Rock type

Rock type has a major influence on slope, soil stability and natural fertility in New Zealand’s hill and mountain lands. Cover deposits such as tephra and loess also influence soil fertility and erosion susceptibility where they occur.

The Rock Type Classification (Lynn & Crippen 1991) provides the standard for LUC mapping based on erosion susceptibility and physical characteristics that are relevant to soil conservation and land use planning.

The classification has four objectives:

1. To group rock types that have similar erosion susceptibilities and characteristics.
2. To concentrate on those rock types that directly influence land surface morphology, and therefore land use.
3. To distinguish rock types that can be recognised and mapped by soil conservators, land managers and earth scientists, with limited formal geological training.
4. To provide information on rock types that can be readily understood and applied by planners and land managers.

Note: In the context of LUC rock type is used to mean any natural aggregate of one or more minerals. It includes extremely weak or loose aggregates (alluvium, gravels, etc.) and harder aggregates (soft rocks and hard rocks). This differs in some respects from geological and engineering terminology. 

The rock type underlying a map unit is also usually the parent material for the soil that forms there.  In addition in some steeper areas, the lithological properties of the underlying parent material are critical in terms of understanding erosion processes and potential erosion severity and therefore determining land use capability.  

See section 2.1 of the LUC Handbook and Rock Type Classification for more information on Rock type and coding conventions.