Video S1. Stress_pipes.avi. Stress pipes begin to develop on the upper-edge of the inclined pipe on the left. Swathes of fine sediment can be seen below the pipe and are relics of the pipe migrating upwards to reach its current stable state.

Video S2. Sand_Sheets.avi. The fluidized zone to the right of the centre scale can be seen to widen to ca4 cm diameter before two discrete pipes form and begin venting sediment separately. The pipe to the right is dominant for most of this process, with the pipe to the left stabilising and venting sediment directly to the surface towards the end of the clip.

SED_1230_sm_VideoS1.avi2894KSupporting info item
SED_1230_sm_VideoS2.avi1723KSupporting info item

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