Fig. 4: Explosive activity on 3 and 4 November and the corresponding electrical and volcanic tremor signals.

a Pictures of different explosive eruption styles on 3 and 4 November: (1) Ash-rich lava fountaining at 23:30:53 UTC on 3 November, producing a plume of approximately 3 km a.s.l. and a flash of volcanic lightning. Courtesy of Francisco Cáceres Acevedo. Reproduced with permission of the copyright holder; (2) Mild ash emissions at 07:44 UTC on 4 November, producing a small ash plume; (3) Gas jetting at 13:11 UTC on 4 November; (4) Strong ash emissions at 17:08 UTC on 4 November, producing a plume of approximately 3 km a.s.l.; (5) Lava fountaining without the generation of a large ash plume in contrast to (1). Picture was taken at 21:51 UTC on 4 November. Courtesy of Francisco Cáceres Acevedo. Reproduced with permission of the copyright holder. b–f Measurements taken between 21:00 UTC on 3 November until 00:00 UTC on 5 November. Numbered pictures in panel a show prevalent activity of the periods 1-5 reported in panels b-f. b Voltage (V) measured by the primary (black line) and secondary (orange line) antennas of BTD2. Close-up plots of the different electrical signatures are shown in Supplementary Fig. 4. c Electrical discharge rate (discharges per 5 minutes) as green vertical bars (left y-axis) and the maximum value of the absolute voltage measured by the primary antenna per 5 minutes in purple (right y-axis with log-scale). d Seismic tremor amplitude, showing the LP amplitude (dash-dotted line) on the left y-axis and the VLP amplitude (solid line) on the right y-axis. The peaks were produced by earthquakes. e First principal component (PC1), which is mostly related to changes in the absolute tremor amplitude. f) Second principal component (PC2), which mainly reflects changes in the volcanic tremor source mechanism.