PARAGLACIAL ROCKSLOPE STABILITY A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy in Geology in the Department of Geological Sciences, University of Canterbury by Samuel Thomas McColl 2012 ABSTRACT The aim of this research was to study the relationship between rock slope stability and glacial processes. An in-depth analysis of our current understanding of how glaciated rock slopes develop instability and movement during deglaciation is presented; this shows that understanding is incomplete without an appreciation of the variable mechanical behaviour of glacier ice. In this thesis, I argue that: (1) The ductile behaviour of ice at low strain rates allows movement of rock slopes buttressed by ice. Field evidence and simple force models are used to explore rate of movement of ice-contact slopes and the conditions under which they evolve. The results indicate that large rockslides can move and deform glacial ice at rates of 10-2 to 102 m-yr. This implies that ice-contact slope movement may be important for slope evolution and the erosion and entrainment processes of glaciers; and (2) the elastic strength of glacier ice at the high strain rates associated with seismic shaking enables ice to modify the response of the surrounding rock to seismic shaking. To explore this, numerical analyses of the interaction between glacial erosion, glacier mass, topography, and earthquake shaking intensity are undertaken. Shaking of mountains of variable shape and with different levels of ice inundation is simulated using FLAC 6.0. The results suggest that complete inundation by ice can significantly reduce shaking intensity. This, in combination with glacial steepening of slopes, may make recently deglaciated slopes more prone to coseismic failure. In the final chapter of the thesis, I present a conceptual model of the evolution of slope stability during stages of glaciation and deglaciation. The model incorporates the ideas presented in the thesis. I then offer recommendations for how our understanding of these processes can be further advanced. Deputy Vice-Chancellor’s Office Postgraduate Office Co-Authorship Form This form is to accompany the submission of any PhD thesis that contains research reported in co-authored work that has been published, accepted for publication, or submitted for publication. A copy of this form should be included for each co-authored work that is included in the PhD thesis. Please indicate the chapter/section/pages of this thesis that are extracted from co-authored work and provide details of the publication or submission from the extract comes: Section 2.2: McColl, S.T., Davies, T.R.H., McSaveney, M.J., 2010. Glacier retreat and rock- slope stability: debunking debuttressing. Geologically active: delegate papers 11th Congress of the International Association for Engineering Geology and the Environment, Auckland, Aotearoa, 5-10 September 2010. Auckland, New Zealand. pp. 467-474 Please detail the nature and extent (%) of contribution by the PhD candidate: This publication was initiated and written by the PhD candidate, and the figures were designed and drafted by the candidate. Some of the ideas presented were suggested by the co-authors, but subsequently modified by the PhD candidate. The contribution by the candidate was over 80%. Please list the co-authors and the nature and extent of the contribution by each below: Name: Timothy Davies. Contribution: Tim provided edits and comments on two versions of the manuscript, and some of the ideas were suggested by Tim. Name: Mauri McSaveney. Contribution: Mauri provided edits and comments on one version of the manuscript. Mauri suggested including the force diagrams (Figures 2.2.2 – 2.2.3) but these were designed and drafted by the PhD candidate. Certification by Co-authors: The undersigned certify that: . The above statement correctly reflects the nature and extent of the PhD candidate’s contribution to this work and the nature and contribution of each of the co-authors . In cases where the PhD candidate was the lead author of the co-authored work he or she wrote the text Name: Timothy Davies. Signature: Date: 4 July 2012 Name: Mauri McSaveney. Signature: Date: 25 June 2012 Deputy Vice-Chancellor’s Office Postgraduate Office Co-Authorship Form This form is to accompany the submission of any PhD thesis that contains research reported in co-authored work that has been published, accepted for publication, or submitted for publication. A copy of this form should be included for each co-authored work that is included in the PhD thesis. Please indicate the chapter/section/pages of this thesis that are extracted from co-authored work and provide details of the publication or submission from the extract comes: Section 4.2: McColl ST.; Davies TRH. Large ice-contact slope movements and glacial buttressing, deformation and erosion. First submitted in May 2012 to the journal Earth Surface Processes and Landforms; revised manuscript submitted