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Science Alert: Experts Respond

Experts respond: Disruption from Chilean volcano ash

Posted in Science Alert: Experts Respond on June 13th, 2011.

A sprawling ash plume from the Chilean Volcano Puyehue-Cordón Caulle, is causing disruptions to flights across the southern hemisphere. The SMC has contacted New Zealand experts for further explanation of the current situation and its impact.

Feel free to use these quotes in your stories. To follow up with these or other local experts, please contact the Science Media Centre.

The following is a combined response from Dr Tom Wilson and Prof Jim Cole at The University of Canterbury and Dr Graham Leonard and Brad Scott at GNS Science. (NB: Quotes can be attributed to Dr Graham Leonard or Dr Tom Wilson)

Tom and Graham are leaders of the international Volcanic Ash Impacts Working Group, and collaborate on ash impacts research. They work closely with colleagues at US Geological Survey, British Geological Survey and various universities to continually update and coordinate ash impact research.  GNS Science is responsible for volcanic advice to MetService Volcanic Ash Advisory Centre in Wellington.

“Puyehue-Cordón Caulle volcano is a complex of eruption vents on the eastern edge of the Lake District of Chile. It is very close to the border with Argentina and the largest town that has received significant (centimetres) of ash fall is San Carlos de Bariloche – a ski resort town in Argentina. Chilean volcanoes often have a significant impact in Argentina because of the prevailing westerly wind directions similar to those in New Zealand. The 2008-present Chaiten eruption has impacted towns in Argentina south of Bariloche.

“Puyehue-Cordón Caulle has erupted a range of magma from rhyolite (very explosive, like Taupo volcano in New Zealand) to basalt (producing small scoria cones and lava, like Auckland Volcanic Field). The current explosive eruption appears to be at the explosive rhyolite-dacite end. Rholite and dacite are explosive because they tend to be cooler and more sticky, so gas that wants to escape from the magma at the earth’s surface tends to explode out breaking the liquid rock up into tiny fragments that cool to ash.

What are the risks facing aircraft that continue to fly? How easy is it to avoid the ash cloud by flying lower or changing routes?

“Ash being sucked into engines is the main risk to aircraft, but there is also an issue with flight control sensors. There is also some risk to the outside of aircraft from ash particles causing abrasion, but this tends to be a longer-term cumulative effect.

“When ash is sucked into jet engines it can cause abrasion, blockage and also melt and deposit on the extremely hot engine parts. It effectively melts back to volcanic glass and stops combustion in the engine.

“Avoidance is the best strategy, because it is still unclear exactly how much ash over how long causes damage. Considerable work internationally is being done following the Eyjafjallajökull eruption to improve the ability to detect and forecast ash concentrations and set thresholds for what is a safe concentration.

“Dense near source ash plumes are usually visible to pilots in the daytime, in clear skies. However, ash clouds cannot be seen by pilots at night. The more dilute/distal plumes are frequently not visible, even in day light.

“The ash plume that has reached New Zealand has travelled east from Chile, over Argentina and the Atlantic, south of Australia and onto New Zealand. This is due to the overall predominantly westerly winds in the Southern Hemisphere. By the time the ash has reached New Zealand it is high in the atmosphere and the plume is very wide.

“Large ash clouds, like the one coming over New Zealand, can be observed by satellites and forecasts are given by Volcanic Ash Advisory Centres, which cover sections of the globe. The Metservice in Wellington hosts the VAAC for New Zealand and the South Pacific. The Darwin VAAC covers Australia and a lot of Southeast Asia.

“Because the area is wide airlines get advanced notice from the VAAC and they can choose to avoid the ash (by flying under it in this case) or not to fly. Changing the routes around the ash would be difficult because the plume is very wide.”

“Wellington VAAC Ash forecast map. There is further information and satellite imagery on the Darwin VAAC website. The satellite imagery is worth a look.

“Interpreting the satellite images: The larger patches of green south of Australia and over New Zealand are ash. Note higher concentrations are in red, so the ash currently over New Zealand is of relatively low concentration.

“The large green patches over Australia are likely local non-volcanic dust.”

