Erosion
In nature, we witness soil erosion, where nutrients and particulates are removed from soil and rock. In addition to diffusion, erosion is another action which contributes to coffee extraction through a process you can think of as washing the surface of the grinds.
Sponge Before
Erosion and the Soapy Sponge
Here is an analogy to help you to better understand erosion: Imagine a sponge full of suds you wish to rinse clean of soap as quickly as possible.