Sinkholes, like landslides, are a form of ground movement that can happen suddenly and with little warning, and that can cause major damage. Sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or rocks that can naturally be dissolved by ground water circulating through them. As the rock dissolves, spaces and caverns develop underground. Sinkholes are dramatic because the land usually stays intact for a while until the underground spaces just get too big, then a sudden collapse occurs. These collapses can be small and have little impact on people, or they can be huge and can occur where a house, road, or other structure is on top. In the United States, the most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania, in what is known as 'karst' topography. Sinkholes are also a problem in many other places around the world