Exploring steep bedrock permafrost and its relationship with recent slope failures in the Southern Alps of New Zealand

Abstract

AbstractThe central region of New Zealand's Southern Alps is characterised by steep, glaciated slopes prone to rock mass failure, but permafrost conditions and any relevance to past or future slope instabilities have received little previous attention. A network of 15 dataloggers was used to record near‐surface temperatures on steep rock walls located about the Main Divide of the Alps and further leeward where the climate is much drier. Mean annual rock temperature (MART) ranged from −1.9 to 5.4°C, corresponding to local 0°C elevations (E0) of 2465–3514 m, with no significant difference observed between the humid and drier mountain ranges. On extremely shaded slopes, the permafrost limit may extend down towards 2000 m, but further measurements are needed to confirm this. E0 levels were modelled as a function of potential solar radiation, allowing steep permafrost distribution to be mapped across the region. From an inventory of 19 bedrock failures occurring about the Main Divide since the mid‐20th century, 13 have initiated from source areas where MART in the range of +/−1.8°C is considered to indicate marginal permafrost conditions. None of these events was triggered by seismic activity, and mostly exhibit scarp areas that include or originate in close‐to‐ridge topography, where the most rapid permafrost degradation might be expected. Copyright © 2009 John Wiley & Sons, Ltd.