High‐frequency observations of melt effects on snowpack stratigraphy, Kahiltna Glacier, Central Alaska Range

Abstract

With an increased volume of melt on many of the world's glaciers, study of how meltwater affects the properties of glacial snowpack becomes essential to our understanding of how glaciers will respond to climate change. We address this problem by studying how snow properties changed on sub‐daily timescales on the Kahiltna Glacier, Alaska, between May 26 and June 10, 2010. During this period, we dug 1.8‐m‐deep snow pits twice daily to record the stratigraphy of melt layers, snow hardness, grain size, and density and sampled for hydrogen isotopic composition (δD) on four occasions. From these data, we show that 65% of the melted surface snow infiltrates and refreezes in the snowpack. This leads to a densification of the snow, a 729% increase in volume of melt layers, and a homogenization of isotopic and physical snow properties. From visual and stratigraphic observations, we show that meltwater flow within the snowpack is conducted primarily along lenses and pipes, where melt layers later form, but that more homogeneous capillary‐based flow is also important. Finally, we show using isotope ratios that post‐depositional alteration is exacerbated with increased melt extent, using the δD profile below a volcanic ash layer as a case study. In the future, similar studies would benefit from this high‐frequency monitoring approach to assessing snowpack evolution, as it allows for a greater understanding of short duration processes. New directions for study would include longer‐term monitoring efforts over a wider spatial snow pit network. Copyright © 2012 John Wiley & Sons, Ltd.

Isotopic evidence for lateral flow and diffusive transport, but not sublimation, in a sloped seasonal snowpack, Idaho, USA

“…This loss of upper portions of the snowpack through melting without major isotopic consequences deeper in our profiles supports the view that melt propagates through discontinuous, preferential pathways, such as pipes and lenses, or as lateral flow along stratigraphic boundaries [e.g., Colbeck , , ; Marsh and Woo , ] until shortly before melt out. Such a process has been imaged directly in warm snowpacks [ Humphrey et al , ; Winski et al , ; Eiriksson et al , ] (Figure S4) and apparently has little isotopic impact on the residual snowpack until wholesale melting late in the season.…”

A 400‐Year Ice Core Melt Layer Record of Summertime Warming in the Alaska Range

“…The cold temperatures throughout the summer at the drill site are also ideal for forming discrete melt layers as opposed to grain growth or slush formation common at warmer sites (Pfeffer & Humphrey, 1998;Winski et al, 2012). The collection of two parallel cores from the same site allows us to quantify the uncertainty of the melt record due to microspatial variations in the snowpack (Winski et al, 2012).…”

“…Refrozen melt layers form when excess energy at or near the glacier surface leads to melting, and meltwater percolates down through the snowpack until freezing at the 0° isotherm (Koerner, ; Pfeffer & Humphrey, ; Pfeffer et al, ; Winski et al, ). Upon burial and compaction into firn and ice, these refrozen melt layers are distinguishable as darker layers with few or no bubbles, surrounded by bubbly ice with well‐defined grains.…”

Strain-rate estimates for crevasse formation at an alpine ice divide: Mount Hunter, Alaska

“…and higher on Mount McKinley (5750 ma.s.l.) (Winski and others, 2012). We therefore assigned a no-slip basal boundary condition.…”