Factors controlling spacing distances of sorted stripes in a low-latitude, alpine environment (Cordillera Real, 16°S, Bolivia)

A total of 1500 spacing distances of sorted stripes were measured on 30 alpine sites in the Bolivian Andes with distinct slope angles, elevations and aspects. Additionally, the geometric evolution of stripes was systematically analysed along a slope with varying inclinations and morphology. We dealt with mainly small-sized stripes (< 40 cm). The scatter observed in the distribution of spacing distances suggests that the factors controlling the geometry of sorted stripes are complex. Among them, we point out the role of slope inclination and coarse sediment supply. They imply that stripe geometry does not depend exclusively on processes operating in soils such as frost heaving and sorting, but also on the dynamics of the flux of coarse materials along the sloping surface. This analysis questions models which assume that sorted stripes are organized according to a strict periodicity whose origin depends on specific physical processes. Particularly, it appears that recent convective models cannot explain the characteristics and the evolution of patterned slopes in this environment. Copyright (C) 2001 John Wiley & Sons, Ltd.