Erosion or corrosion: the wearing away of soil or rock by water, wind, etc.; also the chemical or electrochemical corrosion of materials.
海岸線の浸食で砂浜が年々狭くなっている。
The shoreline is eroding and the beach is getting narrower year by year.
トンネルの鉄骨が浸食を受けて交換が必要になった。
The tunnel's steel frame suffered corrosion and needed to be replaced.