Surface movement in an earthflow complex, Raukumara Peninsula, New Zealand

Abstract

The surface movement of an unstable earthflow complex was studied over a 10-year period using a network of pegs inserted to a depth of 1 m. The mean and maximum surface movement velocities in the transport zones of the two study earthflows ranged from 0.2–0.4 m and 1.7–2.8 m/month respectively. Maximum velocities for individual pegs ranged up to 3 m/month. The movement data indicated that the earthflows were approximately in a steady state for the 10-year duration of the study. Application of Iverson's theory for the kinematics of unsteady, non-uniform landslide movement indicated that the earthflows had Pe values in the range of 0.1 to 2.0 ( Pe is the dimensionless parameter known as the landslide Peclet number). These values indicated that the earthflows showeda blend of plastic and viscous behaviour and that diffusion might be more significant than kinematic-wave propagation in transmitting disturbances.