Volcanism magma produces volcanoes characterised by explosive eruptions, while non-viscous (runny) magma produce volcanoes characterised by effusive eruptions pouring large amounts of lava onto the surface. In some cases, rising magma can cool and solidify without reaching the surface. Instead, the cooled and solidified igneous mass crystallises within the crust to form an igneous intrusion. As magma cools the chemicals in the crystals formed are effectively removed from the main mix of the magma (by a process known as fractional crystallization), so the chemical content of the remaining magma evolves as it solidifies slowly. Fresh unevolved magma injections can remobilise more
Lava delta deltas make attractive sites for building and many villages and towns are located on old lava deltas, such as Garachico on Tenerife. Lava delta Lava deltas, similar to river deltas form wherever sufficient sub-aerial flows of lava enter standing bodies of water. The lava cools and breaks up as it encounters the water, with the resulting fragments filling in the adjacent seabed topography such that the flow can move further offshore sub-aerially. Lava deltas are generally associated with large-scale, effusive type basaltic volcanism. Lava deltas are found mainly associated with volcanic islands, particularly those formed at hotspots as they produce