Shield stages The shield stage of the volcano is subdivided into three phases: the submarine, explosive, and subaerial. During this stage of growth, the volcano accumulates about 95 percent of its mass and it takes on the "shield" shape that shield volcanoes are named for. It is also the stage at which the volcano's eruptive frequency reaches its peak. Submarine phase As eruptions become more and more frequent at the end of the preshield stage, the composition of the lava erupted from the Hawaiian volcano changes from alkalic basalt to tholeiitic basalt and the volcano enters the submarine phase of the shield stage. In this phase, the volcano continues to erupt pillow lava. Calderas form, fill, and reform at the volcano's summit and the rift zones remain prominent. The volcano builds its way up to sea level. The submarine phase ends when the volcano is only shallowly submerged. The only example of a volcano in this stage is Kamaʻehuakanaloa Seamount, which is now transitioning into this phase from the preshield stage. Explosive phase This volcanic phase, so named for the explosive reactions with lava that take place, begins when the volcano just breaches the surface. The pressure and instantaneous cooling of being underwater stops, replaced instead by contact with air. Lava and seawater make intermittent contact, resulting in a lot of steam. The change in environment also engenders a change in lava type, and the lava from this stage is mostly fragmented into volcanic ash. These explosive eruptions continue intermittently for several hundred thousand years. Calderas continually develop and fill, and rift zones remain prominent. The phase ends when the volcano has sufficient mass and height (about above sea level) that the interaction between sea water and erupting lava fades away. Subaerial phase 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. The lava erupted in this stage form flows of pāhoehoe or ʻaʻā. During