A sand dune in northwestern Indiana that draws thousands of visitors a year will stay closed this summer and possibly longer as scientists work to determine what caused a hole to open up and bury a 6-year-old boy alive.
Three more holes a foot or less in diameter have been discovered on Mount Baldy at the Indiana Dunes National Lakeshore since Nathan Woessner (WAYZ'-ner) of Sterling, Illinois, was rescued July 12.
Officials say the holes last a day or less before vanishing.
Scientists believe decaying trees covered years ago by the moving dune may be the cause of the holes, but say more research is needed.
Workers at the Indiana lakeshore and dune parks in Michigan, Oregon, Wisconsin and elsewhere are on alert.