The geomorphology and radar facies of Kaitorete Spit, Canterbury, New Zealand
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Kaitorete Spit is a mixed sand and gravel barrier beach complex that is located at the northeastern end of the Canterbury Bight. Kaitorete Spit was examined during this study using a combination of ground penetrating radar surveys, sedimentological and geomorphological examinations of the barrier beach complex.
The geomorphology formed on Kaitorete has developed in three different environments. At the northeastern end of Kaitorete low elevation spit recurves are formed. South of these are numerous parallel beach ridges, formed by the tops of prograded storm berms. Lacustrine geomorphic features have developed over the marine geomorphology. Small scale cuspate ridges have formed in shallow lake water and associated with lake bottom sediments. Lacustrine beach ridges, lacustrine beach ridge plains and lacustrine spit complexes all formed along the shore of a higher lake.
Nine different radar facies were found developed in the radar profiles collected on Kaitorete Spit. The facies are defined on the basis of their internal reflector patterns. Generally, the reflector patterns could be predicted by interpreting the geomorphic features over which the radar profiles ran. Three of the radar facies revealed reflector patterns that could not be predicted using geomorphology alone.
At the eastern end of Kaitorete Spit, the radar profiles revealed that the marine spit recurves comprise a spit beach overlying a spit platform. It also reveals that the distal end of the spit platform was reworked by tidal currents into a series of seaward prograding foresets. The radar profiles also revealed that immediately the barrier beach reached the edge of the spit platform, a rise in the elevation of the beach crest occurred due to an increase in the wave energy expended on the beach.
In the centre of the barrier beach complex the radar profiles revealed that two long overwash barriers developed, which fill two long (up to 12 km), thin lake outlet lagoons. These lagoons developed as a result of breaching due to a large river overfilling the lake basin. After the initial breach, the longshore drift and lake outflow developed a dynamic equilibrium, resulting in the progressive eastward dislocation of the outlet mouth. The large volume of lake water acted to buffer the high flows of the river thereby, maintaining flow conditions at the outlet channel which were conducive to lagoon elongation.
Associated with the lacustrine spit complexes are scarp-like ridges which have steep reflectors which dip away from the lake. These developed in a similar way to shore-parallel bars, with material moving up the stoss side and avalanching down the lee side.
The combined application of ground penetrating radar and geomorphology reveals a much more complete geological history of an area where outcrop is sparse.