SPATIAL DISTRIBUTIONAND CHANGE IN THE SURFACE ICE-VELOCITY FIELD OF VESTFONNA ICE CAP, NORDAUSTLANDET, SVALBARD, 1995–2010 USING GEODETICAND SATELLITE INTERFEROMETRY DATA BY VEIJO A. POHJOLA 1 , POUL CHRISTOFFERSEN 2 , LESZEK KOLONDRA 3 , JOHN C. MOORE 1,4,5 , RICKARD PETTERSSON 1 , MARTINA SCHÄFER 4 , TAZIO STROZZI 6 AND CARLEEN H. REIJMER 7 1 Department of Earth Sciences, Uppsala University, Uppsala, Sweden 2 Scott Polar Research Institute, University of Cambridge, Cambridge, UK 3 Faculty of Earth Science, University of Silesia, Katowice, Poland 4 Arctic Centre, University of Lapland, Rovaniemi, Finland 5 College of Global Change and Earth System Science, Beijing Normal University, 13 Beijing, China 6 Gamma Remote Sensing and Consulting AG, Gümligen, Switzerland 7 Institute for Marine and Atmospheric Research, Utrecht University, Netherlands Pohjola, V.A., Christoffersen, P., Kolondra, L., Moore, J.C., Pettersson, R.S., Schäfer, M., Strozzi, T. and Reijmer, C.H., 2011. Spatial distribution and change in the surface ice-velocity field of Vestfonna ice cap, Nordaustlandet, Svalbard, 1995–2010 using geodetic and satellite interferometry data. Geografiska Annaler: Series A, Physical Geography. 93, 323–335. DOI: 10.1111/j.1468-0459.2011.00441.x ABSTRACT. During 2007 we launched a geodetic campaign on the Svalbard ice cap Vestfonna in order to estimate the velocity field of the ice cap. This was done within the frame of the IPY project KINNVIKA. We present here the velocity measure- ments derived from our campaigns 2007–2010 and compare the geodetic measurements against InSAR velocity fields from satellite platforms from 1995/96 and 2008. We find the spatial distribution of ice speeds from the InSAR is in good agreement within the uncertainty limits with our geodetic mea- surements. We observe no clear indication of seasonal ice speed differences, but we find a speed-up of the outlet glacier Franklinbreen between the InSAR campaigns, and speculate the outlet is having a surge phase. Key words: Arctic ice cap, Austfonna, GPS, ice speed, InSAR, outlet glacier, surge Introduction The rapid increase of surface air temperatures in several regions of the High Arctic during the last decade, and the projected increase of Arctic tem- peratures in the future is prompting close attention to the stability of the Arctic ice caps. While much of the focus has been on the Greenland ice sheet (e.g. Rignot and Kanagaratnam 2006), mountain glaciers and ice caps in the Arctic are at present, and will over the present century, be a large source of eustatic sea level change (Radic and Hock 2011). One of the large issues at present is to improve the knowledge of how the dynamics of ice masses may change due to warming. Basal lubrication from penetration of surface meltwater to the bed is known to temporarily accelerate the flow of ice along the terrestrial margin of the Greenland ice sheet (Zwally et al. 2002; van de Wal et al. 2008; Phillips et al. 2010) and the mechanism is also observed on Arctic ice caps (Boon and Sharp 2003; den Ouden et al. 2010). Marine-terminating outlet glaciers in ice caps and ice sheets also respond similarly in that they are modulating ocean currents and water mass properties in addition to the atmo- spheric forcing (Holland et al. 2008). To fully understand contemporary cryospheric change, we need observations from a large sample of ice masses, small as well as large, and situated in various settings. Local regimes likely produce a large variability of how the physical processes of glacial flow are affected. For example, the island Nordaustlandet, Svalbard features two large ice caps side-by-side, Austfonna (8120 km 2 ) and Vest- fonna (2402 km 2 ; Fig 1). The mass balance of these two ice caps is seemingly out of phase with each other. Dowdeswell et al. (2008) reported a close to zero mass balance for Austfonna over the past © The authors 2011 Geografiska Annaler: Series A, Physical Geography © 2011 Swedish Society for Anthropology and Geography DOI: 10.1111/j.1468-0459.2011.00441.x 323