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
Ice-marginal lava flow ice sheet's margins. Initially, the lava flow is like any other but when the lava reaches the margins of an ice sheet, the front of the lava flow cools very quickly and thus, forms a barrier (Figure 1). Behind this barrier, the lava begins to pool, ceasing the contact between the hot lava and cold ice. The barrier is left behind as the ice retreats, leaving a thick lava front, which is just a large, steep, and unstable cliff face. The Barrier A fantastic example of a natural lava dam formed from an ice-marginal lava flow is a phenomenon aptly