33.9: Wet Sand Drying Underfoot
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When walking on wet sand, you may have noticed that the surface goes dry under your feet. This is not due to water being squeezed out into the surrounding sand. Instead, the water is absorbed into the sand directly under your feet. This is because you are applying a pressure to the sand under your feet as you walk. When pressure is applied to this sand under your feet, water flows into the pores that have expanded due to the relative shearing of sand particles, as shown in the diagram at the top of this page. Once your foot has been removed, the disturbed grains will settle back into a more dense arrangement and the water will be pushed out of the now smaller pores, and the sand appears wet again.
Video provided with kind permission of Ruben Meerman, 'The Surfing Scientist'. rubenmeerman.com/
The video is also available directly from YouTube: https://www.youtube.com/watch?v=1ssTdOt9DKI&feature=youtu.be