What kind of volcanic material is causing the disruption? Is there any way to compare current conditions / quality of ash to recent Northern hemisphere eruptions?

“The ash reaching New Zealand is very fine, like flour; coarser sand-sized ash has dropped out over Chile and Argentina. This high elevation, very fine ash is very similar to the situation that faced Europe from the Eyjafjallajökull eruption. Because the ash is fine it stays suspended by high elevation winds very easily and travels very far.

“Little or no detectable ash is expected to fall out on the ground in New Zealand, which is similar to the situation in southern and eastern Europe from Eyjafjallajökull.”

What atmospheric conditions are transporting the ash from South America to New Zealand, and are these reasonably common or an unusual occurrence?

“The eruption in Chile, from Puyehue-Cordon Caulle volcano, has erupted ash up to 15 km height in the atmosphere.  At these heights very strong winds exist, known as the jet-stream.  This is also where jet aircraft prefer to fly – with modern transcontinental and transoceanic air routes designed to take advantage of the jet stream’s power, saving both time and fuel.  In the Southern hemisphere at New Zealand’s latitude these winds are predominantly westerly winds. (this is why it takes less time to fly from Australia to New Zealand than from New Zealand to Australia – the jets get ‘pushed’ along when heading east).

“Over recent decades we in New Zealand have seen beautiful sunsets from Australian bushfires and even other past Chilean volcanic eruptions – such as in 1991 following the eruption of Vulcan Hudson (one of the largest eruptions of the 20th century).

“As a result of the prevailing wind direction, ash has to travel the long way from South America to New Zealand usually, passing over or south of Australia first.”

The current advisory states it’s due to an “ongoing eruption”. Is there a possibility of several waves of ash over coming days and weeks? How long is the Chilean volcano likely to remain active?

“This is a large pyroclastic eruption, meaning it is explosive and produces a lot of volcanic ash. It has already continued for days with varying explosivity and with ash reaching a range of elevations, sometimes over 15 km high at the volcano.

“Explosive eruptions can have large bursts after days or weeks of lesser activity, so there is the potential for more waves in coming days or weeks.

“It is difficult to estimate how long a volcanic eruption will continue for, but recent reports from SERNAGEOMIN (the Chilean Geological Survey) suggest that seismicity is decreasing slightly, which might indicate that the eruption is reducing in its intensity.”

How are things likely to change over the next few days?

“The current ash plume over New Zealand is moving east and will eventually clear our airspace over days to perhaps a week.

“Watching the activity at the source in Chile will tell us when any further large plumes are erupted, and we will again have advanced warning of at least days before new ash reaches New Zealand.”

Further comments:

“The ash plume reaching New Zealand is high up and spread out, so little or no detectable ash is likely to fall here. This is only an issue for New Zealand and International aviation flying to NZ.

“However, New Zealand has many volcanoes that can produce volcanic ash, so this is a timely reminder that we are very likely to have to deal with ash from our own volcanoes at times throughout our lives.

“New Zealand’s active volcanoes are monitored by the GeoNet project and work with the NZ VAAC amd CAA during local eruptions to assess the risk from ash clouds.

“We need to look at the impacts near the volcano in Chile and Argentina to get a picture of what we will need to deal with when there is another ash eruption in New Zealand.”

“We have prepared, in conjunction with other members of the Volcanic Ash Impacts Working Group, a set of resources to understand and prepare for ash fall. Please read through them to get prepared for the next ash-producing eruption that occurs in New Zealand

“Also CAA has produced information and policy for aviation in New Zealand (PDF).”


Dr Jan Lindsay, Senior Research Fellow in Volcanic Hazard and Risk, School of Environment,University of Auckland

“Chile, like New Zealand, is volcanically active. The Andes of Chile are a typical example of a subduction zone, where one tectonic plate dipping beneath another at a plate boundary results in volcanism. The volcanism in the Taupo Volcanic Zone in New Zealand is also due to subduction. In well-established (long- lived) subduction zones like the Andes, magma typically has time to evolve to higher silica compositions such as rhyolite. Eruptions of rhyolite magma are among the most explosive on earth, because the magma’s high silica content makes it hard for gases to escape passively. Instead they tend to blast the magma apart into billions of tiny fragments, generating huge, high ash columns.

