Chemical weathering is very complex, but basically it is the reactions between earth materials and atmospheric components such as water, oxygen, and carbon dioxide. Rain, streams, and seawater dissolve some substances from rock and may cause the remaining substances from the rock to crumble. The main causes of chemical weathering is the dissolving action of water. There are other factors that may cause weathering such as humidity, pollution, acid rain, and wind. There are monuments in Luxor, Egypt that have remained visible for over 3500 years, but when the same ruins are sent to New York as a gift from the government in Egypt, the monument quickly is worn away and is no longer legible.
Caves are also products of chemical weathering.
All in all, the surface environment, grain size, and the climate control the rate of chemical weathering. Rivers, mainly fast moving rivers erodes the land by carrying sediment away from one location and depositing it in another. Gravity moves water down, degrading plains and other landforms over time. Deltas are formed where running water moves into standing water. This slow moving erosional force has formed the Missouri River Valley.