The causes and agricultural impacts of large translational landslides: Case-studies from North Island, New Zealand

The size and abundance of active, soft-rock landslides in New Zealand results in extensive, but seldom quantified, damage to productive land. This study draws on case-studies of New Zealand farms affected by large, slow-moving landslides in Tertiary-aged strata, to explore the causes of movement, financial costs, and the current management strategies. While most of the landslides are initiated by stream incision and vary in speed depending on seasonal changes in groundwater, some of these landslides are initiated by as yet unidentified processes. The financial costs are severe and tend to be disproportionate to the area that the landslides occupy, significantly increasing the average per-hectare operating costs. The farmers receive little guidance on management, and in some cases their actions may worsen, rather than reduce movement. Effective management strategies may involve slowing movement, minimizing damage, or retirement of the land, but the scale of the problem renders complete arrest unfeasible.