Abstract. Glacier surges occur regularly in the Karakoram, but the driving mechanisms, their frequency and its relation to a changing climate remain unclear. In this study, we use digital elevation models and Landsat imagery in combination with high-resolution imagery from the Planet satellite constellation to quantify surface elevation changes and flow velocities during a glacier surge of the Khurdopin Glacier in 2017. Results reveal that an accumulation of ice volume above a clearly defined steep section of the glacier tongue since the last surge in 1999 eventually led to a rapid surge in May 2017 peaking with velocities above 5000 m a −1 , which were among the fastest rates globally for a mountain glacier. Our data reveal that velocities on the lower tongue increase steadily during a 4-year build-up phase prior to the actual surge only to then rapidly peak and decrease again within a few months, which confirms earlier observations with a higher frequency of available velocity data. The surge return period between the reported surges remains relatively constant at ca. 20 years. We show the potential of a combination of repeat Planet and ASTER imagery to (a) capture peak surge velocities that are easily missed by less frequent Landsat imagery, (b) observe surface changes that indicate potential drivers of a surge and (c) monitor hazards associated with a surge. At Khurdopin specifically, we observe that the surging glacier blocks the river in the valley and causes a lake to form, which may grow in subsequent years and could pose threats to downstream settlements and infrastructure in the case of a sudden breach.

Abstract. Glacier surges occur regularly in the Karakoram but the driving mechanisms, their frequency and its relation to a changing climate remain unclear. In this study we use digital elevation models and Landsat imagery in combination with high-resolution imagery from the Planet satellite constellation to quantify surface elevation changes and flow velocities during a glacier surge in of the Khurdopin glacier in 2017. Results reveal that an accumulation of ice mass above a clearly defined steep section of the glacier tongue since the last surge in 1999 eventually leads to a rapid surge in May 2017 peaking with velocities above 5000 m a−1, which is among the fastest rates globally for a mountain glacier. The time series of Landsat imagery reveals that velocities increase steadily during a four-year build-up phase prior to the actual surge and that the surge front advances towards the terminus after the peak has passed on the upper tongue. The surge frequency between the reported surges remains relatively constant at 18 (1999 to 2017) and 20 (1979 to 1999) years respectively. It is hypothesized that the surge is mainly initiated as a result of increased pressure melting caused by ice accumulation, i.e. the thermal switch hypothesis. However, surface observations show increased crevassing and disappearance of supra glacial ponds, which could have led to increased lubrication of the glacier bed. Finally, we observe that the surging glacier blocks the river in the valley and causes a lake to form, which may grow in subsequent years and could pose threats to downstream settlements and infrastructure in case of a sudden breach.

Se documentaron cambios en el paisaje en la Cordillera Blanca y la Cordillera Huayhuash del Perú entre 1936 y 2012, enfocándose en la cobertura de glaciares y de la vegetación, así como en los cambios en el paisaje cultural. La fotografía repetitiva (“repeat photography”, una herramienta analítica capaz de ofrecer ampliamente y rápidamente aclaraciones en relación a los cambios en el paisaje y en el uso de la tierra dentro de una región específica) fue el principal método usado, complementado contestimonios orales y una revisión de la literatura pertinente.Los insumos de base para la investigación consistían enfotografías históricas tomadas por las Expediciones de los Clubes Alpinos ( Alpenverein ) de Alemania y Austria a la Cordillera Blanca en 1936 y 1939, además de fotografías tomadas por F. D. Ayres en 1954 para el National Snow and Ice Data Center en Boulder, Colorado. Los resultados sugieren que, desde 1936, la Cordillera Blanca y la Cordillera Huayhuash han experimentado una recesión glaciar extensa y la formación de nuevas lagunas glaciares. En términos del paisaje vegetal, la cobertura de los bosques nativos de Polylepis parece haber mantenido estable, mientras que el área cubierta por las especies no nativas de Eucalyptus y Pinus parece haber aumentado. Al mismo tiempo, el paisaje cultural muestra claramente la expansión urbana.

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