Investigations on Mass Balance and Dynamics of Moreno Glacier based on Field Measurements and Satellite Imagery Dissertation zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaten an der Leopold-ranzens-Universitat Innsbruck eingereicht von Mag. Martin Stuefer Innsbruck) im November 1999 11 ., . ;; )C .• I 2. P.; Abstract The mass luxes and dynamics of Perito Moreno Glacier have been investigated by means of ield mesurements and remote sensing techniques. Moreno Glacier, covering an area of 257.3 km2, is one of the main estern outlet glaciers of the Southern Patagonian Iceield (SPI) . The climate in Patagonia is characterized by westerly winds and wet air rom the Paciic Ocean, which cause abundant precipi­ tation at the SPI; the formidable topographic barrier of the Andes produce sharp local contrasts of climate. High resolution optical images from Landsat and SPOT, as well as SAR images from ERS and RADARSAT satellites were used together with the cartographic maps to analyze the glacier boundaries and to estimate the position of the equilibrium line. The motion ield over the glacier terminus was derived from SIR-C data acquired during a shuttle light in October 1994, applying radar interferometry and amplitude cross-correlation. The ield work was carried out on Moreno Glacier in several campaigns between November 1995 and March 1999. It included ablation and ice motion mesurements at three proiles using stakes, the installation and maintenance of a climate station, and echo sounding of the lake depth close to the glacier front. Using the seismic relection method the ice thickness was mesured along two transverse proiles of the glacier terminus. The measurements along the upper proile, about 7.5 kilometers distant from the calving front, revealed a subglacial trough with an approximately parabolic shape. The annual transport of mass through this proile is about 707 109kga-1 . The maximum ice depth of 684 m indicated a glacier bed rising from 200 m below sea level towards the calving front. The majority of SPI glaciers hs been subject to glacier retreat during the last 40 years. The climate records in Patagonia do not reveal a clear long-term climatic trend. The climate stations in the vicinity of the SPI are sparse, and the few long-term records of air temperature and precipitation are partly inhomogeneous. The few temperature records suggest a warming trend for the region est of the iceields since about 1940. The maritime inluence on Moreno Glacier is shown by continuous meteorological measurements, which are available since November 1995 from the automatic climate station close to the glacier terminus. The mean monthly temperatures of the years 1996, 1997 and 1998 ranged from 0.7°C to 10.1°C. The total ablation of Moreno Glacier is estimated by calculating the mass lx through glacier cross-section and by spatial melting extrapolation. Assuming the glacier to be close to an equilibrium state, a speciic annual net accumulation of 5250 ± 660 kgm-2 is obtained. Small inter-annual variations of ice velocity, a comparatively steep surface in the region of the equilibrium line, and the high ratio of 0.36 of calving lux to net accumulation are probably the resons for the remarkable stability of Moreno Glacier, which is in contrast to other glaciers in this regiOn. a Contents Acknowledgements iv Introduction 1 1 1.1 Background 1 1.2 Patagonian Ice Fields 2 1.3 Previous observations 0 2 Topographic and remote sensing data base 2 6 201 Topographic data of the Moreno area 6 202 Remote sensing data 0 0 0 0 0 0 0 0 0 0 0 0 0 7 20201 Landsat, SPOT and DISP images 9 20202 ERS SAR and RADARSAT acquisitions 10 20203 SIR-C/X-SAR experiment 10 202.4 Aerial photographs 13 Glacier characteristics 3 14 301 Glacier history 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 14 302 Glacier area and estimation of the equilibrium line altitude 17 303 Fluctuations of glacier terminus 0 0 0 0 0 0 18 3.4 Description of glacier surface 21 Field measurements 4 28 401 Climate station 30 402 Ablation 30 403 Stake velocities 44 4.4 Ice thickness 52 405 Geodetic lines and points 55 406 Lake depth 61 Regional climatology 5 64 501 Meteorological stations and data 64 502 Air temperature 66 503 Precipitation 70 5.4 Wind 75 Contents 5.5 Pressure, humidity and radiation at Moreno Base Station . 76 Surface motion by means of SAR 6 83 6.1 Methods . ................. 83 6.1.1 Interferometric motion analysis 83 6.1.1.1 Phase coherence 85 6.1.1.2 Motion analysis 85 6.1.2 Analysis of low direction 93 6.1.3 Amplitude cross-correlation . 94 6.1.4 Comparison of the velocity ield from INSAR and amplitude cross-correlation . 95 n 6.1.5 Measurement uncertainties ... 98 6.2 The motion ield . 