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Abstract

Surging glaciers are abundant in the Karakoram. With today’s satellite data their characteristics can be studied in detail. Historic satellite images (back to 1960s) allow extending the observational records into the past, to determine the timing of previous surges and related surge cycles. Whereas the very high-resolution of Corona images provide numerous details about glacier surface characteristics, quantitative assessments (e.g. length changes, flow velocities) are difficult, as the image stripes have strong geometric distortions, which are difficult to correct with standard image processing software.For this study we created orthoimages and DEMs from Corona stereo images acquired in 1965 and 1967 over the central Karakoram. Within this period, two glaciers (Skamri and South Chongtar) surged, allowing us to determine their past length and volume changes. The positive part of the volume change was 0.22 km³ for South Chongtar and 3.24 km³ for Skamri (which is much larger), but mean surface increase is similar (97 and 115 m, respectively). Although the created DEMs have high uncertainties and many artefacts, the derived elevation changes were large enough to determine realistic volume changes. For Skamri Glacier we also calculated averaged flow velocities from manual feature tracking, using an additional orthoimage from 1966. Velocities reached 13 m/d when averaged over 9 months (1965/66) and 2 m/d over 16 months (1966/67). The former value is comparable to the nine-month average of about 10 m/d for South Chongtar Glacier during its recent surge. This surge is still on-going, pushing forward the down-wasting remnants of Sarpo Laggo glacier.