Salt Weathering in the Namib: Soutrivier and the Coastal Salt Pans

Abstract

In the coastal zone of the Namib salt weathering is a potent agent of rock disintegration. It has also caused the corrosion and failure of various engineering structures. Spectacular examples of the impacts of salt weathering can be seen along the coastal road from Swakopmund to Henties Bay, and where the road from Vogelfederberg to Gobabeb crosses the Soutrivier. At Soutrivier there are salt crusts and efflorescences in and around the damp river bed, and the granites show a wide range of weathering phenomena, including splitting, flaking, alveoles and tafoni. Not only has salt weathering given rise to extensive weathering phenomena but it may help to explain the development of the central Namib plains by a process of ‘haloplanation’, generating the great topographic monotony of some of the Namib coastal plain areas. Furthermore, salt weathering may be an important source of dust which blows off the Namib coast in great plumes. Recently, various experiments based on field exposure of rock blocks over one or more years have demonstrated the rapidity of presumed salt weathering in the Namib. These studies using rock blocks have confirmed that highly aggressive ground conditions occur in the fog belt and within and around coastal salt pans, producing weathering ‘hotspots’. Further inland conditions are less severe and salt weathering is limited to topographic hollows where suitable microclimatic conditions prevail and where groundwater seepage occurs.