These features are caused when fluidised sand "de-waters" and the fluid bubbles up through the sand, pushing the sediment up into a cone shape. Sand volcanoes are common in the Devonian fossil record in UK, and in seismically active areas of the planet. In this case, tectonic activity is unlikely; some form of slumping on the south-west side of the undersea (Wyville-Thomson) Ridge being a more likely cause.