be opened to the public this summer. Other parts of the lakeshore will be open.

The scientists are trying to work out why a hole appeared, trapping Nathan Woessner (WAYZ‘-ner) of Sterling, Illinois, for more than three hours under 11 feet of sand. He recovered after being hospitalized for about two weeks.