A conical body of sand, resembling the form of a small volcano, rarely more than a few metres wide and less than 50cm high. Internally the sand volcano consists of a massive central plug, surrounded by laminated sand paralleling the external form. Sand volcanoes are formed by the extrusion of liquefied sand through a local vent at the surface. The extrusion usually results from a highly liquefied sand below a confining surface layer.