Environmental controls on tephra layer morphology

• Main Author: Thompson, Polly I. J.
• Other Authors: Dugmore, Andrew, Cutler, Nicholas, Attal, Mikael, Lehmann, Caroline, Newton, Anthony, Streeter, Richard, other
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Edinburgh 2023
• Subjects: Environmental controls; tephra layer morphology; surface qualities; past landscapes; tephra; surface environmental conditions; near sub-surface; grain size distribution (GSD); Iceland; Scotland; cryogenic landforms; CT scanning; palaeoenvironmental reconstruction; tephra deposition; tephra downslope; soil micromorphology; stratigraphy; volcanological research
• Online Access: https://hdl.handle.net/1842/40578; https://doi.org/10.7488/era/3343

The overall aim of this thesis is to assess the use of tephra layer morphology to infer surface qualities of past landscapes. By examining how environmental processes affect the development of an enduring tephra record, this thesis assesses the potential of using tephra layer morphology to infer surface environmental conditions of the past. A variety of processes operate at both the land surface and in the near sub-surface that can impact the preservation of tephra layers, and this thesis examines whether this is expressed in layer thickness, morphology and grain size distribution (GSD). A preserved tephra layer may have been fundamentally shaped by the nature of the surface environment at the time the tephra was deposited. These are assessed by examining different tephra layers (up to 20 cm thick) in a variety of different environmental settings in Iceland, collecting over 10,000 individual measurements, combined with controlled experiments in Scotland. A series of case-studied are used: 1) assessing the relationship between tephra layer thickness and GSD with the rate at which the surface tephra deposit is buried and preserved. 2) assessing the effect of small scale topographic features (cryogenic landforms found in Iceland – thúfur) on tephra layer morphology and GSD. 3) identifying the effects of slope angle on the movement of different tephra and the influence of different slope angles on layer formation. 4) evaluating morphological and GSD changes in tephra layers across cultural landscapes to infer land use and 5) testing new ways in which tephra layer morphology can measured and visualised using CT scanning. Results indicate that there are circumstances when environmental processes taking place in the days, weeks, months and years post deposition can indeed alter tephra layer morphology. Therefore, the variable preservation of tephra layers do record aspects of environmental processes and thus may enhance palaeoenvironmental reconstruction. Areas with rapid rates of burial preserve a greater proportion ...