Rum and the Small Isles : A landscape fashioned by geology The rugged, wild, mountainous landscape of Rum owes its creation to a geological history that stretches back nearly 3000 million years. For such a small island the range of scenery is remarkable - from the jagged peaks of Askival and Hallival in the east, to the rounded hills of Orval and Ard Nev in the west and the flatlands of Kinloch Glen. The spectacular panorama from Rum encompasses the sloping RUM AND THE backbone of Eigg, the rich green pasture of diminutive Muck and the carved basalt coastline embracing Canna and the low-lying Sanday. Held together by the sea, these islands combine a richness of landform, colour and texture with ever-changing light and dramatic weather. Find out how this mecca for geologists was formed over millions of years in this riveting tale of deserts and oceans, volcanoes and glaciers. R UM SMALL ISLES AND A LANDSCAPE FASHIONED BY GEOLOGY THE The silhouette of Rum is one of the most dramatic sights on Scotland’s west coast. Its diverse rocks and SMALL the landscapes they form have developed over billions of years as this part of the Earth’s crust moved across the planet. This guide beautifully illustrates the traces of ancient seas and rivers in the rocks ISLES and, more recently, Rum’s violent volcanic history as the North Atlantic rifted open. Finally ice scraped : and carved the land here as over all of Scotland. The perfect book to take along as you explore. A L Aubrey Manning, Author and Broadcaster ANDSC APE About the Authors F Kathryn Goodenough has worked as a field geologist in Scotland for over five years, first for Scottish Natural Heritage and now for ASHIONED the British Geological Survey. She is particularly interested in rocks formed in ancient volcanoes, both in Scotland and across the world. Tom Bradwell is a Quaternary specialist who has been working for the British Geological Survey for two years. Before turning his B Y attention to Scotland, he studied the deposits of modern glaciers in Iceland. GEOL OG Y ISBN 1 85397 370 2 Price £5.95 Scottish Natural Heritage British Geological Survey Visit our website on www.snh.org.uk NATURAL ENVIRONMENT RESEARCH COUNCIL RUM AND THE SMALL ISLES A LANDSCAPE FASHIONED BY GEOLOGY ©Scottish Natural Heritage 2004 ISBN 1 85397 370 A CIP record is held at the British Library NP3K0304 Acknowledgements Authors: Kathryn Goodenough (BGS) and Tom Bradwell (BGS) Text on pages 20, 21 & 22: Alan McKirdy (SNH) Text on page 35: Alison Grant Series editor: Alan McKirdy (SNH) Photography: BGS 5 bottom, 9, 23, 34; Martin Colbeck/Oxford Scientific 5 top; C.H. Emeleus 4; Lorne Gill/SNH 8, 10, 12, 15, 16, 17, 19, 21, 26, 28, 29, 32, 33; A. Graham Leslie 24; Susan Loughlin 13; Patricia & Angus Macdonald/SNH 7, 11, 14, 18, 27, 35 bottom, back cover; John MacPherson front cover, frontispiece; Alan McKirdy 20; National Trust for Scotland 22 top, 22 bottom, 35 top; Rum Excavation Project 30. Illustrations: Elizabeth Pickett/BGS © NERC except for BGS Drawing Office © NERC 3; Craig Ellery page 2. Further copies of this book and other publications can be obtained from: The Publications Section, Scottish Natural Heritage, Battleby, Redgorton, Perth PH1 3EW Front cover image: Tel: 01738 444177 Fax: 01738 827411 View of Rum from the mainland E-mail: [email protected] Back cover image: Web site: www.snh.org.uk Bloodstone Hill, Orval and the Rum Cuillin, Isle of Rum RUM AND THE SMALL ISLES A Landscape Fashioned by Geology by Kathryn Goodenough and Tom Bradwell NW ORVAL ARD NEV FIONCHRA LONG LOCH TORRIDONIAN SANDSTONE WESTERN GRANITE GABBROS AND PERIDOTITES A diagrammatic cross-section through the Isle of Rum, showing the rocks beneath the surface Contents 1. Introduction 24. The Ice Age 2. Rum Through Time 26. Glacial Clues and Patterns in the Stones 3. Geological Map of Rum and the Small Isles 28. High and Dry 4. Setting the Scene 30. Early People on Rum – 8. Ancient Rivers on Rum Exploiting the Island’s Natural Resources 10. The Rum Volcano 32. The Bulloughs and SNH 12. Explosive Eruptions and Pyroclastic Flows 34. The Landscape Today 14. The Shaping of Western Rum 36. Scottish Natural Heritage and the British Geological Survey 16. From Molten Rock to Manx Shearwaters – The Rum Cuillin 37. Geological Code 18. Flowing Lavas 38. Also in the Landscape Fashioned by Geology Series 20. Eigg 39. SNH Publications Order Form 22. Canna and Sanday - Where Rivers and Volcanoes Meet SE ASKIVAL TROLLAVAL BEINN NAN STAC LAYERED GABBROS AND PERIDOTITES The mountainous, wild landscape of the Isle of Rum has long been a mecca for geologists. For such a small island, the range of scenery is truly remarkable - from the jagged peaks of Askival and Hallival in the east, to the rounded hills of Orval and Ard Nev in the west, and the low "stepped" topography north of Kinloch Glen. As we will see, these features can be attributed to a geological history that stretches back nearly 3000 million years and includes deserts and ocean floors, volcanoes and glaciers. 