Volcanism
Volcanism, vulcanism, volcanicity, or volcanic activity is the phenomenon where solids, liquids, gases, and their mixtures erupt to the surface of an
Cause of volcanism
For volcanism to occur, the temperature of the mantle must have risen to about half its melting point. At this point, the mantle’s viscosity will have dropped to about 1021 Pascal-seconds. When large scale melting occurs, the viscosity rapidly falls to 103 Pascal-seconds or even less, increasing the heat transport rate a million-fold.[3]
The occurrence of volcanism is partially due to the fact that melted material tends to be more mobile and less dense than the materials from which they were produced, which can cause it to rise to the surface.[3]
Heat source
There are multiple ways to generate the heat needed for volcanism. Volcanism on outer solar system moons is powered mainly by tidal heating.[1] Tidal heating caused by the deformation of a body’s shape due to mutual gravitational attraction, which generates heat. Earth experiences tidal heating from the Moon, deforming by up to 1 metre (3 feet), but this does not make up a major portion of Earth’s total heat.[4]
During the formative days of a planet, it would have experienced heating from impacts from planetesimals, which would have dwarfed even the asteroid impact that caused the extinction of dinosaurs. This heating could trigger differentiation, further heating the planet. The larger a body is, the slower it loses heat. In larger bodies, for example Earth, this heat, known as primordial heat, still makes up much of the body’s internal heat, but the Moon, which is smaller than Earth, has lost most of this heat.[4]
Another heat source is radiogenic heat, caused by
On Neptune’s moon Triton, and possibly on Mars, cryogeyser activity takes place. The source of heat is external (heat from the Sun) rather than internal. [6][7]
Melting methods
Decompression melting
This happens when solid material from deep beneath the body rises upwards. Pressure decreases as the material rises upwards, and so does the melting point. So, a rock that is solid at a given pressure and temperature can become liquid if the pressure, and thus melting point, decreases even if the temperature stays constant.[8][3] However, in the case of water, increasing pressure decreases melting point until a pressure of 0.208 GPa is reached, after which the melting point increases with pressure.[3]
Flux melting
This occurs when the melting point is lowered by the addition of volatiles, like water.[3] Like decompression melting, it is not caused by an increase in temperature, but rather by a decrease in melting point.[9]
Formation of cryomagma reservoirs
Ascent of melts
Diapirs
When material of a planetary body begins to melt, the melting first occurs in small pockets in certain high energy locations, for example grain boundary intersections and where different crystals react to form eutectic liquid, that initially remain isolated from one another, trapped inside rock. If the contact angle of the melted material allows the melt to wet crystal faces and run along grain boundaries, the melted material will accumulate into larger quantities. On the other hand, if the angle is greater than about 60 degrees, much more melt must form before it can separate from its parental rock. Studies of rocks on Earth suggest that melt in hot rocks quickly collects into pockets and veins that are much larger than the grain size, in contrast to the model of rigid melt percolation. Melt, instead of uniformly flowing out of source rock, flows out through rivulets which join together to create larger veins. Under the influence of buoyancy, the melt rises.[3] Diapirs may also form in non-silicate bodies, playing a similiar role in moving warm material towards the surface.[5]
Dikes
A dike is a vertical fluid-filled crack, from a mechanical standpoint it is a water filled crevasse turned upside down. As magma rises into the vertical crack, the low density of the magma compared to the wall rock means that the pressure falls less rapidly than in the surrounding denser rock. If the average pressure of the magma and the surrounding rock are equal, the pressure in the dike exceeds that of the enclosing rock at the top of the dike, and the pressure of the rock is greater than that of the dike at its bottom. So the magma thus pushes the crack upwards at its top, but the crack is squeezed closed at its bottom due to an elastic reaction (similar to the bulge next to a person sitting down on a springy sofa). Eventually, the tail gets so narrow it nearly pinches off, and no more new magma will rise into the crack. The crack continues to ascend as an independent pod of magma.[3]
Standpipe model
