Geology in winter: The Ardnamurchan Ring Complex

This should have been published back in January, somehow it fell by the wayside. Still, it is a source of wonderful memories, and my girls continue talking about Ardnamurchan.

2015-12-31 11.54.38
Looking south-west from Ardnamurchan Point; the aftermath of Storm Frank

 

I love being outdoors in the wind, in the rain, in midwinter. Under grey skies and after the rain something shifts in the rocks around me. Far from dull, their every fold and twist is magnified by the dampness. Their contours and layering stand out, unusual patterns are magnified in droplets of water, crystals shimmer in any weak glimmer of sunlight, and the colours shine brighter than the surrounding vegetation.

This New Year I spent a week in Ardnamurchan with my young family. Truth be told, there wasn’t a huge amount of scope for geological wanderings – the little I did was with my daughters, or in brief moments alone on the beach as the kids’ kites were flying overhead in the ever-present wind. Two moments stand out, however, and both occurred on the same morning.

The second day we were there proved to be the best forecast. We set out from our cottage for Sanna Bay under gradually-thinning cloud. Secretly I knew that the short drive from Kilchoan would take us through the centre of the Ardnamurchan ring complex – the remnants of a volcano active as the Atlantic Ocean formed. A friend (a geologist!) had remarked before I left; “Ardnamurchan in winter? Well, it’ll be… bleak. Not much to look at!” I had hoped he might be wrong, either that or he might be pulling my leg; suffice to say he had quelled my enthusiasm to the point where I was genuinely astonished as we drove towards the edge of the volcanic centre.

In front of me were the obvious signs of a landscape heavily deformed, rising up at an angle and bending in a lengthy but clear curve – at the same moment my husband and I turned to each other and said “it’s like an ancient version of Lanzarote!” At this point, I took a gamble. I turned to the children in the back of the car – we’re going to drive through a volcano which is now extinct. I had no idea what to expect. The chances were the kids wouldn’t ‘get it’ at all.

Sure enough, the road cut through the wall of black lumpy rock in front of us and as we came up over the edge of the ring complex my mouth dropped open. We were snaking our way down and across the base of an obvious circular incline in the landscape – around us on all sides (save a break towards west and Sanna Bay itself) were steep walls of rock. The kids were twisting around in their seats, looking from one side of the car to the other – are we inside a real volcano? Is this where the lava was, mummy? Look how big it is!

On satellite images the ring complex is clearly visible. Spanning around 7km in diameter from west to east and 6km from north to south, the entire structure is what remains of a series of concentric intrusions during volcanic activity around 60 million years ago. The volcano itself has long been eroded away by ice and the elements – what we were really doing was driving into the former magma chamber. The complex has been heavily studied by geologists and remains a key site for university students to visit during their degree – suffice to say I won’t go into too much detail here as there are many other resources available.

Once down on the shore and the beach I took a few minutes to wander off across the rocks which cut their way in clear dyke formations across the bay. The rock here is informally known as eucrite; a type of gabbro formed deep underneath the Earth’s crust – an igneous rock rather than volcanic (and further evidence that the ring complex is really the remains of a volcano’s deep interior). The crystals in the rock are large, making it coarse-grained and liable to reflect the winter sunlight. This was my second highlight – the sun came out for an hour, and the rocks came alive following the rain the night before, the deep grey-silver surface shining like crinkled tinfoil. A look with a geologist’s loupe reveals a cityscape – streets and buildings, facades and crevices.

From Sanna I succeed in persuading the kids to walk up a nearby ‘hill’ so that we could look back on the whole ring structure. As we did, a golden eagle soared overhead and out towards the lighthouse. For the rest of the week, all the girls wanted to do was ‘drive into the volcano’ again. I think they ‘got it’.

 

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The Ardnamurchan Ring Complex, as seen from Sanna Bay

All text and photographs are copyright L. Reid 2016

 

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