Tephra, tephrochronology and archaeology – a (re-)view from Northern Europe

Abstract

Volcanic eruptions are often, although by no means always, associated with a profuse output of fine pyroclastic material, tephra. While residence time in the atmosphere of the very finest of these particles can be substantial, the deposition of the bulk of volcanic ejecta can be considered instantaneous from a geological, archaeological, and evolutionary perspective. Often these volcanic products can be identified by various chemical and non-chemical means and if the eruption date is known, the occurrence of tephra from a given eruption in stratigraphic sequences provides a powerful means of dating such deposits, or of refining available dating schemes. Furthermore, the occurrence of tephra from the same eruption across sites, regions and in various types of depositional contexts (ice-cores, terrestrial, marine, cultural) holds the potential of linking and thus elucidating the tempi and causes of both environmental and cultural change. Recent years have seen considerable advances in tephrochronology studies, especially regarding the detection of macroscopically invisible micro-or cryptotephras. In parallel with the possibility of detecting hitherto invisible tephras over vastly increased areas, the overall potential of tephrochronology as a major dating tool for both palaeoenvironmental scientists and archaeologists is greatly expanded. The aim of this paper is not to be comprehensive, but to provide a brief and timely general review of tephra studies and their methodologies, and to make a case for better linking tephra research to archaeology, all from a primarily Scandinavian perspective. We argue that the identification of tephra in archaeological sediments should, in due time, become as routine as other types of geo-archaeological analyses, especially given that tephra cannot only act as a useful chronostratigraphic marker, but can also play a role in changing patterns of environmental and cultural change at the level of the site or the region. In order to move towards such integration, a series of methodological challenges have to be met. We outline some of these, and provide pointers as to how and where tephrochronologists and archaeologists can work together more closely.

Cryptotephras: the revolution in correlation and precision dating

“…These recent exemplary studies mark the beginning of an up‐and‐coming area and Riede and Thastrup () in particular, suitably promote the exciting opportunities that lie ahead. Indeed, one of the key outputs of the RESET project is a classic illustration of the resilience of Neanderthals and early modern humans (Lowe et al , ).…”

“…Optimal conditions for cryptotephra preservation are often difficult to foresee with several negative results reported, but the best return seems to be at sites with large cave openings, low‐energy environments where the bioturbation and erosion processes are low, and often within ‘off‐site’ contexts, typically lakes or peat bogs, that can be correlated to occupation sites (Lane et al , ; Housley and Gamble, ). Riede and Thastrup () strongly argued that future studies should adopt a transect strategy whereby archaeological sites as well as nearby lakes or peat bogs should be sampled to fully assess the continuity of cryptotephra deposits.…”

Tephra without Borders: Far-Reaching Clues into Past Explosive Eruptions

“…A widespread tephra isochron holds considerable promise for the correlation and dating of disparate depositional successions. Several recent papers provide a review of the significance of tephra for paleoenvironmental and archeological studies (e.g., Lowe, 2011;Riede and Thastrup, 2013;Lane et al, 2014;Lowe and Alloway, 2014;Davies, 2015), and the quickly developing field of cryptotephra studies has been considered a revolution in correlation and precision dating of Quaternary deposits (Davies, 2015). In this review we briefly summarize the most recent advances in distal tephra and cryptotephra research that embark on challenges but also offer new opportunities for volcanologists and petrologists.…”

Tephra isochrons and chronologies of colonisation

“…The presence of well-dated tephra isochrones within the archaeological stratigraphy is a major asset when building site chronologies (Lane et al, 2014;Riede and Thastrup, 2013). Tephra can be preserved in situ below and/or above anthropogenic layers where the area has been exposed to atmospheric fallout and aeolian sediment accumulation has not been disturbed (Fig.…”