The University of Leeds, School of Geography. Characteristics of surge-type glaciers Hester Jiskoot October 1999 Submitted in accordance with the requirements for the degree of Doctor of Philosophy. The candidate confirms that the work submitted is her own and that appropriate credit has been given where reference has been made to the work of others. HESTER JISKOOT CHARACTERISTICS OF SURGE-TYPE GLACIERS Abstract Glacier surging is an internally triggered oscillatory flow instability in which abrupt increases in flow velocity are accompanied by a downglacier transport of ice and often a marked frontal advance (Meier and Post, 1969). The exact mechanism(s) of surging and surge trigger(s) are still largely unknown as are the factors controlling surging. This PhD research explores and quantifies the relations between surge-type glaciers and glacial and environmental characteristics by isolating factors that discriminate surge-type glaciers from normal glaciers, hence the controls on surging. These controls are then used to verify proposed surge mechanisms. Further, variations in surge behaviour are used to distinguish between groups of surge-type glaciers and surge behaviour. Through multivariate logit analysis, a set of glacial, mass balance related, geological, and thermal attributes of a glacier population in Svalbard were tested on the prevalence of surging. Long glaciers with steep slopes overlying fine-grained lithologies younger than Devonian and with orientations in a broad arc from NW to SE are shown to be more likely to exhibit surge behaviour. Further, polythermal regime and elevation span were found to be strongly related to the likelihood of surging. Residual analysis revealed a number of previously unidentified surge-type glaciers, as well as surge-type glaciers with uncommon characteristics. Glaciers in the Yukon Territory, Canada, were also analysed: long glaciers had increased surge probabilities. Fowler’s index, an indication of a linked cavity surge mechanism, was only found to be significantly increasing the likelihood of surging for shorter glaciers. The findings of the logit analysis suggest that in Svalbard, Kamb’s linked-cavity surge theory is not supported, but surges probably take place through a soft bed mechanism, with a possible thermal control. No significant relation between subglacial geological boundaries or mass balance attributes and surging was found. Possible causes of glacier length and substrate controls on surging are subglacial debris composition, longitudinal stress distribution and hydrological instability. The surge history and behaviour of Sortebræ (68°45′N, 27°05′W), East Greenland was analysed and compared to surges in other regions. Sortebræ’s western flow unit surged between 1933 and 1943 and the glaciers main flow unit surged between 1991 and 1995. Vertical and horizontal movements, as well as surface features of the 1990s surge, were analysed in detail using multi-model photogrammetry. The surge affected an area of 335 km2 and resulted in an ice volume displacement of 18.6±0.4 km3, causing a surplus calving flux of 2.3±0.1 to 5.9±0.4 km3 a-1. In less than 2 years the tidewater front advanced 4-5 km. Sortebræ has a quiescent phase of at least 60 years and a surge phase of 2-4 plus years. The behaviour of this surge and others in East Greenland suggests that the surge mechanism in this region resembles that of Svalbard, rather than other regions. Observations of interacting flow units of Sortebræ suggest that restriction of outflow could be a major control on surging. i HESTER JISKOOT CHARACTERISTICS OF SURGE-TYPE GLACIERS Table of Contents Abstract.....................................................................................................................................i Table of Contents .....................................................................................................................ii List of Figures...........................................................................................................................vi List of Tables ............................................................................................................................viii List of Symbols .........................................................................................................................ix Acknowledgements ..................................................................................................................xii Chapter 1: Glacier Surging and Surge-Type Glaciers 1.1 Introduction and thesis aims ..............................................................................................1 1.2 Research approach.............................................................................................................2 1.3 Glacier surging ..................................................................................................................2 1.3.1 Why study surge-type glaciers? .........................................................................5 1.3.2 The spatial distribution of surge-type glaciers ...................................................6 1.3.3 Variations in surge behaviour ...........................................................................9 1.4 How do we recognise surge-type glaciers?......................................................................11 1.4.1 Surface gradient and geometry of surge-type glaciers .....................................12 1.4.2 Surface features of surge-type glaciers ............................................................14 1.4.3 Proglacial features of surge-type glaciers ........................................................18 1.4.4 Summarising diagnostic features .....................................................................20 1.5 Concluding remarks.........................................................................................................21 Chapter 2: Theoretical Framework: Possible Controls on Surge Mechanisms 2.1 Introduction .....................................................................................................................22 2.2 The essential questions on glacier surging ......................................................................23 2.3 Glacier flow: processes and instabilities..........................................................................25 2.4 Surge theories and boundary conditions..........................................................................30 2.4.1 First and untenable theories..............................................................................30 2.4.2 Stress distribution and glacier surging .............................................................31 2.4.3 Thermal controls on surging and thermal instability mechanisms ..................33 2.4.4 Testing factors related to thermally controlled glacier surging .......................36 2.4.5 Hydrological controls on surging and hydrological instability mechanisms ......................................................................................................37 2.4.6 Water lubrication mechanisms .........................................................................38 2.4.7 Testing factors related to lubrication controlled glacier surging......................42 2.4.8 The linked cavity configuration surge mechanism...........................................43 2.4.9 Testing factors related to stability of linked cavities and conduits ..................51 2.4.10 The deformable bed surge mechanism.............................................................52 2.4.11 Testing factors related to substrate instabilities ...............................................55 2.4.12 Factors restricting outflow and controlling surge termination .........................56 2.5 Summary and listing of variables that can be used to test surge theories........................58 ii HESTER JISKOOT CHARACTERISTICS OF SURGE-TYPE GLACIERS Chapter 3: Review of Previous Research Isolating Surge Controls 3.1 Introduction .....................................................................................................................60 3.2 Previous research to the controls on surging ...................................................................61 3.2.1 Research approaches and details of investigated regions.................................61 3.2.2 The surge index and surge probabilities...........................................................63 3.2.3 Bivariate correlations: conditional surge probabilities ....................................66 3.2.4 Multivariate correlations: multiple correlation techniques...............................67 3.3 Results from previous research........................................................................................68 3.3.1 Length and tributaries.......................................................................................68 3.3.2 Slope and elevation ..........................................................................................71 3.3.3 Is length, width, slope or Fowler’s index a primary control on surging?............................................................................................................72 3.3.4 Orientation and channel curvature ...................................................................73 3.3.5 Terrain, geology and substrate .........................................................................74 3.3.6 Thermal regime ................................................................................................75 3.3.7