Determining change points in data completeness for the Holocene eruption record

Changes in data completeness for the Smithsonian Institution’s “Volcanoes of the World” (VOTW) eruption catalogue, by region and for selected countries, are determined and utilised to estimate average eruption recurrence intervals. In the VOTW database, the number of documented volcanic eruptions has increased markedly since the middle of the last millennium. This is largely attributed to population expansion, geological investigation and improvements in detection and recording technologies, rather than an increase in volcanic activity. Simple methods, such as break-in-slope or stationarity tests, can be used to determine changes in data completeness, but often require subjective choices, introducing additional uncertainty. A Markov chain Monte Carlo simulation method for assessing and determining changes in the completeness of natural hazard event catalogues is adapted to determine the completeness of the database. Data completeness is assumed to follow a step-change model, where the probability of documenting an eruption is Volcanic Explosivity Index-dependent before the change point date and 100 % after. A distribution of candidate change point dates is obtained for each region and country subset which allows uncertainty in the data completeness date to be quantified, and for uncertainty in eruption frequencies to be expressed and propagated through statistical models.