Pyroclastic Density Currents at Gede Volcano (Indonesia); Understanding Past Events and Future Hazard

1,200 years before present, an eruption at Gede volcano produced pyroclastic density currents (PDCs) with runouts of at least 14 km from the source. Today, more than 150,000 people live on top of the deposits produced by this eruption. To understand the threat to these communities from future PDCs, a better understanding of past events such as this one is required; this can be obtained by recreating the events using a physical model. In this work we used Titan2D to recreate the field deposits of two past eruptions at Gede volcano dated at 1.2 and 1.0 kyrs BP using the information gathered from the deposits to set input parameters where possible. When recreating old deposits such as these, determining suitable model input parameters is challenging; and where pertinent information could not be gathered from the field observations we ran a wide range of inputs for the unknown variables, informed by analogous volcanoes allowing us to find the values that best fit the deposits. These best fitting input parameters were then used to build distributions for probabilistic forward modelling. In 10,000 Titan2D simulations we explored: uncertainty in the start location, initial volume, pile dimensions, and basal friction angle by stochastically sampling from distributions of these parameters. These simulations were used to build a hazard map for Gede showing the spatial probability of PDC invasion, along with hazard curves showing the dynamic pressure exceedance probabilities at important localities around the volcano. This information can be used to mitigate the risk associated with potential future PDC events.