1 Rum Through Time RECENT TIMES People arrived on Rum nearly 9,000 years ago and have lived on the islands ever since. QUATERNARY ❄ After 2.4 million years, the climate cooled dramatically, plunging Scotland into an ‘Ice Age’. Very cold glacial 2.4 million years up to and including ❄ episodes were interspersed with warmer periods. During the last main glacial period, from 30,000 to 15,000 years recent times ❄ ago, ice moving westwards from the mainland covered Rum and the Small Isles. From 13,000 to 11,000 years ago ❄ ❄ small corrie glaciers existed on the peaks of Rum, but after 11,000 years ago the ice melted and vegetation began to recolonise the islands. People arrived on Rum, nearly 9,000 years ago and have lived on the island ever since. NEOGENE Tropical conditions are widespread, although the climate cools as the Ice Age approaches. 2.4 to 24 million years ago PALAEOGENE Volcanoes developed on Rum and Skye, pouring lava onto the Earth’s surface. Some magma cooled below the 24 to 65 million years ago surface to form granites and gabbros. CRETACEOUS A shallow sea known as the Sea of the Hebrides covered the area of modern-day Rum. The sediments that were 142 to 65 million years ago deposited in this sea have largely been eroded away, and are not preserved on Rum. JURASSIC PERIOD Rapid sea level change marked the beginning of this period, flooding much of Scotland. Dinosaurs roamed the 206 to 142 million years ago coastal fringes and marine turtles, crocodiles and plesiosaurs swarm in the sea. TRIASSIC Western Scotland was a low-lying area, with a warm, tropical climate. Sandstones containing plant fossils were 206 to 248 million years ago laid down in rivers that flowed across the land. These sandstones can still be seen in northern Rum. PERMIAN Deserts formed around the margins of present-day Scotland, but rocks from this time are not preserved on Rum. 248 to 290 million years CARBONIFEROUS Scotland sat astride of the equator. Tropical forests covered parts of Scotland. Decaying organic matter from 290 to 354 million years these forests accumulated to form coals in central Scotland, but on Rum no new rocks were formed. DEVONIAN Rum lay within an area of high ground where no new rocks were formed, whilst sandstones and limestones were 354 to 433 million years deposited in the surrounding rivers and shallow seas. SILURIAN Continental collision led to the formation of a great mountain chain in Scotland, but this part of 443 to 417 million years the geological history is not preserved on Rum. ORDOVICIAN Continental collision led to the formation of a great mountain chain in Scotland, but this part of the geological 495 to 443 million years history is not preserved on Rum. CAMBRIAN Quartz-rich sandstones and limestones formed in shallow seas. These rocks are seen on Skye and along the 495 to 545 million years north-west coast, but not on Rum. PRECAMBRIAN The basement of Rum, the Lewisian gneisses, formed nearly 3000 million years ago and were then deformed and Before 545 million years metamorphosed during huge mountain-building events. Following these events, the Torridonian sandstones were laid down about 1000 million years ago on the beds of rivers flowing over a rocky landscape. 2 Geological Map of Rum and the Small Isles N A N N A C Kilmory F O D N U S O Kinloch MRF Loch Scresort MRF Harris 0 5 kilometres LLF MRF Lavas Cleadale Granite S O U N D O F R U M Rhyodacite and breccia Gabbros and peridotites Triassic and younger sedimentary rocks Torridonian sandstones Major faults LLF Long Loch Fault MRF Main Ring Fault 3 Setting the Scene Outcrops of Lewisian gneiss on Rum The history of Rum began nearly 3000 million years ago, when some many kilometres in thickness. As the sand and pebbles were compressed of the oldest rocks in the world were formed - the Lewisian gneisses. under the weight of the overlying sediment they formed a sequence of These are metamorphic rocks, which were formed when even older rocks, known as the Torridonian. granitic rocks were buried and heated deep beneath the Earth’s surface. They can be seen in a few scattered outcrops on Rum. At that time, the land that now makes up the Isle of Rum was part of a huge supercontinent. After deposition of the Torridonian sandstones, this By about 1100 million years ago, the Lewisian gneisses had been area remained fairly stable for many millions of years, during which time uplifted by immense movements within the Earth.