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The vanishing views of Fuji 13 October 2009

Posted by admin in Fuji, Japan, volcano culture.
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Mt Fuji from Nippori Fujimi slope on 18 November 2000 (photo by Mr Naofumi Nakajima).
Mt Fuji from Nippori Fujimi slope on 18 November 2000 (photo by Mr Naofumi Nakajima).

Among the many ways in which human beings interact with volcanoes, one of the most important but also least tangible and hardest to quantify is the simplest of all: looking.

Volcanoes are beautiful, often dramatic elements of the landscape, and people like to look at them. But views are fragile things, particularly where volcanoes are close to constantly-changing urban areas in which the construction of buildings and the effects of pollution mean the obstruction of once-valued views. Perhaps the most notable such case is Mount Fuji, and the New York Times‘s ‘Tokyo Journal’ has a report on the efforts of some Tokyo residents to fight back against the loss of treasured views of Fuji:

Protecting a building or a park may be one thing, but how do you protect a view? Saving the view from Nippori’s Fujimizaka would require capping building heights within an elongated fan-shaped corridor three miles long and up to 1,000 feet wide across densely populated neighborhoods. So far, the society has met stiff resistance from city officials and developers in Tokyo, whose properties rose rapidly from the postwar ashes thanks in part to unrestrained construction.

For centuries, the views of Mount Fuji offered by many parts of the Tokyo region have been a celebrated part of Japanese culture: but as Tokyo’s skyscrapers have climbed into the sky, the views have disappeared. Of the sixteen areas of central Tokyo called Fujimizaka, ‘the slope for seeing Mount Fuji’, there is now only one, in Nippori, from which the volcano can still be seen – just. The threat to this last remaining view of Fuji provoked the establishment of the Citizens’ Alliance to save the Fuji-view (CASF): the picture at the top of this post, from the CASF website, shows what they are up against.

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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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