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How Glencoe Was Forged By Fire And Ice

Glencoe is one of Scotland’s most strikingly beautiful glens, with soaring peaks which are snow-capped for much of the year, contrasting with the expansive moors below. The dramatic landscape was forged by ancient movements of ice and rock, fire and air.


Glencoe is the remains of an ancient supervolcano that erupted about 420 million years ago, a legacy of a turbulent geological era. The jagged granite mountains are the remnants of massive volcanic activity which created a whole new geographical range, known as the Caledonian Mountains.


This ancient mountain range extends for over five thousand miles, stretching the globe from eastern North America, east Greenland, Ireland, Scotland, and Norway. They were formed before the North Atlantic Ocean, and were once comparable in height and scale to the Himalayas and the Alps.


As you walk on these special uplands, you are travelling through what was once the blazing furnace of a volcano. Glencoe is thought to be one of the best examples of ‘subsidence caldera’. A caldera (the Spanish word for cauldron) is created when hot molten rock (magma) is forced to the surface of a chamber underneath the volcano.


As the magma chamber empties, the support is lost and the volcano collapses in on itself, to form a ‘cauldron.’ Sometimes this leaves a bowl-shaped depression which fills with water, such as Crater Lake in Oregon, USA, which is thought to be around 7,000 years old. In the Highlands, the granite mountain rocks beneath were left exposed by the volcanic collapse.


Calderas should not be confused with craters, which are formed by the outward explosion of rocks and other materials from a volcano. A caldera is caused by the inward collapse of a volcano, National Geographic explains. Calderas can be uneven, and have parts of their sides missing.


In Glencoe, the results of the subsidence caldera can be seen most strikingly on Bidean nam Bian and at at Sgorr nam Fiannaidh. When you are out walking in this fascinating part of the world, look out for folded metamorphic rocks, such as quartzites and limestones. These rocks have been transformed from sands and silts which once lay on the sea bed.


The base of Aonach Dubh is formed from dark andesite sills and lavas, and is separated by a ridge from the rest of the mountain. Beyond this ledge, the volcanic remains are comprised of lighter coloured rhyolites, tuffs, and ignimbrites, which are rocks formed by the welding of lava and ash during a volcanic eruption.


When the volcanic activity in the region ceased, the Highlands of Scotland were further shaped by the forces of wind and water erosion. During the Ice Age which followed the volcanic era, huge sheets of ice built up on Rannoch Moor, and the glaciers cut through Glencoe, forming the sharp ridges and deep glens which remain today.


As the glaciers melted, the bedrocks of the mountains were broken up by the contracting ice, and the loose rocks which tumbled down the slopes can be seen today in the mountainside screes, and also the rocks and boulders which scatter across the glen.


If you are looking for Glencoe guided walks, please get in touch today.

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