River Feshie, Speyside: Illustrating how modern-day landscapes are formed

Take a walk in this spectacularly beautiful Highland glen and explore the dynamic landscape features created by the action of glaciers and rivers

Glen Feshie. Image: Rowena Hepple, https://outnaboutinscotland.com/2015/07/09/leathad-an-taobhain-carn-dearg-mor-glen-feshie-cairngorms/

Quite simply, if you explore the entire 30-kilometre-long valley of the River Feshie, you’ll encounter some of the most beautiful and inspiring highland landscapes you’ll ever see. From its confluence with the Spey just downstream from Loch Insh, to its furthest headwaters deep in the western Cairngorm Mountains, you’ll also find some excellent examples of classic landforms created by the actions of gravity and flowing water. Add to this mix a welcoming estate with its very successful natural forest regeneration strategy and consequent upsurge in wildlife, and you can see why Glen Feshie has rightly been described as the “jewel in the crown of the Cairngorms”.

Some particular landscape features that you will see are river terraces, braided river channels, alluvial fans, and scree slopes that feed some fine examples of debris cones. All of these features are contained within a long glacial trough with a valley floor that is rarely more than about 400 metres wide, the bottom of which is choked with rock debris left by the last glacial period and still being supplemented by ongoing erosion of the steep valley slopes. The mass of sand, gravel and boulders is constantly being re-worked by the Feshie and its tributaries, making this system a wonderful outdoor laboratory for scientists who study the processes that create valley floors and slopes.

Though often quite spectacular in spate, today’s flow of water down the glen is only a fraction of that which occurred during the melting of the last ice sheet and valley glacier system about 13,000 years ago. Detailed studies have mapped out patches of the original surface left as the ice wasted away and left behind its load of coarse and chaotic sediment dumped on the valley floor. This surface is often pock-marked by hollows formed when stranded lumps of ice eventually melted. You can also see a complex network of former river channels, now stranded above today’s valley floor as several bursts of renewed erosive activity created a succession of up to five river terraces at different levels. Even today, from year to year, the course of the Feshie changes as it migrates over its flat valley bottom. The low gradient and enormous volume of gravel has created one of the most spectacular sets of braided channels in the country.

In the middle reaches of the Glen, upstream from the confluence with the Allt Lorgaidh, the valley narrows and steep rocky cliffs rise up on both sides. Here, a constant rain of rock fragments from the degrading cliffs feeds a series of exceptional debris cones. This is landform creation in action; the valley is filling in before your very eyes!

Finally, in the farthest reaches of the Glen, there is an astonishing ‘elbow’ in the course of the river. Within just one kilometre, the direction of flow is completely reversed in a classic example of river capture. Energised by the great flush of meltwater released at the end of the last glacial period, the River Feshie cut back into the valley of the Geldie Burn and ‘captured’ its headwaters, leaving a marshy col that marks the county boundary between Aberdeenshire and the Highland council areas.

Text contributed by Peter Craig

Find out more
Much more information can be found in this professional account of the Holocene landforms in Glen Feshie: http://jncc.defra.gov.uk/pdf/gcrdb/GCRsiteaccount3049.pdf
Rowena Heppie’s blog entry provides an excellently illustrated account of a walk up part of Glen Feshie: https://outnaboutinscotland.com/2015/07/09/leathad-an-taobhain-carn-dearg-mor-glen-feshie-cairngorms/
Cairngorms National Park website is aimed at younger readers and has information about other topics as well as landforms: http://cairngormslearningzone.co.uk/landscape-geology/cairngorms-national-park-today/geomorphological-processes/

3. At least six active debris cones are spreading over this corner of Creag na Caillich, gradually reducing the angle of slope and eventually contributing to the infilling of the valley below. Image: Rowena Hepple. https://outnaboutinscotland.com/2015/07/09/leathad-an-taobhain-carn-dearg-mor-glen-feshie-cairngorms/

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