A Geopark is an area with an outstanding geological heritage and a strategy to promote that heritage for the benefit of the local community.
So what makes a geopark? A geopark must contain several geological or geomorphological sites of national and international importance. These may be significant because of their scientific quality, rarity, aesthetic appeal or educational value. But geoparks are not just about rocks - they are also about people, and helping communities to understand their Earth heritage, and to benefit from it.
A geopark can include not only sites of geological importance, but also sites of archaeological, ecological, historical or cultural interest. A geopark territory must be large enough to allow for true economic development. Geoparks are driven by local communities that want to celebrate their Earth heritage and thereby achieve sustainable development of their area through 'geotourism'.
A geopark must play an active role in the business of the European Geoparks Network. This involves collaborating with other geoparks on joint projects as well as exchanging ideas on how best to promote geopark activities.
About Lochaber Geopark - mu pairc-geòdha Loch Abair
The Lochaber area is famous for its spectacular scenery. Lochaber Geopark Association aims to raise awareness of the extraordinary story behind the local landscape. Many geological features of national and international importance can be seen right across Lochaber - ranging from a deeply eroded volcano on Rum in the west, to the amazing Parallel Roads of Glen Roy in the east.
The outstanding quality of Lochaber's Earth Heritage was officially recognised in April 2007 when Lochaber was awarded European and Global Geopark status.
For more information about the Small Isles and Lochaber Geopark, visit www.lochabergeopark.org.uk/index.asp
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.
The history of Rum began nearly 3000 million years ago, when some of the oldest rocks in the world were formed - the Lewisian gneisses. These are metamorphic rocks, which were formed when even older granitic rocks were buried and heated deep beneath the Earth's surface. They can be seen in a few scattered outcrops on Rum.
By about 11000 million years ago, the Lewisian gneisses had been uplifted by immense movements within the Earth. Erosion on the surface had worn away these rocks to a bare, hummocky land surface looking rather like that of much of the Outer Hebrides today. The area which today makes up Scotland then lay much closer to the equator and had a warm, arid climate. Torrential rivers flowing across this landscape deposited sand and pebbles that accumulated into a pile of sediment many kilometres in thickness. As the sand and pebbles were compressed under the weight of the overlying sediment they formed a sequence of rocks, known as the Torridonian.
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 area remained fairly stable for many millions of years, during which time the rocks that make up much of the Highlands today were laid down near the margin of the supercontinent. Scotland was separated from the rest of modern Europe by an ocean that gradually narrowed through the process of continental drift - until England and Scandinavia collided with Scotland around 430 million years ago.
This continental collision led to the formulation of a mountain range that may have been as high as the modern-day Alps. The eroded remnants of this mountain chain form much of the Highlands today.
The next chapter in Rum's story began some 250 million years ago, in the Triassic Period, the mountains had been largely eroded away, and the western side of Scotland was a low-lying, arid area with a tropical climate. Sand and pebbles were eroded from higher land to the east and carried westwards by rivers, to be deposited on lower ground where they eventually formed sedimentary rocks. These rocks look similar to the Torridonian sandstones, but the presence of plant fossils indicates that they are much younger.
For over 100 million years, during the Jurassic and Cretaceous periods, the Hebridean area remained close to sea level, with periodic incursions of the sea. During this time sediments, which later formed rocks such as limestones, sandstones and mudstones, were deposited. These rocks can be seen on the neighbouring island of Eigg, but on Rum they were removed by erosion that occurred when the area was raised up above sea level at the beginning of the Palaeogene Period some 65 million years ago.
The beginning of the Palaeogene Period was a key time in the geological history of Rum. Forces operating deep within the Earth began to pull apart the huge continent that included Scotland. As the continental mass was stretched, the Earth's crust began to crack. Magma, formed by the melting of rock many kilometres below the Earth's surface, welled up through these cracks in the crust and erupted from volcanoes. This magma spread out over much of the area in lava flows similar to those seen on Iceland today. Meanwhile, beneath the volcanoes, huge bodies of magma accumulated in magma chambers deep within the Earth's crust. This magma slowly cooled and crystallised to form igneous rocks such as granite and gabbro. Much of the Isle of Rum represents the eroded remains of one of these volcanoes that formed 60 million years ago. Modern techniques used to date rocks accurately have showed us that the active lifetime of the Rum volcano was very short in geological terms - probably only a few hundred thousand years. The volcanic rocks of Rum have been intensely studied by geologists over the last 100 years, allowing us to understand in detail how the Rum volcano evolved. The volcanic features are described in more detail in the following pages.
By 55 million years ago, the volcanoes of northwest Scotland had ceased to erupt, and volcanic activity had shifted to the west as the North Atlantic began to open. The youngest volcanic rock still preserved in Scotland is the lava flow that now forms the distinctive Sgùrr of Eigg.
