Numerical simulation of selforganized stone stripes

Abstract

GEOMETRICALLY regular stripes of stones are found on many unvegetated alpine and polar hillslopes; known as ‘sorted stripes’ because of the characteristic textural sorting between surface stones and fine-grained soil, they contrast markedly with the lack of order typical of natural landscapes. The spacing of the stripes can range from centimetres to metres (about 10–20 times the average stone diameter^1,2), with individual stripes extending down-slope for many tens of metres (Fig. 1). A variety of formative mechanisms have been proposed³, but it is still unclear how such orderly stripes can arise spontaneously, and what dictates the spacing. Here we present two-dimensional computer simulations in which the displacement of surface stones is governed by the preferential growth of needle-ice in stone-free regions of soil during each freezing cycle. Regular patterns of stones and soil that closely resemble natural stripes are found to emerge spontaneously from the model as a result of identifiable feedbacks between soil texture, ice growth and local slope.