Journal Article

Greenland supraglacial lake drainages triggered by hydrologically induced basal slip

Herring, Thomas, McGuire, Jeffrey J., Shean, David E., Joughin, Ian, King, Matt A., Behn, Mark D., Stevens, Laura A., Das, Sarah B.

2015

Overview

A dense network of GPS observations shows that rapid lake drainage events on the western Greenland Ice Sheet are preceded by period of ice-sheet uplift and/or enhanced basal slip. Origins of Greenland's surface lakes Surface lakes are common during the warm season on the Greenland Ice Sheet, especially in middle to lower elevations. These lakes can drain rapidly, often preceded by a hydro-fracturing event. The mechanism behind the hydro-fracturing, and thus the connection between the lakes and the broader Greenland hydrological system, has been unclear. Now, Laura Stevens and colleagues use a dense network of GPS observations to show that rapid lake drainage events at their study site in western Greenland were preceded by uplift events, likely from water entering the basal system from neighboring moulins (vertical conduits connecting the surface and bedrock). The uplift created sufficient stress in the ice sheet to open the hydro-fractures, thus allowing the rapid lake drainage. Although speculative, the authors suggest that the comparative lack of crevassing in upper elevations might limit the geographical spread of the uplift-fracturing mechanism. Water-driven fracture propagation beneath supraglacial lakes rapidly transports large volumes of surface meltwater to the base of the Greenland Ice Sheet 1 . These drainage events drive transient ice-sheet acceleration 1 , 2 , 3 and establish conduits for additional surface-to-bed meltwater transport for the remainder of the melt season 1 , 4 , 5 , 6 . Although it is well established that cracks must remain water-filled to propagate to the bed 7 , 8 , 9 , the precise mechanisms that initiate hydro-fracture events beneath lakes are unknown. Here we show that, for a lake on the western Greenland Ice Sheet, drainage events are preceded by a 6–12 hour period of ice-sheet uplift and/or enhanced basal slip. Our observations from a dense Global Positioning System (GPS) network allow us to determine the distribution of meltwater at the ice-sheet bed before, during, and after three rapid drainages in 2011–2013, each of which generates tensile stresses that promote hydro-fracture beneath the lake. We hypothesize that these precursors are associated with the introduction of meltwater to the bed through neighbouring moulin systems (vertical conduits connecting the surface and base of the ice sheet). Our results imply that as lakes form in less crevassed, interior regions of the ice sheet 10 , 11 , 12 , 13 , 14 , where water at the bed is currently less pervasive 5 , 14 , 15 , 16 , the creation of new surface-to-bed conduits caused by lake-draining hydro-fractures may be limited.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 704/106/125 / 704/106/242 / 704/2151/2809 / Conduits / Drainage / Glacial lakes / Global positioning systems / GPS / Humanities and Social Sciences / Hydrology / Ice / Ice sheets / Lakes / letter / Meltwater / multidisciplinary / Natural history / Science / Studies