Contemporary Climatic Factors Affecting Thermal Weathering of Fractured Sedimentary Rocks of the Niagara Escarpment

The Niagara Escarpment is a prominent landform extending from New York State through southern Ontario into Michigan and Wisconsin, that exposes fractured sedimentary rocks of Paleozoic age. The exposed rocks are affected by thermal weathering processes resulting from strong temperature gradients generated during cold winters and warm summers. However, the degree to which these weathering processes are affected by recent, and potential future climate changes, are not well understood. Here we report observations of rock surface and fracture temperature in sedimentary rocks exposed along the Niagara Escarpment in Hamilton, Ontario during the winter, spring, and summer of 2021. Three field sites along the escarpment were selected for in-situ study. At each site, temperature probes were affixed to the rock surface and inserted into a nearby fracture. Analysis of field site characteristics suggests that aspect and exposure to sunlight strongly affect temperature gradients between rock surface and fracture interior. The influence of atmospheric temperature appears to be weaker in the fracture, which experiences smaller magnitude changes with a lag time. Nevertheless, frequent, rapid shifts from warm to subzero temperatures were recorded throughout the winter months. Gradients of 1°C per minute or greater, considered necessary for thermal shock, were seldom observed during cold periods, but were common during the summer months. This suggests that thermal stress plays a more important role in physical landscape changes during the summer, whereas temperature fluctuations that could stimulate freeze-thaw weathering processes predominate during winter months. Climate modelling using the CanRCM4 regional climate model indicates that the magnitude of thermal stresses will increase over the next century, potentially leading to increased fracturing of the escarpment rocks. The resilience of the escarpment rock to weathering and erosion is likely to decrease concurrently due to lowered thermal conductivity, tensile strength, and Youngs Modulus. The field observations reported here, together with model projections of thermal weathering resulting from continued climate warming, allow a better understanding of weathering and erosion processes affecting this important landscape feature.