Why does dry sand at the beach change color when wet?

Question

(asked by an actual 5yo)

In: Physics

Answer 1

Same reason clothes are darker when they’re wet.

The sand/fabric absorbs light a certain way, and you perceive the rest (i.e. you perceive whatever is being sent back your way).

When water fills the microscopic voids and spaces it also takes a part in that process. Water scatters light fairly well and even the small amounts present in the spaces (either in clothing or between grains of sand) will scatter some light.

That means a bit less light is getting sent back to you, which the eyes/mind perceive as “darker”