Abstract
In 2017–2019 a surge of Shispare Glacier, a former tributary of the once larger Hasanabad Glacier (Hunza region), dammed the proglacial river of Muchuhar Glacier, which formed an ice-dammed lake and generated a small Glacial Lake Outburst Flood (GLOF). Surge movement produced the highest recorded Karakoram glacier surface flow rate using feature tracking (~18 ± 0.5 m d−1) and resulted in a glacier frontal advance of 1495 ± 47 m. The surge speed was less than reports of earlier Hasanabad advances during 1892/93 (9.3 km) and 1903 (9.7 km). Surges also occurred in 1973 and 2000–2001. Recent surges and lake evolution are examined using feature tracking in satellite images (1990–2019), DEM differencing (1973–2019), and thermal satellite data (2000–2019). The recent active phase of Shispare surge began in April 2018, showed two surface flow maxima in June 2018 and May 2019, and terminated following a GLOF on 22–23 June 2019. The surge likely had hydrological controls influenced in winter by compromised subglacial flow and low meltwater production. It terminated during summer probably because increased meltwater restored efficient channelized flow. We also identify considerable heterogeneity of movement, including spring/summer accelerations.
Highlights
Hasanabad was a surge-type glacier situated on the north flank of Hunza Valley in the Central Karakoram (Fig. 1)
The active surge phase of Shispare Glacier started with the beginning of the 2017 melt season (April–May) and terminated in June–July 2019
The active surge of Kyagar Glacier, Karakoram began with the onset of the 2014 melt season (April–May) and continued for 15 months (August 2015)[22]
Summary
Hasanabad was a surge-type glacier situated on the north flank of Hunza Valley in the Central Karakoram (Fig. 1). Surge-type glaciers oscillate between brief (months to years) rapid flow and lengthy (tens to hundreds of years) slow flow or stagnation, which are called the ‘active’ (or ‘surge’) and ‘quiescent’ phases, respectively[6] In the former, a large volume of the glacier’s mass is rapidly transferred from an upper ‘reservoir zone’ into the lower ‘receiving zone.’. In the Karakoram, a large surge-like behavioral spectrum of surface movement has been reported, but the processes controlling their evolution may differ on a glacier-by-glacier basis[20,24,25,26,27]. The subglacial processes and conditions are key (e.g., amount of debris, distribution of stored water and temperature gradient)[9,31,32] to understand the diversity of surge-types and surge-like behavioral spectrum Such information is rare or unknown in the Karakoram, because ground-based observations are difficult to acquire. We accomplish the first aim with the use of multi-temporal and multi-sensor satellite images (Landsat 8 OLI, ASTER and Sentinel-2), digital elevation models (DEMs) of difference, and satellite thermal data to assess surface melt
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