Lava flows are masses of molten rock that pour onto the Earth's surface during an
effusive eruption. Both moving
lava and the resulting solidified deposit are referred to as lava flows. Because of the wide range in (1) viscosity of the different lava types (
basalt,
andesite,
dacite, and
rhyolite); (2) lava discharge during eruptions; and (3) characteristics of the erupting
vent and topography over which lava travels, lava flows come in a great variety of shapes and sizes.