MARION COUNTY, IOWA — A sinkhole in rural Marion County continues growing wider and wider as authorities remain unsure of what is causing it.

The hole was first reported last week, measuring about 20-feet in diameter. Since then, the hole has nearly doubled in size to 35-40 feet in diameter. Marion County officials say the hole is now spreading more to the east and west than it is to the north and south.

County and state officials met on Wednesday to discuss a plan to investigate the cause of the hole. There are a number of former coal mine sites buried in Marion County. An Iowa DNR map shows one of those former mines is adjacent to the field where the sinkhole is opening.

Drone video of the sinkhole captured by WHO 13 photojournalist Randy Schumacher shows a farm fence still stretched across the widening hole. 135th Place remains closed to traffic near the sinkhole.