OLD MAN OF THE MOUNTAIN: RESIDUAL ROCK MASS STRUCTURAL COMPETENCE ASSESSMENT, FRANCONIA NOTCH, NEW HAMPHSIRE

In 2003, the Old Man of The Mountain natural rock profile collapsed from the Cannon Cliff, resulting in a significant public and local economic loss. Because of this, numerous proposals are being made to physically replace the Profile on the cliff in its original size and configuration, using various constructed combinations of heavier rock and lighter weight artificial materials anchored back to the cliff. Significantly, each of these proposals makes the assumption that all unstable parts of that area on the cliff fell away with the collapse, ignoring the possibility that substantial portions of the residual mass may remain unstable and unsuitable for founding such structures. Important field evidence suggests the assumption is faulty and that the residual mass is incompetent: (a) technical climbers frequently report observing substantial volumes of spalling and block fall from the area; (b) post-collapse investigation shows intensive kaolinization weathering of the Conway Granite has deeply penetrated subvertical and subhorizontal discontinuity surfaces up to 20 feet into the cliff behind the rock mass that comprised the Profile; and (c) photograph comparisons of earlier studies with those taken post-collapse show that the 30-40 freeze-thaw cycles/year on the cliff continue to destabilize substantial portions of its open faces. Together, these conditions clearly suggest the residual rock mass is not structurally intact and thus not competent to provide the kind of reliably permanent foundation required by the types of tensional anchorage generally being proposed. Detailed field confirmation and preparation of a stability assessment report is scheduled for mid-2009.