Analysis of relationships between micro-topography and short- and long-term erosion rates on shore platforms at Kaikoura Peninsula, South Island, New Zealand

Abstract

Using long-term data sets of erosion rates for the shore platform at Kaikoura it is possible to assess the relationships between erosion rates over two and ten years. Erosion rates do not tend to vary significantly between the two measurement periods. Using linear regression analysis a difference in the nature of topographic change is identified between mudstone and limestone shore platforms. The mudstone platforms show a consistent mode of topographic change, parallel retreat or smoothing, between the short and long terms. Limestone shore platforms show no consistent mode of topographic change. It is suggested that the consistent behaviour of the mudstone platforms occurs because the mudstone surface is responding as a single unit at this scale of measurement. Erosion rates tend to increase with distance from the seaward edge of the platforms and this may reflect the increasing significance of wetting and drying cycles, as well as the increasing mix of erosional processes as sub-aerial processes increase in importance. This changing mix of erosional processes may also explain the variations in gradient coefficients between short- and long-term erosion rates with distance from the seaward edge of the platforms.