A rootless cone, also formerly called a pseudocrater, is a

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

landform A landform is a land feature on the solid surface of the Earth or other planetary body. They may be natural or may be anthropogenic (caused or influenced by human activity). Landforms together make up a given terrain, and their arrangement ...

which resembles a true

volcanic crater A volcanic crater is an approximately circular depression in the ground caused by volcanic activity. It is typically a bowl-shaped feature containing one or more vents. During volcanic eruptions, molten magma and volcanic gases rise from an ...

, but differs in that it is not an actual vent from which

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

has erupted. They are characterised by the absence of any

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

conduit which connects below the surface of a planet. Rootless cones are formed by

steam explosion A steam explosion is an explosion caused by violent boiling or flashing of water or ice into steam, occurring when water or ice is either superheated, rapidly heated by fine hot debris produced within it, or heated by the interaction of molten ...

s as flowing hot lava crosses over a wet surface, such as a

swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...

, a

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

, or a pond. The explosive gases break through the lava surface in a manner similar to a

phreatic eruption A phreatic eruption, also called a phreatic explosion, ultravulcanian eruption or steam-blast eruption, occurs when magma heats ground water or surface water. The extreme temperature of the magma (anywhere from ) causes near-instantaneous evap ...

, and the

tephra Tephra is fragmental material produced by a Volcano, volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, ...

builds up crater-like forms which can appear very similar to real volcanic craters. Well known examples are found in

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

such as the craters in the lake Mývatn (''Skútustaðagígar''), the Rauðhólar in the region of the capital city

Reykjavík Reykjavík is the Capital city, capital and largest city in Iceland. It is located in southwestern Iceland on the southern shore of Faxaflói, the Faxaflói Bay. With a latitude of 64°08′ N, the city is List of northernmost items, the worl ...

or the ''Landbrotshólar'' of South-Iceland's Katla UNESCO Global Geopark near

Kirkjubæjarklaustur Kirkjubæjarklaustur ( Icelandic for "church farm cloister", pronounced ; often referred to locally as just Klaustur) is a village in the south of Iceland on the hringvegur (road no. 1 or Ring Road) between Vík í Mýrdal and Höfn. It is pa ...

. Rootless cones have also been discovered in the

Athabasca Valles The Athabasca Valles are a late Amazonian-period outflow channel system in the central Elysium Planitia region of Mars, located to the south of the Elysium Rise. They are part of a network of outflow channels in this region that are understood ...

region of

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

, where

flows superheated

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...

in the underlying rocks.

Volcanologist A volcanologist, or volcano scientist, is a geologist who focuses on understanding the formation and eruptive activity of volcanoes. Volcanologists frequently visit volcanoes, sometimes active ones, to observe and monitor volcanic eruptions, col ...

s 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.

Images

Image:MarsCones-ESP_030192_2020.jpg, "Rootless Cones" on

- due to

lava flows Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or unde ...

interacting with

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

( MRO, January 4, 2013) (). Image:Rootless Cones.jpg, "Rootless Cones" on

( MRO, January 4, 2008) () ESP 037643 2060cones.jpg, Rootless Cones, as seen by HiRISE under HiWish program. These group of rings or cones are believed to be caused by lava flowing over water ice or ground containing water ice. 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 The ice quickly changes to steam which blows out a ring or cone. Wikiesp37643 2060cones.jpg, Rootless Cones, as seen by HiRISE under HiWish program. These group of rings or cones are believed to be caused by lava flowing over water ice or ground containing water ice. The ice quickly changes to steam which blows out a ring or cone. Here the kink in the chain may have been caused by the lava changing direction. Wikiesp37643 2060coneslong.jpg, Rootless Cones, as seen by HiRISE under HiWish program. These group of rings or cones are believed to be caused by lava flowing over water ice or ground containing water ice. The ice quickly changes to steam which blows out a ring or cone. Here the kink in the chain may have been caused by the lava changing direction. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. ESP 045384 2065lavaice.jpg, Wide view of field of rootless cones, as seen by HiRISE under HiWish program 45384 2065cones.jpg, Close view of rootless cones with tails that suggest lava was moving toward the Southwest over ice-rich ground, as seen by HiRISE under HiWish program 45384 2065conesclose.jpg, Close view of cones with the size of a football field shown, as seen by HiRISE under HiWish program

References

External links

Pseudocraters and Mars
(PDF file)
Cones and Inflated Lava Flows on Marsvideo and pictures of the formation of pseudocraters at Eyjafjallajökull 2010
{{Portal bar, Solar System Volcanoes Volcanology Volcanic landforms

Images

See also

References

External links