Three Gorges primarily famous for its scenery, the Three Gorges region is also historically and culturally important in China. Many settlements and archaeological sites are in danger of being submerged by the rising reservoir of the Three Gorges Dam. Due to the lithological conditions of its different regions, the valleys of the Three Gorges are narrow in some areas and broad in others. Most narrow valleys occur in regions where there is limestone, which is relatively hard and resists erosion. However, water can flow along deep vertical fractures, eroding underneath. As the limestone bed is gradually undercut, parts of it fall into
Risks to the Glen Canyon Dam of between 500–700 years. Glen Canyon Dam is a concrete arch dam on the Colorado River in northern Arizona in the United States, just north of Page. The dam was built to provide hydroelectricity and flow regulation from the upper Colorado River Basin to the lower. Its reservoir is called Lake Powell, and is the second largest artificial lake in the country, extending upriver well into Utah. The dam is named for Glen Canyon, a colorful series of gorges, most of which now lies under the reservoir. Construction of Glen Canyon Dam started in 1956 and was not finished until