The process that has occurred when limestone in the earth been eaten away by carbonic acid is known as chemical weathering. Carbonic acid is formed when rainwater reacts with carbon dioxide in the atmosphere. This weak acid slowly dissolves the calcium carbonate minerals that make up limestone, creating a variety of karst features such as sinkholes, caves, and underground drainage systems. Chemical weathering is one of the primary processes responsible for the formation of many of the world's most beautiful and iconic limestone landscapes.