Most people know what erosion is? It is when a fluid(commonly water) pushes away an object or a material.
For minecraft, this will make rivers appearing slowly, creating a dynamic map.
How it happen:
Erosion will only appear from water when it is flowing, and will stop when the water can't erode the next block.
When it has reached it's limit(flowing 7 blocks) it will try going downward. to prevent flowing holes through the map, we can say it can't erode anything harder than stone. So the materials that is being eroded is :gravel:, and :sand:.
It will try going downward at all the blocks, but the chances are small untill the limit is reached.
The erosion will happen in one direction when it is started, so when beginning eroding it won't erode any other side creating a hell of water, but it will also begin expanding the width of the river it erodes.
When you see a cave in the real world, it has sometimes appeared from erosion, we may add chalk to Minecraft and chalk may be highly affected by erosion, I won't tell more about chalk, as it's not mainly for this topic.(just wanted to add this, cause of fun :biggrin.gif:)