How can wet wooden wedges split rocks?

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A diagram displays six types of simple machines with labeled illustrations: inclined plane, wedge, screw, lever, wheel and axle, and pulley, each shown with real-world examples like ramps, axes, screws, seesaws, door handles, and pulleys lifting objects. — simple machine Six simple machines for transforming energy into work.

A wedge is a simple machine that tapers to a thin edge, designed for splitting, lifting, or tightening. When used to split rocks, wooden wedges function by exploiting the natural property of hygroscopicity, which is the ability of wood to absorb moisture.12

When a wooden wedge is inserted into a crack in a rock and then wetted, the wood absorbs the water into its cell walls. This absorption causes the wood to swell, leading to a significant increase in its volume. As the wedge expands within the confined space of the rock's fissure, it exerts a powerful outward force against the stone. This mechanical pressure is sufficient to widen the crack and eventually split the rock apart. This technique has been utilized since prehistoric times as an effective application of simple mechanical principles.321