“The eruption of Chile’s Chaitén volcano in 2008 was the first major explosive eruption of rhyolite magma in nearly a century, since the 1912 eruption of Novarupta, in Alaska. At the time the 2008 eruption the volcano was thought to have not had an eruption in over 9,000 years.”

 

Dr James Renwick, Principal Scientist, Climate Variability & Change, NIWA

“The Chilean volcanic eruption is happening at about 40 degrees south latitude (about the latitude of Wellington), in the southern early winter. The ash cloud is being lofted into the lower stratosphere and the upper parts of the troposphere (around 8-12km above the earth’s surface), where the mid-latitude westerly wind circulation is strongest.

“The westerly wind circulation in the upper troposphere flows at around 50m/s in the jet streams. There are two at this time of year – the subtropical jet centred near 30S and the subpolar jet centred between 50 and 60S. The region in between (40-50S) is a region of lighter winds, especially near NZ, but even there, the air is flowing at 30-40m/s in many places. Currently, upper-tropospheric winds are close to their normal strength in most of the Southern Hemisphere, but are a bit stronger than normal across the Tasman Sea on to the North Island.

“The ash cloud appears to have followed the southern side of the subtropical jet stream across the Atlantic and Indian oceans, and on to Australia and New Zealand. The distance around the globe at 40S is about 30,000km, which would take just on a week (7 days) to traverse at 50m/s. So the ash cloud would be expected to take several days to reach NZ, flowing eastwards from South America.”

“Once a cloud of ash gets into the lower stratosphere, it can stay aloft for many days, and can easily circumnavigate the globe several times over.”


Peter Lechner, Civil Aviation Authority Meteorological Manager

What are the risks facing aircraft that continue to fly? How easy is it to avoid the ash cloud by flying lower or changing routes?

“Have a look at all of the information an videos under the Volcanic Ash heading in the CAA Web site.  Altering flight routes in the New Zealand air traffic management system (Airways Corporation) is straight-forward.  We do not have the densities of traffic that Europe has for example.”

What kind of volcanic material is causing the disruption? Is there any way to compare current conditions / quality of ash to recent Northern hemisphere eruptions?

“Generally the ash is made up of very fine silicates – see image below. Different volcanoes will eject slightly different material and to different altitudes.”

Credit: Peter Lechner, CAA

What atmospheric conditions are transporting the ash from South America to New Zealand, and are these reasonably common or an unusual occurrence?

“The ash is being transported by the normal westerly airstream around the planet.  This is normal.  If it were summer the plume would be further south and be less of a potential problem for NZ.”

The current advisory states it’s due to an “ongoing eruption”. Is there a possibility of several waves of ash over coming days and weeks? How long is the Chilean volcano likely to remain active?

“The “waves” of ash will continue to be a problem more or less while the volcano is active. Once the volcano ceases, there will still be about 6 days of ash plume to move around the globe to NZ.”

How are things likely to change over the next few days?

“The ash will ebb and flow, covering parts of NZ at times.”

______________

Further reading suggested by our experts:

GNS Volcano information page

Overview of impacts put together Volcanic Ash Impacts Working group

Detailed paper from their US Geological Survey colleagues, here.

Chapter 4 of the following has some images of damage to engines, and descriptions. (PDF)

Good blog summaries are here:

http://volcanism.wordpress.com/

Here is an update on the eruption in English as of 7 June from the Smithsonian Global Volcanism Programme:
http://www.volcano.si.edu/reports/usgs/#puyehue

Here is a Google Translated link to the latest updates from Chile’s volcano monitoring agency Sernageomin:
http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&sl=es&tl=en&u=http%3A%2F%2Fwww.sernageomin.cl%2F

In the August International Civil Aviation Organization (ICAO) Journal -
Page 6 onwards summarises what has happened in ash and aviation since Eyjafjallajökull:
http://www.icao.int/icao/en/jr/2010/6504_en.pdf

 

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