Rock Avalanches on Glaciers: Processes and Implications

• Main Author: Reznichenko, Natalya
• Format: Other/Unknown Material
• Language: English
• Published: University of Canterbury. Geological Sciences 2012
• Subjects: Rock avalanche; supraglacial rock avalanche; comminution; glacier; moraine; glacial sediment; ablation; debris-cover; glacial mass balance; advance; retreat; glacial regime; glacial geomorphology; aclimatic advance; microsedimentology; agglomerates; palaeoclimate; moraine chronology; rock-avalanche-driven advance; the Southern Alps of New Zealand; Norway; Hooker; New Zealand
• Online Access: http://hdl.handle.net/10092/6524; https://doi.org/10.26021/9139

This thesis examines the role of rock avalanches in tectonically active terrains including the effects of the deposits on glacier behaviour and their contribution to moraine formation. The chronologies of mountain glacier fluctuations, based on moraine ages, are widely used to infer regional climate change and are often correlated globally. In actively uplifting mountain ranges rock avalanches that travel onto the ablation zone of a glacier can reduce ice-surface melting by insulating the ice. This can cause buried ice to thicken due to slower ablation and can significantly alter the overall glacier mass balance. This glacier response to supraglacial rock avalanche deposits can confound apparent climatic signals extracted from moraine chronologies. This thesis investigates the processes through which rock avalanche deposits may affect glaciers and develops a new technique to identify the presence of rock avalanche debris in glacial moraines. From laboratory experiments on the effects of debris on ice ablation it is demonstrated that the rate of underlying ice ablation is controlled by diurnal cyclicity and is amplified at high altitude and in lower latitudes. The relatively low permeability of rock avalanche sediment in comparison with non-rock avalanche supraglacial debris cover contributes to the suppression of ablation, at least partly because it greatly reduces the advection of heat from rain water to the underlying ice. The laboratory findings are supplemented by field investigations of two recent rock avalanche deposits on glaciers in the Southern Alps of New Zealand. This work demonstrates that the rock avalanche deposits are very thick (10 m at Aoraki/Mt. Cook and 7m at Mt. Beatrice) and almost stopped the ablation of the overlying ice. This resulted in the formation of an ice-platform more than 30 m high. This led to a reduction of the existing negative mass balance of the affected Tasman and Hooker Glaciers. There was little noticeable alteration of the overall glacial regime due to the small scale of ...