Rock fall at the Takiroa rock art site, May 2010, Duntroon, North Otago, New Zealand

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Cox, S.C. 2010 Rock fall at the Takiroa rock art site, May 2010, Duntroon, North Otago, New Zealand Lower Hutt, N.Z.: GNS Science. GNS Science report 2010/31 20 p. 

Abstract: A rock fall of ~35 m3 volume collapsed from limestone cliffs at Takiroa, Duntroon, North Otago overnight on 25-26 May 2010 during a severe and prolonged rain storm. Unwitnessed, the collapse occurred between two areas of historic and culturally important Mâori rock art that receive ~20,000 visitors per year. Estimated to weigh between 40 and 77 tonnes, the debris damaged a path, garden and fences but the art was unaffected. Roots and soil on the failure surface indicate that the collapse occurred on a pre-existing fracture in the rock. The failed rock mass was deeply undercut and steeply overhung. The overhung nature of the cliff, low rock-mass strength and gravity, were main contributing factors with final failure interpreted to be triggered by water during heavy rainfall. The failure has highlighted that cliffs are naturally unstable. Earlier collapses have occurred at the site and future rock falls are inevitable, although the frequency is very difficult, if not impossible, to quantify. A full geotechnical review should consider improved signage and natural hazard warning; path design to minimise visitor exposure time to the hazard; rock-scaling; engineering support; and management of water/runoff. While issues of public safety are quite distinct from the protection and curation of cultural heritage, methods employed to achieve positive outcomes in both areas have some overlap. (auth)