June 2012. Please detail the nature and extent (%) of contribution by the PhD candidate: The manuscript was conceived and written by the PhD Candidate. All of the figures were conceived, designed, and drafted by the PhD candidate. All of the data collected, analysis, and interpretation was by the PhD candidate. The equations were developed by the candidate but received minor modifications from the co-author. The main idea presented in the manuscript, that the ductile behaviour of ice cannot support slopes, was suggested by Tim but the approach for describing and modelling the process, and refinements to the idea were a result of discussion between both authors. The contribution by the PhD candidate was over 80%. Please list the co-authors and the nature and extent of the contribution by each below: Name: Timothy Davies. Contribution: Tim provided edits and comments on 4 versions of the manuscript, and suggested modification to some of the equations. Certification by Co-authors: The undersigned certify that: . The above statement correctly reflects the nature and extent of the PhD candidate’s contribution to this work and the nature and contribution of each of the co-authors . In cases where the PhD candidate was the lead author of the co-authored work he or she wrote the text Name: Timothy Davies. Signature: Date: 4 July 2012 Deputy Vice-Chancellor’s Office Postgraduate Office Co-Authorship Form This form is to accompany the submission of any PhD thesis that contains research reported in co-authored work that has been published, accepted for publication, or submitted for publication. A copy of this form should be included for each co-authored work that is included in the PhD thesis. Please indicate the chapter/section/pages of this thesis that are extracted from co-authored work and provide details of the publication or submission from the extract comes: Section 4.3: McColl ST; Davies TRH; McSaveney MJ (in press) The effect of glaciation on the intensity of seismic ground motion, Earth Surface Processes and Landforms. Please detail the nature and extent (%) of contribution by the PhD candidate: The publication was initiated and written by the PhD candidate. All of the modelling, analysis and most of the interpretation was by the PhD candidate, as was the design and drafting of the figures. The main idea, that glaciers modify the co-seismic shaking of mountains, was suggested to the candidate by Timothy Davies but refinement of the idea, the approach for modelling it, and the development of the idea into a conceptual model for understanding slope processes, was that of the PhD candidate. The candidate contributed to over 80% of the publication. Please list the co-authors and the nature and extent of the contribution by each below: Name: Timothy Davies. Contribution: Tim provided edits and comments on 2 versions of the manuscript and discussed the ideas with the candidate on several occasions. Tim helped with some of the interpretations of the results. Name: Mauri McSaveney. Contribution: Mauri provided edits and comments on 2 versions of the manuscript, in particular making suggestions to the terminology used. Mauri had discussions with the candidate about some of the results and interpretation. Certification by Co-authors: The undersigned certify that: . The above statement correctly reflects the nature and extent of the PhD candidate’s contribution to this work and the nature and contribution of each of the co-authors . In cases where the PhD candidate was the lead author of the co-authored work he or she wrote the text Name: Timothy Davies. Signature: Date: 4 July 2012 Name: Mauri McSaveney. Signature: Date: 25 June 2012 Deputy Vice-Chancellor’s Office Postgraduate Office Co-Authorship Form This form is to accompany the submission of any PhD thesis that contains research reported in co-authored work that has been published, accepted for publication, or submitted for publication. A copy of this form should be included for each co-authored work that is included in the PhD thesis. Please indicate the chapter/section/pages of this thesis that are extracted from co-authored work and provide details of the publication or submission from the extract comes: Appendix A: McColl ST; Davies, T.R. 2011. Evidence for a rock-avalanche origin for `The Hillocks' "moraine", Otago, New Zealand. Geomorphology 127: 216-224 Please detail the nature and extent (%) of contribution by the PhD candidate: This publication was written by the PhD candidate. The co-author developed the hypothesis but the candidate collected the data, made his own interpretations, and designed and drafted the figures. The contribution by the candidate was over 80%. Please list the co-authors and the nature and extent of the contribution by each below: Name: Timothy Davies. Contribution: Tim developed the hypothesis and provided edits and comments on two versions of the manuscript. Certification by Co-authors: The undersigned certify that: .