This model of volcanic eruption, while now discredited, explains observations very well, which newer models cannot. The model posits that magma rises through a rigid open channel, in the lithosphere and settles at the level of hydrostatic equilibrium. Despite how it explains observations well, such as an apparent concordance of the elevation of volcanoes nearby each other, it cannot be correct, as the lithosphere thickness derived from it is too large for the assumption of a rigid open channel to hold.[3]
Cryovolcanic melt ascent
Unlike silicate volcanism, where melt can rise by its own buoyancy until it reaches the shallow crust, in cryovolcanism, the water (cryomagmas tend to be water based) is denser than the ice above it. One way to allow cryomagma to reach the surface is to make the water buoyant, by making the water less dense, either through the presence of other compounds that reverse negative buoyancy, or with the addition of exsolved gas bubbles in the cryomagma that were previously dissolved into it (that makes the cryomagma less dense), or with the presence of a densifying agent in the ice shell. Another is to pressurise the fluid to overcome negative buoyancy and make it reach the surface. When the ice shell above a subsurface ocean thickens, it can pressurise the entire ocean (in cryovolcanism, frozen water or brine is less dense than in liquid form). When a reservoir of liquid partially freezes, the remaining liquid is pressurised in the same way.[5]
For a crack in the ice shell to propagate upwards, the fluid in it must have positive buoyancy or external stresses must be strong enough to break through the ice. External stresses could include those from tides or from overpressure due to freezing as explained above.[10]
There is yet another possible mechanism for ascent of cryovolcanic melts. If a fracture with water in it reaches an ocean or subsurface fluid reservoir, the water would rise to its level of hydrostatic equilibrium, at about nine-tenths of the way to the surface. Tides which induce compression and tension in the ice shell may pump the water farther up.[5]
A 1988 article proposed a possibility for fractures propagating upwards from the subsurface ocean of Jupiter’s moon Europa. It proposed that a fracture propagating upwards would possess a low pressure zone at its tip, allowing volatiles dissolved within the water to exsolve into gas. The elastic nature of the ice shell would likely prevent the fracture reaching the surface, and the crack would instead pinch off, enclosing the gas and liquid. The gas would increase buoyancy and could allow the crack to reach the surface.[5]
Even impacts can create conditions that allow for enhanced ascent of magma. An impact may remove the top few kilometres of crust, and pressure differences caused by the difference in height between the basin and the height of the surrounding terrain could allow eruption of magma which otherwise would have stayed beneath the surface. A 2011 article showed that there would be zones of enhanced magma ascent at the margins of an impact basin.[5]
Note that not all of these mechanisms, and maybe even none, operate on a given body.[5]
Gentle and explosive eruptions
Cause of explosive activity
A volcanic eruption could just be a simple outpouring of material onto the surface of a planet, but they usually involve a complex mixture of solids, liquids and gases which behave in equally complex ways.[3] Some types of explosive eruptions can release energy a quarter that of an equivalent mass of TNT.[11]
Volcanic eruptions on Earth have been consistently observed to progress from erupting gas rich material to gas depleted material, although an eruption may alternate between erupting gas rich to gas depleted material and vice versa multiple times.[12] This can be explained by the enrichment of magma at the top of a dike by gas which is released when the dike breaches the surface, followed by magma from lower down than did not get enriched with gas.[3]
The reason the dissolved gas in the magma separates from it when the magma nears the surface is due to the effects of temperature and pressure on gas solubility. Pressure increases gas solubility, and if a liquid with dissolved gas in it depressurises, the gas will tend to exsolve (or separate) from the liquid. An example of this is what happens when a bottle of carbonated drink is quickly opened: when the seal is opened, pressure decreases and bubbles of carbon dioxide gas appear throughout the liquid.[3]
Fluid magmas erupt quietly. Any gas that has exsolved from the magma easily escapes even before it reaches the surface. However, in
Generally, explosive cryovolcanism is driven by exsolution of volatiles that were previously dissolved into the cryomagma, similar to what happens in explosive silicate volcanism,[10] which is what is mainly covered below.
