Rootless cone

A rootless cone, also formerly called a pseudocrater, is a volcanic landform which resembles a true volcanic crater, but differs in that it is not an actual vent from which lava has erupted. They are characterised by the absence of any magma conduit ("root") 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. The water from the wetland heats up and forms steam underneath the lava. The explosive gases eventually break through the lava surface in a manner similar to a phreatic eruption, and the tephra builds up crater-like forms which can appear very similar to real volcanic craters.

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.

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.Kvöldfréttir Stöðvar Tvö "Viðtal við Ármann Höskuldsson eldfjallafræðing" Fréttastofa Stöðvar Tvö

Martian rootless cones Rootless cones have also been discovered in the Athabasca Valles region of Mars, where lava flowed over superheated groundwater in the underlying rocks.Jaeger, W. L. et al. (2008) Morphologic Characteristics and Global Distribution of Phreato-volcanic Constructs on Mars as seen by HiRISE, Lunar and Planetary Science XXXIX PDF. Retrieved 2010-07-11. Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473 Many such rootless cones have been imaged by the HiRISE camera on the Mars Reconnaissance Orbiter (MRO).

Rootless cone

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