Rootless cone

They are characterised by the absence of any magma conduit which connects below the surface of a planet.

Rootless cones are formed by steam explosions as flowing hot lava crosses over a wet surface, such as a swamp, a lake, or a pond.

Well known examples are found in Iceland such as the craters in the lake Mývatn (Skútustaðagígar), the Rauðhólar in the region of the capital city Reykjavík or the Landbrotshólar of South-Iceland's Katla UNESCO Global Geopark near Kirkjubæjarklaustur.

Rootless cones have also been discovered in the Athabasca Valles region of Mars, where lava flows superheated groundwater in the underlying rocks.

[2] Volcanologists witnessed the formation of a rootless cone for the first time in history during a steam explosion in connection with the first eruption of Eyjafjallajökull in March 2010.