The Coal Authority is investigation a hole in North Midlothian which opened up last month.
The 10m wide and 6m deep hole in a wheat field south of Edinburgh, was reported to the authority before Christmas.
Since then it has been investigating the cause.
Coal Authority public safety and subsidence team regional project manager James Hammond said: “In December 2018, we received a report of a hole in a field in North Midlothian.
“Our regional team responded quickly to erect fencing to secure the area.
“We will be undertaking thorough investigations to determine the cause of this incident.
“If these investigations conclude that it is a result of historical coal mine workings, we will undertake ground remediation work to make the area safe.”