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Pumice in the North Atlantic

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Pumice in the North Atlantic Ocean-transported pumice in the North Atlantic Anthony Newton PhD University of Edinburgh 1999 Declaration I, Anthony Newton hereby declare that the work contained herein is my own and has not previously been presented for examination. Any contributions by others is acknowledged in the text. September 1999 ii For Keith Newton 1930-1984 iii “Some days we would pass through pumice lying in ridges, each piece uniformly the size and appearance of a bath sponge, then again we should pass through perfect fields of small yellow pumice spread evenly over the surface just for all the world like a green field of grass covered all over with buttercups, and the undulation of the swell of the trade wind produced an indescribably pretty appearance.” (Reeves, 1884). iv Abstract The overall aims of this study are to identify the sources of the widespread Holocene pumice deposits found along the coasts of the North Atlantic region and establish the ages of the source eruptions. In order to tackle this, it is necessary to determine whether it is possible to “fingerprint” the pumice of individual eruptions and link ocean-transported material with the established tephrochronological framework based on the stratigraphy of airfall deposits. Over 1500 electron probe microanalyses and over 200 Secondary Ion Mass Spectrometry analyses have been undertaken on pumice and tephra samples. These are the first high quality grain specific analyses carried out on ocean-transported pumice in the North Atlantic. Current knowledge of the extent of pumice distribution in the North Atlantic region is assessed for both shoreline (natural) and archaeological contexts. Pumice pieces have been recovered from Holocene raised shorelines of north-west Iceland for the first time. Further original fieldwork in Norway has confirmed the presence of multiple levels of brown, black and grey pumice on mid-Holocene Norwegian raised beaches and white pumice on early- Holocene shorelines. Archaeological pumice, donated by collaborators, from sites in the British Isles has also been analysed. The number of archaeological sites where pumice has been recorded has been doubled to 150. All of the analysed pumice can be correlated to volcanic activity in Iceland. These analyses establish that the majority of the mid- to late-Holocene pumice found in the North Atlantic area is dacitic and produced from Katla. A collaborative project identified 17 silicic tephra layers (SILK layers) produced by the Katla, ten of which are linked to pumice production between c. 6600 and 1626 14C years BP. Geochemically different and older pumice also occurs in Mesolithic archaeological sites in Scotland and this was also produced by Katla. Some of this older Mesolithic pumice was probably erupted by Katla c. 7000 14C years BP. The remainder of the pumice was erupted by early Holocene activity at Katla, which also deposited pumice on the flanks of the volcano. In addition, early Holocene activity from Öræfajökull produced pumice found on a raised shoreline in Norway. The 1362 AD eruption of the same volcano produced the white pumice found in three medieval archaeological sites in Scotland. The pumice found on raised shoreline in Svalbard was produced by eruptions from both Katla and the island of Jan Mayen. Crucially, the most prolific Icelandic producer of distal tephra layers, Hekla, is not the source of any of the pumice found around the North Atlantic. It is suggested that this could be because of the fragile nature of the Hekla pumice. This work shows that high quality geochemical data is essential if correlations are to be made between pumice deposits and sources, and highlights both the potential and limitations of the use of pumice as a tephrochronological tool. v Acknowledgements Without the help of many friends, colleagues and strangers it would have been impossible to finish this thesis. Many thanks to my supervisors Dr Andrew Dugmore and Prof. David Sugden for their encouragement and support over the years. Guðrún Larsen has often provided invaluable information, support and samples, which would have been impossible to obtain from any other source. Without her collaboration this thesis and much of the other research I have been involved in would not have been completed. Thank you. Prof. Paul Buckland has always been enthusiastic about my work and has been a constant supplier of pumice of all shapes and sizes from virtually everywhere. No piece of pumice is too small. Particular thanks must go to the many people who have assisted me in the field. Andrew Dugmore has helped on many fieldtrips and has always been there with his infectious enthusiasm. Malcolm Murray provided invaluable help, surveying skills and that crucial extra pairs of eyes during the Norwegian fieldwork. Rob Rolph provided the same enthusiastic support in Strandir and a calm head during a crisis. Hreggviður Norðdahl