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Tephra not good for the teeth 29 September 2009

Posted by admin in calderas, current research, Germany, Laacher See, natural hazards.
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Are supervolcanoes bad for your teeth? Those of us who grind our teeth whenever slapdash science journalists throw the word ‘supervolcano’ into any story connected with a large-ish volcanic eruption have certainly found this to be so (take a bow, Discovery Channel). However, take out the spurious supervolcano angle and there is a serious scientific story here* about the mechanisms through which volcanic activity directly affects the material basis of human existence.

The Laacher See eruption was a significant volcanic eruption that took place in the Eifel volcanic zone in what is now western Germany around 13,000 years ago. The eruption plume may have reached 20 km altitude and the volume of material ejected was around 6.3 cubic km (source), which on the Volcanic Explosivity Index makes it a VEI=5 or 6. The resulting caldera, filled with water to form a rather lovely lake, is now known as the Laacher See. This eruption, it has been argued, had wide-ranging effects on contemporary human societies, causing large-scale depopulation and migration, disrupting and bringing to an end some cultures and leading to the creation of others.

The eruption covered a vast area with pulverized volcanic debris – the Laacher See Tephra. The tephra reached as far as southern Scandinavia and northern Italy: it has been traced up to 1100 km north, 600 km south, and 100 km southwest of the Laacher See caldera. This very fine and highly abrasive material would have covered everything, making any food consumed by animals and people in affected areas into a form of unpleasant and unhealthy sandpaper. An article in the October 2009 Journal of Archaeological Science (link to abstract at ScienceDirect) by Felix Riede of Aarhus University and Jeffrey M. Wheeler of the University of Cambridge investigates the issue of tephra as a dental abrasive:

Our results show that the Laacher See tephra contained particles roughly twice as hard as even the hardest portions of any of the teeth investigated. We also suggest that fluoride-induced weakening of dental enamel may have further aggravated tooth wear. These mechanisms may have acted in concert to produce elevated levels of, in particular, animal mortality, which in turn may have led to an abandonment of the affected landscapes.

The article suggests that the tephra may have continued to affect the landscape for as much as 300 years after the eruption. Interestingly, recent research based on studies of the current Chaitén eruption suggests that the impact of ashfall from past eruptions has been significantly underestimated, so tephra deposited by eruptions such as Laacher See may have spread wider, and endured for longer, than has been previously thought.

Parts of the Eifel volcanic zone have been active in the very recent past (geologically speaking: less than 10,000 years ago). Current activity at Laacher See itself, says Hans-Ulrich Schmincke’s Volcanism, is marked by ‘a strongly CO2-bubbling area about 200 m long along the east shore … The composition of these gases is magmatic and closely resembles those of Lake Nyos’, and ‘The area around the Laacher See basin is characterized by elevated microseismic activity’ (p. 207). Schmincke regards the Laacher See volcano as dormant, not extinct.

P.S. Dr Klemetti has posted about Laacher See and its abrasive tephra at Eruptions, and has accumulated some very interesting comments on the topic.

* To be fair, the Discovery Channel has quite a decent news report on the Laacher See Tephra research. Just try to ignore the two instances, one being in the title, of that word ‘supervolcano’, and the accompanying picture of a volcano utterly unrelated to the story being reported.

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Comments

1. Gijs - 29 September 2009

Great post on the subject! Laacher See is definitely one of my favourite volcanoes. It’s only 200 km from where I live, and having such a volcano in my ‘backyard’ is pretty awesome. I go there a lot to collect rock samples, to do field trips with my students, and to just enjoy the volcanic landscape. I’m going there again this saturday to prepare another field trip and to collect some minerals with some friends. Who’s joining us ^_^ ?

I’m not very sure on the status of Laacher See as being a ‘dormant’ volcano. Most of the volcanoes in the area are monogenetic, so the chance of new eruptions happening in the future (http://volcanism.wordpress.com/2009/09/21/australia-overdue-for-volcanic-eruption/ ) at sites other than the Laacher See seem te be pretty big. On the other hand, what does the word ‘chance’ really mean in geology…

2. admin - 29 September 2009

Thanks for the comment, Gijs. Schmincke calls Laacher See ‘dormant’, but perhaps one of the (many) problems with the dormant/extinct terminology is that ‘dormant’ is often understood – popularly, at least – as meaning ‘will erupt again’, whereas ‘has erupted in the past, currently shows some activity, *may* erupt again’ would be better. If less concise.

So, the active degassing would justify Laacher See being regarded as dormant rather than extinct, even if a future eruption at this particular site is unlikely. New monogenetic volcanoes elsewhere in the same area would be, as you say, the most likely form new eruptive activity would take.

It all goes to show, northern Europe is as volcanically interesting as anywhere else!


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