Extended Data Fig. 1: Same-scale comparison of seismic reflection profiles of the Modgunn Vent crater and the Figge Maar blow-out crater in the German North Sea.

a. Seismic reflection profile of the Modgunn Vent crater with its base marked by a red dashed line and down-lapping seismic reflections indicate episodic infill of the crater originally ~80 m deep. b. Seismic reflection profile of the Figge Maar crater with time-converted bathymetric grids from 1995 and 2018 and an original crater floor reconstruction from 1964 revealing the rapid infill of up to 25 m of sediments within a period of only 54 years. The refilling of the 37 m-deep Figge Maar blow-out crater in the southern North Sea demonstrates how quickly eruption induced seafloor depressions can be refilled and may serve as a partial analogue for the Modgunn Vent (Thatje et al., 1999). For the Figge Maar blow-out crater, the strong currents in a shallow water sediment-rich environment provided enough material to fill much of the depression within half a century. Although these conditions imply the Figge Maar infill was likely far more rapid than could be the case for the Modgunn Vent crater, the depositional geometries are very similar to those indicated by seismic reflections within the Modgunn Vent crater. The similar seismic geometries suggest that the crater formed rapidly and some of the material displaced during crater formation may have provided the lowermost crater infill.