Fig. 2: Tracking the PDCs along the flanks with visible and thermal imagery.
From: Unraveling pyroclastic density current dynamics with multiparameter geophysical sensing
a, b respectively show two snapshots recorded by the LBZ camera during PDC1 and PDC2. The empty blue and red stars, respectively, indicate the approximate initial location of the masses that generated PDC1 and PDC2. ts1 and ts2 mark the approximate start times of PDC1 and PDC2, respectively. The blue and red stars show the position of the pyroclastic front in the visible images at 2-second intervals. tf1 (07:23:08 UTC) and tf2 (15:18:12 UTC) in a, b, respectively, indicate the moments when PDC1 and PDC2 first appear in the video frames. te1 (07:23:30 UTC) and te2 (15:18:24 UTC) indicate the arrival times at sea of the two PDCs. c Exhibits distance vs. time plot for PDC1 (blue) and PDC2 (red) with the corresponding average front velocities (41.6 and 59.2 m/s, respectively). These velocities are well reproduced by numerical simulations (see the Results section). The blue and red lines represent the distance along the SdF calculated at every time step from average front velocities and different friction angles δ. d–g Four thermal images from the ROC camera on 4 December 2022 showing the onset of PDC2. We observe the detachment and downslope movement of the mobilised mass (white dashed profile) that breaks away from the NE crater (NEC, labelled in d) and descends the SdF, triggering PDC2.
