Diurnal Cycles of Meltwater Percolation, Refreezing, and Drainage in the Supraglacial Snowpack of Haig Glacier, Canadian Rocky Mountains

Abstract

Meltwater refreezing and storage in the supraglacial snowpack can reduce and delay meltwater runoff from glaciers. These are well-established processes in polar environments, but the importance of meltwater refreezing and the efficiency of meltwater drainage are uncertain on temperate alpine glaciers. To examine these processes and quantify their importance on a mid-latitude mountain glacier, we measured the temperature and meltwater content in the upper 50 cm of the supraglacial snowpack of Haig Glacier in the Canadian Rocky Mountains. Thermistors and Time Domain Reflectometry (TDR) probes were installed at 10-cm intervals at two sites in the glacier accumulation area from May to September, 2015. A Denoth meter was used to make point measurements for comparison with the TDR inferences of snowpack dielectric properties. These data are supplemented by automatic weather station data, used to calculate surface melt rates and drive a model of subsurface temperature, refreezing, and drainage. We observed a strong diurnal cycle in snow water content throughout the summer melt season, but subsurface refreezing was only significant in May; after this, overnight refreezing was restricted to a thin surface layer of the snowpack. Overnight decreases in water content after May are associated with meltwater percolation and drainage. There was negligible meltwater retention in the snow on a daily basis, but the refrozen water does represent an "energy sink," with 10-15% of the available melt energy diverted to melting refrozen meltwater. This reduces the total meltwater runoff from the site, even though no meltwater is retained in the system.

Mapping Snowmelt Progression in the Upper Indus Basin With Synthetic Aperture Radar

“…Early in the ablation season, the entire depth of liquid water within the snowpack can refreeze overnight (Mätzler and Hüppi, 1989). Later in the season, the bulk of the snowpack more often remains wet with a thin layer of refreeze just at the surface, typically in the first 10 centimeters; in this case, the snowpack remains ripe but the refrozen crust presents an energy deficit that must be overcome before melt can resume the next day (Macelloni et al, 2005;Samimi and Marshall, 2017). The "recycling" of melt water due to nightly refreeze can act as a significant energy sink.…”

“…The "recycling" of melt water due to nightly refreeze can act as a significant energy sink. For example, Samimi and Marshall (2017) concluded that 10-15% of available melt energy for a given season was diverted to warm and melt refrozen meltwater on the Haig Glacier in Canada.…”

“…In early melt seasons of 2015, 2017, and 2018, diurnally different pixels occur at higher elevations than wet snow. As saturated snow does not store water beyond its capillary pressure requirements over time (e.g., DeWalle and Rango, 2008;Samimi and Marshall, 2017), a change in liquid water content due to overnight drainage does not necessarily explain the spatial context of early season diurnal changes in radar response. In other words, if the entire snowpack typically drains to its irreducible water content overnight, explanation (2) does not explain diurnally differing pixels occurring at higher elevations than wet snow in the early melt season.…”

“…Recall that Mätzler and Hüppi (1989) found C-band backscatter to be sensitive to refrozen crusts over a dry snowpack, but relatively insensitive to refrozen crusts over a ripe snowpack (1989). As melt-freeze crusts over a ripe snowpack can occur throughout the melt season (Macelloni et al, 2005;Samimi and Marshall, 2017), the early season prevalence of diurnally different radar signals seems most likely due to a refreeze of liquid water overlying a dry snowpack. If this is the case, diurnally differing radar signals can offer important insight into portions of the snowpack that are experiencing surface melt but not yet contributing to runoff, or still in the warming and ripening phases.…”

In situ measurement of meltwater percolation flux in seasonal alpine snowpack using self potential and capillary pressure sensors

“…Measurement of capillary pressure using 10 porous cup tensiometers was described by Colbeck (1976) and Wankiewics and De Vries (1978), although more recent use is not widely reported. Measurement of water saturation in snow has been accomplished using dielectric methods (Denoth, 1989) and time domain reflectometry (TDR) (Diaz et al, 2017, andSamimi andMarshall, 2017). The use of electrical methods is emerging as a possible approach to measure flux in percolating meltwater.…”