Anticrack nucleation as triggering mechanism for snow slab avalanches

Area of Science:

• Snow science
• Geophysics
• Avalanche research

Background:

• Snow slab avalanches are initiated by shear failure in weak snow layers.
• Theory predicts critical crack length increases with decreasing slope for shear propagation.
• Experimental observations contradict this, showing constant or decreasing critical crack length on gentler slopes.

Purpose of the Study:

• To investigate the discrepancy between theoretical predictions and experimental observations of critical crack length in snow slab avalanches.
• To explain the mechanism behind constant or decreasing critical crack length on gentler slopes.
• To identify the conditions necessary for slab avalanche release.

Main Methods:

• Analysis of experimental data on artificially introduced cracks in snow layers.
• Theoretical modeling of fracture mechanics in stratified snowpack.
• Investigation of crack propagation under varying slope angles and snow properties.

Main Results:

• Observed critical crack length remains constant or decreases as slope angle decreases.
• Volumetric collapse of the weak layer during failure is identified as the key mechanism.
• This collapse leads to the formation and propagation of mixed-mode anticracks.

Conclusions:

• The observed phenomenon is explained by volumetric collapse and mixed-mode anticrack propagation.
• Anticrack propagation can occur even with crack-face friction impeding sliding.
• Slab avalanche release may require two distinct conditions to be met: layer collapse and fracture propagation.