Soil creep: Problems raised by a 23 year study in Australia

In October 1965 and February 1966, 55 Young-pits were installed in tropical Northern Territory (NT) and temperate New South Wales (NSW). Pits were mon itored in 1968, 1971 and 1974; also, for the NT only, in 1988. In each regi on, half of the pits are on weathered granite, and half on sandstone. Local relief is 30 m or less, and slopes are up to 20 degrees. Annual rainfall i s evenly distributed in the NSW sites (800 mm a(-1)), but is confined to th e five to six month wet season in NT (1200 mm a(-1)). Six pits suffered ext ernal disturbance and so were not analysed. Analysis of 160 rods in 49 undi sturbed pits shows: (1) vectorial movement generally not downslope parallel to the ground surface, but dominated by a vertically downward component; ( 2) significant uphill and vertically upward components of movement for many rods; (3) a weak correlation between total movement and sine of slope; (4) rapid movement during 1965-68, and slow movement thereafter; (5) significa ntly higher creep rates on the NT granites than on all other sites, perhaps because mound-building termites are especially active there. We conclude t hat our data do not support soil creep models which assume that all movemen t is downslope and slope-parallel. Repeated long-term measurements are esse ntial to distinguish long-term creep rates from the short-term effects of d isturbance. Copyright (C) 1999 John Wiley & Sons, Ltd.