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Funding: This work was supported by the NERC Doctoral Training Partnership Ph.D. studentship: NE/ L002558/1 to PT. We explore whether the rate at which a tephra deposit is buried influences the variability (thickness and grain size distribution) within the tephra layer subsequently preserved within the stratigraphic record. This has important implications for understanding how processes of soil formation interact with the creation of a volcanic record. To assess the relationship between soil formation and the preservation of tephra layers, the thickness and grain size distribution of the Katla 1918 tephra in Iceland and the rate at which it was buried (inferred from the thickness of the overlying soil) was measured 1620 times at six locations. Tephra layer thickness does not correlate with rate of burial, but the proportion of original deposit retained does, and variations in grain size distribution are correlated with burial rate. Our results indicate that whilst medium term (i.e. years-decades) burial processes may contribute less to tephra layer variability than environmental processes operating immediately after deposition, rapid burial facilitates better preservation of the original fallout characteristics with important implications for the accurate reconstruction of past volcanic eruptions based on tephra layer characteristics. There are two key implications: firstly, sites need to be chosen where surface characteristics minimise the initial alterations of tephra deposits, and secondly sites with rapid burial will produce the best quality data, although workable data can be gathered elsewhere if areas of uncertainty are acknowledged. Publisher PDF

This paper reflects on the application of tephrochronology in geomorphology. A common use of tephra layers is to define isochrons and use them to date environmental records. Applications of tephrochronology with the greatest practical utility, however, involve both classic isochrons (layers with an extensive distribution, distinctive well-characterised properties and good independent dating) and all other tephras present, including poorly-identified, unprovenanced and re-mobilised units that define time transgressive horizons. The effective use of this ‘total tephrochronology’ requires replication across multiple sites, the clear identification of primary tephra deposits and re-mobilised deposits, combined with a good understanding of when tephra deposits truly define isochrons. Large scale replication of tephra stratigraphy is possible (and desirable) with terrestrial sequences, and can offer a detailed understanding of both geomorphological processes and human interactions with the environment. It is possible to use sequences of unprovenanced tephras as a ‘barcode’ to undertake local correlations and refine the application of well-known marker horizons to environmental records. High frequency and high resolution measurement of both the units between tephra layers and the tephra layers themselves can identify subtle shifts in landscape stability and land use.

We provide evidence of rapid, recent environmental change in two lakes in the highlands of central Mexico. Multiple sediment cores were obtained from Lago de Zirahuén (Michoacán) and Laguna de Juanacatlán (Jalisco). Analysis of diatom assemblages, magnetic susceptibility, and metal concentrations was carried out, with the chronology provided by 210Pb dating, 14C dating, and tephrochronology. There is evidence of catchment disturbance during the colonial period in both basins, but the most striking feature at both sites is the rapid change in diatom assemblages during the last 20 y, indicating the onset of eutrophication. Limnological data from Lago de Zirahuén support this interpretation, although none are available from Laguna de Juanacatlán. Paleolimnology is a powerful tool in tracking recent change, particularly in the absence of regular limnological monitoring programs. These lakes appear to be highly sensitive to changes in catchment exploitation, which must be considered in future drainage basin management.