Explosive eruption physics
Silica-rich magmas cool beneath the surface before they erupt. As they do this, bubbles exsolve from the magma. As the magma nears the surface, the bubbles and thus the magma increase in volume. The resulting pressure eventually breaks through the surface, and the release of pressure causes more gas to exsolve, doing so explosively. The gas may expand at hundreds of metres per second, expanding upward and outward. As the eruption progresses, a chain reaction causes the magma to be ejected at higher and higher speeds.[3]
Volcanic ash formation
The violently expanding gas disperses and breaks up magma, forming a colloid of gas and magma called volcanic ash. The cooling of the gas in the ash as it expands chills the magma fragments, often forming tiny glass shards recognisable as portions of the walls of former liquid bubbles. In more fluid magmas the bubble walls may have time to reform into spherical liquid droplets. The final state of the colloids depends strongly on the ratio of liquid to gas. Gas-poor magmas end up cooling into rocks with small cavities, becoming vesicular lava. Gas-rich magmas cool to form rocks with cavities that nearly touch, with an average density less than that of water, forming pumice. Meanwhile, other material can be accelerated with the gas, becoming volcanic bombs. These can travel with so much energy that large ones can create craters when they hit the ground.[3]
Pyroclastic flows
When a colloid of volcanic gas and magma falls back to the ground, it can create a density current called a pyroclastic flow. The colloid is somewhat fluidised by the gas, allowing it to spread. These can often climb over obstacles, and devastate human life.[3]
Other explosive eruption mechanisms
An explosive eruption is usually triggered by exsolution of volatiles, discussed above. But there are other ways to create an explosive eruption.
Phreatic eruption
When water turns into steam in a phreatic eruption, it expands at supersonic speeds, up to 1,700 times its original volume. This can be enough to shatter solid rock, and hurl rock fragments hundreds of metres.[13]
A phreatomagmatic eruption occurs when hot magma makes contact with water, creating an explosion.[14]
Clathrate hydrates
One mechanism for explosive cryovolcanism is cryomagma making contact with
Water vapor in a vacuum
If a fracture reaches the surface of an icy body and the column of rising water is exposed to the near-vacuum of the surface of most icy bodies, it will immediately start to boil, because its vapor pressure is much more than the ambient pressure. Not only that, but any volatiles in the water will exsolve. The combination of these processes will release droplets and vapor, which can rise up the fracture, creating a plume. This is thought to be partially responsible for Enceladus’s ice plumes.[5]
Lava types
When magma erupts to a planet’s surface, it is termed lava. Viscous lavas form short, stubby glass-rich flows. These usually have a wavy texture. More fluid lavas have surface textures divided into different types.[3]
Pillow lava
These form when a trigger, often lava making contact with water, causes a lava flow to cool rapidly.[3][15]This splinters the surface of the lava, and the magma then collects into sacks that often pile up in front of the flow, forming a structure called a pillow.[3]
A'a lava
This type of lava has a rough, spiny surface made of clasts of lava called clinkers.[16] Block lava is another type of lava, with less jagged fragments than in A’a lava.[17]
Pahoehoe lava
By far the most common lava type, both on Earth and probably the other terrestrial planets. It has a smooth surface, with various billows and swales and folds.[3]
Types of volcanism
Silicate volcanism
Silicate volcanism occurs where silicate materials are erupted. Silicate lava flows, like those found on Earth, solidify at about 1000 degrees Celsius.[18]
Mud volcanoes
