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West Elk Mine • to a precise pattern and as with other deformational processes in nature, crack orientation may be quite variable. The transverse tension cracks that locally occur above the longwall mining face often have a dynamic history. They open when the longwall face moves beneath a particular area, and they close again when the longwall face moves out of the area of mining influence. Longitudinal cracks occur above, and roughly parallel to the edges of the longwall mining panel above the gate road pillars and the haulageway (or beltway) pillars. Longitudinal tension cracks commonly remain open, particularly in areas above gate roads with arigid- pillar configuration. The cracks may stay open or close in areas above gate roads with a combination rigid-pillar/yield-pillar configuration. However, as discussed in Exhibit 60B, it is unlikely that cracks will occur in colluvium and alluvium in the stream valleys of the South of Divide mining area. Compression features (bulges and warps) also occur above the longwall mining panels in areas where the ground surface undergoes compression in the subsidence process. The compression features occur toward the center of the mining panel in zones of maximum compression, and are usually more diff-cult to recognize. They often are masked, or absorbed, by soil and colluvium, or are hidden in the brush and grass. They also may be indistinguishable from natural humps and mounds in the soil and colluvium. • Pseudo Subsidence Features (Gravity-Induced Tension Cracks) Cracks have been observed on high, steep ridges, near cliffs, and in landslides, in the Box Canyon and Apache Rocks mining areas. These cracks look very much like subsidence cracks, but cannot be, since no mining occurred in the area where they were observed. A good example of agravity-induced cracks is the extensive crack that Mr. Dunrud observed on the narrow ridge of West Flatiron in August 2002. This crack was as much as 3.5 in wide and 150 ft long. This was not amining-related crack because no mining had occurred in the area. The possibility of gravity-induced cracking in the rugged country above planned mining activities at the West Elk mining areas is a good reason to perform baseline studies of the area prior to mining so that these features can be documented prior to any mining. Cracks and bulges caused by landslides are other types of gravity-induced features that may appear to be related to subsidence, particularly in areas that have been, or are being, undermined. However, landslide-induced features are related to the geometry of the landslide rather than the mine geometry. For example, cracks are most common in the upper area of a landslide, whereas, bulges are most common in the lower area of the slide. This spatial and geometric relationship to a landslide footprint on steep, unstable slopes, rather than the mine geometry can usually be used to differentiate between gravity-induced and mine-induced surface features. • Subsidence Prediction Based on Local Mining Experience - 2.05.6 (6)(e)(i)(C) 1.05-t 08 Revised June 2005 PRlO