Haleakalā, or the East Maui Volcano, is a massive, active shield volcano that forms more than 75% of the Hawaiian Island of Maui. The western 25% of the island is formed by another volcano, Mauna Kahalawai, also referred to as the West Maui Mountains. The tallest peak of Haleakalā, at 10,023 feet, is Puʻu ʻUlaʻula. From the summit one looks down into a massive depression some 11.25 km across, 3.2 km wide, and nearly 800 m deep.