 Meandering rivers form on low gradient areas that where the water is driven down the slope but the actual dynamics of the flow and erosion allow the channel to deviate from the main downslope direction. So I've drawn a map view of meandering river here and the slope will be going down this way but the dynamics of the variations in the Reynolds number including the flow speed and the water depth cause the river to build out these bends. And so if we look at one of these meanders here what's happening is that the flow is coming around like this and it's being deflected by the outside of the bend. And that means that the there's a force of water into the bend here. So that you tend to get erosion where the flow is going into the river bank. Also the water on the outside of the bend has to move a farther distance than the water on the inside of the bend. And so you also have a higher flow speed on the outside than the inside. So the flow speed outside is greater than the flow speed on the inside of the bend. And that means that the Reynolds number is higher and so you end up with erosion more erosion sort of all the way in through here. And because the water is moving more slowly on the inside you tend to get deposition on the inside of the bend here. So this dynamic of erosion and deposition tends to drive the formation of these river bends or meanders. So we can look at a cross-section of the river channel and look at that variation as well. So if we look at a cross-section through here. So what happens through time is our flow speed is highest over here and the water depth is pretty large. So over time this part goes away and sediment accumulates on the inside of the bend here. So you end up with a systematic channel migration going this way and what you accumulate in the rock record is what gets deposited on the inside of the bend as long as it's not later, eroded later. So this inside of the bend is called the point bar because it's sort of the point around which the river is migrating. And so over time you end up with a migration of the channel and the accumulation of sediment. We can look at the grain sizes that are likely to be deposited in the channel and we have the deepest point here and we have faster flow on this side. So the deepest point is called the Thalweg and in general on the outside of the bend relative to Thalweg is where you have the erosion and you have the deposition on the inside. So this point is the point with the highest Reynolds number where sediment is actually being deposited. So you end up with the coarsest sediment deposited here and all the grain sizes are transported there and up here is where you can only accumulate finer sediment. The coarsest grains don't get transported up there but you can get the finer sediments deposited in this stone here. So as the point bar migrates what you see are coarser grains overlaid by finer grains going upward. And so the next layer would have some of the coarser grains, finer grains with each part of the migration. We also get distinctive sedimentary structures that form reflecting the migration of bed forms from the deepest part of Thalweg of the flow up to the finer parts on the point bar. So we have the fastest flow down at the bottom and so typically that would be upper planar lamination or trough cross stratification here. So we can get the upper planar and the trough cross stratification with the trough cross stratification being due to the sinuous dune crest or regular dune crest migrating. Planar cross stratification is also common and that's from the migration of straight crested dunes. So we can get that as a sedimentary structure and then as the flow speed goes down and the water depth goes down grain size is smaller and we tend to get a ripple cross lamination that is reflecting also reflecting that that lower flow speed. The deposits are very nicely organized with a clear grain size variation from coarser to finer and sedimentary structures that show a higher flow upward into a lower flow. Thanks for watching.