Editing Eruption column

{{Short description|Cloud of hot ash and volcanic gases emitted during an explosive volcanic eruption}}
{{More citations needed|date=July 2021}}
[[File:Tonga Volcano Eruption 2022-01-15 0320Z to 0610Z Himawari-8 visible.gif|thumb|Satellite animation of the initial eruption column and shockwave from [[Hunga Tonga–Hunga Haʻapai]] on 15 January 2022]]

An '''eruption column''' or '''eruption plume''' is a cloud of super-heated [[Volcanic ash|ash]] and [[tephra]] suspended in [[volcanic gas|gases]] emitted during an [[explosive eruption|explosive volcanic eruption]]. The volcanic materials form a vertical column or [[Plume (fluid dynamics)|plume]] that may rise many kilometers into the air above the vent of the volcano. In the most explosive eruptions, the eruption column may rise over {{convert|40|km|mi|abbr=on}}, penetrating the [[stratosphere]]. Injection of [[Particulate|aerosols]] into the stratosphere by volcanoes is a major cause of short-term [[Volcanic winter|climate change]].

A common occurrence in explosive eruptions is ''column collapse'' when the eruption column is or becomes too dense to be lifted high into the sky by air convection, and instead falls down the slopes of the volcano to form [[pyroclastic flow]]s or [[pyroclastic surge|surge]]s (although the latter is less dense). On some occasions, if the material is not dense enough to fall, it may create [[pyrocumulonimbus]] clouds.

==Formation==
[[File:Pinatubo91eruption plume.jpg|thumb|upright=1.35|Eruption column over [[Mount Pinatubo]] in the [[Philippines]], 1991]]
Eruption columns form in explosive volcanic activity, when the high concentration of [[Volatile (astrogeology)#Igneous petrology|volatile materials]] in the rising [[magma]] causes it to be disrupted into fine [[volcanic ash]] and coarser [[tephra]]. The ash and tephra are ejected at speeds of several hundred metres per second, and can rise rapidly to heights of several kilometres, lifted by enormous [[convection]] currents.

Eruption columns may be transient, if formed by a discrete explosion, or sustained, if produced by a continuous eruption or closely spaced discrete explosions.

==Structure==

The solid and liquid materials in an eruption column are lifted by processes that vary as the material ascends:<ref>{{cite web | url = http://www.sci.sdsu.edu/volcano/ | title = How volcanoes work – The eruption model (QuickTime movie) | work = San Diego State University | access-date = 2007-06-30 | archive-url = https://web.archive.org/web/20070701000926/http://www.sci.sdsu.edu/volcano/ | archive-date = 2007-07-01 | url-status = dead }}</ref>

* At the base of the column, material is violently forced upward out of the crater by the pressure of rapidly expanding gases, mainly steam. The gases expand because the pressure of rock above it rapidly reduces as it approaches the surface. This region is called the ''gas thrust region'' and typically reaches to only one or two kilometers above the vent.
* The ''convective thrust region'' covers most of the height of the column. The gas thrust region is very turbulent and surrounding air becomes mixed into it and heated. The air expands, reducing its density and rising. The rising air carries all the solid and liquid material from the eruption entrained in it upwards.
* As the column rises into less dense surrounding air, it will eventually reach an altitude where the hot, rising air is of the same density as the surrounding cold air. In this neutral buoyancy region, the erupted material will then no longer rise through convection, but solely through any upward momentum which it has. This is called the ''umbrella region'', and is usually marked by the column spreading out sideways. The eruptive material and the surrounding cold air has the same density at the base of the umbrella region, and the top is marked by the maximum height which momentum carries the material upward. Because the speeds are very low or negligible in this region it is often distorted by stratospheric winds.

==Column heights==

[[Image:MtRedoubtedit1.jpg|thumb|left|Eruption column rising over [[Redoubt Volcano]], Alaska, on 21 April 1990, which reached a height of about {{convert|9|km|mi|abbr=on}}<ref name="BGVN1990">{{cite web | url=http://volcano.si.edu/volcano.cfm?vn=313030#bgvn_199004 | title=Bulletin of the Global Volcanism Network; volume 15 number 4 (April 1990) | publisher=[[Smithsonian Institution]] | work=[[Global Volcanism Program]] | date=1990 | access-date=14 January 2018}}</ref>]]

The column will stop rising once it attains an altitude where it is more dense than the surrounding air. Several factors control the height that an eruption column can reach.

