Laserfiche WebLink
3 <br />slide. Observations continued on the western bounding edge of the slide, and <br />concluded in a neighboring pit where the sequence of coal seams and bounding strata <br />were visible in the highwall (figure 1). <br />The toe of the slide exhibited chazacteristics of an earthflow, with a pile of rubble <br />pushed up along the toe of the leading edge that retained intact sedimentary layering <br />(figure 2). The rubble was characterized by blocks of rock piled to the top surface of the <br />toe of the rockslide, an estimated height of 50 feet. The rockslide's toe was <br />characterized by intact layers of rock strata. Blocks of rock separated by faults exhibited <br />slightly different dip angles, ranging between 4 and 15 degrees. The regolith on top of <br />each block was IocalIy disturbed by underlying fractures that were offset, and exhibited <br />a jumbled, chaotic appearance adjacent to faults that~cut through the rock strata. A <br />compressor (white squaze) at the upper left corner of figure 2 moved at least 60 feet <br />during the slide according to a company official. . <br />The observation traverse progressed up-dip along the crest of the dip pit, <br />approximately tangential to the toe of the slide. Moving up-dip approximately 1,000 <br />feet from the toe of the slide, the layers of strata involved in the failure appeazed to be <br />intact and the occurrence of fault offsets decreased and disappeared. Rock layers were <br />very well preserved incorrect stratigraphic order, although sandstone at the top of the <br />sequence commonly exhibited a jumbled appeazance where blocks had been offset <br />along pre-existing joint sets. The strata appeared to have experienced flexure during <br />movement, causing the leading edge of the strata sequence to ramp up nearest to the <br />toe and destabilize some joint-bounded sandstone blocks in the top layer of the strata <br />sequence (figure 3). The pile of talus developed at the edge of the intact portion of the <br />slide continued to be present up-dip where the leading edge of the slide had entered the <br />dip pit and encountered the highwall. Using a laser range finder, the height of the <br />intact strata sequence that represents the rockslide's toe, as well as the covering slope of <br />talus, was estimated to be approximately 80 feet. <br />Observations continued up-dip along the crest of the G-1 dip pit to the major bounding <br />slump scarp, termed by mine.personnel as the "Grand Canyon." This feature <br />represents a normal fault that resulted in opening a wide chasm in the slump area <br />developed at the head of the rockslide. The width of the chasm was estimated to be <br />nearly 300 feet, and was littered with large (refrigerator- to Volkswagen-sized) blocks of <br />sandstone that had spalled off along pre-existing joints as the chasm opened. The floor <br />of the chasm exhibited a hilly, hummocky surface of disaggregated regolith and soil, <br />and trended toward the west or west-southwest in an arced shape before curving out of <br />sight (figures 4 and 5). <br />The observation traverse continued up-dip across the exposed surface of the H seam, <br />which had been stripped of overburden but not yet mined. Very faint tension cracks <br />were present in the surface of the H seam, highlighted by recently fallen snow and by <br />