mud and sand volcanoes

mud and sand volcanoes Mud and sand volcanoes are positive topographic features that have many of the aspects of normal phreatomagmatic volcanism resulting from explosive interaction between hot magma and water. They are fed from a chamber of mud or sand through clastic dykes or spines so that they extrude at the surface. Mud volcanoes (also referred to as mudlumps or mud/shale diapirs) range in diameter from less than a metre to several hundred metres. They are associated particularly with places where sedimentation rates are high, where there is a large supply of mud, and where methane generates in the near-surface sediments. In front of the present Mississippi delta, for example, suddenly emergent mudlump islands are a hazard to shipping. Others are well imaged on seismic sections across the Barbados accretionary prism, where tectonic compression is thought to have been an important trigger for the migration of high-pressure pore waters, muds, and gases.

Sand volcanoes range in diameter from a few centimetres to several metres. When seen on the surface of bedding planes, they are more or less circular with a central vent and crater and a surface of radially arranged sand-flow lobes with rounded edges. They are the result of liquefied sand being extruded through a local vent to the surface and reflect the release of pressure from a liquefied layer following a shock, perhaps caused by a seismic event or storm waves at the surface.

Harold G. Reading