The falls had a total drop of about 375 feet (114 metres). They were formed when the Paraná River, after crossing the red sandstone Maracaju (Mbaracayú) Mountains, was forced through canyon walls and narrowed abruptly from a width of 1,250 feet (381 metres) to 200 feet (61 metres). The churning water created a deafening noise that could be heard for a distance of 20 miles (32 km). A constant rainbow hovered over the site. The falls probably represented the greatest volume of falling water in the world, and they were a tourist attraction for many years. The Itaipu (Itaipú Dam) hydroelectric plant nearby, which was completed in 1982 and in 2004 increased in capacity to 14,000 megawatts, totally submerged the falls. The reservoir thus created covered an area of 521 square miles (1,350 square km). The Itaipu complex of dams and spillway curves almost 5 miles (8 km) across the Paraná River and is one of the world's largest hydroelectric plants.