A day or so after a volcano erupts media often reports on the clean-up operations undertaken when the volcanic ash (or tephra) is dispersed by winds and deposited on communities. I thought I would use this blog post to summarise a key finding of a recently published review paper by colleagues and myself (available here for free until 14 November).
The video above from the recent Calbuco eruption in Chile shows that ash is incredibly disruptive to society and potentially damaging to property. One of the key methods of reducing the impacts ash can have on a community is to efficiently clean-up and dispose of it where it can be managed. It is for this reason that clean-up operations often involve the mobilisation of large workforces to remove the ash.
One of the most interesting findings from our paper was that there appears to be a somewhat inherent scale of response across the 30 different clean-up operations all over the world spanning about 50 years.
I don’t want to dwell on some of the details of the graph (see the paper for specifics) but essentially what it shows is the amount of volcanic ash deposited on a community (x-axis) and the amount of volcanic ash removed and disposed of from the community (y-axis) during coordinated clean-up operations (municipal operations). For clarity, 1,000 m3/km2 is roughly consistent with about 1 mm thickness across a city (10,000 m3/km2 = 1 cm… etc).
If communities removed 100% of volcanic ash the trend would follow the dashed-dotted line. Clearly this isn’t the case. What this suggests is for low amounts of ash (1 mm) just a few percent is removed and disposed (note log scale). Whereas for large amounts (30-40 cm) a much higher percentage is removed. We suggest one of the reasons for this is that the amount of ash removed is consistent with some of the common thresholds given for volcanic ash impacts in urban areas. At low levels municipal authorities concentrate on cleaning roads and leave private property owners to deal with any clean-up on their own. At greater ash thickness it then becomes necessary for municipal authorities to provide assistance to private property owners to clean-up as the volume of ash on a property can become very large.
This provides useful information for municipal authorities as well as for those modelling volcanic impacts and risks which until now have relied on very limited evidence.
The full paper is available free until November 14 from here.