Controls on debris-covered glacier fronts in Central and Western Svalbard A study of arctic glacier termini Ineke Irene Rookus Master Thesis submitted for the degree of Master of Science in Geosciences 60 credits Institute of Geosciences Faculty of Mathematics and Natural Sciences UNIVERSITY OF OSLO November 2016 Controls on debris-covered glacier fronts in Central and Western Svalbard A study of arctic glacier termini Ineke Irene Rookus Master thesis in geosciences UNIVERSITY CENTRE IN SVALBARD UNIVERSITY OF OSLO November 2016 © Ineke Irene Rookus 2016 Controls on debris-covered glacier fronts in Central and Western Svalbard Ineke Irene Rookus Cover picture: Longyearbreen in September 2014, by Ineke Irene Rookus http://www.duo.uio.no/ Print: Reprosentralen, Universitetet i Oslo Controls on debris-covered glacier fronts in Central and Western Svalbard Abstract Debris-covered ice is both common and can greatly change the response of a glacier to climate change. Therefore, realistic predictions of future water availability and global sea-level change need to include debris-covered ice. This study presents an empirical model that estimates the debris-covered ice surface of glaciers of up to 15 km2, based on the clean ice surface area. Analysis of 91 glacier termini in Nordenskiöld Land, Oscar II Land and Prins Karls Forland, on which the model is based, result in a clear negative correlation, and probable relation, between a glacier’s clean surface area and its debris- covered fraction. Differences in geology, topography and climate do not seem to impact the correlation between clean glacier size and debris cover. However, surge-type glaciers are unlikely to form debris-covered termini. Longyearbreen, a glacier of which the front is covered by on average 0.5 m of debris (n=36), serves as a field example in this study. The debris on this glacier is sourced by avalanches and rockfall events and transported supra- and englacially, occasionally by glacial streams. Temperature sensors have been installed at different depths in the debris layer. The resultant time series are combined with weather data and on-field observations, like slumping and collapses during and straight after mid- freezeback rain showers. Analysis of the data indicates that the debris cover is a better insulator during summer-time than during winter-time. This may explain the great impact that a debris cover can have on a glacier’s response to climate change. Overall, climatic changes towards dry conditions are likely to enhance debris-covered ice preservation, but the perfect scenario to preserve debris-covered ice would combine wet autumns, cold, dry and/or windy winters and dry summers. 1 Controls on debris-covered glacier fronts in Central and Western Svalbard Acknowledgements Special thanks go to my supervisor, professor Ole Humlum for his encouraging and enthousiastic manner of suppervision and his help and understanding when progress was slow. I could in all honesty not have wished fo a better supervisor. Many people helped me out during the fieldwork campaigns and this thesis would not have been here without their help. Great thanks go to Dani Roehnert, for all her help and companionship in the field and in particular for her relentless digging. Untill one attempts to dig a meter deep hole in a glacial debris layer, my gratetute for her help in this cannot be fully understood. My thanks also go to professor Hanne Christiansen for providing the temperature sensons and extracting the data from them. Without her help at these times when professor Ole Humlum was not in Svalbard the temperature measurements couldn not have been performed. I would also like to thank Kjersti Kalhagen and Stefan Schöttl for their long days out doing snowdepth measurements on Longyearbreen with me. Although the results could unfortunately not be used to their full potential, as choises have to be made and time is always limited, these first days of fieldswork formed the best thesis start anyone can have. And last but definately not least, I ow a big thank you to Emil Kiesbye Larsen and Stijn Hofhuis for helping me dig the temperature sensors up again a year later. I must confess they could have hardly realized what kind of harsh work they signed up for, just a few weeks after moving to Svalbard. And I am much obliged to their enthousiastic attitude and relentles digging efforts in ground that is simply not ment for digging. 2 Controls on debris-covered glacier fronts in Central and Western Svalbard Contents 1. Introduction .................................................................................................................................... 5 2. Description of study areas .............................................................................................................. 7 2.1. Location of study areas ........................................................................................................... 7 2.2. Recent climatic history and current climate ......................................................................... 10 2.3. Glaciation extent and distribution over the archipelago ...................................................... 12 2.4. Extent and distribution of debris-covered glacier ice ........................................................... 14 3. Theoretic background ................................................................................................................... 16 3.1. Bigger picture: Holocene history of Svalbard and Longyearbreen ....................................... 16 3.2. Formation of debris-covered glacier margins ....................................................................... 18 3.3. Deformation processes within and underneath debris covers ............................................. 21 3.4. Surging and debris-covered glacier termini in Svalbard ....................................................... 22 4. Methods: Glacier margins along the West Coast of Svalbard and in Central Spitsbergen ........... 23 4.1 Deciding how much of an area is ice-cored .......................................................................... 23 4.2 Length, area and orientation measurements ....................................................................... 29 4.2.1 Modelling debris-covered glacier surface against clean glacier size ............................ 29 4.2.2 Calculating headwall and side-slope surface areas ...................................................... 30 4.2.3 Measuring wind direction by snow-drifts ..................................................................... 32 5. Results: Glacier margins along the West Coast of Svalbard and in Central Spitsbergen .............. 33 5.1 Small-scale study of glaciers within 20 km of Longyearbreen .............................................. 33 5.2 Large-scale study of glaciers along the West Coast of Svalbard and in Central Spitsbergen 35 5.2.1 The influence of glacier size .......................................................................................... 35 5.2.2 Terminal shapes and glaciation differences.................................................................. 42 5.2.3 Exceptions to the rule: small glaciers with little ice-core in the marginal zones .......... 44 5.2.4 The influence of headwall area on debris-covered ice ................................................. 47 5.2.5 Surging and debris-covered ice ..................................................................................... 48 5.2.6 The influence of wind on glacier orientation ................................................................ 53 3 Controls on debris-covered glacier fronts in Central and Western Svalbard 6. Interpretation: Glacier margins along the West Coast of Svalbard and in Central Spitsbergen .. 56 6.1 Small glaciers, large debris covers ........................................................................................ 56 6.2 Climatic differences and different types of debris-covered glacier fronts ........................... 58 6.3 Causes for the negative trend between glacier size and the debris-covered area .............. 60 6.4 Surging and debris-covered ice ............................................................................................. 62 7. Introduction to an in-depth study of a Central Spitsbergen glacier: Longyearbreen ................... 66 8. Methods specific to Longyearbreen ............................................................................................. 67 8.1. Geomorphological observations, mapping and debris thickness measurements ................ 67 8.2. Temperature recording ......................................................................................................... 69 9. Results specific to Longyearbreen ................................................................................................ 71 9.1. Formation of Longyearbreen’s debris-covered terminus ..................................................... 73 9.2. Current state of Longyearbreen’s debris-covered terminus ................................................ 76 9.3. Deformation of the debris cover on Longyearbreen’s terminus .......................................... 81 9.4. Temperature recording: Heat transfer in the debris layer ................................................... 85 9.4.1. Background ................................................................................................................... 85 9.4.2. Data analysis ................................................................................................................