NUMERICAL-SIMULATION OF SELF-ORGANIZED STONE STRIPES

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 diameter1,2), 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.