To create the island, a 30 meter (98-foot) layer of earth was created on top of the seafloor with 21 million cubic meters of landfill. The material was excavated from three separate mountains. As of 2008, the total cost of Kansai Airport was $20 billion USD, including land reclamation that has been necessary to prevent its continued sinkage (7.1 centimeters per year as of 2008) into the bay.
Kansai opened in 1994 to relieve overcrowding at Osaka International Airport, which now handles only domestic flights. Zoomed-out images of the area here.
(See all Orbital Views here)