 So today I want to talk about glaciers, ice sheets, and ice transport. So one of the interesting things about ice is that the viscosity of ice is very hot. It flows very, very slowly, and there's a lot of friction within the flow. And that means that the Reynolds number, which is the flow depth, the flow speed, the density over the viscosity is very, very low. So it's well less than 500, which is our boundary between transitional and laminar flows. So glaciers are laminar. So the flow being laminar means that the transport of sediment by ice is fundamentally different than it is in a water or an air type flow. So this is one key aspect of glacier transport, or ice transport that's really important. So the second thing I want to talk about is the weather and characteristics. So there are several key aspects of this. One of the main things that defines where glaciers and ice transport are prevalent is the cold temperatures. So the cold has two effects, one of which is that the chemical weathering is very slow. And so you tend not to have very much chemical weathering going on in glacial environments. And the second thing is that the freeze thaw aspects. And this is, of course, the physical weathering. And there are lots of details about how pressure melting of the ice at the bottom of a glacier can produce liquid water that can then squeeze into cracks under the glacier to enhance the freeze thaw. Sometimes glaciers will freeze to the bottom and can pluck rocks out of the bottom. So there are a lot of ways that this freeze thaw weathering processes entrains sediment into the glaciers. And that is mostly a physical process. So we have physical weathering dominates as the second part of this. And if you think about that in terms of the sediment composition, this really implies that the composition of sediment transported by glaciers is the same as the composition of the material that it is eroding. So we have this freeze thaw process, but there's also a second process that can count in under weathering, but I'm going to put it separate because it's really important for glaciers. So that's the grinding of grains. So that does fit within the physical weathering here. The idea is that if you have ice and you have rock, the ice is flowing over that rock and it's laminar. So the grains and ice crystals are all moving parallel to each other. And what happens is if you have a rock here that's near the base of the flow, it gets pulled downstream in the ice flow and it tries to go in a straight line. Just like in a water flow, at the base of the flow there's a lot of friction. And what happens is this rock gets dragged along the bottom here. So you have lots of friction and that friction ends up grinding the rock away. So often what you see in terms of a rock, say you have a rock and it's ground along the bottom, you end up with flat surfaces called facets. So you end up with rocks that have these unusual, very flat surfaces. You also get the products of that grinding. When you grind something away it produces very, very, very fine particles. And that is called rock flour. It's called flour because it has a very similar texture to wheat flour or something that you would bake with. The third thing is that as these rocks scratch, the bedrock, the rocks are grinding over, also get smoothed out. And so we call these, they get smoothed out to the point it's flat like pavement. So we call them glacial pavements. And then sometimes there are weaknesses in the rock down below or there's a particularly hard rock sitting above that and they often have grooves or striations. And those striations would be on the glacial pavement and can also be on the faceted clasts. Thanks for watching.