The Southern Alps of New Zealand form a southwest-northeast trending barrier that lies across the prevailing westerly circulation in the middle latitudes of the Pacific Ocean. Orographic uplift of the maritime winds results in extremely high precipitation on the west coast and a steep precipitation gradient into the rainshadow areas to the east of the main divide. The maximum precipitation falls in a zone parallel to the first range a few kilometers west of the main divide and peaks at around 12,000 mm/y (Griffiths and McSaveney 1983). Within 10 km east of the main divide the precipitation falls to less than 300 mm/y. Thus, the interaction of the tectonic setting and the westerly circulation act as an important control on landscape development of the South Island (Whitehouse 1988).
In New Zealand, there has been considerable debate surrounding the controls of contemporary erosional processes, and several studies have suggested that rainfall is the major control on denudation rates. In a study of South Island catchments, Griffiths (1979, 1981) concluded that rivers draining the western Southern Alps have suspended sediment yields that are about 10 times higher than world average rates for mountainous areas. He suggested that almost all the variations in sediment yield are explained by variations in mean annual rainfall. In another study, Adams (1980) argued that lithology, tectonic uplift rates, and Quaternary geomorphological history including glaciation were also important controls on sediment yields. In yet another study, Pickrill (1993) examined sediments that have accumulated in fiords and suggested that sediment yields ranged from 28 to 209 t/km²/y, in comparison with Griffiths' figure of 13,300 t/km²/y for the Cleddau River, which flows into Milford Sound.
More recently, Hicks et al. (1996) examined a larger, updated data set for 203 New Zealand catchments and found that average annual sediment yields vary over 4 orders of magnitude, from less than 20 t/km²/y to almost 30,000 t/km²/y. This study concluded that the main controls on sediment yield are mean annual rainfall and basin geology, which includes lithology, the level of tectonic activity, and the Quaternary history of the catchment. The high sediment yields from the west coast are a consequence of the combined effects of the high mountains and the high orographic precipitation produced by the interaction of the mountains with the prevailing westerly airstream (Whitehouse 1988).
The extremely high rates of landscape evolution in the Southern Alps make the landscape a superb natural laboratory for the study of geomorphological processes. Our research within this environment includes:
Behaviour of glaciers in tectonically active alpine landscape
This work focuses on reconstruction of how glaciers behaved during Pleistocene ice advances in the trunk valleys that drain the Southern Alps. Using studies of the structure and sedimentology of glacial deposits the extent and behaviour of ancient glaciers can be reconstructed. Understanding the contemporary glacier dynamics may provide analogues for ancient glaciers, and their responses to climatic fluctuations. We have studied the contemporary landforms around the margins of the Tasman Glacier, as well as reconstructed landsystems models for several trunk valleys on the east of the main divide.
Landscape response to disturbance events
This work focuses on understanding how slopes and rivers respond to disturbance events such as coseismic mass movements and high magnitude rainfall events and indeed if such disturbance events have distinct signatures. We have extracted cores from most small lakes in south Westland and examined the sediments, carbon content, pollen and magnetic properties. Using radiocarbon dating we are developing a chronology of catchment disturbance events which, using geochemical signatures, we have attempted to link responses to different parts of the catchments. In addition we are monitoring aggradation/degradation processes on alluvial fans that flow into the lakes we have cored.
Adams, J., 1980. Contemporary uplift and erosion of the Southern Alps, New Zealand. Geological Society of America Bulletin 91:1-114.
Griffiths, G.A., McSaveney, M.J. 1983. Distribution of mean annual precipitation across some steepland regions of New Zealand. New Zealand Journal of Science 26:197-209.
Hicks, D.M., Hill J., Shankar, U. 1996. Variation of suspended sediment yields around New Z ealand: the relative importance of rainfall and geology. In: Erosion and Sediment Yield: Global and Regional Perspectives. Proceedings of the Exeter Symposium, July 1996. Wallingford: IAHS Press, pp 149-156.
Pickrill, R.A. 1993. Sediment yields in Fiordland. Journal of Hydrology (New Zealand) 31:39-55.
Whitehouse, I.E. 1988. Geomorphology of the central Southern Alps, New Zealand: the interaction of plate collision and atmospheric circulation. Zeitschrift für Geomorphologie 69:105-116.
Related Student Theses and Dissertations
Coombes, K. 1997. Late Peistocene glaciation and geomorphic development of the Von-Oreti valley, northern Southland. Unpublished MSc thesis, in Geography, at the University of Otago, Dunedin, New Zealand. 133 pp. [abstract]
Larking, R. 1999. The development of landforms during the transition from a glacially dominated system to a fluvially dominated system. Unpublished MSc thesis, in Geography, at the University of Otago, Dunedin, New Zealand. 133 pp. [Abstract]
Mager, S. 1999. An environmental reconstruction of the Tekapo formation using facies analysis. Unpublished MSc thesis, in Geography, at the University of Otago, Dunedin, New Zealand. 145 pp. [Abstract]
Vandergoes, M. 1993. Post glacial vegetation and climate change in the southern Takitimu Mountains. Unpublished PGDipSci dissertation, in Geography, at the University of Otago, New Zealand. 79 pp.
Vandergoes, M. 1996. Post glacial vegetation and climate change in western Southland. Unpublished MSc thesis, in Geography, at the University of Otago, Dunedin, New Zealand. 149 pp. [abstract]
Vandergoes, M. 2000. A high resolution record of late quaternary vegetation and climate change, South Westland, New Zealand. Unpublished PhD thesis, in Geography, at the Unversity of Otago, Dunedin, New Zealand. 149 pp. [abstract]
Wallace, S. 2001. Mapping glacial landforms in the Pukaki and Tekapo Lake basins. Unpublished PGDipSci dissertation, in Geography, at the University of Otago, New Zealand. 53 pp. [abstract]