The Science of Sand Waves, Silver Lake Dunes Edition

Sand Waves

Sand Waves, photo by Charles Bonham

Confession: I probably don’t give Silver Lake Dunes State Park enough love. What an incredible place.

In Scientific American Robert S. Anderson, associate professor of earth sciences at the University of California at Santa Cruz explains why regular, wavelike shapes form when the wind blows over the sand on the beach for a long time:

Ripples in sand, found on both beaches and dunes, are one of nature’s most ubiquitous and spectacular examples of self-organization. They do not result from some predetermined pattern in the wind that is somehow impressed on the surface, but rather from the dynamics of individual grains in motion across the surface. They arise whenever wind blows strongly enough over a sand surface to entrain grains into the wind. The subsequent hopping and leaping of these grains is called saltation. Saltating grains travel elongated, asymmetric trajectories: Rising relatively steeply off the bed, their path is then stretched downwind as they are accelerated by drag forces. They impact the sand surface centimeters to tens of centimeters downwind, typically at a low angle, around 10 degrees. It is this beam of wind-accelerated grains impacting the sand surface at a low angle that is responsible for ripples.

“An artificially flattened sand surface will not remain flat for long. (Try it on the beach or on the upwind side of a dune and see for yourself.) Small irregular mottles in the sand surface, perhaps a couple centimeters in wavelength, rapidly arise and grow once the wind starts to blow hard enough to initiate saltation. They then slowly organize themselves into more regular waves whose low crests are aligned perpendicular to the wind direction and begin to march slowly downwind. Typical ripple spacing is about 10 centimeters, whereas the typical height of the crests above the troughs is a few millimeters. The pattern is never perfect, but instead the ripple crests occasionally split or terminate, generating a pattern that looks remarkably like one’s fingerprint.

Read on for a whole lot more including Michigan Sea Grant educator Walt Hoagman explaining how the speed of wind (and water) over sand influences the waves.

View Charles’s photo background bigilicious and definitely check out his incredible Silver Lake Dunes photos.

More science, more dunes and more summer wallpaper on Michigan in Pictures.

2 thoughts on “The Science of Sand Waves, Silver Lake Dunes Edition

  1. This shot was taken after the high winds in the area last week. If I can get out on the dune early in the morning after a wind storm the footprints have been erased by the wind and the dune is a magical place to commune with nature and enjoy God’s handy work.
    The sand on much of Silver Dunes is hard packed making it easier to walk across, you don’t sink in like you do on Sleeping Bear Dunes. I walk across the dune using the path of least resistance, meaning I don’t walk up a steep dune but walk across the flatter areas to get to areas of interest. Then I’m carful not to walk through areas I might want to photograph. There are many interesting shaped stumps and sand patterns on the dune that I like to photograph so I take the distant shots first then slowly sneak up on on my subject as I go, leaving the close up and macro shots for last.
    I like to say that Silver Dunes is Michigan’s best kept secret, hope you get the opportunity to enjoy it sometime.

    Liked by 1 person

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s