11 - Frost Shattering

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Frost shattering is caused by thermal stress.

It has been found to occur in both Autumn and Spring but from different processes. During Autumn the main processes acting on the ground and rock are freeze thaw cycles and the extent of cracking is determined by the extent of freezing and moisture availability.

Alternatively the spring shattering is caused primarily by refreezing of moisture.

Models of frost shattering:

The volumetric increase of water caused by state change (9%). This must occur in a closed system for pressure to build and cause shattering, often requiring rapid downward freezing sealing pores in the rock.

Segregation Ice Model: expansion of micro-cracks and pores initiated by ice growth.

Thermal Stress: Micro pores exist in rocks with moisture contained, when the Thaw occurs and water changes state the expansion causes the thermal shock and shattering.

Frost shattering of geomorphological importance (Swedish Lappland):

Diurnal and cyclonic freezing occurred more frequently during the summer months. This short term freeze-thaw activity was of low significance to the geomorphic processes, therefore blockfields and talus in lappland can be mainly attributed to the long term annual freeze.

Shallow frost action seems to be more likely during the Autumn period before the snow accumulation (due to insulation).

Evidence for frost bursting is mainly qualitative with reports of rifle - like cracking cited as evidence for frost cracking. There is active debate over the cause of such weathering between ice segregation and hydrofracture.

The study found that the amount of rockfall tended to exhibit a positive relationship with the amount of rainfall. However further analysis revealed that precipitation and moisture availability played two separate roles, moisture within the system aids the initial weathering but also the secondary transport of weathered material.

French 2007 60-79

Nyberg 1993

Matsuoka & Murton 2008

Sass 2005