Sand Boil

A sand boil, also called a sand volcano or sand blow, is a small cone of sand built up when water under pressure forces its way up through a bed of sand or dirt and ejects sand from a central point, so that the ground appears to boil. The cone slopes settle at the sand natural angle of repose and typically carry a crater at the summit, giving the feature, which ranges from millimeters to meters across, the look of a miniature volcano.