Caves are formed by the erosive action of water. Over long periods of time, underground water sources dissolve chemicals in the ground or rock, thus creating a hole. When the water levels decrease, we are left with a cave.
1 Additional Answer
There are several factors. You have acidic water flowing, wind and natural earth settling all involved in the formation of caves and how they form.
A cave or cavern is a hollow place in the ground, especially natural underground space large enough for a human to enter. Caves form naturally by the weathering of rock and often extend deep underground....