Utilization of 6 x 6 cm format vertical aerial photographs for repetitive mapping of surface morphology and measurement of flow velocities of a small glacier in a remote area: Glaciar Soler, Hielo Patagonico Norte, Chile

Using vertical aerial photographs taken manually with a 6 x 6 cm format camera in 1984, 1986 and 1999, the surface morphology of the ablation area of Glaciar Soler, Hielo Patagonico Norte (northern Patagonia icefield), Chile, was studied. Glaciar Soler has an area of 50.9 km(2); the ablation area below the icefall is about 7 km long and 2 km wide. An uncontrolled aerial-photographic mosaic for the area below the icefall was assembled from 40-60 aerial photographs, oil which the surface morphology was mapped from interpretation of stereo pairs of the enlarged photographs (scales of 1: 4500 to 1: 8000). The mapped features include debris-free and debris-covered ices, ogive bands and waves, crevasses, supraglacial streams, moulins, medial moraines, troughs and grooves. A total of 32-34 pairs of ogive bands were recognized, from which an average flow velocity of about 160 m a(-1) was deduced. The spacing of a pair of light and dark ogive bands indicates that the flow velocity ranges from about 350 in a(-1) near the icefall to some 100 m a(-1) near the snout. Comparison of the field-measured data with the ogive spacing indicates that the seasonal variation in flow velocity of Glaciar Soler is very large, probably because of variation in the amount of basal sliding.