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The aim of this thesis is to evaluate the use of microscopic volcanic ash (‘cryptotephra’) layers for providing information on the timing, characteristics and spatial extent of past volcanic ash clouds. The fine ash produced by explosive eruptions can travel long distances and even in low concentrations represents a hazard for aviation. Understanding the frequency and nature of ash clouds is important if economic and social losses are to be mitigated. This thesis is split into two research compartments. Compartment 1 focusses on understanding the limits of tephrochronology and investigates cryptotephra preservation and reworking bias in lakes and peatlands. Compartment 2 focusses on applying cryptotephras as records of ash cloud events. In addition to the objectives which fit into the two research compartments, two overarching objectives were outlined. These objectives focus on conducting new field campaigns in order to fill spatial gaps in existing cryptotephra records through the development of new, high quality tephrostratigraphies. I examine tephra layers from 13 new sites and contribute toward filling spatial gaps in northern European tephra records in northern Sweden, Poland, Wales and Southern England. Three new tephra layers are identified as part of this study, two in northern Europe: a basaltic tephra, CLA-L1 most likely derived from an eruption of the Iceland’s Grímsvötn volcano and SN-1, from the Icelandic Snæfellsjökull volcano - identified for the first time in mainland Europe. Finally, the AUC-1 tephra traced to a probable Ecuadorian source, represents the first discovery of a Holocene cryptotephra in the Amazon basin and highlights the opportunities for extending tephrochronology to tropical peatlands. In this study I present a number of methodological advances which are important for the design of future tephra studies, including: the replicability of tephrostratigraphies from a mid-latitude peatland; differences in lake and peatland records even at sites in close proximity; and the robustness of tephra glass shard geochemistry to acidic conditions and acid extraction. Beyond methodological advances, this study demonstrates how cryptotephra records can be utilised in new ways to compliment proximal records of volcanism; includes the first comprehensive analysis of distal tephra shard size (9500 shards); and presents a new recurrence estimate for the frequency of ash cloud events over northern Europe (44 ± 7 years).

This thesis investigates new late Quaternary vegetation records from four sites in the Craven District of the Yorkshire Dales. The chosen sites fall along an east-west transect broadly following the line of the south Craven Fault. The rationale for site selection was not based on conventional palynological considerations of potential for rich core samples, rather to provide a range of different locations within a distinct micro-region each existing in some specific proximity to known archaeological features. The logic was to attempt to get beyond broad 'natural' climatological and vegetational inferences to understand the nature and level of potential anthropogenically produced change at a local scale as a sub-set of natural change in a broader regional zone over time. The sites reveal varied vegetation histories from the Late Glacial period to the present day and all show signs of being influenced by changes in their arboreal structure at some time, although no two sites have exactly the same vegetation communities until around 5000 BP when the tree canopy is opened to allow an open grassland to dominate. The results indicate the possibility that Betula values, in particular, might indicate cooling events found in the Greenland ice cores for Greenland Interstadial 1 as well as the Pre-boreal Oscillation and the Holocene 9.3 ka BP Event. Closer chronological control of such values could help to determine whether vegetational dynamics were synchronous with fluctuations in temperature and the speed with which trees respond to severe temperature fluctuations. Various hiatuses identified during analysis of the cores may be caused by human influence on the wetlands, given that archaeological evidence from caves shows human occupation of the Craven area from the late Upper Palaeolithic onwards.