Glacier surging in the West Kunlun Shan

• Main Author: Chudley, Thomas Russell
• Format: Thesis
• Language: English
• Published: Apollo - University of Cambridge Repository 2016
• Subjects: Austfonna; Svalbard; glacier; Ice cap
• Online Access: https://dx.doi.org/10.17863/cam.8759; https://www.repository.cam.ac.uk/handle/1810/263417

The cryosphere of High Mountain Asia represents the third-largest glacial system on Earth, with a glacierised area of ~40 800 km2 (Bolch et al., 2012) and a mass balance of -26 ± 12 Gt a-1: ~10% of the global contribution of the cryosphere to sea level rise (Vaughan et al., 2013). The glaciers of the Karakoram and West Kunlun Shan represent the second major global centre of surge activity (Sevestre and Benn, 2015) and also mark a region of anomalous glacier behaviour known as the ’Karakoram Anomaly’ (Hewitt, 2005), whereby widespread glacier stability and even growth contrasts with the global norm (Bhambri et al., 2013; Gardelle et al., 2012; Kääb et al., 2015). Despite the motivations presented by this unusual behaviour, understanding of glacial dynamics in the region is underdeveloped due to a scarcity of data and studies in the area, with even the dominant surge mechanism remaining unclear (Quincey et al., 2015). This study aims to expand the current dataset of surging in the region by characterising a series of surges identified in a small range at the western end of the West Kunlun Shan. This site exists between the Karakoram and the site of the one previous surging study in the region (Yasuda and Furuya, 2015), allowing for the analysis of surging behaviour across a wide longitudinal range. The objectives of this study are: (i) to identify the long-term spatial and temporal distribution of surges in the study region; (ii) to assess surge dynamics over the course of the most recent surges; and (iii) to characterise observed surge behaviour in the context of established surge mechanisms and regional climatic and glaciological behaviour. A combination of a decadal-scale range of remotely sensed imagery, manual tracking of terminus position change, and cross-correlation feature-tracking methods are used to identify and characterise surge dynamics in the range. A total of ten glaciers were observed to surge between 1972–2016 – 11.3% of the total population. Statistical analysis showed that these glaciers were more likely to be wider than non-surging glaciers, which is in line with previous findings, and terminate at lower altitudes, which is a new finding that here is linked to the increased likelihood of warm beds at lower altitudes. Distribution is biased to the northern range in the study area, which could be related to differing topographies in the north and south ranges, but could also be linked to geological differences. Surge dynamics do not conform to classical understandings of surge mechanisms. Some characteristics are indicative of thermal (Svalbard-type) surges, with relatively slow velocities and build-up and termination periods lasting months–years. However, some unusual behaviours are also reminiscent of hydrological surges, including shorter return periods (~4 decades) and surge periods (~2–6 years) than typical thermal surges. These factors have been previously identified in adjacent studies (Quincey et al., 2015; Yasuda and Furuya, 2015), suggesting that the unusual behaviours observed across various surge studies in HMA are not anomalous, but instead indicative of a unique surge mechanism that is related to, but distinct from, traditional surge mechanisms. Finally, observations were made of eight glacier surges that are temporally coincident to an unusual degree, which conflicts with understandings of glacier surging as a behaviour forced entirely by internally regulated mechanisms. Although conclusions presented here are highly speculative, links were made to a hydro-thermodynamic mechanism recently put forward by Dunse et al. (2015) to explain hydrologically forced thermal surging on an outlet glacier of the Austfonna ice cap. This conclusion is supported by records of anomalously high temperatures during the surge initiation period, and can also be interpreted in the context of long-term climate changes in the region, recently linked to increased surge incidence in the Karakoram. This study has expanded the record of surges in the WKS, and made an unusual discovery that further validates recent literature proposing a relationship between surging and climate. These findings are important both in terms of understanding more about regional glaciology and climate, but also in better understanding surge behaviour as a whole.