Changes in water in the american southwest lake mead is an artificial lake formed by the hoover dam, covering parts of both arizona and nevada. it has a surface area of 640 km. the area has been experiencing a drought since 2000, and the water level has dropped 43 meters (140 feet). how many cubic kilometers (km) of water have disappeared during this drought? hint: recall that volume is equal to depth x length x width, and assume the area of the lake is the same at the surface as it is at 43 m depth.