A major subfeature of Hualālai is "Puu Waawaa", Hawaiian for "many-furrowed hill", a volcanic cone standing tall and measuring over in diameter. It extends for , and has a prominence of , north of the summit at . The cone is constructed of trachyte, a type of volcanic lava that exists at no other volcano on Hawaii. Trachyte flows move more slowly than the typically "runny" Hawaiian lavas, a characteristic caused by its high (over 62%) silica composition (typical basalt is only 50% silica). Geologists hypothesize that Puu Waawaa originally formed during a pumice eruption a little over 100,000 years ago, and has continued to build itself since then, with at least three distinct trachyte flows recognized. The eruptions, although partially covered by flows from Hualālai and Mauna Loa, have built a distinctive structure known as the Puu Anahulu ridge.