1,000-YEAR PATTERN OF EROSION IN ARID ENVIRONMENTS FROM WARI PRE-COLUMBIAN TERRACES IN SOUTHERN PERU

An extensive system of agricultural terraces abandoned c. 1,000 years ago by the Wari civilization of southern Peru provides an ideal setting for studying patterns and rates of dryland erosion. The terraces, which have remained virtually untouched since their abandonment, may serve as a proxy for documenting degradation of natural surfaces.

The pattern of erosion over the last 1,000 years may be determined from comparison of digital elevation models of the observed morphology with the reconstructed original morphology of the Wari terraces. These terraces show intense erosion; channels have formed with different degrees of development. Several of the channels are interconnected, cutting through various terraces, indicating a more advanced stage of development. Lowering of the terrace surface by wash processes occurs throughout the system and show an average depth of erosion of 40-50 cm.

Material removed from the terrace treads, chiefly gravel, has accumulated on the upslope edge of the next lower terrace surface, mainly as wash deposits, an sometimes as fans. Within the channels, fine material has been washed away leaving gravel-size material. Despite the re-deposition of material on the terrace, erosion is the dominant process.

Constructed earthworks such as the pre-Columbian terraces of Southern Peru are a useful tool for understanding the pattern and rate of surface degradation under dryland conditions.