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Chapter 3 observed to be generally successful between two and five years after reclamation work is completed. Activities resulting in disturbance on steep or unstable slopes of soil types with high erosion or mass movement hazard may result in increased erosion or trigger land slides. These hazards and related effects of disturbance are more likely to be present where existing geologic hazards and steep slopes are identified in Figure 3-2. Disturbances on these slopes may also prove more difficult to revegetate and stabilize during reclamation. The GMUG Forest Plan calls for limiting ground- disturbing activities on unstable slopes and highly erosive areas. Further, the Forest Plan recognizes special leasing stipulations may be required to prohibit occupancy on steep or highly erosive slopes. Appendix C identifies potential lease stipulations for protecting or mitigating effects to soils, geologic hazards, and slopes. Alternative C Impacts to surface features resulting from topographic and geologic changes imposed by longwall mining subsidence from this altemative would be to a lesser degree than Alternative B due to a decrease in the area of mining and avoidance of the Deep Creek channel. The reduced area of mining area would have fewer disturbances from both surface use (43 acres) and subsidence. Seven feet of subsidence is likely in most areas. Up to 14 feet of subsidence could occur in some areas if multiple-seam mining occurs. Subsidence would not occur to the degree as Altemative B in areas east of Deep Creek. Soils Impacts to soils resulting from this alternative will be less than Altemative B due to a decrease in the area of mining and avoidance of the Deep Creek channel. The reduced mining area would also have fewer disturbances from both surface use and subsidence. Impacts to the Deep Creek channel and significant portions of the basin would be avoided, thereby reducing the potential for channel adjustments and sediment loading. Other impacts to the soil resource are expected to be comparable to Dry Fork Lease-By-Application FEIS Affected Environment and Environmental Consequences those resulting from the Proposed Action with only the area of impacts reduced. 3.2.4.1 Cumulative Effects Alternative A Topography and Geology The area would not be leased and no mining would occur; therefore, all topographic and geologic conditions within the Dry Fork LBA tract would remain in their current state. The North Fork Valley has numerous existing natural landslides and other unstable features that contribute to topographic changes in the area, These processes will continue to occur. In addition, the areas north and northwest of the Dry Fork LBA tract have been subsided by mining of one or more coal seams. The area immediately west of the Dry Fork LBA tract is leased, and the permitting process for actual mining is currently underway. This mining-induced subsidence has and will continue to contribute changes to the general topography in this area. Sinec 1981, lowering of the land surface by an estimated 2 to 10 feet within the angle of draw has occurred. These changes in elevation are not noticeable to the causal observer (USDA Forest Service 2003a). Mining in approved and permitted areas to the north and south of the tract would occur over the next 10 to 15 years and would impart similar impacts on the land surface as described in this section. Subsidence in these adjacent areas will occur, lowering the land surface. Surface-tension cracks may form in isolated areas. Existing surface-tension cracks on sandstone outcrops have been noted in the western portion of Section 28, T13S, R90W (a place known as Apache Rocks) and in the northern portion of section 27, T13S, R90W. These surface-tension cracks range from 1 to 3 inches wide, extend up to 50 feet laterally on the surface, and are believed to range from 20 to 50 feet in depth. These cracks formed on ridge tops in rigid sandstone layers are not expected to close completely, but will be locally visible for years to come. 3-13