LUANG PRABANG, Laos -- Travelers heading to the Pak Ou caves, a major tourist attraction on the western banks of the Mekong River, 25 kilometers upriver from Luang Prabang in northern Laos, will see the construction of an enormous 1,460-megawatt hydropower dam. Earth movers and silos dot the denuded hillsides around the dam wall rising from the river. Trucks frequently cross a newly built bridge across the Mekong to deliver construction materials.