also accompanied me to Strandir on a less dramatic trip and provided and translated Icelandic tide tables. Many thanks also to Jane Boygle, Sukhvir Parmar and Richard Corrigan for their help on my first quick visit to Strandir. Also to Fiona Foley who helped with fieldwork in Norway. Stienar Nilsen identified several pumice sites in Hitra, Norway and donated some of the pumice he had collected over the years. Prof. Sven Jakobsson kindly allowed me to search the collections of the Náttúrugripasafnið (Museum of Natural History) in Reykjavík and remove some of the pumice. Acknowledgement must also be made to the trusty old Lada which provided interesting, but surprisingly reliable transport in Norway and on one visit to Strandir. Toyota must be thanked for building their vehicles strong and the Icelanders for having very soft bogs. Also many thanks to the kind people who run the Hotel Djúpavík, Strandir. Gillian Boniface kindly provided accommodation for Malcolm and myself in Bergen and Guðriður and Hafliði have done the same on countless occasions in Reykjavík. Mary made and Bob christened the whale which was the star of the Norwegian fieldwork, thanks. vi This thesis would not have been possible without the generous donations of pumice by archaeologists and other researchers. These people also kindly supplied much supplementary information often from unpublished work. So thank you in alphabetical order: Dr Torbin Ballin, Dr Beverley Ballin-Smith, Jerry Biglow, Prof. Paul Buckland, Dr. Ann Clarke, Dr Ciara Clarke, Dr Claire Cotter, Trevor Cowie, Dr Barbara Crawford, Iain Crawford, Dr Anne Crone, Dr Bill Finlayson, Dr Ewan Mackay, Dr Ann MacSween, Dr Rod McCullagh, Dr Steve Mithen, Prof. Ian Ralston and Melanie Smith. Thanks also to Trevor Cowie and Alison Sheridan for running the pumice searches on the NMS databases. All of the geochemical analyses were undertaken at the Department of Geology at the University of Edinburgh. Electron probe microanalyses were carried out with the kind assistance of Dr Peter Hill, Dr Stuart Kearns and Simon Burgess. Ion probe analyses and scanning electron microscope work were supervised by Dr John Craven. X-ray Fluorescence analyses were undertaken by Dr Dodie James. Instrument time for the ion probe analyses was provided by NERC Scientific Services and funding for fieldwork in Norway and Iceland was provided by two generous grants from the Carnegie Trust for the Universities of Scotland. I am particularly grateful to Malcolm who read the whole text and Maeve who read Chapter 1. They both suggested essential changes and supplied encouragement when it was needed most. Any mistakes in this work, however, are my own. Maeve and Sarah also helped me piece the final versions of my thesis together, thank you. Also many thanks to my friends in Geography and elsewhere for the laughs and friendships which have kept me going and helped me finish this thesis. I am also grateful to Dr Bill Phillips and Prof. David Gilbertson for taking the time to carefully read my thesis and suggest many constructive comments. I would like to finally thank my Mum for all her love, help and support over the years. vii List of Contents DECLARATION ii ABSTRACT v ACKNOWLEDGEMENTS vi LIST OF FIGURES xii LIST OF TABLES xix 1. PUMICE: PRODUCTION, TRANSPORTATION AND DEPOSITION 1.1 AIMS 1 1.2 IMPORTANCE 1 1.2.1 Volcanological 2 1.2.2 Archaeological/Environmental 3 1.3 INTRODUCTION 3 1.4 THE NATURE OF PUMICE AND TEPHRA 4 1.5 PUMICE FORMATION 5 1.5.1 Dry pumice formation 6 1.5.2 Wet pumice formation 10 1.5.3 Subglacial pumice formation 15 1.6 TRANSPORTATION OF PUMICE 19 1.6.1 Waterlogging of pumice 19 1.6.2 Near source processes 20 1.6.3 Oceanographic processes 23 1.6.4 Summary of pumice transportation 37 1.7 DEPOSITION AND REWORKING OF PUMICE DEPOSITS 37 1.7.1 Deposition and reworking of pumice 38 1.7.2 Human activity 38 1.8 SUMMARY OF CHAPTER 1 39 2. NORTH ATLANTIC PUMICE: A CRITICAL REVIEW 2.1 INTRODUCTION 40 2.2 SPATIAL AND TEMPORAL DISTRIBUTION OF PUMICE 40 2.2.1 Canada and Greenland 42 2.2.2 Svalbard 44 2.2.3 Iceland 49 2.2.4 Scandinavia 52 2.2.5 British Isles 66 viii 2.2.6 Summary of the spatial distribution and temporal of pumice in the North Atlantic 92 2.3 ORIGIN OF PUMICE 93 2.3.1 Geochemical data 93 2.3.2 Possible sources 96 2.3.3 Transport routes 98 2.4 SUMMARY OF CHAPTER 2 100 3. PUMICE FROM RAISED BEACHES: NEW DATA 101 3.1 INTRODUCTION 101 3.2 PUMICE SITES 102 3.2.1 Surveying techniques 102 3.2.2 Norway 103 3.2.3 Iceland 115 3.2.4 Scotland 125 3.2.5 Summary of new finds from raised shorelines 125 3.3 GEOCHEMICAL ANALYSES: TECHNIQUES 126 3.3.1 Electron Probe Microanalysis 126 3.3.2 X-ray Fluorescence Analysis 129 3.3.3 Secondary Ion Mass Spectrometry 131 3.3.4 Summary of geochemical analytical techniques 132 3.4 GEOCHEMICAL ANALYSES OF PUMICE 133 3.4.1 Norway 133 3.4.2 Iceland 156 3.4.3 Scotland 163 3.4.4 Summary of the new geochemical data 167 3.5 COMPARISON WITH PUBLISHED DATA 168 3.6 SUMMARY OF CHAPTER 3 171 4.
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