 Waves make very interesting bed forms because as the wave passes over the sediment surface the water flows in two different directions to make some fundamentally different than current ripples. So if we have waves here, if the waves are traveling to the right, the motion of any given water particle in a wave is going up on one side and down and around on the other. So it makes these circular orbits and as you get deeper into the water those those circles get smaller and then if you have a sediment surface down at the bottom, so here is the sediment. The water can't actually flow up and down as what happens is you end up with water flowing back and forth. So what this means is that when the water is flowing, if the water is flowing fast enough to transport grains, when it's flowing to the right, you end up with grains getting picked up or rolled but picked up by the Bernoulli effect and getting transported in this direction. When the flow is going in the other direction, so the lighter blue in this direction, grains will get picked up and transported in the new downstream. So as the waves passes, the flow direction changes every few seconds. So what this means is that the bed forms are switching back and forth in terms of directions and the transport direction of the grains is also switching back and forth. So if we come over here and draw a ripple, what we'd see is ideally a current ripple. If the flow is going this way, you'd end up with a set of ripples with the steeper slope on the lee side or down flow side, right? But because the waves switch directions, as soon as the wave turns around, you tend to erode off the top of the ripple and it actually wants to go the other direction. So what happens is that instead of propagating in one direction, the ripples actually stay in place. And this image down here is a picture from a lake in British Columbia and you can see that the waves crests are here and they're moving off to the right and then you can see the shadows of the wave ripples in the sediment at the bottom. So if you could look at this over time, if it was a movie, those crests would actually stay in place and so if we have our sediment here, this is our ripple, right here the crests stay in place through time but the sediment gets transported off on one side versus the other. So you'd get a little bit of sediment transport on that side and I'm going to draw it without the erosion since I can't really erase. You get a little bit on the other side and so what happens is it looks fundamentally different than a current ripple because you have lamina that dip in both directions and that dipping direction tells you that the flow was going in two directions because the lamina always dip pointing towards the downstream part of the flow. So we can actually, we can see this lamination in sediments and rocks. So in this particular case, we have the pencil for scale and what we see is we see lamina dipping in both directions and sometimes you can see that some lamina truncate others, for example right there and there are some that are coming down here and are truncated by a lamina over here. And in this particular case, particularly right under the pencil, you can also see that the lamina have a symmetric geometry across the tops. So the second key point is that the ripples crests are symmetric when you can actually see the crests. So we have lamina dipping in two directions and symmetric ripple crests.