A Speed Limit on Ice Shelf Collapse through Hydrofracture

Abstract

Increasing surface melt has been implicated in the collapse of several Antarctic ice shelves over the last few decades, including the collapse of Larsen B Ice Shelf over a period of just a few weeks in 2002. The speed at which an ice shelf disintegrates strongly determines the subsequent loss of grounded ice and sea level rise, but the controls on collapse speed are not well understood. Here we show, using a novel cellular automaton model, that there is an intrinsic speed limit on ice shelf collapse through cascades of interacting melt pond hydrofracture events. Though collapse speed increases with the area of hydrofracture influence, the typical flexural length scales of Antarctic ice shelves ensure that hydrofracture interactions remain localized. We argue that the speed at which Larsen B Ice Shelf collapsed was caused by a season of anomalously high surface meltwater production.

Observations of Buried Lake Drainage on the Antarctic Ice Sheet

“…The GrIS has been shown to be a self‐regulated system, whereby surface melt volume is not correlated with annual ice flow velocity, at least in marginal regions (Tedstone et al., 2015; van de Wal et al., 2015), and surface lake drainage events have less of an effect on basal lubrication and ice flow than previously assumed (Poinar et al., 2017). In contrast, Antarctic ice shelves that buttress 75% of the continent (Fürst et al., 2016) (significantly more than the floating ice around Greenland Hill et al., 2017) are vulnerable to meltwater‐induced flexure and fracture, processes that pose a direct threat to ice‐shelf stability (Banwell et al., 2013; Robel & Banwell, 2019; Scambos et al., 2000, 2009), and therefore mass loss from the AIS as a whole (Rydt et al., 2015; Scambos et al., 2004). We hypothesize that the lake observed in our study may drain recurrently, based on Landsat 8 evidence that water ponds in the same topographic depression (Figures S5a–S5d) during the melt season on an almost annual basis.…”

“…Meltwater plays an important role in mass loss for the Greenland (GrIS) and Antarctic (AIS) ice sheets. GrIS mass loss is primarily driven by surface runoff (Enderlin et al., 2014; van den Broeke et al., 2009), while on the AIS, meltwater that ponds on the ice shelves surrounding the continent may indirectly lead to mass loss by invoking flexure and fracture (Banwell & MacAyeal, 2015; Banwell et al., 2013; Robel & Banwell, 2019). This ponding meltwater decreases ice‐shelf stability (Scambos et al., 2000, 2009) and may allow faster flow of glaciers and ice streams to the ocean (Rydt et al., 2015; Scambos et al., 2004).…”

Long‐Term Increase in Antarctic Ice Sheet Vulnerability Driven by Bed Topography Evolution

“…The model includes ice cliff failure and ice shelf hydrofracture (Text S2), which are recently proposed mechanisms for enhancing rapid marine ice sheet retreat (Pollard et al, 2015) that may be required to reproduce past sea level variability (DeConto & Pollard, 2016). These processes remain controversial (Clerc et al, 2019; Edwards et al, 2019; Robel & Banwell, 2019), and the retreat rate caused by marine ice cliff instability is poorly constrained. We therefore present ice sheet model results with and without these processes included.…”

Marine Ice Cliff Instability Mitigated by Slow Removal of Ice Shelves

“…Satellite images show Larsen B disintegrated over at least a week (Rack & Rott, ). A recent model of ice‐shelf collapse by hydrofracture of melt ponds (Robel & Banwell, ) proposed that the rate of ice‐shelf collapse is limited by localized interactions between melt ponds, and that Larsen B was a special case of exceptionally rapid collapse due to an anomalous melt season. As such, the removal of a buttressing ice shelf prior to the potential initiation of runaway cliff failure may take days to weeks (longer than the relaxation time of ice), implying the elastic limit of our solution is not physically relevant.…”