The Rheological Behavior of Firn: Experimental Observations of Dislocation Creep via Grain Boundary Sliding

How does grain size, strain state, and microstructure influence the rheological behavior of ice compaction among glaciers and ice sheets?

Firn_notebook.ipynb

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Experimental results	Mechanism map for firn

Key Points

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• Constant stress laboratory experiments were performed on H20 ice powder samples with roughly uniform grain size varying from 5 to 550 micrometers (µm) in radius.
• Two rheologically-distinct creep regimes emerged, characterized by their grain size sensitivity and stress dependence: dislocation creep (n ~ 3.7, p ~ 0) and disGBS (n ~ 1.6, p ~ 0.9).
• Flow laws resolved the disGBS mechanism as predominantly rate-limiting for natural conditions, such as in glaciers and ice sheets.

Data

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Output from compaction tests (compaction*.csv) and pressure-density profiles (site-name*.csv) are contained in the data/ subfolder.

Paper Figures

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Figure 1: From (a) Breant et al. (2017) (their Figure 3) and (b) Faria et al. (2014) (their Figure 7).

Figure 2: Photographs taken in the laboratory and diagram made with PowerPoint

Figure 3: flow_law_fiting.py

Figure 4: mechanism_maps.py

Table S1: calc_dens_rates.py

Workflow

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The programming workflow is available in Firn_notebook.ipynb, where each .py script is ran in an easy to follow sequence.