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Nicola Webb

MSc in Geography  Nikki Webb near Namche Bazaar, Nepal

 

Research:

An evaluation of glaciated valley landsystems: environmental reconstruction of the Ohau Valley, MacKenzie Basin, New Zealand.

 

Supervisor: 

Assoc. Prof. Sean Fitzsimons 

 

Aims:

To critique the literature inorder to obtain and understanding of the 'glaciated valley landsystem' and determine its validity in high precipitation, tectonically active areas.

To characterise the sediment-landform assemblages of the moraine and outwash exposures of the Ohau Valley.

To characterise the subsurface via GPR profiling, and compare with exposed sediments.

To construct a model of the style of landform development for the glacial formations within the Ohau Valley.

To compare and contrast the Ohau Valley glacial landforms with other glaciated valleys in New Zealand and worldwide. 

 

Abstract:

Landsystems are conceptual models that allow characterisation of a landscape by the topographic expression of landforms, from which inferences can be made about the underlying geology and therefore processes of formation. All of which is based on an assumption that surface form is a good indictor of landform development. The Glaciated Valley Landsystems (GVLS) has been used for the last 30 years to reconstruct environmental conditions, and landform development in formerly glaciated valleys. Where possible analysis of sedimentary facies is employed in conjunction with the GVLS approach to environmental reconstruction to enable processes of formation to be genetically linked to surface form. Where soil and vegetation are well established it is not always possible to undertake a detailed sedimentary analysis, as is the case within the Ohau Valley. However this presents an opportunity to utilise a relatively new method of glaciological investigation, ground-penetrating radar (GPR), to test the assumed link between surface expression of landforms and subsurface structure. This technique also provided the basis for the reconstruction of landform development in a tectonically active glaciated valley of high precipitation, temperate climate, and high supraglacial debris load, which is a set of environmental conditions that is currently underrepresented in glaciological literature.  

 
The study focused on the moraines of two formations (Tekapo and Mt John), and found evidence for a range of processes, including glaciotectonic deformation, stagnant ice melt beneath a debris mantle, and incremental moraine development over successive advances to the same terminal location. Indeed the landforms of the Ohau Valley show a high degree of complexity, probably as a result of: 1) a re-advancing ice margin, 2) constrained glacier and landform development within a narrow valley and 3) large pre-existing landforms all acting as a barrier to glacier behaviour. The landforms studied were recognised as being both polygenetic and polyepisodic in origin, and when relating this back to the glaciated valley landsystem is was clear prediction of landform development based on the surface form would have grossly underestimated or erroneously predicted their depositional history. Considering this there is an urgent need to update or modify the GVLS to accommodate more recent developments in glaciological understanding, particularly with reference to polygenetic, polyepisodic and glaciotectonic landforms.

 

© 2009 Department of Geography, University of Otago, Dunedin, New Zealand