Once a volcano has added enough mass and height to end frequent contact with water, the subaerial substage begins. During this stage of activity, the explosive eruptions become much less frequent and the nature of the eruptions become much more gentle. Lava flows are a combination of pāhoehoe and ʻaʻā. It is during this stage, that the low-profile "shield" shape of Hawaiian volcanoes is formed, named for the shape of a warrior's shield. Eruption rates and frequencies peak, and about 95% of the volcano's eventual volume forms during a period of roughly 500,000 years.