Meltwater drainage and iceberg calving observed in high-spatiotemporal resolution at Helheim Glacier, Greenland

Abstract

Marine-terminating glaciers lose mass through melting and iceberg calving, and we find that meltwater drainage systems influence calving timing at Helheim Glacier, a tidewater glacier in East Greenland. Meltwater feeds a buoyant subglacial discharge plume at the terminus of Helheim Glacier, which rises along the glacial front and surfaces through the mélange. Here, we use high-resolution satellite and time-lapse imagery to observe the surface expression of this meltwater plume and how plume timing and location compare with that of calving and supraglacial meltwater pooling from 2011 to 2019. The plume consistently appeared at the central terminus even as the glacier advanced and retreated, fed by a well-established channelized drainage system with connections to supraglacial water. All full-thickness calving episodes, both tabular and non-tabular, were separated from the surfacing plume by either time or by space. We hypothesize that variability in subglacial hydrology and basal coupling drive this inverse relationship between subglacial discharge plumes and full-thickness calving. Surfacing plumes likely indicate a low-pressure subglacial drainage system and grounded terminus, while full-thickness calving occurrence reflects a terminus at or close to flotation. Our records of plume appearance and full-thickness calving therefore represent proxies for the grounding state of Helheim Glacier through time.

Tidewater-glacier response to supraglacial lake drainage

“…1a ). The lakes fill and drain during the melt season 30 , 31 , exposing optically bright surfaces of smooth, previously submerged ice in the days immediately following drainage 26 , 30 (Fig. 1b , Supplementary Figs.…”

“…We prescribe to be zero at both marine- and land-terminating margins of the glacier. This boundary condition represents the approximately hydrostatic pressure expected at the marine terminus, given observations of glacier surface height and bed elevation that indicate the glacier is near flotation on 2007/236 24 and interpretations of a transiently floating terminus in more recent years 31 when the terminus has retreated back to near its location on 2007/236 (Fig. 1a ).…”

Seasonal flow types of glaciers in Sermilik Fjord, Greenland, over 2016–2021

“…If there is some runoff control at Helheim Glacier, this suggests that the subglacial hydrologic system remains inefficient through the melt season. Recent studies using subglacial modeling (Poinar et al, 2019;Sommers et al, 2022) and direct observations of plumes (Melton et al, 2022;Everett et al, 2016), however, suggest a seasonally channelized subglacial environment on the lower reach of Helheim Glacier. These conclusions are not necessarily inconsistent.…”

Partial melting in polycrystalline ice: Pathways identified in 3D neutron tomographic images

“…Despite the large literature on meltwater flow summarized by Fowler and Iverson (2022) there is still considerable debate about structural controls on melt migration as well as permeability creation, but it is clear that meltwater flow paths must exist over a wide range of length and time scales. Although hydrofracturing and crevasse formation (Melton et al, 2022;van der Veen, 2007) may 50 be the most efficient mechanism of permeability development in glaciers, microcracks and shearing may be a smaller-scale mechanism. It has also been suggested that meltwater flow through hydrofractures (crevasses) to the basal region of an ice mass is analogous to magmatic processes (Alley et al, 1988;Weertman, 1971) and this can influence glacial dynamics.…”