Definition: A savanna biome is a woodland biome which has seasonal water availability and includes, across its entire spatial extent, trees spaced sufficiently far apart to allow an unbroken layer of grass, sedge (Cyperaceae) or rush (Juncaceae) communities to live.
Definition: An opening, or rupture, in the Earth's surface or crust, which allows hot, molten rock, ash and gases to escape from deep below the surface.