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Subsidence Evaluation For Exhibd 608 South of Divide Mining Area Page 18 9.1 Potential Impact of Water on Subsidence in Wet Mining Areas As discussed in Section 3.0, the moisture content of the caved and downwarped rocks controls the amount of subsidence that can be expected. In the South of Divide mining area where water might be encountered in an area equal to, or greater than, the width of the proposed longwall panels, maximum veriical displacement may be expected to approach O.St. 10.0 POTENTIAL IMPACTS OF SUBSIDENCE AND MINE-INDUCED SEISMIC ACTMTY ON LANDSLIDES AND ROCKFALLS 10.1 Landslides The landslides listed below are all naturally occurring features, which become less stable, or become unstable and slide, during periods of increased precipitation. A review of aerial photographs of the Apache Racks, Box Canyon, and South of Divide mining areas, which were taken in 1963 and 2004, show that the slides listed below appeared to be more stable in 1963 than they are now. Dunrod observed that many of the existing landslides during periods of high precipitation were less stable, or became unstable and moved in the mid 1980s and mid 1990s. The landslides in the southeast side of West Flatiron and on the west side of Deep Creek in the Apache Rocks mining area showed no visual effects when longwall mining occurred beneath the areas. It therefore seems apparent that wet seasons affect landslides more than does longwall mining. During very wet periods, however, landslides that are already unstable may locally be triggered by mine subsidence- A total of twelve landslides, landslide areas, or landslide and rockfall areas, have been mapped in the Apache Rocks, Box Canyon, and South of Divide mining areas during field mapping with the U.S. Geological Survey (USGS) in the 1980s and also during the awual subsidence observations in these areas (all the landslides listed in the Apache Rocks and Box Canyon mining areas occur in Township 13 South, Range 90 West). 1. Apache Rocks mining area a. Landslide located just north of Mimesota Reservoir in SW'/+ of Section 29. No mining has occurred in the area. b. Landslide area located above mined longwall panels 14 and 15 in NW'/+ of Section 26. These landslides appeared to be unaffected by longwall mining beneath them. c. Landslide area located on the west side of Deep Creek, located above the southeastern part of mined longwall panel 17 in the NW'/+ of Section 35_ This landslide also appeared to be unaffected by mining below when observed in July 2003. i ss1-032sso WrrghtWarerEngineers, Inc.