Hello and welcome back to Fossils on Friday, where we are continuing to look at igneous rock. Last week we began to explore where igneous rock comes from – molten lava from Earth’s mantle, also called magma.
This week, lets talk more about volcanoes. We’ve already said that many volcanoes occur where there is a fracture in the Earth’s crust, usually along a fault line, where two plates come together. When this happens, the magma is pushed up out of the crust, and onto the surface, becoming lava. The lava then solidifies into brand new rock.
This new rock has come up out of the earth’s crust, meaning it is classified as an extrusive rock, because it has extruded out of the Earth’s crust, and onto the surface.
Extrusive rocks often have brilliant shapes and patterns, due to them being expelled out of the Earth. Volcanoes have different levels of lava viscosity, as well as how much force they are expelling it, which creates different igneous rock formations. Powerful explosions produce lava ‘bombs’, others produce a slow, steady flow, with one layer cooling before another layer forms on top.
There are relatively few volcanoes in Britain, as most of the igneous rock formed intrusively (which we will discuss next week – see if you can work out what it means!). However one prominent British volcano is actually Ben Nevis! The summit is the collapsed dome of an extinct volcano, meaning the volcano itself would have originally been much higher!