A mud volcano is formed when fluids and gases under pressure erupt to the surface, bringing mud with them. This pressure can be caused by the weight of overlying sediments over the fluid which pushes down on the fluid, preventing it from escaping, by fluid being trapped in the sediment, migrating from deeper sediment into other sediment or being made from chemical reactions in the sediment. They often erupt quietly, but sometimes they erupt flammable gases like methane.[19]
Cryovolcanism
Cryovolcanism is the eruption of volatiles into an environment below their freezing point. The processes behind it are different to silicate volcanism because the cryomagma (which is usually water-based) is normally denser than its surroundings, meaning it cannot rise by its own buoyancy.[20][5]
Sulfur
Sulfur lavas have a different behaviour to silicate ones. First, sulfur has a low melting point of about 120 degrees Celsius. Also, after cooling down to about 175 degrees Celsius the lava rapidly loses viscosity, unlike silicate lavas like those found found on Earth.[18]
Phreatic eruption
A phreatic eruption can occur when hot water under pressure is depressurised. Depressurisation reduces the boiling point of the water, so when depressurised the water suddenly boils.[21] Or it may happen when groundwater is suddenly heated, flashing to steam suddenly.[22]
A phreatomagmatic eruption occurs when hot magma makes contact with water, creating an explosion.[23]
Occurrence
On Earth, volcanoes are most often found where
Large eruptions can affect atmospheric temperature as ash and droplets of sulfuric acid obscure the Sun and cool Earth's troposphere. Historically, large volcanic eruptions have been followed by volcanic winters which have caused catastrophic famines.[24]
Earth's Moon has no large volcanoes and no current volcanic activity, although recent evidence suggests it may still possess a partially molten core.[25] However, the Moon does have many volcanic features such as maria[26] (the darker patches seen on the Moon), rilles[27] and domes.[28]
The planet
There are several extinct volcanoes on Mars, four of which are vast shield volcanoes far bigger than any on Earth. They include Arsia Mons, Ascraeus Mons, Hecates Tholus, Olympus Mons, and Pavonis Mons. These volcanoes have been extinct for many millions of years,[32] but the European Mars Express spacecraft has found evidence that volcanic activity may have occurred on Mars in the recent past as well.[32]
In 1989, the
A 2010 study of the
See also
- Bimodal volcanism
- Hotspot
- Igneous rock
- Intraplate volcanism
- Magmatism
- Prediction of volcanic activity
- Seafloor spreading
- Volcanic arc
- Volcanic rock
- Volcanology
References
- ^ doi:10.1007/s11430-022-1085-y.)
{{cite journal}}
: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link - ^ "Volcanoes on Earth and beyond". 27 October 2021.
- ^ a b c d e f g h i j k l m n o p q r s t "Volcanoes" (PDF).
- ^ a b c Anand1, A. Bland2, McBride3, Moore4, Rothery5, Schwenzer6, Widdowson7, Wright8, Mahesh1, Philip2, Neil3, Elaine4, David5, Susanne6, Mike7, Ian8. "Origins of planets and of planetary layering" (PDF).
{{cite web}}
: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link) - ^ a b c d e f g h i j k Fagent1, Lopes2, Quick3, Gregg4, Sarah A.1, Rosaly M.C.2, Lynnae C.3, Tracy K.P.4. "Chapter 5 Cryovolcanism" (PDF).
{{cite web}}
: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link) - ^ Burnham, Robert (2006-08-16). "Gas jet plumes unveil mystery of 'spiders' on Mars". Arizona State University web site. Retrieved 2009-08-29.
- ^ https://www2.mps.mpg.de/solar-system-school/lectures/planetary_interiors_surfaces/markiewicz.pdf.
{{cite web}}
: Missing or empty|title=
(help) - ^ Earle, Steven; Earle, Steven (September 2015). "3.2 Magma and Magma Formation".
- ^ Earle, Steven; Earle, Steven (September 2015). "3.2 Magma and Magma Formation".
- ^ a b M.1, S.J.2, E.L.3, C.R.4, Neveu1, Desch2, Shock3, Glein4. "Prerequisites for explosive cryovolcanism on dwarf planet-class Kuiper Belt objects" (PDF).
