Editing Eruption column (section)

==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>