| 英文摘要： |
Unlike glaciers in other parts of the world, Karakoram glaciers seem to be stable or gaining in mass in response to global climate change, a phenomenon known as 'the Karakoram anomaly'. Many of the glaciers experience irregular, frequent, and sudden advances (surges) that pose an increasing threat of ice dam lake formation and subsequent outburst flooding throughout the region. In this study, we document 179 glacial lake outburst floods (GLOFs) that occurred from 1533 to 2020 in five major valleys. Sixty-four of the events took place after 1970, and 37 of these had remote sensing imagery that covered the GLOF formation to breaching sequence. Thirty-six glaciers were associated with GLOFS due to ice-front advance building ice barriers in rivers. The Kayger and Khurdopin glaciers are the most hazardous examples, being responsible for 31.8% of major GLOFs in the entire Karakoram. Using a cross-correlation feature-tracking technique on remote sensing imagery, we analyzed ten surge glaciers and documented six surge events from 1990 to 2019. Results show periodic surge cycles for the Khurdopin, Kyager, Shishper, and Chilinji glaciers of c. 15-20 years, with a surge velocity in the mid-2010s higher than that of the late 1990s for all studied glaciers. The higher velocity of a glacier increases the risk of flooding downstream of the terminus because the transfer of a huge ice mass towards the terminus during the surge is a key factor for formation and reformation of series of ice-dammed lakes, thus determining the magnitude and frequency of outburst flood events. The response of Karakorum glaciers to global warming and climate forcing, comprising a continuum of glacier mass gain, ice thinning and ice advance, has resulted in lake formation and ice dam failures. We predict the frequency of GLOFs will increase in the future. These findings support the increasing anomalous behavior of glaciers in the Karakoram region. To synthesize the detailed observations, a conceptual model is presented of ice-dammed lake formation and GLOF initiation in response to glacier surging. |
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