In a random sample of 52 valley-side profiles at Tangoio, mass movements are shown to occur preferentially on profiles with a northerly aspect, which are long, or steeply sloping. Detailed measurements of 27 debris slide and two slump scars dating from a storm in May 1971 enable an estimate of the rate of erosion of loess and volcanic ash from valley-sides to be made. Valley-side slopes are changing from a convexo-concave equilibrium form under the original forest towards a new, more rectilinear equilibrium form under grass.