This metadata record describes an image of land predicted to be at risk of severe mass movement erosion for the South Island. The image was produced using the Highly Erodible Land model that identifies land at risk to the main forms of mass-movement soil erosion in New Zealand: landsliding, gullying, or earthflow erosion. If the land has protective woody vegetation, then it is not at risk (Dymond et al., 2006). The Highly Erodible Land model identifies five classes of land at risk of erosion: (1) High landslide risk – delivery to stream; (2) high landslide risk – non-delivery to steam; (3) Moderate earthflow risk; (4) Severe earthflow risk; and (5) Gully risk. Landsliding occurs on steep slopes where the soils do not have protective tree roots. The slope angle at which land is considered at risk to landsliding depends on rock strength. Where land is steeper than this slope threshold and does not have woody vegetation, it is considered at risk to landsliding. There is no slope threshold for land at risk to gullying or earthflow erosion. Where land is at risk to gullying or earthflow erosion and does not have woody vegetation, it is considered at risk. The different types of mass-movement soil erosion are not ranked in severity, except for earthflow risk which has extreme and moderate classes of risk. Use: These data provide a regional perspective on land at risk of soil erosion.

More information on this dataset and how it relates to our environmental reporting indicators and topics can be found in the attached data quality pdf.