Final answer:
Unfractured bedrock breaks down more slowly because it has fewer surfaces for weathering agents like water to infiltrate, thus reducing the rate of physical and chemical weathering.
Step-by-step explanation:
Large, unfractured bedrock breaks down more slowly than if it were fractured because the absence of fractures means there are fewer surfaces for weathering agents like water to penetrate and cause weathering. Fractures in rock provide pathways that allow water and other chemical agents to infiltrate the rock structure, accelerating the weathering process. This includes both physical weathering, where rock breaks down into smaller pieces without changing its mineral composition, and chemical weathering, where the minerals within the rock may be dissolved or transformed into other minerals.
Furthermore, fracture-free bedrock has fewer surfaces exposed to environmental factors such as temperature fluctuations, which can lead to thermal stress and physical breakdown. Fractured rocks have more surface area exposed, which increases their vulnerability to these processes. In short, the more intact and unbroken the rock is, the less susceptible it is to the varied mechanisms of weathering.