Some reflections on the Eyjafjallajoekull ash cloud

Over the weekend I have been watching and reading the media response to the aviation ban resulting from the Eyjafjallajoekull ash cloud, and reading some of the online discussions.  I would like to make four observations from a natural hazards perspective:

A. This event is the result of a "perfect storm".
I have been surprised by the lack of reflection by the media, including by some scientists (see below), that the current event really is the result of an extraordinary set of circumstances.  To generate the current crisis, three events had to occur simultaneously.

1. The volcano had to suffer an eruption that puts large amounts of ash high into the atmosphere.  Many eruptions do not do this, which is why we rarely see these types of crises even though eruptions occur regularly around the world.  In fact this volcano has been erupting for a month, but the initial events did not inject ash into the high atmosphere. 
2. The jetstream needed to be located over Iceland.  If the jetstream had been to the south then the ash would not have been brought to Europe.  
3. The atmospheric conditions over Europe had to be extraordinarily stable.  Those of us who live here know that what we are seeing in northern Europe is not typical (though it is not all that rare either).  Usually we see a conveyor belt of low pressure systems from the southwest.  At the moment we have stable high pressure and no wind, which means the ash is lingering.

If any of these three conditions had been different then this event would not have occurred.  It is the rare (and quite unlikely) confluence of these three conditions that have led to where we are.

2. Some pronouncements by scientists really have not helped. 
The media are now in a pickle as they have to keep the story on the front page, but finding new angles is a challenge.  For this reason, alarming pronouncements by scientists are a goldmine.  A number of prominent scientists (no names) have been warning that the eruption could go on for months, or even years, and that Hekla might cause an even bigger eruption.  For goodness sake, please stop!  There are no indications that Hekla is about to erupt; the linkage between Eyjafjallajoekull and Katla are not clear; if it did erupt, a similar problem is not inevitable if the jetstream or the European weather conditions are different; and it is not helping to raise concerns about another eruption.  In a similar manner, suggesting that the volcano might cause us problems for months or years is not helping either.  Yes, an eruption may continue, but the chances that it will continue to inject ash into the high atmosphere are not high, and most of the time the ash wouldn't be brought over Europe.

Unfortunately, doom-laden predictions undermine the credibility of science and scientists when the situation calms down, as it inevitably will.  This is not helpful.

3. Environmental science / natural hazards research is grossly underfunded
The third lesson is that these events can have a big impact on our lives and our economy, but our investment in research into them is pitiful.  The limited capability that we have in Europe to collect good samples from the upper atmosphere is all to obvious, for example.  A comparatively small investment in the science would reap large rewards at a time like this, and would provide financial benefits many times greater than the costs.  If there is one thing that should come out of this it is a recognition that we have to invest in hazards research.

4. The general understanding of risk is very poor
It has been extraordinary to see pronouncements that the successful operation of the test flights over the weekend means that the flight ban is an over-reaction.  The fact that a small number of flights can successfully operate does not mean that the skies are safe.  It may be that the safety of, say, only 1 flight in 10,000 is put at risk by the ash, caused by very isolated pockets od denser / more abrasive material.  As there are 28,000 flights per day in Europe, this would not be an acceptable risk.  Unfortunately, due to the lack of research we do not know what true probabilities, but the Finnish F-18 engines suggest that they are far from trivial.

The Tennessee flow slide accident - what went wrong?

The fallout from the recent flowslide accident at the Tennessee Valley Authority's (TVA) Kingston power plant in the USA on 22nd December, which I highlighted here, continue. There is an increasing sense that this was an unacceptable failure (it is hard to argue with that) and that it was lucky that there was not a loss of life in the accident.

