The influence of sediment budget on geomorphic activity of the Tasman Glacier, Mount Cook National Park, New Zealand

• Main Author: Kirkbride, Martin
• Format: Other/Unknown Material
• Language: English
• Published: University of Canterbury. Geology 1989
• Subjects: Mount Cook; New Zealand; Thermokarst
• Online Access: http://hdl.handle.net/10092/4921; https://doi.org/10.26021/9237

Previous studies of sediment transport by valley glaciers have emphasised the dependence of rates of transport on glacier dynamics, in turn a function of climatic environment. Very few studies have considered cases where it is the debris in transport that plays a major role in affecting the dynamics of the glacier. This study of the Tasman Glacier explains the interdependence of ice and debris fluxes in a tectonically-active maritime alpine environment. Glaciological monitoring has allowed the construction of a model of Twentieth-Century glacier behaviour. A model of medial moraine dynamics has been formulated from theoretical and empirical studies of debris in transport. Feedbacks between glacier flow structure, sediment routeways, supraglacial debris accumulation, ablation, glacier thickness and gradient have resulted in a positive sediment budget in the lower glacier and the growth of a 20 km2 debris mantle. Insulation of underlying ice by the debris mantle has led to the preservation of a 7 km long ice tongue which would have ablated away within the last century without the protective mantle. The flow structure of the glacier has been radically affected by debris mantle spread and changes to the ablation gradient, causing slow downwasting and reduced surface gradient with no terminal retreat. Studies of clast shape have revealed that much debris supplied to the terminus of the Tasman Glacier has been modified by water action rather than by glacial action. It is concluded that sediment transfer in the lower glacier is dominantly by fluvial transport in englacial conduits rather than by truely glacial transport. The implication is that much rounded debris found in older moraines was modified during high-level transport through the glacier. Twentieth-Century negative mass balance has resulted in the formation of thermokarst lakes at valley glacier termini in the region. Growth and coalescence of these lakes has heralded the onset of the first phase of rapid terminal retreat for at least 5,000 years in the ...