Impact of small-scale vegetation structure on tephra layer preservation

Nick A Cutler,Richard T Streeter,Olivia M Shears,Andrew J Dugmore

doi:10.1038/srep37260

Abstract

The factors that influence tephra layer taphonomy are poorly understood, but vegetation cover is likely to play a role in the preservation of terrestrial tephra deposits. The impact of vegetation on tephra layer preservation is important because: 1) the morphology of tephra layers could record key characteristics of past land surfaces and 2) vegetation-driven variability in tephra thickness could affect attempts to infer eruption and dispersion parameters. We investigated small- (metre-) scale interactions between vegetation and a thin (<10 cm), recent tephra layer. We conducted surveys of vegetation structure and tephra thickness at two locations which received a similar tephra deposit, but had contrasting vegetation cover (moss vs shrub). The tephra layer was thicker and less variable under shrub cover. Vegetation structure and layer thickness were correlated on the moss site but not under shrub cover, where the canopy reduced the influence of understory vegetation on layer morphology. Our results show that vegetation structure can influence tephra layer thickness on both small and medium (site) scales. These findings suggest that some tephra layers may carry a signal of past vegetation cover. They also have implications for the sampling effort required to reliably estimate the parameters of initial deposits.

Highlights

Layers of tephra preserved in the stratigraphic record are sometimes uniform, with sharply defined upper and lower boundaries
Given that most land surfaces have some sort of vegetation cover, a greater understanding of the interaction between plants and tephra deposits would have global utility in the interpretation of tephra layers and their origins
The Fossdalur-moss site (Fm) was mossy heathland; the Fossdalur-birch (Fb) site had a canopy of short-statured birch and a grassy ground layer

Summary

Introduction

Layers of tephra (pyroclastic fragments of different sizes) preserved in the stratigraphic record are sometimes uniform, with sharply defined upper and lower boundaries. Recent work has suggested that vegetation cover at the site of deposition may influence the morphology of thin, terrestrial tephra layers on a landscape scale[1] (smaller-scale relationships remain largely unexplored). If vegetation structure does influence preservation, some tephra layers could, in principle, be used to infer characteristics of the surface environment contemporaneous with the eruption. Correlation between small-scale vegetation structure and tephra layer thickness could give new insights into land surfaces at the time of past volcanic eruptions. The signal generated by heterogeneous vegetation could have a major impact on the production of isopach maps from stratigraphic records and the reconstruction of past fallout volumes To assess this phenomenon, we surveyed a recently deposited tephra layer in areas of contrasting vegetation cover.

Methods

Results

Discussion

Conclusion