The more silica content in the magma the more viscous thicker the magma is. Gas cannot escape easily from a viscous magma allowing it to collect. Gases expand within a magma as it nears the earth s surface where pressures are lower the violence of an eruption is related to how easily gases escapes from the magma.
Basalt Is A Dark Fine Grained Igneous Rock With Generally 45 55 Silica Sio2 It Is Mostly Very Liquid And Feeds Effusive Ha Igneous Rock Basalt Rock Basalt