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. Pseudocraters are also known as rootless cones, since they are characterised by the absence of any magma conduit which connects below the surface of the earth.
Pseudocraters are formed by steam explosions as flowing hot lava crosses over a wet surface, such as a swamp, a lake, or a pond. The explosive gases 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 like the craters in the lake Mývatn (Skútustaðagígar), the Rauðhólar in the region of the capital city Reykjavík or the Landbrotshólar in the southeast of Iceland. Pseudocraters have also been discovered in the Athabasca Valles region of Mars, where lava flows superheated groundwater in the underlying rocks.
See also 
|Wikimedia Commons has media related to: Pseudocraters|
- 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.
- Kvöldfréttir Stöðvar Tvö "Viðtal við Ármann Höskuldsson eldfjallafræðing" Fréttastofa Stöðvar Tvö