the seam, the goaf increases. This goaf collapses under the weight of the overlying strata. The strata approximately 2.5 times the thickness of the coal seam removed collapses and the beds above settle on to the collapsed goaf. This collapsing can lower surface height, causing problems such as changing the course of rivers and severely damaging building foundations. Comparison with room and pillar method Longwall and room and pillar methods of mining can both be used for mining suitable underground coal seams. Longwall has better resource recovery (about 80% compared with about 60% for room and pillar method), fewer roof support consumables are needed, higher volume coal clearance systems, minimal manual handling and safety of the miners is enhanced by the fact that they are always under the hydraulic roof supports when they are extracting coal. Automation Longwall mining has traditionally been a manual process in which alignment of the face equipment was done with string lines. Technologies have been developed which automates several aspects of the longwall mining operation, including a system that aligns the face of the retreating longwall panel perpendicularly to the gate-roads. Briefly, Inertial navigation system outputs are used in a dead reckoning calculation to estimate the shearer positions. Optimal Kalman filters and smoothers can be applied to improve the dead reckoning estimates prior to repositioning the longwall equipment at the completion of each shear. Expectation-maximization algorithms can be used to estimate the unknown filter and smoother parameters for tracking the longwall shearer positions. Compared to manual control of the mine equipment, the automated system yields improved production rates. In addition to productivity gains, automating longwall equipment leads to safety benefits. The coalface is a hazardous area because methane and carbon monoxide are present, while the area is hot and humid since water is sprayed over the face to minimize the likelihood of sparks occurring when the shearer picks strike rock. By automating manual processes, face workers can be removed from these hazardous areas. Environmental impacts As with many mining techniques, it is important to consider the local and regional environmental impacts from longwall mining. Subsidence Longwall mine subsidence (LWMS) is an anthropogenic process that has many ecological and environmental impacts, particularly on soil health and water movement in a region where LWMS is heavily done. This is important to consider as some longwall mine sites can span lengths of several kilometers. That being said, hydrological