98 6.2.1 Comparison to stake velocities 99 On the dynamic behaviour of Moreno Glacier 7 102 7.1 Velocity variation with depth . 102 7.2 Glacier sliding ......... 106 Mass balance 8 112 8.1 Ablation . 112 8.1.1 Areal extrapolation of stake measurements . 113 8.1.2 Estimation of multi-year ablation with degree-days . 115 8.2 Calving rate . 116 8.2.1 Introduction ........... 116 8.2.2 Determination of calving speed . 117 8.2.3 Ice export . 117 8.3 Ice discharge through B proile . 121 8.4 Accumulation . 123 Comparison with other freshwater calving glaciers 9 125 9.1 Characteristics of SPI glaciers . 125 9.1.1 Ameghino Glacier ........... 126 9.2 reshwater calving glaciers in other regions . 132 9.2.1 Nordboglacier ............. 132 Summary and conclusion 10 135 Bibliography 139 A Chronological description of ield activities 147 A.1 Field measurements in November/December 1995 . 147 A.2 Field mesurements in March/ April 1996 . 148 A.3 Field measurements in November /December 1996 . 149 Contents A.4 Field measrements in March/ April 1997 . 150 A.5 Field measurements in November 1997 .. 150 A.6 Field measurements in March/ April 1998 . 151 A. 7 Field measurements in March/ April 1999 . 151 B Positions measured with GPS 152 B.1 Stakes ..... 152 B.2 Seismic stations . 152 C Meteorological station 159 C.0.1 Technical details . 159 C.0.2 Data capture, processing and transfer . 15lll9 C.0.3 Sensors . 160 D Seismograph 161 E Lake depth measurements 162 Acknowledgements The investigations described in this thesis have been carried out within the coop­ eration of a number of people all of whom I am grateful to. My greatest debt of gratitude is to my supervisor Helmut Rott. He gave me insights into a very fsci­ nating and interesting ield. His valuable proposals and his tireless eforts were the driving force to write and inish this thesis. I want to thak Pedro Skvarca, Direcci6n N acional del Antartico of Argentina, for the collaboration and fruitful discussions. Pedro Skvarca's local relationships, knowledge of the region, and his eforts to provide all necessary facilities were of inestimable value for the ield activities. I am grateful to Heirich Miller, the second supervisor of the thesis, for his helpful comments and the uncomplicated logistic support by the Alfred Wegener Institute for Polar and Marine Research. Thanks to all my friends and colleagues of the remote sensing group at the Institut fUr Meteorologie und Geophysik, Universitat Innsbruck, for numerous dis­ cussions and creating nice and productive atmosphere. Special thanks to Andreas Siegel, who provided and applied the interferometry-software and showed a lot of patience in discussions. Special thanks to Thoms Nagler and Wolfgang Rack, who contributed to this work by joining me during ield mesurements on Moreno Glacier, by giving valuable comments, by proof-reading and providing programming abilities to improve the results. The ield activities were carried out with the help of several people. Among others, I wish to thank Alfons Eckstaller from the Alfred Wegener Institute for Polar and Marine Research, who worked in the ield under hardest circumstances and analyzed seismic data. I want to thank Teodoro Tocons, Juan Carlos Quinteros and Stephan Hoinger. Thanks also to Luciano Pera and the Minitrekking Organisation, to Nicolas Benedetti, Berni Roil, and all the mountain guides for their support and the enjoyable hours at the Moreno Base Camp. Especially, I am grateful to all people who helped in .the rescue operation after my accident on Moreno Glacier on 20 March 1996. I like to thank Martin unk for the valuable discussions and Manfred Nothegger for proof-reading. I am very grateful to Erich Heucke for providing an excellent steam-drill, and to ranz Weitlaner for all the electronic solutions. The depart­ ment head Michael Kuhn and numerous people of the Institut fir Meteorologie und Geophysik is gratefully acknowledged. IV Chapter 1 Introduction 1.1 Background Glaciers are climate indicators which ofer remarkable information on former en­ vironmental conditions. In view of increasing greenhouse gases and the difer­ ent regional impacts of global warming, glaciological investigations in the South­ ern Hemisphere are of signiicant interest. Despite the fact that the Patagonian Iceields are the largest ice masses in temperate climate of the Southern Hemi­ sphere, only few glaciological investigations have been carried out in Patagonia so far [Warren and Sugden, 1993]. Field research has focused on only a few outlet glaciers. The Patagonian Iceields hold key palaeoenvironmental information. The study of the glacier dynamics and the glacier mass balances is of main importance for the understanding of past environmental changes. This thesis was supported by the Austrian Science Fund (FvVF) projects Nr.