No health threat from Chilean volcano ash – experts

In response to queries from worried parents, experts has have issued an explanation of why New Zealanders don’t need to worry about health dangers from ash fall from the Chilean volcano plume.

Following a number of quries from media and concerned parents and schools, experts Thomas Wilson (Natural Hazards Research Centre, University of Canterbury) with the help of Graham Leonard (GNS Science) released the following plain language explanation.

Why aren’t we being told to wear masks to protect us from ash fall?

This is a good question.  Parents are showing excellent knowledge of what do during a volcanic ashfall – well done to them!

However in this situation we are dealing with a volcanic ash plume, rather than volcanic ash fall.  A volcanic ash plume (or ash cloud as it’s described in the media) is a mixture of volcanic ash and gases suspended in the atmosphere.  Ash fall is when ash actually falls to the ground.

The ash plume which is being transported over New Zealand is extremely fine grained (like talcum powder) and very diffuse (very low concentrations) in the high atmosphere.  And it is being transported along by very strong upper atmosphere winds.  All of these factors contribute to keeping the ash particles up in suspension.

It seems strange, but the ash doesn’t really fall out of this plume.  It’s density is so low and the winds in the upper atmosphere so strong, that it remains in a plume at a certain elevation in the atmosphere –  in this case it seems the plume is between 8-10 km altitude over New Zealand.  Over time the plume will become so mixed and diffuse that eventually it disappears.

This is why planes, such as Air New Zealand, are able to fly around or under the ash plume safely.

As a result, it is extremely unlikely that we will get any ash fall in New Zealand from this particular situation.  The ash plume is likely to remain at high elevations as it passes over New Zealand.

If any small amount of ash did fall out over New Zealand, it is highly unlikely to be in sufficient concentrations to be a threat to any person’s health.  You would be much more at risk from traffic pollution for example (or liquefaction dust in my case!).

However, GNS Science is actively monitoring the situation and will issue a warning if ashfall is a possibility. This will be a well publicised warning in mainstream media and will issue advice about what to do.

Hope all is well – and you are enjoying the sunsets!!