Tectonic Archaeology as a Foundation for Geoarchaeology

This article proposes a new subdiscipline, Tectonic Archaeology, based on the efforts of Japanese archaeologists to deal with the effects of earthquakes, volcanic tephra cover, and tsunami on archaeological sites. Tectonic Archaeology is conceived as an umbrella term for those efforts and as a foundation for Geoarchaeology in general. Comparisons distinguish between Geoarchaeology and Tectonic Archaeology, and a survey of major archaeological journals and textbooks reveals how the concept of ‘tectonics’ and specifically the processes of Plate Tectonics have been treated. Al-though the term ‘tectonics’ occurred fairly frequently, particularly as affecting coastlines and sea levels, it was not thoroughly defined and discussed. Volcanic activity was most mentioned in journals due to its provision of resources and modification of the landscape, while the 2011 earthquake and tsunami in Japan seems to have stimulated more studies in Archaeoseismology. The textbooks were found to have scattered references to Plate Tectonic processes but no clear approach tying these together. The major exception is the Encyclopedia of Archaeology which addresses volcanoes, Archaeoseismology, and tsunami—soon to be linked together vis à vis Earth processes. Tectonic Archaeology attempts first to explain the processes of Plate Tectonics to underwrite investigation of their effects; it is applicable worldwide, in continental and coastal contexts.

Modulation of glacier ablation by tephra coverage from Eyjafjallajökull and Grímsvötn volcanoes, Iceland: an automated field experiment

We report results from a field experiment investigating the influence of volcanic tephra coverage on glacier ablation. These influences are known to be significantly different from those of moraine debris on glaciers due to the contrasting grain size distribution and thermal conductivity. Thus far, the influences of tephra deposits on glacier ablation have rarely been studied. For the experiment, artificial plots of two different tephra types from Eyjafjallajökull and Grímsvötn volcanoes were installed on a snow-covered glacier surface of Vatnajökull ice cap, Iceland. Snow-surface lowering and atmospheric conditions were monitored in summer 2015 and compared to a tephra-free reference site. For each of the two volcanic tephra types, three plots of variable thickness (∼ 1.5, ∼ 8.5 and ∼ 80 mm) were monitored. After limiting the records to a period of reliable measurements, a 50-day data set of hourly records was obtained, which can be downloaded from the Pangaea data repository (https://www.pangaea.de; doi:10.1594/PANGAEA.876656). The experiment shows a substantial increase in snow-surface lowering rates under the ∼ 1.5 and ∼ 8.5 mm tephra plots when compared to uncovered conditions. Under the thick tephra cover some insulating effects could be observed. These results are in contrast to other studies which depicted insulating effects for much thinner tephra coverage on bare-ice glacier surfaces. Differences between the influences of the two different petrological types of tephra exist but are negligible compared to the effect of tephra coverage overall.

Development of Probabilistic Risk Assessment Methodology Against Volcanic Eruption for Sodium-Cooled Fast Reactors

The objective of this paper is to develop a probabilistic risk assessment (PRA) methodology against volcanic eruption for decay heat removal function of sodium-cooled fast reactors (SFRs). In the volcanic PRA methodology development, only the effect of volcanic tephra (pulverized magma) is taken into account, because there is a great distance between a plant site assumed in this study and volcanoes. The volcanic tephra (ash) could potentially clog air filters of air-intakes that are essential for the decay heat removal. The degree of filter clogging can be calculated by atmospheric concentration of ash and tephra fallout duration and also suction flow rate of each component. This study evaluated a volcanic hazard using a combination of tephra fragment size, layer thickness, and duration. In this paper, functional failure probability of each component is defined as a failure probability of filter replacement obtained by using a grace period to filter failure. Finally, based on an event tree, a core damage frequency has been estimated by multiplying discrete hazard frequencies by conditional decay heat removal failure probabilities. A dominant sequence has been identified as well. In addition, sensitivity analyses have investigated the effects of a tephra arrival reduction factor and prefilter covering.