Rootless cone

A rootless cone, also known as a pseudocrater or explosion crater, is a volcanic landform that resembles a true volcanic cone but is not directly connected to a magma chamber beneath the surface. Instead, it is formed by phreatic explosions caused when lava flows over a wet surface, such as a marsh, lake, or ice-covered area. The intense heat of the lava flash-boils the water, generating steam explosions that eject surrounding material (typically tephra and underlying sediments) into the air. This material then accumulates around the explosion vent, gradually building a cone-shaped structure.

Unlike true volcanic cones, rootless cones do not have a feeder pipe extending deep into the Earth's mantle. They are solely surface features related to the interaction of lava with water or ice. Multiple rootless cones can often form in clusters along the path of a lava flow. Their size and shape depend on the amount of available water and the volume and flow rate of the lava. The term "rootless" refers to the absence of a magmatic root or conduit.