Frost action refers to the process where water in soil or rock freezes and expands, causing physical changes in the material. When temperatures drop, moisture in the ground can freeze, leading to an increase in volume. This expansion can create pressure on surrounding materials, resulting in cracks or displacements. As the temperature rises and the ice thaws, the water can seep into these cracks, repeating the freeze-thaw cycle. Over time, this repeated action can weaken structures, such as roads and buildings, and contribute to soil erosion. Understanding frost action is important in fields like civil engineering and geology.