Science, Maths & Technology
Why do volcanoes erupt?
...physical processes occurring within a plinian eruption column make it convenient to describe it in three parts. [Ejecta] A plinian eruption column, showing the gas thrust region, the region of convective ascent, and the umbrella cloud. In the lower part of the column, fragments are driven upwards by the force of expanding gas in the conduit. This is called the gas thrust...