Eruption and Irruption are homophones i.e two similar sounding words. However their meanings are little different.
Eruption means to burst out like the outbreak of a volcano or a war or a disease
Japan has seen many volcanic eruptions.
Continuous rains caused the eruption of dengue in many parts of north India.
Irruption means a sudden violent breaking in or an invasion
The irruption of Pakistani troops was much condemned by the political leaders.
A huge mob irrupted at the stadium in protest of the National Games.