Volcanoes can be formed by plumes of magma originating in this layer of the Earth below the crust
... A "
mantle plume" is a bubble of material which rises to the surface layers from the 
deep ... Magma consists of remelted material from Earth's crust and fresh ... of 
crust can be forced back down into the deeper regions of the Earth,... [DOC] [TLE] Earth's Interior & Formation of Magmas - Tulane University [PAR] Jan 24, 2007 ... Magmas do not form everywhere beneath the surface of the Earth.