Glaciar Upsala, Patagonia: rapid calving retreat in fresh water

Abstract

The calving rates and calving styles of temperate glaciers that calve into fresh water are distinctively different from those of temperate tide-water glaciers. These contrasts are important for interpreting and predicting the response of ice masses to climate change. Glaciar Upsala is a large calving outlet of Hielo Patagónico Sur (southern Patagonia ice field). Its twentieth-century retreat has been climate-driven but significantly modulated by calving dynamics and by the transition from melting to calving at its eastern terminus. Here, the onset of rapid calving in the early 1980s initiated retreat at ≤440 m a−1. The 1992–93 calving rate (vc) is estimated to be 60 m a−1 in a mean water depth (hw) of 67 m. A vc/hw relationship for fresh water based on 14 sites around the world, including seven deep-water sites, confirms both the linear dependency of vc on hw and the contrast between calving rates in tide water and fresh water. As yet, no physical explanation for this contrast exists, but differences in subaqueous melt rates, longitudinal strain rates and crevassing may provide a partial explanation.

Multiple re‐advances of a Lake Vättern outlet glacier during Fennoscandian Ice Sheet retreat, south‐central Sweden

“…In the fjord-like freshwater terminating outlets of the Patagonian icecaps, contemporary ice-front retreat is occurring at 10s-100s m a À1 , an order of magnitude faster than in relatively shallower glacial lake settings in the Southern Alps and European Alps (e.g. Warren et al 1995;Skvarca et al 2002;Warren & Kirkbride 2003). V€ attern margin change rates are at least twice as fast as reconstructed rapid retreat episodes of marine fjord outlet glaciers during the Lateglacial and early Holocene in Greenland (80-100 m a À1 : Young et al 2011;Hughes et al 2012) and Arctic Canada (~60 m a À1 : Briner et al 2009), yet more comparable to cases of fjord retreat from the Norwegian and Svalbard marine margins of the NW European ice sheets (~100-500 m a À1 : Vorren & Plassen 2002;Dowdeswell et al 2008;Mangerud et al 2013).…”

Active ice‐sheet deglaciation and ice‐dammed lakes in the northern Cairngorm Mountains, Scotland

“…lake stage. Studies of modern lake-terminating glaciers provide empirical evidence that water of this depth is associated with a calving rate of c. 100 myr-' (Funk & Rothlisberger 1989;Warren et al 1995). Thus, to maintain the ice dam and a stable lake level, ice velocity towards the Glenmore terminus must have been equal to this calving speed.…”

Calving retreat and proglacial lake growth at Hooker Glacier, Southern Alps, New Zealand

“…The relationship between water depth and calving rate at Hooker Glacier does not follow the generally accepted trend of calving rates increasing as the glacier retreats into deeper water, as have been generally reported elsewhere (e.g. Funk & Röthlisberger 1989;Warren et al 1995). Following Kirkbride and Warren (1999), and Dykes and Brook (2010), a future retreat scenario for Hooker Glacier is presented in Figure 8.…”

“…The Uc-Dw relationship The relationship between Uc and Dw in Hooker Glacier does not appear to follow the trend at other glaciers worldwide (e.g. Funk & Röthlisberger 1989;Warren et al 1995). This trend is of increasing calving rates with increasing water depth.…”

“…Waterline melting causes the development of thermal erosional notches, which promote calving of the subaerial ice cliff (Röhl 2006). The water depth-calving rate (Uc-Dw) relationship established empirically from other lake-calving glaciers (Funk & Röthlisberger 1989;Warren et al 1995) assumes that calving rates will increase as a glacier retreats back into a bedrock overdeepening increasing water depths. The relationship does not require consideration of the processes operating at the terminus (Kirkbride & Warren 1999) and varies between regions, within regions and over time for a single glacier (van der Veen 2002).…”