What Was The Cause Of The Eruption At Mount St Helens In 1980?

Well the magma built up very viciously in the underground rocks and then the molten rock exploded from the top of the volcano.  The tectonic plate underneath the volcano must have swerved in collision to the one next to it.  (Scientists are unaware of exactly what caused the volanic eruption but we now think that it must have been something to do with the carbon dioxide levels and methane levels in the magma.) I hope this helps i work for the NAV National Aviates of Volanoes we work in finding out exactly what causes a volcano and how we can prevent it good luck!