Fig. 5

FlowDIR output for forecasting the directionality of the 2018–2019 BAFs at Merapi volcano (Indonesia), the direction of the flow is shown in all panels with a red shaded area. a The DEM (Darmawan et al. 2017, 10 m resolution) with initialisation points (N = 49) shown as red crosses, and the crater buffer outlined in black. b The travel direction probability for each secondary intercardinal direction bin, calculated using the azimuthal elevation difference (AED) functionality. The standard error on the 49 initialisation points is shown for each bin as a red bar located at the wider end of the probability bin. Diamonds at each bin’s centre point depict the elevation difference. The presence of larger markers would indicate directions that exceed the elevation threshold (unlikely to be overtopped), however, in this case study all diamonds are the smaller size (likely to be overtopped). c The least cost path (LCP) matrix which shows the summed inverse propagation step number for each cell in the path taken from the initialisation point to the buffer limit, over all initialisation points shown in panel a, with more likely exit points indicated by higher values at the buffer limit. d The elevation profile for the buffer extent as outlined in panel a