Apo, Mount (äˈpō) [key], active volcano, 9,690 ft (2,953 m) high, on S Mindanao island, the Philippines. It is the highest peak of the islands. Mt. Apo has a snowcapped appearance but is actually covered with white sulfur. Mt. Apo National Park (281 sq mi/728 sq km; est. 1936) is there.