irruption

plural irruptions

1. countableuncountableThe action of irrupting or breaking into; a violent entry or invasion; an inbreaking; an intrusion.

   The Trojan irruption into the Greek camp is related in Book XV of the Iliad.

   2 more examples

   [I]t was not till arts and ſciences began to revive after the irruption of the Barbarians into Europe, that any thing of this kind appeared.

   1748, [Tobias Smollett], The Adventures of Roderick Random. […] In Two Volumes., 2nd edition, volume I, London: Printed for J. Osborn in Pater-noster-Row, →OCLC, page vi

   At that time it was thought that the critical section, in which an irruption of water from the river was to be feared, lay under the Shoots, but this proved not to be the case. Indeed, relatively little trouble was experienced from the Severn. The very serious flooding, which twice submerged part of the works, came from an underground river, (now known as the Great Spring), the presence of which was unsuspected.

   1948 September and October, “Weekend Works in the Severn Tunnel”, in Railway Magazine, page 299

2. countableuncountablebiologyAn abrupt increase of an animal population.

   Extreme rainfall events predict irruptions of rat plagues in central Australia.

3. broadlycountableuncountableAn abrupt increase in the size of a movement or organization.

   How can we explain this irruption of young people self-identifying as socialists?