2007-11-30_REPORT - C1980007 - Laserfiche WebLink

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Fall 2007 Subsidence and Geologic Field Observations Box Canyon, Apache Rocks, and South of Divide Mining Areas 5.13 Photographic Observation Point 9 This point was used during this fall 2007 field visit to observe and photograph the Highway 133 landslides, which have been described in the 2005 and 2006 reports. This location, located 200 to 300 feet above the North Fork, provides a good, uncluttered view of the major landslides east of Box Canyon (Figure 42) and the landslide located west of the mouth of Box Canyon (Figure 43). 5.13.1 Landslide Located East of the Mouth of Box Canyon This landslide occurred suddenly during a period of high precipitation in the mid 1990s (Figure 42). The sound and tremor produced by this event was heard and felt at the West Elk Mine office 8,000 to 9,000 feet to the west. A block of bedrock failed along fractures, became detached, slid downward, and came to rest in its original orientation, as indicated by the vertical orientation of the pine trees on the slump block. No changes have been observed in this slide since 2005, except the landslide scar and associated slide rocks appear more weathered (compare Figure 42 with Figure 30, page 37 of the 2005 report and page 38 of the 2006 report). 5.13.2 Landslide Located West of the Mouth of Box Canyon This landslide initially occurred during a period of high precipitation in the mid 1980s and not as a result of mining activities. It occurred within a few years after construction of Highway 133 on the south side of the North Fork (Figure 43). In contrast to the landslide east of the mouth of Box Canyon, multiple movements have occurred on this landslide during periods of high precipitation in the mid 1980s and mid 1990s. No movement was observed of this landslide area since July 2005 (compare Figure 43 with Figure 32, page 40 of the 2006 report). • 831-032.780 Wright Water Engineers, Inc. Page 57 November 2007