Year of Award

2025

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Geosciences

Department or School/College

Department of Geosciences

Committee Chair

Joel Harper

Commitee Members

Natalie Bursztyn, Kelsey Jencso

Keywords

firn, temperature gradient metamorphism, Greenland Ice Sheet, meltwater infiltration

Subject Categories

Glaciology

Abstract

The microstructure of polar firn governs its porosity, permeability, and compaction rate, and is therefore important to studies of surface elevation change, heat and gas exchange, and meltwater infiltration on ice sheets. Previous work on high-elevation, dry-firn has identified two distinct atmospheric drivers of kinetic grain growth in deposited snow, but both mechanisms result in near-surface mm-scale layers. In this work, we show that meltwater infiltration through surface wetting fronts and deep preferential flow in the Greenland Ice Sheet (GrIS) percolation zone leads to the formation and preservation of centi- to decimeter scale layers of faceted firn, ranging from faceted squares to depth hoar, up to 16m below surface. We analyze nearly a decade of subsurface temperature time series along a transect in the Western GrIS percolation zone to characterize the thermal regimes affiliated with meltwater infiltration mechanisms and whether conditions are conducive to kinetic grain growth. Furthermore, we compute vapor flux from temperature to estimate the magnitude of potential faceting, as well as employ SNOWPACK to simulate grain sphericity changes due to wetting fronts and preferential flow. Results suggest 2 primary faceting “mechanisms,” both intrinsic to the seasonal generation and infiltration of meltwater: “wet layer onset” and preferential flow/piping. Wet layer onset was the most significant, leading to the largest sphericity reductions and best-preserved faceted layers. Moreover, the rate at which the wetting front descended was determinant of the degree of faceting, with faster wetting fronts producing low sphericity, enduring faceted layers. As more of the GrIS experiences melt, constraining the influence of faceted layers on meltwater storage, surface elevation change, and chemical species transport will become increasingly important. This work is organized into three chapters: Chapter 1 presents the main findings of the research in a condensed format intended for publication; Chapter 2 contains a literature review on snow metamorphism and ice sheet faceting; Chapter 3 expands upon Chapter 1, featuring extended methodologies, additional results, and discussion.

Download

Included in

Glaciology Commons

Share

COinS
 

© Copyright 2025 Kirsten Leigh Gehl