Weathering can be: Physical: Temperature – expansion and contraction; Water – freezing and thawing; Water – waves, rivers (tumbling), rain drops; Wind – sand blasting. Chemical: Rain is a mild form of carbonic acid due to the dissolved carbon dioxide it contains. This can quickly react with some rocks dissolving it away (Limestone) or more slowly on other rocks by dissolving away the weaker elements of the rock holding it together. Biological: Burrowing of animals; Plants growing in cracks where the roots can produce physical pressure on the rocks, or some roots can exude chemicals that weaken the rocks; Wear and tear of rock paths by human traffic. `