Intrinsic factors include the diameter of the erupting vent, the [[gas]] content of the magma, and the [[velocity]] at which it is ejected. Extrinsic factors can be important, with winds sometimes limiting the height of the column, and the local thermal temperature gradient also playing a role. The atmospheric temperature in the [[troposphere]] normally decreases by about 6-7 [[Kelvin|K]]/km, but small changes in this gradient can have a large effect on the final column height. Theoretically, the maximum achievable column height is thought to be about {{convert|55|km|mi|abbr= on}}. In practice, column heights ranging from about {{convert|2-45|km|mi|abbr=on}} are seen.

Eruption columns with heights of over {{convert|20-40|km|mi|abbr=on}} break through the [[tropopause]] and inject [[particulate]]s into the [[stratosphere]]. Ashes and aerosols in the troposphere are quickly removed by [[Precipitation (meteorology)|precipitation]], but material injected into the stratosphere is much more slowly dispersed, in the absence of [[weather]] systems. Substantial amounts of stratospheric injection can have global effects: after [[Mount Pinatubo]] erupted in 1991, global temperatures dropped by about {{convert|0.5|C-change|F-change|abbr=on}}. The largest eruptions are thought to cause temperature drops down to several degrees, and are potentially the cause of some of the known [[mass extinction]]s.

Eruption column heights are a useful way of measuring eruption intensity since for a given atmospheric temperature, the column height is proportional to the fourth root of the mass eruption rate. Consequently, given similar conditions, to double the column height requires an eruption ejecting 16 times as much material per second. The column height of eruptions which have not been observed can be estimated by mapping the ''maximum'' distance that pyroclasts of different sizes are carried from the vent—the higher the column the further ejected material of a particular mass (and therefore size) can be carried.

The approximate maximum height of an eruption column is given by the equation.
:H = k(MΔT)<sup>1/4</sup>
Where:
:k is a constant that depends on various properties, such as atmospheric conditions.
:M is the mass eruption rate.
:ΔT is the difference in temperature between the erupting magma and the surrounding atmosphere.

==Hazards==

===Column collapse===
[[File:MtStHelens Mushroom Cloud.jpg|thumb|The eruption column produced by the [[1980 eruption of Mount St. Helens]] as seen from the village of [[Toledo, Washington]], which is {{convert|35|mi|km|abbr=on|order=flip}} away. The cloud was roughly {{convert|40|mi|km|abbr=on|order=flip}} wide and {{convert|15|mi|km ft|abbr=on|order=flip}} high.]]
Eruption columns may become so laden with dense material that they are too heavy to be supported by convection currents. This can suddenly happen if, for example, the rate at which magma is erupted increases to a point where insufficient air is entrained to support it, or if the magma density suddenly increases as denser magma from lower regions in a [[Igneous differentiation|stratified]] [[magma chamber]] is tapped.

If it does happen, then material reaching the bottom of the convective thrust region can no longer be adequately supported by convection and will fall under [[gravity]], forming a [[pyroclastic flow]] or [[pyroclastic surge|surge]] which can travel down the slopes of a [[volcano]] at speeds of over {{convert|100-200|kph|mph|abbr=on}}. Column collapse is one of the most common and dangerous volcanic hazards in column-creating eruptions.

===Aircraft===

Several eruptions have seriously endangered aircraft which have encountered or passed by the eruption column. In two separate incidents in 1982, airliners flew into the upper reaches of an eruption column blasted off by [[Galunggung|Mount Galunggung]], and the ash severely damaged both aircraft. Particular hazards were the ingestion of ash stopping the engines, the sandblasting of the cockpit windows rendering them largely opaque and the contamination of fuel through the ingestion of ash through pressurisation ducts. The damage to engines is a particular problem since temperatures inside a [[gas turbine]] are sufficiently high that volcanic ash is melted in the [[combustion chamber]], and forms a glass coating on components farther downstream of it, for example on turbine blades.

In the case of [[British Airways Flight 9]], the aircraft lost power on all four engines, and in the other, nineteen days later, three of the four engines failed on a Singapore Airlines 747. In both cases, engines were successfully restarted, but the aircraft were forced to make emergency landings in [[Jakarta]].

