Air travel disruptions following major volcanic eruptions

Following major volcanic eruptions, plumes of ash and steam raise many kilometers into the atmosphere where ash can be dispersed over a wide area. The injection of this material into the atmosphere effects the evolution of atmospheric chemistry and can influence short term weather patterns. The ash in the atmosphere also makes it unsafe for airplanes to travel through, as was the case following the eruption in Iceland last April which resulted in tens of thousands of flight cancellations.

Extent of the Plume from the Eyjafjallajökull Volcano in Iceland, from earthobservatory.nasa.gov

A volcanic plume has to be buoyant to reach 10's of km into the atmosphere. The hot gases and ashes cool as the plume rises in the atmosphere, and the plume expands. This keeps the plume less dense than the surrounding atmosphere and keeps the plume rising, in the same way bubbles rise in a glass of soda.

Sarychev Peak Eruption June 12, 2009 taken from the International Space Station, from earthobservatory.nasa.gov

Work was completed at NASA's Goddard Space Flight Center to investigate how these plumes rise. While there are numerous conditions that are looked at, the effects of vent geometry has on supporting a buoyant plume was investigated. Computer models of volcanic plumes originating from linear and circular vents were constructed. From the simulations the maximum height at which a buoyant plume can reach was determined. Simulations were done with different vent openings to see if a linear vent can produce a plume which can reach heights similar to that of plumes from circular vents.

Maximum predicted plume heights on Earth as a function of vent area. The linear vent results are shown for multiple choices of active fissure length

The results show that when buoyancy is sustained, linear vents appear to be equally capable of injecting ash and volatiles into the atmosphere. For analogous mass flux rates at the vent, the maximum heights to which linear and cylindrical plumes can rise are comparable. However, in some cases where the length of an active linear vent is smaller than the radius of the circular vent, the entrainment area of the linear plumes is significantly less than the cylindrical equivalent. Thus the range of vent widths that can sustain a buoyant plume is narrow and linear plumes are more likely to collapse and not inject ash high into the atmosphere.

For a more detailed description, please see the paper Glaze et al., 2011

Glaze, L. S., S. M. Baloga, and J. Wimert (2011), Explosive volcanic eruptions from linear vents on Earth, Venus, and Mars: Comparisons with circular vent eruptions, J. Geophys. Res., 116, E01011, doi:10.1029/2010JE003577.