CLIMATIC INFLUENCES ON THERMAL WEATHERING OF FRACTURED ROCK

In temperate climates, temperature plays a significant role in the weathering of rock outcrops, which are subject to both cold winters and warm summers. Pre-existing fractures are particularly susceptible to seasonality in temperature as they are propagated by thermo-mechanical processes such as freeze-thaw weathering, thermal shock, and fatigue. Climate change in temperate regions will shift the climatic drivers of these processes, with significant implications for fracture formation and propagation. We examined the temperature on the surface of rock outcrops and within fractures along the Niagara Escarpment in Hamilton, Ontario over 16 months to determine how present, and potential future changes in the thermal regime impact weathering processes. Our initial findings indicate that freeze-thaw weathering processes are predominant in winter months, whereas conditions for thermal weathering (e.g., shock, fatigue) exist during the summer. Using the winter-summer transition as an analogue for future climate change, we suggest that warming temperatures and changes in precipitation will shift the weathering regime away from freeze-thaw processes and will enhance the impact of thermal shock and fatigue in temperate regions. Climatic projections, using an ensemble of localized regional climate models, indicate future conditions will increase thermal stresses at fractured outcrops along the escarpment, with a concurrent decrease in thermal shock resistance in the exposed dolostones. This implies that climate change will increase the rate of weathering of fractured rock. While these findings can be generalized to temperate regions, site-specific characteristics such as aspect and lithology strongly modulate weathering processes and should be considered in further work.