Land- to lake-terminating transition triggers dynamic thinning of a Bhutanese glacier

Abstract

Abstract. There have been rapid increases in both the number and expansion of the proglacial lakes across High Mountain Asia. However, the relationship between proglacial lakes and glacier dynamics remains unclear in the Himalayan region. Here we present the surface elevation, flow velocity changes, and proglacial lake expansion of Thorthormi and Lugge glaciers in the Lunana region, Bhutanese Himalaya, during the 2000–2018 period using photogrammetry and GPS survey data. The lake expansion and surface lowering rates, and flow velocity field of Lugge Glacier, a lake-terminating glacier, have remained approximately constant since 2000. Conversely, there has been accelerated proglacial lake expansion and a two-fold increase in the thinning rate of Thorthormi Glacier since 2011, as well as a considerable speed-up in the flow velocity field (> 150 m a−1). We reveal that the lake formation and transition of Thorthormi Glacier from a land- to lake-terminating glacier have triggered glacier speed-up and rapid thinning via a positive (compressive) to negative (extensional) change in the emergence velocities. This study provides the first evidence of dynamic glacier changes that are associated with proglacial lake formation across the Himalayan region.

Ice Dynamics and Morphological Changes During Proglacial Lake Development at Exploradores Glacier, Patagonia

“…In addition, longitudinal crevasses (oriented parallel to the glacier centerline) are observed as well as splaying crevasses near the margin (Figure 2). This regime and the observed surface uplift found in profiles (Figures 3C,E), are indicators of glacier deceleration and a compressional regime (e.g., Sato et al, 2021a). Therefore, surface velocity and surface elevation changes observations indicate that within the study area the high ablation rates are partially compensated by the upstream glacier.…”

“…Further work should prioritize establishing an ice-flow dynamic model to test hypothesis/predictions regarding Exploradores Glacier response to climate drivers and calving fluxes (e.g., Tsutaki et al, 2019;Sato et al, 2021a). Efforts should focus on modelling the complete ablation area to explore downwasting rates below the icefall which could be attributed to dynamic thinning (e.g., Tsutaki et al, 2013).…”

“…Moreover, glacier flotation is associated with extensive regimes where surface velocity increases towards the terminus (e.g., Tsutaki et al, 2013;Tsutaki et al, 2019). In the case of Exploradores Glacier, glacier surface velocity decreases towards the terminus showing similar behavior to land terminating glaciers (e.g., Tsutaki et al, 2019;Sato et al, 2021a). This can be interpreted as the glacier has not reached flotation yet, or a coherent section of the lower trunk is well grounded.…”

“…Glacier-lake interaction can often present tipping points or switching behavior: the formation of a proglacial lake and a calving front can shift the glacier from slow to fast retreat (Kirkbride and Warren, 1999). Examples of studies on proglacial lake formation include: the Southern Alps of New Zealand (e.g., Kirkbride, 1993;Kirkbride and Warren, 1999;Purdie and Fitzharris, 1999;Quincey and Glasser, 2009;Dykes et al, 2011), the European Alps (e.g., Tsutaki et al, 2013), Iceland (e.g., Baurley et al, 2020), and the Himalayas (e.g., Haritashya et al, 2018;King et al, 2018;Tsutaki et al, 2019;Sato et al, 2021a). In particular, proglacial lake formation associated with the disintegration of debris-covered glaciers has been generalized in a three-phase sequence of retreat (e.g., Kirkbride, 1993;Purdie and Fitzharris, 1999;Quincey and Glasser, 2009;Sakai et al, 2009;Benn et al, 2012).…”

Ice‐Marginal Proglacial Lakes Across Greenland: Present Status and a Possible Future

“…Ice velocities on the edge of the GrIS are locally enhanced by ice-marginal lakes compared to those from land terminating margins (Figure 2b, Figure SI_1b in Supporting Information S1) typically by a factor of ∼+25%. The association of faster-flowing ice with ice-marginal lakes compared to glaciers terminating on land is relatively well-documented elsewhere (e.g., Baurley et al, 2020;Dell et al, 2019;King et al, 2018;Liu et al, 2020;Pronk et al, 2021;Sato et al, 2021;Sutherland et al, 2020;Tsutaki et al, 2013Tsutaki et al, , 2019Tsutaki et al, , 2011. However, for the GrIS, whilst ice velocities might be higher in the vicinity of lakes than at land-terminating ice-margins (Figure 2b, Figure SI_1b in Supporting Information S1), this does not currently translate into receipt of very much ice (discharge) because; (a) whilst acknowledging the large uncertainty in the ice thickness data set especially on the margins of the GrIS the ice in those areas is thin, at least in comparison to the thickness of marine terminating outlet glaciers (Figure SI_1b and 1d in Supporting Information S1) and, (b) at present ice-marginal lakes on the GrIS are predominantly situated on the lateral margins of glaciers, that is, oblique to the main flow direction, rather than at termini (e.g., Figure SI_1a in Supporting Information S1).…”