Ploughing boulders on the Rock and Pillar Range, south‐central New Zealand: Their geomorphology and alpine plant associations

Abstract

The first Southern Hemisphere descriptions of the geomorphology of currently active ploughing boulders, together with a wide range of relevant site factors and associated vegetation patterns, are provided for the high‐alpine zone of the Rock and Pillar Range, south‐central New Zealand. Heavy winter snow accumulation on an upper leeward slope, combined with a periglacial environment characterised by frequent freeze‐thaw cycles and persistent strong westerly winds are conducive to the downslope movement of large blocks of chlorite schist, derived mainly from the weathering of locally numerous shaft tors. Downslope movement of variously shaped boulders up to 5.81 m3 (or 14.64 ± 1.00 metric tons) were up to 18.8 mm yr‐1 (mean = 11.4 ± 4.0), over the last 3 decades. Such boulder movement has produced distinctive but variable furrows upslope, lateral levees and frontal “bow waves”. The associated vegetation succession is also variable, but generally consistent with that recently described from the adjacent Old Man Range during the first 24 years following major mechanical disturbance of a high‐alpine cushionfield.