Soil constraints to development in the Port Hills, Banks Peninsula : With special reference to urban development in Paparua County :[dissertation], Dip. Nat. Res. [Diploma in Natural Resources] project, Centre for Resource Management

Abstract

The Port Hills comprise of the Northern section of Banks Peninsula, generally between Lyttelton harbour and the Christchurch urban area. Banks Peninsula con­sists of the eroded calderas of Lyttelton and Akaroa volcanoes which were active during late Miocene and early Pliocene times (12-16 m.y. ago). The volcanic cones of andesitic and basaltic composition developed offshore, and radial drainage patterns were well established by the commencement of the Pleistocene some 2 million years ago. Glacial outwash gravels to a depth exceeding 300 meters were deposited during the Pleistocene. Much of Banks Peninsula was blanketed in loess, derived from fine rock flour, produced by glacial grinding of greywacke basement rocks during the Pleistocene. Subsequent erosion of loess has produced a complex pattern of in situ loess, colluvial loess, loess volcanic colluvium and exposed volcanic rock. These have formed the parent materials for the soils of Banks Peninsula. The majority of soils of the Port Hills contain high percentages of loess and may be subject to erosion. The most serious types being, tunnel gully erosion and slide avalanche flow mass movements. Recent urban expansion onto the loess derived soils of the Port Hills has been subject to difficulties caused by the erosive nature of the soils. An understanding of the dominant soil types and the susceptibility to erosion is necessary if further problems are to be anticipated, avoided or overcome.