natural action, natural process, activity, action - a process existing in or produced by nature (rather than by the intent of human beings); "the action of natural forces"; "volcanic activity"

percolation, infiltration - the slow passage of a liquid through a filtering medium; "the percolation of rainwater through the soil"; "the infiltration of seawater through the lava"

change - the action of changing something; "the change of government had no impact on the economy"; "his change on abortion cost him the election"

percolation - the filtration of a liquid for extraction or purification