Similar damage to aircraft occurred due to an eruption column over [[Mount Redoubt (Alaska)|Redoubt]] volcano in [[Alaska]] in 1989. Following the eruption of Mount Pinatubo in 1991, aircraft were diverted to avoid the eruption column, but nonetheless, fine ash dispersing over a wide area in Southeast Asia caused damage to 16 aircraft, some as far as {{convert|1,000|km|mi|abbr=on}} from the volcano.

Eruption columns are not usually visible on [[weather radar]] and may be obscured by ordinary clouds or night.<ref>{{cite journal | title = Visualization of Volcanic ash clouds | journal = IEEE Computer Graphics and Applications | date = July 1995 | volume = 15 | issue = 4 | pages =34–39 |author1=Mitchell Roth |author2=Rick Guritz | doi = 10.1109/38.391488}}</ref> Because of the risks posed to aviation by eruption columns, there is a network of nine [[Volcanic Ash Advisory Center]]s around the world which continuously monitor for eruption columns using data from satellites, ground reports, pilot reports and meteorological models.<ref>{{ cite web | url = http://www.bom.gov.au/info/vaac/index.shtml | title = Keeping aircraft clear of volcanic ash - Darwin Volcanic Ash Advisory Center | work = Australian Government - Bureau of Meteorology | access-date = 2007-06-30}}</ref>

==See also==
* [[Cryovolcano]]
* [[Enceladus]] – a volcanically active moon of planet Saturn
* [[Mount Pelée]]
* [[Pele (volcano)]]
* [[Peléan eruption]]
* [[Plinian eruption]]

==References==
<references/>

==Further reading==

* {{cite book |author1=Casadevall T.J. |author2=Delos Reyes P.J. |author3=Schneider D.J. | year = 1993 | chapter = The 1991 Pinatubo Eruptions and Their Effects on Aircraft Operations | title = Fire and Mud: Eruptions and Lahars of Mount Pinatubo, Philippines | publisher = US Geological Survey/Philippine Institute of Volcanology & Seismology | chapter-url = http://pubs.usgs.gov/pinatubo/contents.html | access-date = 2007-06-30}}
* {{cite journal | author = Chakraborty P. | year = 2009 | title = Volcanic mesocyclones | journal = Nature | volume = 458 | issue = 7237 | pages = 495–500 | url = http://web.mechse.illinois.edu/research/gioia/Art/nature07866.pdf | doi = 10.1038/nature07866 | display-authors = etal | bibcode = 2009Natur.458..497C | pmid = 19325632 | s2cid = 1129142 }}{{dead link|date=September 2017 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{cite journal |author1=Glaze L.S. |author2=Baloga S.M. | year =1996 | title = Sensitivity of buoyant plume heights to ambient atmospheric conditions: Implications for volcanic eruption columns | journal = Journal of Geophysical Research | volume = 101 |issue=D1 |pages = 1529–1540 | doi = 10.1029/95JD03071 | bibcode=1996JGR...101.1529G}}
* {{cite journal | author = Scase, M.M. | year = 2009 | title = Evolution of volcanic eruption columns | journal = Journal of Geophysical Research | volume = 114 | issue = F4 | pages = F04003 | doi = 10.1029/2009JF001300 | bibcode=2009JGRF..114.4003S| doi-access = free }}
* {{cite journal | doi = 10.1007/BF01079681 | author = Woods, A.W. | year = 1988 | title = The fluid dynamics and thermodynamics of eruption columns | journal = Bull. Volcanol. | volume = 50 | pages = 169–193 | issue=3|bibcode = 1988BVol...50..169W | s2cid = 140193721 }}
* {{cite journal |author1=Wilson L. |author2=Sparks R.S.J. |author3=Huang T.C. |author4=Watkins N.D. | year = 1978 | title = The control of volcanic column heights by eruption energetics and dynamics | journal = Journal of Geophysical Research | volume = 83 |issue=B4 | pages= 1829–1836 | doi = 10.1029/JB083iB04p01829 | bibcode=1978JGR....83.1829W|citeseerx=10.1.1.550.7357 }}

==External links==
{{Commons category|Eruption columns}}
*[http://vulcan.wr.usgs.gov/Glossary/VolcanicBlasts/framework.html USGS information]
*[https://web.archive.org/web/20050411061831/http://lvo.wr.usgs.gov/zones/30410914-052_caption.html Description of Galunggung eruption column]

{{Volcanoes}}

[[Category:Volcanoes]]
[[Category:Volcanic eruptions]]
[[Category:Explosive eruptions]]
[[Category:Volcanic degassing]]
[[Category:Tephra]]