The event bush is a new formalism for organizing knowledge in various fields of geoscience, particularly suitable for hazard assessment purposes. Acting as an intermediary between expert knowledge and the well-established field of Bayesian belief networks, the event bush allows at the same time a variety of other applications, linking geoscientific knowledge to the field of artificial intelligence and uniting probabilistic, deterministic, and fuzzy approaches. In this paper, we present basic principles, mathematical formulation, guidelines for application, and examples, including the connection with Bayesian belief networks. Further development of the method will include spatial and temporal modelling, implementation in mapping in GIS medium, formalization by means of predicate logic, definition of variable states in BBNs by membership functions based on the event bush semantics, and other applications.