Helen Czerski On...Sand

Why Does Sand Go Dry When You Step On It?

- Dr Helen Czerski

There’s something about walking barefoot along a sandy beach, just above the line of the waves, that is always special. Being the first to step on newly smoothed sand is liberating, and it’s as though you’re making a fresh start with every step. But something odd is happening. As each foot presses on the damp sand, you see a circle of lighter coloured dry sand spread out around it, which shrinks back as your foot lifts off. It’s weird, because you might expect that pushing the sand downwards would allow water to flood in. If anything, you’d expect the sand near your foot to get wetter, not drier. But sand is strange stuff, and that dry layer is showing you one of its oddest properties.