Variations in tephra stratigraphy created by small-scale surface features in sub-polar landscapes

We explore the effect small-scale surface features have on influencing the morphology and grain-size distribution (GSD) of tephra layers within the Quaternary stratigraphy of sub-polar landscapes. Icelandic thufur, small cryogenic earth mounds, are used to assess how and why the morphology and GSD of tephra layers vary over such formations. Through measurement of tephra layer thickness and GSD, Hekla 1947 and Grimsvotn 2011 tephra layers are analysed. Results indicate that such microtopographic features do indeed alter the form of tephra deposits and therefore the tephra layer that is preserved in the stratigraphy. Tephra thickness is significantly greater in hollows than on the thufur crests. There is greater variation in tephra thickness measurements from thufur in comparison to control measurements from a surface where thufur are absent. Thufur crests contain larger grain sizes than hollows, for both H1947 and G2011 tephras; however this was only statistically significant for the G2011 tephra. Such morphological patterns are thought to arise from an interplay of tephra characteristics, altered topography from the thufur formations and earth surface processes operating at the sites. This study provides insight into the potential of tephra layer morphology and internal structures as indicators of Quaternary landforms and processes. Additionally, it provides important context for the appropriate sampling of tephra layers to infer volcanological processes, as the characteristics of preserved layers do not necessarily reflect those of the original fall-out.