This week we have some sand from Cannon Beach, Oregon, which is most famous for this big, beautiful rock:
Located on the Oregon coast just south of the Columbia River mouth, I passed through Cannon Beach last summer on my drive to Vancouver.
The most peculiar thing about this sand was that it squeaked when I walked on it. You read that correctly- it made a squeaky noise when you stepped in it, which was a delightful surprise. I had heard about this phenomenon before, but never experienced it myself. “God, that’s weird!” says one Youtuber after running their hands through the sand at Cannon Beach:
This “singing sand”, is due to localized shear: as you step into the sand, it causes the grains to rub past one another and generate sound [Humphries, 1966]. This tends to happen if the sand grains are well-sorted (all more or less the same size) and highly spherical [Lindsay et al., 1976]. In the photograph below, the sand grains don’t look particularly spherical, but they are indeed quite consistent in size (just compare with one of the more poorly-sorted samples we looked at in previous weeks).
However, sand does not always sound so cute: it can also make apocalyptic booming noises. “Booming sands” have been documented before in sand dunes, sounding like the world’s most enormous and terrifying swarm of bees. The sound seems to depend on the grain size and the layer of sand that is avalanching down the slope[Vriend et al., 2007], although there is still some debate about the actual mechanism.
Something to think about the next time you hear a strange noise at the beach or in the desert!
Sources
Andreotti, B., Bonneau, L., & Clément, E. (2008). Comment on ‘‘Solving the mystery of booming sand dunes’’by Nathalie M. Vriend et al. Geophys. Res. Lett, 35, L08306.
Humphries, D. W. (1966). The booming sand of Korizo, Sahara, and the squeaking sand of Gower, S. Wales: a comparison of the fundamental characteristics of two musical sands. Sedimentology, 6(2), 135-152.
Lindsay, J. F., Criswell, D. R., Criswell, T. L., & Criswell, B. S. (1976). Sound-producing dune and beach sands. Geological Society of America Bulletin, 87(3), 463-473.
Vriend, N. M., Hunt, M. L., Clayton, R. W., Brennen, C. E., Brantley, K. S., & Ruiz‐Angulo, A. (2007). Solving the mystery of booming sand dunes. Geophysical research letters, 34(16).
Coastally Curious 