Message 73 of 155 (752308)
03-10-2015 12:42 PM
Reply to: Message 6 by Faith
03-09-2015 10:47 AM
waves, big waves, small waves, breaking news about breaking waves
| ... ALL the sediments have sediments above and below them. This can happen by settling out or by successive deposition by waves. Just think it through with an eye to how it COULD HAVE WORKED. |
Breaking waves pick up objects, the more energy in the breaking waves (a function of height) the larger is the material picked up
Large storm waves scour the beaches of sand and transport it offshore into bars. Smaller waves that break over the bars can pick up the finer material and transport it back to the beach. I see this all the time at my parents house on Cape Cod. One of the things I would like to do is install a camera that takes a picture at each low tide so you can observe how the beach moves back and forth.
These storm waves will pickup any silt or sand layers, so your global waves have no hope of leaving them undisturbed while they lay another layer down -- the fines will be mixed up.
Waves that don't break do not move sediment -- this is why the storm waves drop the sand etc as it is carried away from shore once the sediment is carried out to the area of non-breaking waves.
Curiously people have studied how waves actually work (I know a scientist at Scripps Oceanographic that actually studies waves ... ), and so they KNOW how waves work.
Let's look at non-breaking waves from above:
In a longitudinal wave the particle displacement is parallel to the direction of wave propagation. The animation at right shows a one-dimensional longitudinal plane wave propagating down a tube. The particles do not move down the tube with the wave; they simply oscillate back and forth about their individual equilibrium positions. Pick a single particle and watch its motion. The wave is seen as the motion of the compressed region (ie, it is a pressure wave), which moves from left to right.
Notice the red dots moving back and forth. The only way material is transported is when the wave breaks and falls into the trough. Now a cross section view (same link):
Water waves are an example of waves that involve a combination of both longitudinal and transverse motions. As a wave travels through the waver, the particles travel in clockwise circles. The radius of the circles decreases as the depth into the water increases. The movie below shows a water wave travelling from left to right in a region where the depth of the water is greater than the wavelength of the waves. I have identified two particles in yellow to show that each particle indeed travels in a clockwise circle as the wave passes.
Notice how the (circular) movement diminishes with depth, and at about 3 wave-heights (crest to trough) it is essentially still. If the bottom is above this range it will cause the wave to trip, which is why waves break on shores.
A wave breaking on shore will pick up and suspend material with the size depending on the wave height\energy. Large waves will deposit rocks on the beach and keep sand and silt suspended as the waves return. This can cause scouring on the beach and I have seen rocks exposed at low tide covered by sand before a storm and then uncovered by the storm (and the sand/silt/fines that are suspended are deposited on a sand bar just out of the active wave action area.
Non-breaking waves do not transport material from one location to another, they do not disperse sediment or suspended particles.
Breaking waves scour the bottom and suspend particulate matter in the turbulence of the breaking wave, with the size of the suspended particles related to their size and settling velocities.
Your succession of waves (a) will not deposit graded layers on top of graded layers and (b) will not leave layers of silt behind.
| ... Just think it through with an eye to how it COULD HAVE WORKED. |
The above is (somewhat simplified) how it DOES WORK. I don't have to imagine it.
|This message is a reply to:|
| ||Message 6 by Faith, posted 03-09-2015 10:47 AM|| ||Faith has responded|
|Replies to this message:|
| ||Message 75 by Faith, posted 03-10-2015 1:04 PM|| ||RAZD has responded|