Editing Longwall mining (section)

==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 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.

=== Fracturing and water quality ===
Longwall mining can result in geological disruptions in the rockbed, and can in turn affect water movement and result in water moving away from the surface, through the mined area, and into the [[aquifer]]. A resulting loss in surface water can negatively impact riparian ecosystems.<ref name=":1">{{Cite news|url=http://australiancoalalliance.com/Information/TEC%20LCM%20Report_final.pdf|title=IMPACTS OF LONGWALL COAL MINING ON THE ENVIRONMENT IN NEW SOUTH WALES|date=January 2007|work=Total Environment Centre|access-date=February 14, 2019}}</ref>

On top of this, if there are present dams near to the longwall mining site, this could doubly impact the [[Riparian zone|riparian ecosystems]] as it would have a reduced inflow rate as well as the loss to the underlying rock fracturing.<ref name=":1" />

As of 2014, measures were taken by the Australian government to mitigate water impacts from longwall mining. Legislative assemblies have called for action to improve mine infrastructure to minimize disturbances.<ref>{{Cite web|url=http://iesc.environment.gov.au/publications/subsidence-longwall-coal-mining|title=Fact sheet - Subsidence from longwall coal mining {{!}} Independent Expert Scientific Committee on Coal Seam Gas and Large Coal Mining Development|website=iesc.environment.gov.au|access-date=2019-04-10}}</ref>

As a result of bedrock cracking from mining beneath waters such as lakes or rivers, there have been groundwater losses of varying extents. Mines within a few hundred meters of the surface are susceptible to receiving great inputs of water from these bodies. Moreover, after mining interference disturbing the natural landscape near the mines, the natural water flow paths can be redirected which results in additional erosion across a stream or river bank. Additional mining in concentrated areas continuously move these water flow paths, which take years to return to their original states.<ref name=":5"/>

=== Ecosystem impacts ===
Many ecosystems rely on the annual consistency of water inputs and outputs, and disturbing these patterns can result in unsustainable conditions for species reliant on water for species reproduction. Longwall mining can also result in localized water temperature change, stimulating algal bloom which can use up available oxygen required for other species health.<ref name=":5">{{Cite journal |last=Dawkins |first=A. |date=2003 |title=Potential Management and Rehabilitation Requirements of Environmental Effects From Longwall Subsidence on Streams, Lakes and Groundwater Systems |url=https://ro.uow.edu.au/cgi/viewcontent.cgi?referer=https://www.bing.com/&httpsredir=1&article=1165&context=coal |journal=University of Wollongong & the Australasian Institute of Mining and Metallurgy |volume=1 |pages=117–124 |via=Geoterra}}</ref>

Longwall mining has limited available research on the impacts of nearby forests, however emerging satellite imagery studies have shown possible relations to drier surface soil near regions where longwall mining has recently occurred. In addition to drier soils, forest canopy moisture has been observed to be reduced.<ref>{{Cite web|url=https://landsat.gsfc.nasa.gov/assessing-longwall-mining-impacts-on-forests-above/|title=Assessing Longwall Mining Impacts on the Forests Above « Landsat Science|access-date=2019-04-10}}</ref>

=== Gas emissions ===
Longwall mines have been observed to release [[Methane|methane gas]], a common [[greenhouse gas]] into the environment, however the increase of a typical longwall mine face from {{convert|200|to|300|m}} was not found to release significantly more methane.<ref name=":2">{{Cite web |url=https://www.cdc.gov/niosh/mining/works/coversheet494.html |title=Prediction of Longwall Methane Emissions: An Evaluation of the Influence of Mining Practices on Gas Emissions and Methane Control Systems |website=www.cdc.gov |language=en-us |access-date=2019-04-10}}</ref><ref>{{Cite book |last1=McCall |first1=F. E. |last2=Garcia |first2=F. |last3=Trevits |first3=M. A. |last4=Aul |first4=G. |date=1993-12-31 |title=Methane gas emissions during longwall mining |language=en |osti=143760}}</ref> [[Methane emissions]] from closed longwall mines can continue for up to fifteen years, however it is possible to measure the volume of potential methane emissions based on water flow in the closed mines.<ref name=":2" />