THE WEATHERING BOUNDARY LAYER: REVISITING THE CONCEPTUAL MODEL THROUGH STONE CONSERVATION

The Weathering Boundary Layer Model was proposed nearly 10 years ago as an alternative conceptualization of weathering processes. It more accurately considers rock and mineral weathering factors from a microscopic scale (the boundary layer at which weathering reactions take place) rather than from a top-down synoptic scale common to climatic geomorphology. The weathering boundary layer model portrays a factorial relationship of weathering rate as a function of abiotic and biotic weathering agents, physical and chemical properties of the parent material, environmental factors (e.g. temperature, moisture) important at the boundary layer, input and output of material, exposed surface areas, scale, time, and change of conditions over time.

Entrenched ideas are difficult to displace, and the ideas espoused with the Weathering Boundary Layer Model have not yet made a significant impact in pedology and geomorphology, despite the abundance of new research on weathering at microscopic scales. In contrast, researchers involved in stone conservation readily recognize and apply weathering boundary layer concepts. The study and management of architectural and sculptural stone deterioration require an appreciation of microenvironmental factors (to the scale of micropore climates and capillary hydrology), and an understanding of parent material variation at centimeter scales. Stone conservation researchers also tackle the complex synergies of multiple weathering processes operating over time.

The Weathering Boundary Layer Model exists now as a conceptualization. Like Jenny's soil factor relationship, the model is not yet a solvable equation. But, the model sets up a methodology for testing and quantification. The applications are broad, but it appears that inquiry, redefinition, and ultimate validation of the Weathering Boundary Layer Model most likely rests on the progress made in stone conservation studies.