Predicted and observed glacier pulsations in the Hissar-Alay of Central Asia

Abstract. Surge-like glacier instabilities in Central Asia remain underexplored, particularly in regions where such phenomena have low intensity or are poorly captured by existing inventories. In 1980, Glazirin and Shchetinnikov (GS1980) proposed a classification method to calculate the spatial distribution of "pulsating" glaciers in the Hissar-Alay range, predicting unstable flow at 194 candidates – over 20 % of the examined sample – and claiming highly accurate detection (above 75 %). This stands in contrast to the very limited number of pulsations found in subsequent studies, which typically report fewer than 10 surge-type glaciers within the region. Here, we address this discrepancy by reassessing the GS1980 predictions, using a newly compiled multi-sensor satellite dataset covering nearly six decades. We systematically examine glacier dynamics in the region, assessing ice flow instabilities from changes in terminus position, ice thickness, and surface morphology. We identify 171 glaciers that exhibit pulsating behavior, corresponding to 25 % of the sample. Flow instabilities tend to be modest in scale, with slow advances and long active phases (mean duration of 14 years). We find that the GS1980 model shows some ability to distinguish pulsating from stable-flowing glaciers; however, its predictive power is lower than claimed, due to the simplifying assumptions of its morphology-based approach and the uncertainties in the input data. Our results indicate that pulsations in the region are more widespread than previously reported, but fall at the weaker end of the spectrum of glacier instability, which may not be well represented by a sharp binary classification (surge-type versus stable). As more detailed satellite records become available, we suggest that a more nuanced framework may be useful to recognize and interpret subtler instabilities of small glaciers.