During the next 50 million years, the area around Rum underwent periodic erosion in a mostly warm, sub-tropical climate. This continued until about 2.4 million years ago, when the climate cooled dramatically and glaciers formed in Scotland. The landscape of Rum owes its appearance largely to the action of these glaciers; the corries, sharp peaks and deep U-shaped valleys on the island are all products of glacial erosion. During the last 2 million years glaciers have repeatedly scoured away soils and younger sediments, leaving the underlying rocks spectacularly exposed. Since about 750,000 years ago, intensely cold glacial episodes have been interspersed with brief warm interglacial periods. At the peak of one of these glacial episodes the whole island would have been almost completely covered by an ice sheet flowing from the mainland westwards. The most recent of these major glaciations was at its peak on 20,000 years ago. Around 11,500 years ago the climate warmed rapidly to give the temperate, maritime, conditions experienced today. Following the melting of the ice, much of the west of Scotland rose up as it adjusted to the removal of the weight of the glaciers, and hence the relative sea level fell rapidly. The sea level around Rum has continued to fall gradually over the last 6000 years or so as the island steadily rises
The Small Isles, Lochaber's volcanic islands
The dramatic ‘Small Isles’ of Canna, Eigg, Muck and Rum in the far west of Lochaber have a fiery past that tells us of a time when active volcanoes dominated the north-west coast of Scotland, This intense volcanic activity occured as continental drift split Scotland from North America with the opening of the North Atlantic.
The Small Isles are home to a fascinating variety of rocks, ranging from the 3-billion years old Lewisian Gneiss, to the remains of volcanoes which erupted around 60 million years ago. Canna, Eigg and Muck are made up of almost exclusively of volcanic rocks. These were erupted 60-65 million years ago when things started to get volcanically violent!
The stopping points on the Lochaber geotrail help to explain the forces that have created the distinct features of the Small Isles: one of the stops is situated in thecapark in the Small Isles ferry port of Mallaig, another is on Eigg, right at the end of the Pier causeway.
The Rum Cuillin; an ancient volcano
From the ferry you’ll enjoy excellent views of the Small Isles. Look out for the sight of the high Rum Cuillin towering over the other Small Isles. These mountains are the eroded roots of an ancient volcano that started life as a huge dome around 2,000 metres high. The dome was created as molten rock, or magma, rising up through cracks in the Earth's crust, collected in a magma chamber, a few kilometres below the surface of the Earth, and the rocks above were pushed upwards.
Evidence for the existence of this dome can still be seen on the slopes of the Rum Cuillin, where the layers in the Torridonian rocks are inclined steeply away from the adjacent igneous rocks.
Eventually, the pressure on the domed rocks became too great and they cracked, producing a series of fractures around the dome. The rocks of the dome collapsed downwards, forming a massive roughly circular crater known as a caldera. The walls of this caldera were unstable, and so the floor of the caldera gradually became covered with the debris of rockfalls and landslides. This debris, which consisted largely of blocks and pebbles of Torridonian sandstone and Lewisian gneiss, was gradually compressed to form rocks known as breccias that can be seen in Coire Dubh.
Magma continued to rise up into the magma chamber beneath the caldera, and was eventually erupted onto the Earth's surface. The erupting magma was silica-rich, thick and sticky, and so it did not flow out easily from the volcano; instead it was ejected in explosive eruptions, throwing out hot ash and fragments of volcanic rock that spread out across the caldera floor in searing-hot gas clouds known as pyroclastic flows.
Several episodes of explosive volcanic activity occurred, each separated by further collapse of the caldera. The rocks that formed from these pyroclastic flows are called rhyodacites. They can be seen in various places around the margins of the Rum Cuillin, and they are particularly well exposed on the ridge between the summits of Ainshval and Sgurr nan Gillean.
Walk along the road from the landing stage towards Kinloch Castle and have a closer look at the rocks on the shoreline. These are the 1,000 million year old Torridonian sandstones, dark pink in colour, that have been pushed aside by pressure from molten lava.
Follow the path uphill from Kinloch Castle towards Coire Dubh. This is the main path up the mountain of Hallival and is signposted ‘Rum Cuillin’. After about 1km the rock you’re walking on will change from Torridonian sandstone to breccia – a rock made of angular fragments of Torridonian sandstone and gneiss. This rock was formed inside a volcano, when the dome created above a magma chamber began to fracture and collapse.
Rum’s Giant’s Causeway
In the south of the island, the jagged peaks of the Rum Cuillin are formed from Gabbro, a hard rock that are quite different from those that underlie the rounded hills to the west. There, lavas that were erupted from later volcanoes - possibly those on Skye and Mull - form the top parts of the hills of Fionchra, Orval and Bloodstone Hill. On the west side of Fionchra, the lavas have cooled into a columnar structure like that at the Giant's Causeway in Northern Ireland. These lavas lie on top of sedimentary rocks called conglomerates, which contain many rounded pebbles, laid down in rivers flowing across the land surface before the lavas were formed.
At Bloodstone Hill, holes and cracks in the rock are filled with green agate which contains many tiny red flecks, and this is thus known as bloodstone. This agate is composed mostly of silica, and was formed from heated water flowing through the rocks. This water dissolved minerals from the surrounding rocks, then precipitated them again into cracks when it cooled. The red flecks are tiny crystals of iron minerals, which have been oxidised on exposure to air, turning red.
