The crossword solution for the term 'crumble gradually' is 'ERODE'. Erosion is a natural process that occurs when wind, water, and other elements wear away at the surface of the earth. It can cause rocks and soil to break down and move from one place to another. Erosion can also occur due to human activities such as farming, construction, and mining. Over time, erosion can cause landforms to change shape and form, leading to changes in the landscape.