Sands of Time

The Florida plateau, that part of the Earth that holds Florida up out of the ocean ... at least for the moment ... was formed just 530 million years ago. As well as being much larger in the distant past, it wasn't really recognizable as FLORIDA until between four and six thousand years ago. Then you would have found it familiar... bays, estuaries, Everglades, and of course, beaches.

Florida Beaches are a treasure in sand. It is a matter of perspective we don't truly understand while we remain Earthbound. Even from space it is difficult to grasp.

It is a rare day when the entire coastline of the southeastern United States is cloud free at the same moment. January 9, 2009 was nearly such a day, and, from the perspective of the MODIS instrument on the Aqua satellite, the ocean also happened to be sunglint free at the same time.



We often take our beaches for granted, though: Before you curl your toes into the warm beach sand or run splashing into the water, take a moment to partake in the wonderful world of coastal formation! Coastal formation occurs on several scales, ranging from the motions of the planets all the way down to the interactions of molecules of water.

On the largest scale, coastlines are formed from two processes: coastal emergence and coastal submergence. Coastal emergence happens when land emerges out of the water. This can occur, for example, when a mountain range at a plate boundary is uplifted. Imagine the coastline of Chile, closely paralleled with the Andes Mountains. Millions of years ago the Andes were pushed up from the crust, forming a new coastline.

Far more coastlines, however, have been formed by submergence. Coastal submergence occurs when the water level of the ocean rises significantly, flooding formerly inland regions. The entire east coast of the U.S., for example, is a coast of submergence. The majority of today's coastlines are of this type because of the rise in sea level following the last Ice Age.

There are many ways that coastlines are continually changing...Coastal Processes



Beach formation on a more familiar scale deals with actual aggregate movement- SAND. Put simply, the Sand Man's day job is to shovel beach sand, a lot of beach sand. The movement of beach sand happens in two ways. The movement of sand perpendicular to the beach and the movement of sand along the beach. Both are caused by a combination of wave motion water currents, and wind. Wave motion animation.

Sand movement toward and away from a beach is dependent largely on the TYPE OF WAVE. Waves known as spilling breakers, or constructive waves that surge water up on the beach, depositing sand and dissipating the wave's energy. A Plunging breaker, or destructive wave, tends to collapse in on itself, sucking sand away from the beach in a backwash and contributing energy to the following wave.

Currents also have a significant effect on the movement of sand in and out from the beach. If waves are responsible for the movement of sand on and off the beach, then currents are responsible for the movement of sand to and from the waves. Beaches are always on the move! Check out the SWASH?

Imagine a grain of sand being taken away from the beach. As this grain is swirled about in a tempestuous fury of foam and churning water, it is eventually picked up by a current known as a rip current or rip tide. These "rip tides" funnel outward between underwater sand bars and then die out in deeper water. The grain of sand then drifts towards the sandbar, settling down until picked up once again by an incoming wave. That wave will eventually deposit the sand on the beach, repeating the cycle. Because rip tides only occur between breaks in under-water sandbars, they don't have enough force to cause a net movement of sand away from the beach.
(Thank you William Nicoll, http://www.thetartan.org/2005)

(If you're ever stuck in a riptide, swim parallel to the beach and you'll soon escape its grasp!)







Another type of current, known as long-shore drift is responsible for the movement of sand parallel to the beach. Long-shore drift occurs because waves often strike beaches at an angle. When they do this, the waves deposit sand along one direction and pull it away on another. This tends to form a zig-zag movement of sand along the edge of the beach, pushing sand in the direction that the waves are striking. This movement is responsible for the formation of several coastal structures including spits, hooks, tombolos, and coastal bars.

This drift has important consequences for the man-made development of coastal regions. Beachfront worth billions of dollars in property value can disappear as sand slowly moves down the coast. Many coastal towns build erosion control structures along their beaches... not always with the greatest of success.

Groins, jetties, seawalls, and breakwaters are basically walls made of concrete, wood, or piles of rocks in attempts to manage the flow of sand and reduce coastal erosion. The continued over-development of coastal regions is just like building your house on a sea-side glacier. Sure, it may look stable now... but eventually it really is going slip right out from under you and fall into the sea.

It's just a matter of time.




NOTE: AN EXCELLENT REVUE OF THIS MATERIAL IS HERE !


Juliane likes this site... for longshore current


Lexi, you might be interested in the Rubber Ducky study.

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What do you think?


Are we ignoring science when we build right on the beach? ..Is that a good thing?


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