Tidewaterglaciers:frontalflowaccelerationand basalsliding Andreas Vieli, 1,2 Martin Funk, 2 Heinz Blatter 1 1 GeographischesInstitut, * Eidgeno«ssischeTechnischeHochschule,Winterthurerstrasse190,CH-8057Zu« rich,Switzerland 2 Versuchsanstaltfu« rWasserbau,HydrologieundGlaziologie,ETHZentrum,Gloriastrasse37/39,CH-8092Zu« rich,Switzerland ABSTRACT . A numerical glacier-flow model finite-element method) is used to sug- gesttheprocessesthatcontroltheflowbehindthecalvingfrontofatidewaterglacier.The model is developed for grounded calving glaciers and includes an effective-pressure-de- pendent sliding law.The sliding law is implemented by adding a soft basal layer with a variableviscosity.ThemodelisappliedonHansbreen,atidewatercalvingglacierinSval- bard. Comparisonbetween modeled surface velocities and observed velocity data shows goodagreement.Weconcludethattheflowofagroundedcalvingglaciercanbemodeled withaneffective-pressure-dependent slidinglaw. INTRODUCTION The flow dynamics of tidewater calving glaciers is of great in- terestbutpoorlyunderstoodMeier,1994;VanderVeen,1996). Increasing surface flow velocities towards the calving front have been observed on several grounded calving glaciers, in- cluding Hansbreen, Spitsbergen; Columbia Glacier, Alaska Krimmel and Vaughn, 1987); Glaciar Moreno, Patagonia Rott and others, 1998); and Nordbogletscher, Greenland Funk and Bo« sch,1990). Understanding the processes control- ling the flow fieldbehind a calving front is essential for devel- oping a physically based model for calving. It is known that basal sliding strongly affects the flow of grounded calving gla- ciers Kamb andothers,1994; Meier andothers,1994;Van der Veen, 1996). Effective pressure ice-overburden minus water pressure) is suggested as one important controlling factor for basal sliding Iken,1978; Buddandothers,1979; Bindschadler, 1983). ThisstudyconcentratesonHansbreen,agroundedcalv- ing glacier in Svalbard, for which an extensive dataset ex- ists. A numerical glacier-flow model, including basal sliding, is used to suggest the important processes that con- troltheflowbehindthecalvingfront. DATABASEANDFIELDOBSERVATIONS Hansbreen is a tidewater calving glacier situated at Horn- sund, southern Spitsbergen. The glacier covers an area of 57km 2 and is about 16km long Fig. 1). It ends in the sea with a 1.3km wide calving front. The front height above water level is 30^40m. The glacier bed along the frontal 10km is below sea level. Since the establishment of the Pol- ishpolar station inthe vicinityof Hansbreen in1957, several glaciological investigations have been carried out, and an extensive dataset of Hansbreen is available Jania and Kaczmarska,1997). It includes glacier surface topography from photogrammetry, bed topography from radio-echo soundings Glazovskiy and others,1991) and depth sound- ings of the fjord in front of the glacier Gi _ zejewski,1997). Furthermore, annually measured frontalpositions and sur- Annalsof Glaciology 31 2000 # International Glaciological Society * Now Institute for Climate Research. Fig. 1. Map of Hansbreen showing surface solid contour lines) and bed dashed contour lines) topography.The con- tour intervals are 50 m.The location of the stakes, used for velocity measurements by terrestrial survey, are shown with the corresponding stake numbers 1^7) used in the text.The dashed-dotted line indicates the flowline used for the model calculations. 217 Downloaded from https://www.cambridge.org/core. 08 Nov 2021 at 11:42:02, subject to the Cambridge Core terms of use.