 Bedrock gets broken down into sedimentary particles that could be transported by various processes. So that breakdown of rock into smaller pieces that are able to be transported is the process of weathering. And there are two general classes of weathering. One is a physical breaking of the rocks and the other is a chemical alteration of the rocks. And they both produce sedimentary particles. So for weathering, we have the physical breaking of rocks. So some of those processes include freeze-baw cycling. And obviously this happens in climates where the water can actually freeze. So what happens in that case is that you might have a little fracture in a rock. So here's your rock. And when it's warm, a little bit of water can filter down into this fracture, liquid water. And then as water freezes, it expands, ice floats on water because it's less dense than that ice. So as it freezes, it puts a force onto the rock on either side and the crack tends to propagate. So this is a process that's really common in cold areas where you get this process. So this process is really common in cold areas where the temperatures get low enough to freeze the water in these cracks. If it's too cold and the water never melts, it's difficult for this to happen. So I describe this as a rock, but it can also happen between crystal grains. So say for example I have some crystals here. A little bit of water can squeeze in between the crystals. And those boundaries between crystals say in a granitic rock that has large feldspars and quartz can actually, it often breaks along crystal boundaries. So a local example of where this type of process happens significantly would be Yosemite National Park where we have granitic plutons and the freeze thought cycling is one of the ways that break the rocks to make those beautiful cliffs. So another way that you can get physical weathering is with salt crystal formation. And this is very similar to the freeze thought cycling in that in this particular case you have a rock with a fracture in it and my water is going to be a different color this time instead of blue. So you end up with water in here and if there are ions in that water, say you're near the ocean, the water evaporates and as it evaporates salt crystals form. So you can get halite forming or carbonate or gypsum and when those crystals form again they put force on the crack on the sides of the crack and force it open. So this salt crystal formation happens in places where you have a lot near the ocean where you have a lot of salt spray. So a third process is simply with temperature changes. So this is less efficient but the basic idea with the temperature changes when something's hot it expands, when it gets warmer it expands and when it gets cold it contracts. And that's true of rocks and minerals and rocks and grains in rocks and particularly since the grains and minerals can be different colors they will have different temperatures and the different mineral properties will also make them expand and contract at different rates. So a dark grain will absorb more heat than a white grain when it's sitting in the sun and so it will end up getting hotter. So we have these temperature changes that are due to the thermal expansion of minerals and grains. So this is particularly noticeable in areas with intense sun and when you have hot days and cold nights. So for example out in the desert after a hot day when the sun goes down there's a lot of heat gets radiated into the atmosphere from the rocks. And I've been in Joshua Tree National Monument and you can actually sometimes hear little pings coming from the rock as the minerals are cooling off and you end up breaking the connections between the crystals and the rock. So this is a lot like the freeze saw cycling when I said that some of the water can get between the crystal boundaries and force the crystals apart that's a big process in the temperature cycling. And then there are also a number of other ways that rocks break. So for example if there's an avalanche of rock as it lands it breaks up. So collisions between rocks when they're in transport break them up. And then of course you can have something like a meteorite impact would cause a lot of fracturing of the rocks as well. So chemical weathering processes are significantly different than the physical ones. In the case of chemical weathering what you have is you have a reaction between water and the minerals in the rock. And there are multiple types of reactions that can happen that depend on the mineral and the composition of the water. But in general we're going to categorize this into two distinct types. One is dissolution and the second one is alteration. In dissolution the main idea is that you have a mineral and you have water. And they react to form ions and the water. So basically the ions will just flow with the water and this process does not actually produce any sedimentary grains on its own. So if you just have straight dissolution you have no sediment grains produced. However you can produce grains of say one mineral that dissolves quite well. An example would be halite which is basically table salt or carbonate minerals, calcium carbonate are ones that tend to dissolve. So those will just go to sodium and chlorine and calcium and bicarbonate ions. This process can produce grains if for example there's a mineral that doesn't dissolve mixed in with these. So a lot of times there's a little bit of quartz in carbonate rock and those quartz grains will be left over from the process of dissolution. But the main idea is that it produces ions that then go flow with the water and don't affect the sediment transport itself. So alteration is a process where you basically have minerals plus water. And it goes to ions, water, and new minerals. So an example of that would be say a feldspar. It says plagioclase which is a calcium feldspar. When it reacts with water it tends to produce calcium ions and clay minerals. And so the alteration produces new minerals and these can be act as sedimentary particles. So this alteration is one of the main processes that give us mud grains. So I mentioned the clay minerals and you can also have iron oxides or pretty common or other metal oxides. So what happens with the chemical weathering is you're basically altering the rock into new minerals or dissolving it and creating ions. With the physical weathering you're just breaking it down into smaller pieces. Thanks for watching.