Karst sinkholes | Luoquanyan Village of Xuan’en County, Hubei province

Karst landscapes are formed primarily by the dissolution of bedrock … Rainwater, which is slightly acidic, picks up carbon dioxide as it runs through the soil, becoming more acidic. It then trickles, rushes and flows through cracks in the bedrock, slowly widening them into tunnels and voids. Over time, if a cave chamber gets large enough, the ceiling can gradually collapse, opening up huge sinkholes.