McKellar, I.C. 1973 The susceptibility of Lake Manapouri shoreline to slumping at low lake levels. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 156 19 p.
Abstract: Low lake levels reduce the lateral support that lake water gives to the unconsolidated shoreline deposits. Consequent gravity-induced movements cause shearing in the weak clays on which these sediments rest, and produce tension cracks at the surface and slumping towards that lake. This process is a man-induced form of the natural process of shoreline degradation that has continued during the part 10,000 years as the lake level has fallen. Slumping and tension cracks appear to be confined to a relatively small area of shoreline east of Stockyard Cove and Calm Bay in an attractive and well used part of the lake. Surprise Bay is the most-affected area. Evidence points to a distinctive grey clay as the material in which slope failure occurs. Its distribution has been mapped as an indicator of shoreline susceptibility to slumping. Removal of small non-vegetated patches of this clay from ''bedrock'' by slumping and wave erosion produces temporary water turbidity. Small areas that have had these patches of clay completely removed and basement rock exposed should prove aesthetically acceptable. Whee slumping occurs in clay supporting flat areas of shoreline vegetation, that areas above low water are reduced and patches of bare clay are exposed. Rotational slumping with displacements of about one foot are not smoothed out quickly by wave action and will take over a year to alter to any extent, especially in sheltered areas. Tension cracks with little or no displacement can be partially or completely filled in by movement of sand and gravel under wave action. (auth)
