What does the term "retreat mining" mean?

The term "retreat mining" specifically refers to a technique where miners extract coal from a coal seam while leaving behind pillars of coal to support the mine structure. After the majority of the coal has been extracted from the area, these support pillars are later removed, allowing the mine to collapse in a controlled manner. This process is designed to maximize the extraction of coal while ensuring safety during the mining operation.

This method is advantageous because it allows for a thorough extraction of coal, using the initial structural support of the pillars before ultimately removing them. The controlled collapse can prevent unexpected hazards and improve the safety for miners still working in adjacent areas.

In contrast to other mining techniques, such as the continuous extraction process described in other options, retreat mining specifically capitalizes on the systematic removal of both coal and structural supports in a staggered approach, making it a unique method in the field of coal mining.