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.

Extraordinary video of a Jokulhlaup in Iceland

A jokulhlaup is a sudden release of water from beneath a glacier.  One of the key triggers for Jokulhlaup is the eruption of a volcanic beneath an icecap.  It shouldn't be a surprise to hear that jokulhlaups have been triggered by the Eyjafjallajokull eruption that is causing such chaos across Europe (guess who was supposed to go to Hong Kong on Thursday...), and increasingly beyond.

Now, a jokulhlaup is not technically a landslide, but as these flood carry vast amounts of debris they are at the hyper-concentrated flow / debris flow end of the flood spectrum.  On that basis I thought it reasonable to show this fantastic video of a jokulhlaup cascading off the margins of the Eyjafjallajokull volcano on 14th April 2010:



Incredible!

Is a lavafall a landslide?

The Mountain Cat Geology blog has an astonishing image of a lavafall in Iceland following the recent eruption (click on the image for a better view in a new window):

I wonder whether this is technically a landslide, given that it is a mass movement consisting entirely of rock?

El Salvador landslide disaster

The nature of the landslide disaster in El Salvador caused by Hurricane Ida is now becoming a little clearer. The largest event appears to have happened in the town of Verapaz, where it appears that a debris flow hit and destroyed part of the town. The reported death toll is 16 people, with a further 47 thought to be missing.

There are two intriguing aspects to this landslide. The first is that the maps seem to show that Verapaz is some distance from the San Vicente volcano (also known as Chichontepec volcano) from which the landslide (probably actually technically a lahar) came, as the Google Earth image below shows:

So, I wonder whether the landslide actually affected this town - in which case it is very large indeed- or whether it was one of the smaller communities nearer to the volcano.

Second, this area was affected by an earthquake on 13 February 2001, which killed over 300 people. www.elsalvador.com has an interesting comparison image:

This is clearly not the same street.

Acciording to this abstract, In that earthquake two landslides were triggered on San Vicente volcano (the volcano shown above). Part of the abstract states (note my emphasis):

"Large landslides dammed two major rivers, the Río El Desagüe and Río Jiboa, and two large slides occurred on Volcán San Vicente. The ±1.5-million-m³ Río El Desagüe landslide temporarily dammed the river and formed a shallow, 1.5-km-long lake, but the dam has been overtopped and is stable. The ±12-million-m³ Río Jiboa landslide blocked about 700 m of the valley with debris composed of poorly consolidated tephra, and the upstream lake could potentially have been as deep as 60 m and about 2 km long. A 20-m-deep spillway was excavated to decrease the maximum lake volume and reduce the possible catastrophic failure of the unstable landslide dam. On the northern flank of Volcán San Vicente, ±250,000 m³ of loose landslide debris filled the upper part of Quebrada El Blanco; remobilization of this material in debris flows could inundate part of a downstream village. On the volcano's northwest flank, ±200,000 m³ of lithified andesite blocks slid in the upper part of Quebrada Del Muerto, but this material will not likely remobilize and threaten downstream settlements.."

Verapaz is to the north of the volcano.

The presence of potentially dangerous landslides on the northern flank of the volcano is fairly clear:

The Casita landslide revisited

One of the most deadly hurricanes of modern times was Hurricane Mitch, which tracked across Central America in late October 1998. Many of the tens of thousands of victims were killed by landslides. Perhaps the most notable event was a lahar (a volcanic landslide) that swept down from near the summit of Casita volcano in Nicaragua, killing about 2500 people over the course of its 6 km path (and some more in the hyper-concentrated flow (debris rich flood) events that travelled a further 10 or so kilometres from the toe of the slide. Unfortunately, despite the magnitude of this event the amount of published literature about it has remained quite limited. It is therefore terrific that a paper has just been published by Graziola Devoli and her colleagues (Devoli et al. 2009) that seeks to summarise the published and unpublished reports about this remarkable landslide.

Wikipedia has a very decent image of the upper track of the landslide, which gives a pretty good idea of the scale of this event:

Whilst MDA have a great overview image of the source, track and runout zone:

Complex landslides such as this are poorly understood. In particular, as in the landslides that I highlighted in Sichuan, the mechanisms of initiation and movement are quite intricate. Devoli et al. (2009) have used a range of geological, geotechnical and analytical techniques to get a better idea of what happened.

The landslide was triggered by very heavy rainfall - they suggest that about 750 mm (that's about a years worth for where I live) of rain fell in a little over 80 hours. Interestingly, they conclude that the landslide can be divided into three key phases:

1. Failure started in a fractured and altered volcanic breccia in the northern area of the scarp which released a volume of about 260,000 cubic metres. The flow that developed from this failure swept downslope and entrained colluvium deposits at the toe of the slope in the southern part in less than about 40 seconds.
   
2. The rapid removal of the colluvium on the slope triggered a second failure. This also originated in the scarp shown on the image above. In this phase about 640,000 cubic metres of volcanic breccia slipped over a unit of clay-rich pyroclastic deposits. It is unclear as to whether this flow joined the first one or occurred separately. Either way, blocks in this flow travelled 9 km or more downslope.
   
3. The third and final stage consisted of a as a sudden debris / rock avalanche that originated in the uppermost section of what is how the landslide scar. This failure, with a volume of 690,000 cubic metres, appears to have occurred very soon after the first two events.

In the aftermath there has been considerable concern raised about the likelihood of failure of the entire flank of Casita Volcano (indeed, even I have published on this theme - see van Wyck de Vries et al. 2000). The paper concludes that under conditions of high groundwater instability of these flanks can occur, although as we understand these very large failures so poorly I would be cautious in the interpretation of this particular result. This is a slope that needs an active monitoring programme for sure.

References
Devoli, G., Cepeda, J. and Kerle, N. 2009. The 1998 Casita volcano flank failure revisited — New insights into geological setting and failure mechanisms. Engineering Geology, 105, 65-83.

van Wyk de Vries, B., Kerle, N., Petley, D., 2000. A sector collapse forming at Casita
volcano, Nicaragua. Geology 28, 167–170.