At rift zones, plates are moving apart and magma comes to the surface and erupts. Volcanoes grow because of repeated eruptions. There are three main kinds, or shapes, of volcanoes based on the type of materials they erupt. Stratovolcanoes build from eruptions of lava and tephra that pile up in layers, or strata, much like layers of cake and frosting. These volcanoes form symmetrical cones with steep sides.
Shield volcanoes form from eruptions of flowing lava.
The lava spreads out and builds up volcanoes with broad, gently sloping sides. The shape resembles a warrior's shield. Cinder cones build from erupting lava that breaks into small pieces as it blasts into the air. As the lava pieces fall back to the ground, they cool and harden into cinders that pile up around the volcano's vent. Cinder cones are very small cone-shaped volcanoes.