The effects of environmental changes on weathering, gravitational rock deformation, and landslides.

Abstract

AbstractThe effects of climatic change on the processes of weathering, slow and long-term gravitational deformation of rocks, and rapid landslides are discussed. Weathering processes, which result in landslide materials, create weathering profiles during variable time periods ranging from tens of years to geologic time. Additionally, weathering determines the location of potential slip surfaces or landslide behaviour. However, the characteristics of weathering profiles are poorly understood. Some types of rocks are weathered rapidly and form weathering profiles that favour landsliding; slopes composed of those rocks are affected by environmental change through weathering. Unwelded ignimbrite is one of the most vulnerable rocks with recurrence intervals of landsliding less than a few hundred years. Other vulnerable rocks include marine mudstones and sandstones. Weathered granite is also vulnerable to weathering because it is reweathered when it is exposed by erosion. Reweathering of granite results in an abrupt weathering front that forms the slip surface during heavy rains. Gravitational deformation of a rock mass (mass rock creep) proceeds gradually but continuously, sometimes concentrating at a specific depth but other times spreading over various depths beneath a slope. The distributed deformation creates many fractures, eventually changing the rock mass to rock debris; the debris is supported by plant roots but may fail if the support is lost after logging, wildfire, or environmental changes, or with further deformation. Changes in groundwater conditions affect the stability of rock slopes. Groundwater that drains from a rock mass under a temperate climate would be locked in if the temperature drops and the resultant freezing of the rock surface creates a membrane surrounding the rock mass. Such a membrane effect could generate a rockfall on a steep rock cliff because of the increase in bulk weight.