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. All in all, the rate of chemical weathering is controlled by the surface environment, grain size, and the climate.
Alluvium is all the sediment that is deposited by running water.
Deltas are formed where running water moves into standing water. The Missouri River Valley has been formed by this slow-moving erosional force. Tributaries are bodies of water which flow into a larger river. These form valleys within a larger valley, leaving hills on each side. Fluvial landscape is the landscape formed by rivers.