We have modeled the complex material and process entities and properties of volcanic eruptions and structures in the Volcanism Ontology (VO) applying several top-level ontologies such as Basic Formal Ontology (BFO), SWEET, and Ontology of Physics for Biology (OPB) within a single framework. The upper level framework separates the entities into investigative and volcanism entities, and each further separated into their own BFO framework. This allows for VO to be one of the best steps towards a domain ontology to cover the complexity found in volcanology. When deployed on the web, VO will be used to explicitly and formally annotate data and information collected by volcanologists based on domain knowledge. This will enable the integration of global volcanic data and improve the interoperability of software that deal with such data.