At http://geology.gsapubs.org/content/early/2012/03/16/G33117.1.abstract … we have a large body of sand in the northern region of the North Sea basin which is described as extrusive. Where did it extrude from? There is enought sand there to bury Manhattan Island or the whole of London, under several metres in depth. The sand, it seems, vented to the sea floor during the Pleistocene epoch. Does vent imply pump out of the ground?
For some parts of the Pleistocene the North Sea basin was dry land – probably for most of the time.
The explanation, it is claimed, is that high pressure fractured the sea b ed so that fluidised sand moved rapidly through fissures to the surface – and mixed with sea water (or some of that underground water). This allowed the sand to be transported several km to from sheets of sand covering an area 260km in length and up to 125m thick.
The same story can be found at www.livescience.com/31295-giant-sand-mass-discovered.html … where it is almost verbatim. It tells us geologists have found the world's largest extrusive body of sand – so far. The sand erupted across the sea floor – mixed with water. Currently it straddles an oil field (and was found by oil drilling activities). How many other extrusions of sand are hiding under the oceans and seas of the world?