Temporal changes of Glaciar Mayo and Laguna Escondida, southern Patagonia, detected by remote sensing data

Glaciar Mayo, covering an area of 43 km2, is an eastern outlet glacier of the Southern Patagonian Icefield at its narrowest part. Aerial photographs from 1970, an optical satellite image of 1986 and synthetic aperture radar (SAR) images of the SIR-C/X-SAR, acquired in 1994, were used to investigate changes of the glacier terminus and of an ice-dammed lake, and to derive the surface velocity in the ablation area. In 1970, the glacier was damming a lake, Laguna Escondida, covering 8.6 km2. The analysis of the 1986 image reveals a 56% decrease in the area of the lake, the size in the SAR images from 1994 is similar. The western front of Glaciar Mayo advanced slightly between 1970 and 1986 and then retreated by about the same amount until 1994, whereas the eastern front retreated during both periods. The retreat of Glaciar Mayo is in accordance with the general glacier recession observed during the last three decades for almost all glaciers of the Patagonian icefields. Striking features in the images are two major debris bands across the terminus, the first originating from rock fall before 1959, the second from rock fall between 1970 and 1986. The second band was displaced between 1986 and 1994 with an average velocity of 288 m/year (79 cm/day). For the same trajectory, a motion of 80 cm was derived for a 24 h period in October 1994 with L-Band SIR-C data by means of interferometry. The agreement of the velocities derived by the two methods indicates little seasonal and interannual variability of ice motion, as observed also on the neighbouring Glaciar Perito Moreno.