How dirt cones form on glaciers: Field observation, laboratory experiments, and modeling

Area of Science:

• Glaciology
• Geomorphology
• Environmental Science

Background:

• Dirt cones are natural, meter-scale glacial surface structures composed of ice covered by debris.
• Their formation mechanism, driven by differential ablation and debris insulation, is not fully understood.

Purpose of the Study:

• To investigate the physical mechanisms governing dirt cone formation on glaciers.
• To develop a model that quantitatively reproduces observed dirt cone structures.

Main Methods:

• Field observations of dirt cone formation in the French Alps.
• Laboratory experiments simulating cone development under controlled conditions.
• Two-dimensional numerical simulations coupling discrete element and finite element methods for thermal and mechanical analysis.

Main Results:

• The insulating properties of the debris layer significantly reduce underlying ice melt compared to bare ice.
• Differential ablation deforms the ice surface, initiating grain flow and conic shape development.
• Cone growth ceases at a steady state where insulation balances heat flux from the increased surface area.

Conclusions:

• The insulating effect of debris is the primary driver of dirt cone formation.
• A model integrating thermal and mechanical processes can accurately predict dirt cone morphology.
• Understanding dirt cones provides insights into glacial ablation processes and debris-mantled ice behavior.