{{cite web}}
: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link) - .
- doi:10.1177/030913338100500318.)
{{cite journal}}
: CS1 maint: numeric names: authors list (link - ^ Cronin, Shane (December 9, 2019). "Steam-driven volcanic eruptions difficult to predict, still poorly understood".
- ^ Mcnair, B. (January 10, 2024). "What Are Phreatomagmatic Eruptions and How They Form?".
- PMID 35351895.)
{{cite journal}}
: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link - ^ "Lava Flow Forms". National Park Service.
- ^ "lava". Britannica. 13 February 2024.
- ^ a b "Sulphur vs. Silicate". Volcano World. 4 January 2012.
- ^ R.Hudec, Michael (December 20, 2022). "What are mud volcanoes?". The Conversation.
- ^ Klemetti, Erik (25 September 2023). "Cryovolcanism's Song of Ice and Fire".
- doi:10.2312/eskp.051. Retrieved 2024-03-17.
- ^ "VHP Photo Glossary: Phreatic eruption". Volcano Hazards Program. U.S. Geological Survey. Retrieved 13 November 2010.
- ^ Mcnair, B. (January 10, 2024). "What Are Phreatomagmatic Eruptions and How They Form?".
- .
- S2CID 130734866.
- ^ "Mare". Volcano World. Oregon State University. January 4, 2012. Retrieved 12 November 2023.
- ^ "Sinuous Rilles". Volcano World. Oregon State University. January 4, 2012. Retrieved 17 November 2023.
- ^ "A Lunar Mystery: The Gruithuisen Domes". Moon: NASA Science. Retrieved 2024-01-06.
- .
- .
- .
- ^ a b "Glacial, volcanic and fluvial activity on Mars: latest images". European Space Agency. February 25, 2005. Retrieved August 17, 2006.
- ^ "Exceptionally bright eruption on Io rivals largest in solar system". W.M. Keck Observatory. November 13, 2002. Archived from the original on August 6, 2017. Retrieved May 2, 2018.
- ISBN 978-0-12-385938-9, retrieved 2024-01-06
- PPARC. March 16, 2005. Archived from the originalon March 10, 2007. Retrieved July 4, 2014.
- ^ Smith, Yvette (March 15, 2012). "Enceladus, Saturn's Moon". Image of the Day Gallery. NASA. Retrieved July 4, 2014.
- ^ "Hydrocarbon volcano discovered on Titan". New Scientist. June 8, 2005. Archived from the original on September 19, 2007. Retrieved October 24, 2010.
- ^ Jaggard, Victoria (February 5, 2010). ""Super Earth" May Really Be New Planet Type: Super-Io". National Geographic web site daily news. National Geographic Society. Archived from the original on February 9, 2010. Retrieved March 11, 2010.
External links
- "Glossary of Volcanic Terms". G. J. Hudak, University of Wisconsin Oshkosh, 2001. Retrieved 2010-05-07.
- Crumpler, L. S.; Lucas, S. G. (2001). "Volcanoes of New Mexico: An Abbreviated Guide For Non-Specialists" (PDF). Volcanology in New Mexico. New Mexico Museum of Natural History and Science Bulletin. 18: 5–15. Archived from the original (PDF) on 2007-03-21. Retrieved 2010-04-28.
Further reading
Cosmic-solar radiation as the cause of earthquakes and volcanic eruptions
Melting behaviours of the candidate materials for planetary models
Explosive volcanic eruptions triggered by cosmic rays: Volcano as a bubble chamber
Thermodynamics of gas and steam-blast eruptions
Prerequisites for explosive cryovolcanism on dwarf planet-class Kuiper belt objects
Phreatomagmatic and Related Eruption Styles
https://www2.mps.mpg.de/solar-system-school/lectures/planetary_interiors_surfaces/markiewicz.pdf