Fig. 2: Orthophoto-mosaics obtained at a depth of 4500 m show the mining imprints on the seafloor.

a Orthophoto-mosaic with 2 mm × 2 mm pixel resolution from part of the second mining strip (Fig. 1b), showing the nodule collector imprints on the seafloor as mining lanes, the “light bulb” turns, and nodule piles. b A sea anemone (Actiniaria)⁸⁸, a benthic animal capable of cleaning itself from sediment⁸⁹, is shown as an example of the resolution achieved. c, d Orthophoto-mosaic of the same seafloor part before (c) and after (d) the mining trial. e Image-derived digital elevation model (DEM) of the seafloor part shown in (d). A depth profile across the caterpillar track (red line) shows the erosion depth caused by the nodule collector and the humps on each side of the track due to sideways sediment extrusion under the caterpillar tracks. The zero-depth refers to the unmined seafloor between the two caterpillar tracks along the same mining lane. The maximum depth shown has been formed after the sediment redeposition and consequently could be smaller than the true erosion depth. f Orthophoto-mosaic of the track of the nodule collector while performing the light bulb turning manoeuvre at the end of a lane and the deposited nodule pile (≈ L 5 m × W 2 m × H 0.9 m). The sideways sediment extrusion under the caterpillar tracks is larger along the “light bulb” turn manoeuvres. g Image-derived DEM of the same area with a pixel resolution of 5 mm × 5 mm. A three-dimensional orthophoto-mosaic of this area is also shown in Supplementary Fig. S1.