Editing Longwall mining (section)

=== 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 flow systems, root systems from trees, and vegetative species can suffer from the amounts of soil being removed beneath them, and these stresses lead to surface erosion.<ref>{{Cite web |url=https://www.australianmining.com.au/news/study-measures-the-environmental-impacts-of-longwall-mining-subsidence/ |title=Study measures the environmental impacts of longwall mining subsidence |date=2010-04-27|website=Australian Mining |language=en-AU|access-date=2019-02-09}}</ref>

Abandoned mines are also an issue concerning areas where residential development has moved in. Houses erected near abandoned longwall mines face the threat of future damage from sinkholes and poor [[soil quality]], even up to thirty years after mine abandonment.<ref name=":0">{{Cite web |title=Final Report - Effects of Longwall Mining |website=www.dep.state.pa.us |url=http://www.dep.state.pa.us/dep/deputate/minres/Longwall/report02/finalreport.htm#TOC2_2 |access-date=2019-02-09}}</ref>

Since longwall mining is namely, very long, it can affect areas of over {{convert|200|acre}}. Over these largest spans, it has been observed that longwall mines underlying mountainsides demonstrate more visible subsidence in mountain landscapes than it does for valley landscapes.<ref name=":0" />

There have been cases of surface subsidence altering the landscape above the mines. At Newstan Colliery in [[New South Wales]], Australia "the surface has dropped by as much as five metres in places" above a multi-level mine.<ref name="env/water-iss/long-20090609-c29x">{{cite web
  | last = Cubby
  | first = Ben
  | title =  Longwall mine plan a threat to water supply
  | work = [[Sydney Morning Herald]]
  | publisher = Fairfax Media
  | date = 2009-06-10
  | url = http://www.smh.com.au/environment/water-issues/longwall-mine-plan-a-threat-to-water-supply-20090609-c29x.html
  | accessdate = 2010-06-02
  | quote = Longwall mining, in which broad panels of coal a few metres high and hundreds of metres wide are bored out of the earth, causes ground above the mines to subside.}}</ref> In some cases the subsidence causes damage to natural features such as drainage to water courses<ref name = "smh.com.au/2007/11/19/1195321697140">{{cite web
  | last = Frew
  | first = Wendy
  | title = Risk to life, but more mining under bridge
  | work = Sydney Morning Herald
  | publisher = Fairfax Media
  | date = November 20, 2007
  | url = http://www.smh.com.au/news/environment/risk-to-life-but-more-mining/2007/11/19/1195321697140.html
  | accessdate = 2010-06-02
  | quote = Longwall mining has already resulted in substantial damage to riverbeds, swamps and water catchments in the area}}</ref> or man-made structures such as roads and buildings. "[[Douglas Park, New South Wales#Natural heritage|Douglas Park]] Drive was closed for four weeks because longwall panels&nbsp;... destabilised the road. In 2000, the State Government stopped mining when it came within 600 metres from the twin bridges. A year later there were reports of 40-centimetre gaps appearing in the road, and the bridge had to be jacked sideways to realign it."<ref name = "smh.com.au/2007/11/19/1195321697140" />{{Rp|2}} A 2005 geotechnical report commissioned by the [[Roads & Traffic Authority]] warned that "subsidence could happen suddenly and occur over many years".<ref name = "smh.com.au/2007/11/19/1195321697140" />

However, there are several mines, which were successfully mined with little to no measurable surface subsidence including mines under lakes, oceans, important water catchments and environmentally sensitive areas.{{citation needed|date=June 2013}} Subsidence is minimised by increasing the block's adjacent chain pillar widths, decreasing extracted block widths and heights, and by giving consideration to the depth of cover as well as competency and thickness of overlying strata.