As you journey towards Canna, you’ll notice that there is a flat platform of rock about 30 or 40 metres above sea level around the coast of Rum. This goes round most of the island and was cut about 100,000 years ago before the last glacial ice cover, when the sea level was much higher than it is today. When the last glaciers melted and the weight of the ice was removed, the Earth’s crust ‘bounced back’ – making it higher than it was before. This effect created what are known as ‘raised shorelines’. You’ll see similar raised shorelines around the other Small Isles.
Canna and Sanday
Canna and Sanday are composed largely of lavas, part of the major lava field that is exposed in northwestern Rum and extends to northern Skye. These basalt lavas were probably erupted from a major volcano on what is now the Isle of Skye. Canna is special for three main features. First is the lava pile, where individual lava flows can be traced for several kilometres on the island. Second is the agglomerate, featuring angular blocks of basalt and dolerite mixed with Torridonian sandstone, a unique evidence of explosive volcanic activity. Third is the conglomerate which is inter-bedded with the lavas of Canna and Sanda and helps to establish the sequence of volcanic events on the island.
Where rivers and volcano meet
This conglomerate is what makes Canna of particular interest. It shows how the area was traversed by fast-flowing rivers at the same time that the volcano was erupting. Great thicknesses of boulder conglomerate were deposited by this river. The boulders were rounded as they were carried along in the fast flowing river currents. Some are over a metre in diameter, indicating the strengths of the currents involved. Pebbles in these deposits have been matched with bedrock from Skye, suggesting that the river flowed from the north.
On the north-east tip of the island sits Compass Hill. It’s called this because iron in the hill’s basalt rocks affects compasses up to 3 miles away!
Like Canna, Eigg is largely made up of basalt lava flows. These are most easily seen in the cliffs that dominate the northern part of the island in Cleadale, which were eroded by the ice out of the Beinn Bhuidhe plateau. A closer look reveals how the cliffs are far from being static, as weathering from the rain are still causing landslides, and the Beinn Bhuidhe plateau is slowly collapsing on its edges.
The Sgurr of Eigg
Rivers flowing across the basalt lava plateau eroded deep channels over time. The prominent peak of An Sgurr actually marks the location of one of these river valleys. During one of the last eruptions from the volcano on Rum, thick lava flowed along a river valley and cooled to form a rock called pitchstone. This lava is much harder than the surrounding basalt and while the rock of the valley sides has worn away, the lava that once filled it now stands out as a great prow. Quick cooling also means that the lava formed giant hexagonal columns, much like the Giant's Causeway.
Eigg’s Jurassic Park
Eigg is also a place of famous discoveries. The Victorian geologist Hugh Miller unearthed the fossilised remains of Jurassic sea turtles, a crocodile and a plesiosaur in rocks at the northen part of the island. These date back to the ‘age of the dinosaurs’, particularly the Jurassic and Cretaceous periods, when Eigg was submerged beneath shallow tropical seas. Walking to Laig beach, you come across ancient oysters beds, dating back to the time where shellfish thrived in brackish sea and prehistoric sea-creatures such as the plesiosaur fed ancient squids called belemnites.
The Singing Sands
The famous ‘singing sands of Eigg consist of pure quartz grains from the Jurassic sandstone outcrops around the north end of the island. If you walk on the sand in dry weather, the texture creates a shrill ‘singing’ squeak. An impressive feature of the sandstone itself is the amount of huge concretionary boulders, some 2 metres across, which either protrude from the cliff face, or litter the rock platform below like giant pocked marbles. These have formed by migration of calcite within the sands, a process calculated on one model as taking about 5 Millions years to reach the size now seen.
Muck, the smallest and flattest of the Small Isles, is also made up of lava, although it is the island furthest away from volcanic centres. As in Canna and Eigg, it is easy to see the lava flows, dark basalt and reddish dolerite lavas, which probably came from a volcano on Mull.
A unique feature
What is remarkable on Muck is the extraordinary number of dykes interesecting the lava flows: about 40 between Camas Mòr and Port Mòr alone, and 134 on the southerna and eastern coast! The dykes stand out prominently, making walls often 20 or 30 ft high, 5 to 6 metres. Parallel to each other, they all follow the same regional direction and occured when magma rose in the deep fissures most probably created by volcanic action on Rum.
Camas Mòr, the Big Bay, is Muck's answer to Eigg Jurassic park. There, a most impressive succession of rocks spanning the whole period can be found, with oyster beds, algal limestones, laminated mudstones and thin sandstones recording the gradual withdrawal from the sea.
The Great Gabbro dyke
Muck's great gabbro dyke, over 50 m wide, forms a cliff along the east side of Camas Mòr. Cutting the Jurassic limestones, this dyke has generated a large number of exotic minerals along the contact where the nature of the limestone is changed and it is assimilated into the gabbro. It is a Mecca for keen mineralogists.