Pediment Escarpment Retreat Rate in the Huasco Area of the Atacama Desert, Chile

Two levels of pediments have developed in the Huasco area of the Atacama desert (Y. Akagi 1972). The upper pediment rim is about 100 meters in height and the lower is about 30 meters. The free face between the two levels is about 20 meters in relative height and has retreated about 800 meters to its present position.Along the Huasco River, there are two levels of fill terraces. The upper terrace has a broad surface and the lower has a narrow one (Fig. 1). It is supporsed that the upper terrace is a filltop terrace and the lower is a fill strath terrace. Sand dunes, constructed of materials transported from the seacoast, cover most of the terrace surfaces to a distance of up to 6 kilometers from the river mouth. One exception is a small spot about 3 kilometers from the river mouth. At this point the upper terrace surface is approximately 100 meters high.The base-level of the upper pediment correlates with the upper terrace surface. Development of the lower pediment occured after the formation of the upper terrace surface. Identification of the upper terrace surface formation period will permit an estimate of the retreat of the free face.It is still unclear, but since the upper terrace surface appears to have formed during the Gunz-Mindel interglacial period (400, 000-200, 000 B. P.), the retreat rate of the free face seems to be about 2-4mm/year.