Aspects of the geomorphology of the Greywacke Ranges bordering the Lower and Middle Waikato Basins

Abstract

The fault-bounded blocks which make up the Greywacke Ranges bordering the Lower and Middle Waikato Basins have a deep red-weathered regolith and are covered by mantles of volcanic ash which can be used for dating ground surfaces. The drainage texture is exceedingly fine compared with that of Dartmoor (U.K.) and Unaka Mountains (U.S.A.) This is attributable to rainfall type, regolith, vegetation cover and soil physical properties. The major types of mass movement are deep fossil slumps on upper slopes where the regolith is deep; debris slides on mid- and lower slopes where the regolith is thin; and seepage heads controlled by ground water conditions. The valley floors show both stream incision, and aggradation resulting from infill with mass movement debris. Deforestation has increased the frequency of mass movement during high intensity rainstorms and the slopes are at present becoming adjusted to changed equilibrium conditions.