Ocean beaches, pounded by relentless large waves, often exhibit a scalloped shoreline. The scalloped beach is highly visible in the center of this picture of a gravel beach on the Pacific Ocean at Lima, Peru. Click on the image for a zoomed-in view.
I don't know the physics of what creates the scalloped
appearance of beaches, but I have my hunches from my very
limited knowledge of hydrodynamics and similar phenomena
elsewhere. I believe that these wavy contours where
the surf meets beach are caused by lateral currents in the
ocean, possibly by oblique incidence of the surf. The
surf this day intersected the beach parallel to the
shoreline, but the scallops could have been made from an
earlier oblique surf and the beach hasn't had time to
re-form. It could also be due to a lateral
current. Whenever fluids of different densities and
resistivities flow past each other, waves tend to form at
the interface with the waves perpendicular to the relative
direction of flow. Leaf-litter on a street
after hard rains is an example (see PPOW
for October 19, 2007). Wave clouds are a similar
February 26, 2010). Sand dunes in a desert are
The scalloped beach also occurs frequently on a smaller
scale. The image at the right is a beach in a cove on
a lake. If the beach is bombarded by repeated waves
from passing motorboats, the waves strike the shore from an
angle and the scalloped shoreline soon appears. The
lake was otherwise calm. The foot prints on the beach
in the photo at right gives the scale - much smaller than
the Lima beach where cars and people are small dots in the
distance. Click on both images for larger views.
Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us. Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to firstname.lastname@example.org.
All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion. These photos and discussions may be used for private individual use or educational use. Any commercial use without written permission of the photoprovider is forbidden.