This AP image is a good starting point as it is much clearer from this as to what has happened:

Perhaps the most useful resource though is this article from the www.tennessean.com, which I thoroughly recommend. It provides an excellent interpretation of what happened in the lead up to the accident. They have provided two aerial images of the site, before:

And after:


The gist of the article is as follows:

1. The failure occurred on a 20 m high embankment constructed primarily from ash blocks that collected in the base of the plant's burners. The fly ash is deposited into the lagoon in a wet state;
   
2. In November 2003 the lagoon suffered from a blow out (failure) caused by piping and seepage (i.e. water starts to flow through the ash, which then induces erosion. This then allows a pipe to form, which collects, channels and accelerates the flow, allowing erosion to intensify. This can rapidly create a weak zone);
3. In December 2003 a mitigation scheme was proposed, consisting of "a series of trench drains at different levels on the dike, another drain at the base of the mound and a riprap (i.e. armoured) channel."
4. This mitigation scheme was completed in October 2005
5. In 2006 a further failure occurred, with a 1.5 x 1.5 m section failing through seepage, releasing some ash;
   
6. This section was repaired and wells were installed behind the embankment, presumably to lower water pressure, monitored using 30 shallow piezometers;
7. The article mentions that the embankment was inspected and passed in a report produced on 15th February 2008 and found to be stable, but that "plant operators were commended for mowing the landfill slopes. Trees too large to be mowed should be cut, the stumps removed, the area backfilled with soil and seeded". "They mentioned small trees being removed," said Tschantz, the dam safety consultant. "I'm wondering if trees had a role to play. You don't just pull those things out. The root channels have to be filled and compacted."

In December 2008 the site received 125 mm of rainfall (the average for December is 70 mm). Failure occurred on 22nd December.

Clearly it is far too early to identify exactly what has gone wrong or who, if anyone, is to blame. The key issues must be to clear up the mess and to learn the lessons, especially if there are other sites that are also vulnerable to failure. One suspects that the costs of this incident will be very high indeed - far more than the cost of constructing a safe embankment in the first place.

I do recommend the article (here) - it appears to be a good piece of journalism.

As an aside, it appears from the images that sections of the embankment have been moved intact (see image below - these can also be seen in the photo at the top of this post):

The sides of the embankment also appear to have failed (marked "lateral failure?" above). This suggests to me that pore pressures in the ash were very high indeed. I wonder if a factor here is the use of ash in the embankment as its comparatively low density might have made the embankment rather vulnerable to failure due to high buoyancy forces.

Ash flowslide at Knoxville, Tennessee

A few months ago Shaanxi Province in China suffered a dreadful flowslide when the dam holding back mine wastes collapsed, releasing an avalanche of material onto the town below. About 260 people were killed. On 22nd December, what appears to be a similar failure occurred at Knoxville in Tennessee, USA, when the retaining wall holding back coal ash from the Tennessee Valley Authority Kingston Steam Plant in Harriman power station collapsed, releasing an estimate 2 million cubic metres of waste, which then flowed down slope (image from Knoxnews).


Fortunately, the area below was only sparsely inhabited, so in this case no-one has been killed, but about a dozen homes have been rendered uninhabitable and, as the picture above shows, a train was also hit (image from Knoxnews).


Microsoft Virtual Earth has this rather nice black and white image of the site, which I have annotated to show the salient features (click on the image for a better view in a new window):


The image below shows the crown of the failed area (see annotation) - comaprison with the above image confirms which part of the storage pond has failed (image from Knoxnews):


However, as the image below shows, the failure affected a very large part of this lower set of ponds (image from Knoxnews):


My current interpretation of what has happened is shown below, which is an annotated zoom-in of the MicrosoftVirtual Earth image above:


Interestingly, the mass of mobile ash also appears in places to have caused the ground to fail without flowing. This image shows the access road to the site - note how the material has moved forward over the road without fluidising (image from Knoxnews):


That such a failure should occur is extraordinary, given that the danger of flowslides has been known for over 40 years. The only fortunate aspect of this is that no-one was killed, which seems to be a matter of luck given the volume and mobility of this landslide. However, coal ash is an unpleasant material (which is why it is stored in ponds like this), sometimes containing lad, arsenic and mercury amongst other heavy metals, although in very low concentrations. The major issue will probably be dealing with the sludge before it enters the watercourses.

Accidents like this should not be allowed to happen - they are utterly avoidable. I hope that a review is underway to ensure that there is no repeat.