These two clods led to the fragmentation of the Earth's crust, and the first underwater eruptions. The sea floor was filled with lava constructing the first volcanic cones protruding from the sea. Etna is still active, with an average of one eruption every five years. Lava and magna have the same meaning, referring to the process whereby a mass of silicates is melted at high temperatures in which gas, aluminium, sodium, potassium, phosphorus, zinc and other chemical elements are dissolved. There are two different kinds of eruptions, depending on the composition of the lava.
Explosive eruptions occur when the lava is dense due to a big quantity of silicate.
Effusive eruptions occur when the lava is fluid, with a low amount of silicate. In the latter case, the lava flows out from lateral craters in the volcano. Etna is not cone shaped for this reason, the eruptions are normally effusive rather than explosive. The Central crater normally expels only steam, while the other two discharge rocks and ash coupled with explosions and earth tremors. The seriousness of an eruption does not depend only on the amount of lava that is spewed out, but also on the duration of the effusion.