Aerial view of a channelized a'a flow on Mauna Loa Volcano, Hawai'i. Credit: J. D. Griggs / U.S. Geological Survey.
A lava flow is a mass of molten rock that pours onto 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.