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Fall 2008 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />northern edge of' this gravity-induced crack is located very close to the southern edge of the <br />MDW' pad located over Lon-wall Panel 21 where more extensive surface cracking has been <br />observed in the massive sandstone cliffs since longwall nllnlllg occurred. It was easy to <br />determine that this was not a mining-related crack because no mining had occurred in the area. <br />The possibility of gravity-induced cracking in the rugged country above planned nulling activities <br />at the West Elk Mine is a good reason to pertOrin baseline studies of the area prior to mining so <br />that these features can be documented. <br />• <br /> <br />SANE <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />f <br /> <br />' :A <br />, <br />? <br />? <br />_„? ?C;s, te- <br />.? <br />s = <br />; <br />. <br />, <br />?, ,_ .. ?, <br />i i <br />, <br />Figure 4. Gravity-induced tension cracks located above unmined coal in the upper, massive <br />sandstone of the Ohio Creek Member of the Mesaverde Formation, (looking northwest). Joints <br />have opened up a foot or so due to gravitational stresses under little or no lateral constraint. <br />• <br />831-032.790 Wright Water Engineers, Inc. Page 8 <br />December 2008