Spatial and Temporal Glacier Flow Velocity Changes in Southern Patagonia Icefield: 2002-2011

Recent studies of the Greenland and Antarctic ice sheets showed that the ice sheets are thinning but accelerating, and contribute increasingly to global sea level rise. Patagonia Icefield is the largest temperate ice masses in the southern hemisphere, and also contributes to the global sea level rise because most glaciers in this area have been retreating recently. However, the flow velocity fields remain largely unknown. In order to clarify a relation between the calving front's retreat and speedup, it is important to monitor the spatial and temporal changes of flow velocities in Patagonia Icefield. In this study, we measured flow velocity fields of 7 large calving glaciers in Southern Patagonia Icefield (Moreno, Grey, Upsala, Viedma, O'Higgins, PioXI, Occidental), applying pixel-offset (feature tracking) technique to the radar images derived from ALOS/PALSAR and Envisat/ASAR. We assumed that glacier flows parallel to surface slope based on SRTM4 digital elevation model. In addition, we measured positions of glacier front using SAR intensity images, and compared with the temporal changes of flow velocities. Among the 7 glaciers we measured, PioXI glacier and Upsala glacier revealed large temporal changes. PioXI glacier accelerated in 2003, 2005, and 2007, and behaved differently from any other glaciers. The flow velocity at the southern front reached 6.5 m/day in the summer 2003, while it was 1.8 m/day in the summer 2011. In Upsala glacier, the flow velocity increased over time. The flow velocity in the middle part was about 3.1 m/day in 2010-2011, while it was about 1.7 m/day in 2003-2005. The SAR intensity image showed a retreat of the calving front by about 4 km from December 2002 to February 2011.