Rock Avalanches on Glaciers: Processes and Implications

Reznichenko, Natalya

Rock Avalanches on Glaciers: Processes and Implications

dc.contributor.author	Reznichenko, Natalya
dc.date.accessioned	2012-04-19T01:08:43Z
dc.date.available	2012-04-19T01:08:43Z
dc.date.issued	2012	en
dc.description.abstract	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 the debris covered area (4 and 1% of the ablation zones for the Tasman and Hooker Glaciers, respectively) but there is a significant contribution to supraglacial debris, which is passively transported toward the terminus. A conceptual model of the response of mountain valley glaciers to emplacement of extensive rock avalanche debris on the ablation zone has been proposed for the effect of this type of debris on terminal moraine formation based on enhanced ‘dumping’ of supraglacial sediments. A new technique has been developed to distinguish rock-avalanche-derived sediment from sediment of glacial origin, based on the sedimentary characteristics of the finest fraction. Examination of rock avalanche sediment under the Scanning Electron Microscope showed that finer particles tend to form strong clumps, which comprise many smaller (down to nanometre-scale) clasts, named here ‘agglomerates’. These agglomerates are present in the ﬁne fraction of all examined rock avalanche deposits and absent in known non-rock-avalanche-derived glacial sediments. The agglomerates are characteristics of sediment produced under the high-stress conditions of rock avalanche emplacement and contrast with lower-stress process sub- and en-glacial environments. It is demonstrated that these agglomerates are present in some moraines in the Southern Alps of New Zealand that have been attributed to climate fluctuation. Consequently, this technique has the potential to resolve long-standing arguments about the role of rock avalanches in moraine formation, and to enhance the use of moraines in palaeoclimatological studies.	en
dc.identifier.uri	http://hdl.handle.net/10092/6524
dc.identifier.uri	http://dx.doi.org/10.26021/9139
dc.language.iso	en
dc.publisher	University of Canterbury. Geological Sciences	en
dc.relation.isreferencedby	NZCU	en
dc.rights	Copyright Natalya Reznichenko	en
dc.rights.uri	https://canterbury.libguides.com/rights/theses	en
dc.subject	Rock avalanche	en
dc.subject	supraglacial rock avalanche	en
dc.subject	comminution	en
dc.subject	glacier	en
dc.subject	moraine	en
dc.subject	glacial sediment	en
dc.subject	ablation	en
dc.subject	debris-cover	en
dc.subject	glacial mass balance	en
dc.subject	advance	en
dc.subject	retreat	en
dc.subject	glacial regime	en
dc.subject	glacial geomorphology	en
dc.subject	aclimatic advance	en
dc.subject	microsedimentology	en
dc.subject	agglomerates	en
dc.subject	palaeoclimate	en
dc.subject	moraine chronology	en
dc.subject	rock-avalanche-driven advance	en
dc.subject	the Southern Alps of New Zealand	en
dc.subject	Norway	en
dc.title	Rock Avalanches on Glaciers: Processes and Implications	en
dc.type	Theses / Dissertations
thesis.degree.discipline	Geology	en
thesis.degree.grantor	University of Canterbury	en
thesis.degree.level	Doctoral	en
thesis.degree.name	Doctor of Philosophy	en
uc.bibnumber	1763416	en
uc.college	Faculty of Science	en