Development of shore platforms on Kaikoura Peninsula, South Island, New Zealand: II: The role of subaerial weathering

The role of subaerial weathering in the development of shore platforms on Kaikoura Peninsula is investigated. Evidence for weathering came from a number of distinctive surface morphologies on platforms: salt crystal growth, water layer weathering, and slaking. Schmidt Hammer test data showed that weathering had occurred and that rock strength was reduced through weathering by as much as 50%. Weathering processes on shore platforms rely on repeated wetting and drying, and for this reason the number of wetting and drying cycles was estimated. It was found that the number of wetting and drying cycles depend not only on the pattern of tidal water levels but also on algae growth and desiccation. The number of cycles ranged from 104 to 379 per year. At elevations low in the tide range, fewer cycles occurred; the greatest number occurring between the peaks of spring and neap tides, and where rainfall adds to the number. The zone of most cycles was estimated to occur between 0.6 and 0.9 m above mean sea level on the more landward margins of platforms. It is at these elevations that the highest rates of erosion occur. Based on these results, it is argued that the development of shore platforms at Kaikoura results from subaerial weathering caused by repeated wetting and drying. This is contrary to the view that shore platforms result from marine erosion.