HYDROLOGICAL PROCESSES Hydrol. Process. 25, 54–63 (2011) Published online 5 August 2010 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/hyp.7816 Controls on spatial variability in snow accumulation on glaciers in the Southern Alps, New Zealand; as revealed by crevasse stratigraphy Heather Purdie, 1,2 * Brian Anderson, 1 Wendy Lawson 2 and Andrew Mackintosh 1 1 Antarctic Research Centre, Victoria University of Wellington, P. O. Box 600, Wellington, New Zealand 2 Department of Geography, University of Canterbury, Private Bag 4800, Christchurch, New Zealand Abstract: Net accumulation measurements from two glaciers located on opposite sides of the New Zealand Southern Alps were used to explore processes controlling spatial variability. The degree of variability, as measured by the spatial variogram, differed in each of the three successive years, but the lowest variance occurred on both glaciers in March 2008, after a hot and dry summer. Strong relationships between net accumulation and elevation within the accumulation area were only found on Franz Josef Glacier (FJG), despite this being the primary control used in glacier mass balance modelling. Interaction between wind and topography was found to be important to the distribution of net accumulation on both glaciers. The crevasse stratigraphy method is an ideal way to gain good spatial coverage of net accumulation, and particularly suited to glaciers with high annual precipitation. Copyright  2010 John Wiley & Sons, Ltd. KEY WORDS glacier; spatial variability; crevasse stratigraphy Received 14 February 2010; Accepted 14 June 2010 INTRODUCTION Snow accumulation and its spatial variability is the great- est uncertainty in both measurement and modelling of glacier mass balance (Jansson and Pettersson, 2007). The degree of spatial variability affects how accurately mass balance can be measured, and how well any one mass bal- ance measurement point represents the glacier as a whole (Fountain and Vecchia, 1999). Spatial variability in snow accumulation influences the amount of water equivalent contained in a glacier catchment; important for irriga- tion, hydro-electricity generation, recreation and tourism. Improved understanding about the spatial variability of snow accumulation will help clarify the processes con- trolling accumulation variability, and thereby assist in glacier mass balance modelling and water resource man- agement. On valley glaciers, mass balance is strongly controlled by elevation (Paterson, 1994; Fountain and Vecchia, 1999) and mass balance models rely on this relation- ship when calculating accumulation and ablation, some- times from remote climate data (Fitzharris and Garr, 1995; Oerlemans, 2001; Anderson et al., 2006). How- ever this relationship is seen to weaken in the accumu- lation area, as the control exerted by temperature (the variable most strongly correlated with elevation) lessens and other processes come into play (Hodgkins et al., * Correspondence to: Heather Purdie, Antarctic Research Centre, Victoria University of Wellington, P. O. Box 600, Wellington, New Zealand. E-mail: heather.purdie@gmail.com 2005; Machguth et al., 2006). Significant spatial vari- ability in accumulation has been found between adja- cent glaciers (Machguth et al., 2006), suggesting that glacier-scale processes may be more important than regional-scale processes at controlling snow accumula- tion distribution. In mountainous regions orographic processes result in precipitation enhancement as moist air parcels are forced up and over a topographic barrier, cooling and condens- ing with the associated reduction in temperature (Barry, 1992). Increased height of a topographic barrier gener- ally leads to increased precipitation, whereas the width of the barrier affects the location of the precipitation max- ima (Colle, 2004; Barstad et al., 2007). The height of the freezing level, and air-mass properties lee of a bar- rier, also influence precipitation distribution, particularly on lee slopes (Zangl, 2005, 2008). In New Zealand a rapid rise in topography beginning at the Alpine Fault, and culminating at the Main Divide of the Southern Alps, leads to a large precipitation gradient and a precipitation maxima of ¾10 m a 1 (Griffiths and McSaveney, 1983; Henderson and Thompson, 1999). Previously it has been believed that this maxima occurs west of the Main Divide (Henderson and Thompson, 1999), but recent research suggests that there may also be a secondary or sub- sidiary maxima immediately east of the Main Divide (Kerr, 2009). At local-scale, preferential deposition and redistribu- tion of snow by wind are important controls on spa- tial variability in snow accumulation, both resulting in increased snow accumulation on lee slopes (Liston Copyright  2010 John Wiley & Sons, Ltd.