Lochaber has a rich and varied geological heritage spanning million of years. The area boasts a great variety of different rock types and landscape features which make this a perfect place for a wealth of different outdoor activities.
Between 1000 Ma and 600 Ma (million years ago) sandy and muddy sediments were deposited on the floor of the ancient Iapetus Ocean. These sediments were buried deeply and metamorphosed by the collision of several different crustal segments during the closure of the Iapetus Ocean some 420 Ma. All around Lochaber, but especially along the Road to the Isles and in Glen Nevis, you can view these complex metamorphic rocks - psammites, pelites, quartzites, schists, slates and metamorphic limestones. They represent the exposed root of the enormous Caledonian mountain chain which once extended from the Appalachians, Newfoundland, Greenland, across Scotland to Scandinavia and Spitsbergen.
During the Caledonian Orogeny or mountain building episode (470-400 Ma) there was extensive igneous activity associated with the great upheavals in the land. The lavas and granites of Ben Nevis, Glencoe and Glen Etive are of outstanding interest. It was in these three locations that geologists who first mapped the area a century ago discovered the evidence of major caldera collapse. Marvellous exposures of one of these caldera structures can be seen from the roadside in Glencoe. Though not so readily accessible the rocks of Ben Nevis also tell a similar story of a complex caldera collapse. In fact the lavas that make up the north face of Ben Nevis, the highest summit in the British Isles, are only preserved today because they subsided more than 600 metres into a large caldera. The surrounding Ben Nevis granites were formed from the cooling of a large body of magma (molten rock) which rose within the earth's crust. The heat from this magma 'baked' the surrounding metamorphic rocks forming hardened outcrops of schist enjoyed by countless climbers in Glen Nevis today.
During this same period there was widespread tension in the earth's crust which resulted in countless NE/SW trending igneous dykes being injected into local rocks. Where these are significantly softer than the country rock they weather out to produce deep gullies and stream ways, often forming the line of popular winter climbs or river courses. Ossian's Cave in Glencoe was formed when a huge block of rock fell out of a dyke, and the Lower Falls in Glen Nevis have been eroded along twin dykes cutting through granite.
The Great Glen Fault was also most active at the close of the Caledonian Orogeny between 430 Ma and 400 Ma. Movement along the fault caused the rocks on the north-west side of the fault to slide many tens of kilometres (possibly over 100km) in a south-westerly direction. The rocks along the fault itself were pulverized by the long history of movement and have since been eroded to produce the Great Glen, an important trough cutting right across the Highlands from Fort William to Inverness much used for pleasure boating.
Around 65 Ma the continents of North America and Eurasia started to drift apart as the North Atlantic Ocean grew. This resulted in a major episode of volcanic activity along what was to become the North West coast of Scotland. Vast outpourings of basaltic lava built up the terraced hillsides seen today on Eigg and in Morvern. The islands of Rum, Eigg, Muck and Canna as well as Morvern and Ardnamurchan host a great range of igneous features including the roots of ancient volcanoes. The gabbro ring dyke on the Ardnamurchan peninsula is a very popular rock climbing destination.
Lochaber, like all of Scotland, was subject to a series of glacial and interglacial periods over the last two million years. These ice ages left us a legacy of deep glacially carved glens, and even deeper sea lochs providing outstanding opportunities for sailing and sea kayaking. The last glaciers finally melted away some 10, 000 years ago, but during the final glacial interlude (11,500 years ago) ice built up on western hills and formed natural dams as it flowed into the entrances to Glens Gloy, Roy and Spean. Water backed up and spilled over the nearest col free of ice. The glacially dammed lakes created shorelines at the height of these cols. The Parallel Roads of Glen Roy are a world famous example of this type of feature and attracted many learned scientists including Charles Darwin bent on unravelling their story.
The geology of the area has played a part in the local economy for more than 300 years. The slate quarries at Ballachulish were opened in the late 17th century, and continued to operate until 1955. Slate gives a distinctive character to many of the older buildings in the area. Lead, silver and zinc ores were extracted from mines at Strontian between 1722 and 1904. The mineral Strontianite was first identified from the same mines, and it was from this mineral that the element Strontium was isolated for the first time in 1808. In the 1980s baryte was extracted from the same area for use as a drilling mud in the offshore oil industry. Mica was mined in Knoydart during the Second World War. Exceptionally pure quartz sand has been mined at Lochaline since the 1940s. For the last 15 years hard-rock aggregate has been produced from the superquarry in the Strontian granite at Glensanda. Limestone is currently extracted for agricultural use and as road aggregate at Torlundy.
Lochaber Geopark
In January 2004 a public meeting was held in the Council Chambers in Fort William to consider the suggestion that Lochaber should seek to create its own Geopark. That evening saw the setting up of a steering group, and in May 2004 Lochaber Geopark Association was formerly constituted. The association is committed to increasing local and visitor appreciation and understanding of the rich geological heritage found within Lochaber.
As Lochaber's initiative gathers steam, the association is striving to win UNESCO accreditation of their efforts and have Lochaber recognised in the near future as a member of the European Geopark Network.
We are convinced that Lochaber has a magnificent geological heritage, which makes it well worthy of recognition as a geopark. Whereas some of the existing geoparks have just one feature of outstanding geological interest, we believe that within Lochaber there are numerous such examples. The Parallel Roads of Glen Roy and the Great Glen Fault are well known, but the ancient lavas and granites of Ben Nevis, Glen Coe and Glen Etive are very special too, as are the younger igneous rocks found in Ardnamurchan, and the Small Isles.
The area is popular with visitors not only because of its spectacular scenery, but also because of the superb opportunities it offers for geological education and research. Many colleges and universities choose Lochaber as a venue for geological fieldwork courses. Popular itineraries include Glen Coe, the shoreline at Onich and around Loch Leven, Glen Roy, Ardnamurchan and along the 'Road to the Isles' to Mallaig. Unravelling the story behind the local igneous and metamorphic rocks has helped our understanding of the very complex processes involved in the formation of large mountain chains.
European Geoparks
To be awarded European Geopark status an area not only has to have an important geological heritage, but also a sustainable development strategy or plan.
The aim of geoparks is to
- protect and promote geological heritage to the public
- use geology to promote sustainable economic development usually through geotourism
- make a real difference to local communities
The idea behind the geopark concept is to raise awareness of Europe's geological heritage in a way that brings sustainable economic benefit to local communities.
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